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3
Cellular Level
of Organization
PowerPoint® Lecture Presentations prepared by
Alexander G. Cheroske
Mesa Community College at Red Mountain
© 2011 Pearson Education, Inc.
Section 1: An Introduction to Cells
• Learning Outcomes
• 3.1 Describe the cell and its organelles,
including the composition and function of
each.
• 3.2 Describe the chief structural features of the
plasma membrane.
• 3.3 Differentiate among the structures and
functions of the cytoskeleton.
• 3.4 Describe the ribosome and indicate its
specific functions.
© 2011 Pearson Education, Inc.
Section 1: An Introduction to Cells
• Learning Outcomes
• 3.5 Describe the Golgi apparatus and indicate
its specific functions.
• 3.6 Describe mitochondria, indicate their
functions, and explain their significance to
cellular function.
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Section 1: An Introduction to Cells
• Typical cell
• Smallest living unit in the body
• ~0.1 mm in diameter
• Could not be examined until invention of
microscope in 17th century
Animation: Your Cells
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Section 1: An Introduction to Cells
• Cell theory
1. Cells are building blocks of all plants and
animals
2. All new cells come from division of preexisting
cells
3. Cells are smallest unit that perform all vital
physiological functions
© 2011 Pearson Education, Inc.
Cells are the building blocks of all
plants and animals.
All new cells come from the division
of pre-existing cells.
Nutrients
Division
Cell
Cells are the smallest units that perform
all vital physiological functions.
O2
Wastes
CO2
Growth
New
cells
The cell theory
Epithelial tissue
Connective tissue
Muscle tissue
The differentiation of the four tissue types from a single cell:
the fertilized ovum
Neural tissue
Figure 3 Section 1
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Section 1: An Introduction to Cells
• Each cell maintains homeostasis
• Coordinated activities of cells allow
homeostasis at higher organizational levels
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Section 1: An Introduction to Cells
• Cells vary in structure and function but all descend
from a single fertilized ovum
•
Fertilized ovum contains genetic potential to
become any cell
•
Cell divisions occur creating smaller, different
parcels of cytoplasm
•
Cytoplasmic differences turn off/on specific genes
in DNA and daughter cells become specialized
•
•
= Differentiation
Differentiated cells are responsible for all body
functions
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Section 1: An Introduction to Cells
• Extracellular fluid
• Watery medium surrounding cells
• Called interstitial fluid (interstitium, something
standing between) in most tissues
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Module 3.1: Smallest living units of life
• Cell components
• Plasma membrane (cell membrane)
• Separates cell contents from extracellular fluid
• Cytoplasm
• Material between cell membrane and nuclear
membrane
• Colloid containing many proteins
• Two subdivisions
1. Cytosol
•
Intracellular fluid
2. Organelles (“little organs”)
•
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Intracellular structures with specific functions
Module 3.1: Smallest living units of life
• Organelles
• Nonmembranous
• Not completely enclosed by membranes
• In direct contact with cytosol
• Examples:
• Cytoskeleton
• Microvilli
• Centrioles
• Cilia
• Ribosomes
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Module 3.1: Smallest living units of life
• Organelles
• Membranous
• Enclosed in a phospholipid membrane
• Isolated from cytosol
• Examples:
• Mitochondria
• Nucleus
• Endoplasmic reticulum
• Golgi apparatus
• Lysosomes
• Peroxisomes
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Module 3.1: Smallest living units of life
• Organelles
• Microvilli
• STRUCTURE: membrane extensions containing
microfilaments
• FUNCTION: increase surface area for absorption
• Cytoskeleton
• STRUCTURE: fine protein filaments or tubes
• Centrosome
• Organizing center containing pair of centrioles
• FUNCTION:
• Strength and support
• Intracellular movement of structures and materials
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Module 3.1: Smallest living units of life
• Organelles
• Ribosomes
• STRUCTURE: RNA and proteins
• Fixed: attached to endoplasmic reticulum
• Free: scattered in cytoplasm
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Module 3.1: Smallest living units of life
• Organelles
• Peroxisome
• STRUCTURE: vesicles containing degradative enzymes
• FUNCTION:
• Catabolism of fats/other organic compounds
• Neutralization of toxic compounds
• Lysosome
• STRUCTURE: vesicles containing digestive enzymes
• FUNCTION:
• Removal of damaged organelles or pathogens
© 2011 Pearson Education, Inc.
Module 3.1: Smallest living units of life
• Organelles
• Golgi apparatus
• STRUCTURE: stacks of flattened membranes
(cisternae) containing chambers
• FUNCTION: storage, alteration, and packaging
of synthesized products
• Mitochondria
• STRUCTURE:
• Double membrane
• Inner membrane contains metabolic enzymes
• FUNCTION: production of 95% of cellular ATP
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Module 3.1: Smallest living units of life
• Organelles
• Nucleus
• STRUCTURE:
• Fluid nucleoplasm containing enzymes, proteins,
DNA, and nucleotides
• Surrounded by double membrane
• FUNCTION:
• Control of metabolism
• Storage/processing of genetic information
• Control of protein synthesis
Animation: Nucleus
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Module 3.1: Smallest living units of life
• Organelles
• Endoplasmic reticulum (ER)
• STRUCTURE: membranous sheets and channels
• FUNCTION: synthesis of secretory products, storage,
and transport
• Smooth ER
• No attached ribosomes
• Synthesizes lipids and carbohydrates
• Rough ER
• Attached ribosomes
• Modifies/packages newly synthesized
proteins
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Module 3.1 Review
a. Distinguish between the cytoplasm and
cytosol.
b. Describe the functions of the cytoskeleton.
c. Identify the membranous organelles and
describe their functions.
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Module 3.2: Plasma membrane
• Plasma membrane
• Selectively permeable membrane that controls:
• Entry of ions and nutrients
• Elimination of wastes
• Release of secretions
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Module 3.2: Plasma membrane
• Plasma membrane components
• Glycocalyx
• Superficial membrane carbohydrates
• Components of complex molecules
• Proteoglycans (carbohydrates with protein attached)
• Glycoproteins (protein with carbohydrates attached)
• Glycolipids (lipids with carbohydrates attached)
• Functions
• Cell recognition
• Binding to extracellular structures
• Lubrication of cell surface
© 2011 Pearson Education, Inc.
Module 3.2: Plasma membrane
• Plasma membrane components (continued)
• Integral proteins
• Part of cell membrane
• Cannot be removed without damaging cell
• Often span entire cell membrane
• = Transmembrane proteins
• Can transport water or solutes
• Peripheral proteins
• Attached to cell membrane surface
• Removable
• Fewer than integral proteins
© 2011 Pearson Education, Inc.
Structure of the plasma membrane
EXTRACELLULAR FLUID
Glycocalyx
(extracellular
carbohydrates)
Integral protein
with channel
Glycolipid
Integral
glycoproteins
CYTOPLASM
Integral (transmembrane) proteins
= 2 nm
Peripheral proteins
Cytoskeleton
(microfilaments)
Figure 3.2
© 2011 Pearson Education, Inc.
1
Module 3.2: Plasma membrane
• Plasma membrane structure
• Thin (6–10 nm) and delicate
• Phospholipid bilayer
• Mostly comprised of phospholipid molecules in
two layers
• Hydrophilic heads at membrane surface
• Hydrophobic tails on the inside
• Isolates cytoplasm from extracellular fluid
Animation: Cell Membrane Barrier
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The phospholipid bilayer that forms the
plasma membrane
Hydrophilic
heads
Hydrophobic
tails
Cholesterol
Figure 3.2
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Module 3.2: Plasma membrane
• Plasma membrane functions
• Physical isolation
• Regulation of exchange with external
environment
• Sensitivity to environment
• Structural support
• Lipid bilayer provides isolation
• Proteins perform most other functions
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Figure 3.2
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3
Figure 3.2
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3
Module 3.2 Review
a. List the general functions of the plasma
membrane.
b. Which structural component of the plasma
membrane is mostly responsible for its ability to
isolate a cell from its external environment?
c. Which type of integral protein allows water and
small ions to pass through the plasma
membrane?
© 2011 Pearson Education, Inc.
Module 3.3: Cytoskeleton
• Cytoskeleton (cellular framework) components
1. Microfilaments
• <6 nm in diameter
• Typically composed of actin
• Commonly at periphery of cell
• Microvilli
• Finger-shaped extensions of cell membrane
• Has core of microfilaments to stiffen and anchor
• Enhance surface area of cell for absorption
• Terminal web (layer inside plasma membrane in cells
forming a layer or lining)
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Module 3.3: Cytoskeleton
• Cytoskeleton (cellular framework)
components (continued)
2. Intermediate filaments
• 7–11 nm in diameter
• Strongest and most durable cytoskeletal
elements
3. Microtubules
• ~25 nm in diameter
• Largest components of cytoskeleton
• Extend outward from centrosome (near nucleus)
© 2011 Pearson Education, Inc.
Structures of the cytoskeleton
Microvilli
Microfilaments
Plasma membrane
Terminal web
Microvilli
SEM X 30,000
Intermediate filaments
Microtubule
Secretory vesicle
Mitochondrion
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Endoplasmic
reticulum
Figure 3.3
1
Module 3.3: Cytoskeleton
• Centrioles
• Cylindrical structures
• Composed of microtubules (9 groups of triplets)
• Two in each centrosome
• Control movement of DNA strands during cell
division
• Cells without centrioles cannot divide
• Red blood cells
• Skeletal muscle cells
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The structure of centrioles
Microtubules
in centriole
Figure 3.3
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3
Module 3.3: Cytoskeleton
• Cilia
• Long, slender plasma membrane extensions
• Common in respiratory and reproductive tracts
• Also composed of microtubules
• Nine groups of pairs surrounding a central pair
• Anchored to cell surface with basal body
• Beat rhythmically to move fluids or secretions
across cell
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The structure of cilium
Plasma
membrane
Microtubules
Basal
body
Figure 3.3
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4
The action of a beating cilium
Power stroke
Return stroke
Figure 3.3
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5
Module 3.3 Review
a. List the three basic components of the
cytoskeleton.
b. Which cytoskeletal component is common to
both centrioles and cilia?
c. What is the function of cilia?
© 2011 Pearson Education, Inc.
Module 3.4: Ribosomes
• Ribosomes
• Protein synthesis
• Two subunits (1 large, 1 small) containing
special proteins and ribosomal RNA (rRNA)
• Must join together before synthesis begins
• Free ribosomes
• Throughout cytoplasm
• Manufactured proteins enter cytosol
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Small ribosomal
subunit
The two subunits of a
functional ribosome
Large ribosomal
subunit
Figure 3.4
© 2011 Pearson Education, Inc.
1
Module 3.4: Ribosomes
• Endoplasmic reticulum (ER)
• Network of intracellular membranes attached to
nucleus
• Forms hollow tubes, sheets, and chambers
(cisternae, singular, cisterna, reservoir for
water)
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Module 3.4: Ribosomes
• Endoplasmic reticulum (ER)
• Two types
1. Smooth (SER)
• Lacks ribosomes
• Tubular cisternae
2. Rough (RER)
• Has attached (fixed) ribosomes
• Modification of newly synthesized proteins
• Export to Golgi apparatus
• Proportion of SER to RER depends on the cell
and its functions
© 2011 Pearson Education, Inc.
The structure of the endoplasmic reticulum (ER)
Nuclear
envelope
Cisternae
Tubular
cisternae
Smooth
endoplastic
reticulum (SER)
Figure 3.4
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2
– 3
Figure 3.4
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3
Module 3.4: Ribosomes
• Functions of SER
• Synthesis of phospholipids and cholesterol
• Synthesis of steroid hormones
• Synthesis and storage of glycerides in liver and
fat cells
• Synthesis and storage of glycogen in skeletal
and liver cells
© 2011 Pearson Education, Inc.
The structure and function
of rough endoplasmic
reticulum (RER)
Fixed
ribosomes
mRNA strand
Ribosome
Transport vesicles
Enzyme
Growing
polypeptide
Protein
Glycoprotein
As a polypeptide is
synthesized on a
ribosome, the growing
chain enters the
cisterna of the RER.
The polypeptide
assumes its
secondary and
tertiary structure.
The complete protein
may become an
enzyme or a
glycoprotein.
Glycoproteins,
proteins, and enzymes
not destined for rough
ER are packaged in
transport vesicles.
Transport vesicles
deliver proteins,
enzymes, and
glycoproteins to the
Golgi apparatus.
Figure 3.4
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4
Module 3.4: Ribosomes
• Function of RER
• Polypeptide synthesized on attached ribosome
• Growing chain enters cisterna
• Polypeptide assumes secondary/tertiary
structures
• Completed protein may become enzyme or
glycoprotein
• Products not destined for RER are packaged
into transport vesicles
• Deliver products to Golgi apparatus
© 2011 Pearson Education, Inc.
Module 3.4 Review
a. Describe the immediate cellular destinations of newly
synthesized proteins from free ribosomes and fixed
ribosomes.
b. Describe the structure of smooth endoplasmic reticulum.
c. Why do certain cells in the ovaries and testes contain
large amounts of smooth endoplasmic reticulum (SER)?
© 2011 Pearson Education, Inc.
Module 3.5: Golgi apparatus
• Golgi apparatus
• Functions
1. Renews or modifies plasma membrane
2. Modifies or packages secretions for release from cell
(exocytosis)
3. Packages special enzymes within vesicles for use in
cytosol
• Typically consist of 5–6 flattened discs (cisternae)
• May be more than one in a cell
• Situated near nucleus
Animation: Golgi Apparatus
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Module 3.5: Golgi apparatus
• Golgi apparatus
• Steps of function
1. Products from RER arrive at the forming face
in transport vesicles
2. Transport vesicles fuse with Golgi apparatus
and empty contents into cisternae
•
Enzymes modify products
3. New vesicles move material between cisternae
4. Product arrives at maturing face
© 2011 Pearson Education, Inc.
Module 3.5: Golgi apparatus
• Golgi apparatus
• Products
• Membrane renewal vesicles
• Add to plasma membrane
• Secretory vesicles
• Contain products to be discharged from the cell
• Fuse with plasma membrane and release
contents into extracellular environment
• Enzymes for cytosol
• Contained within lysosomes (lyso-, a loosening
+ soma, body)
• Isolate damaging chemical reactions
© 2011 Pearson Education, Inc.
Module 3.5: Golgi apparatus
• Lysosomes
• Isolated intracellular location for toxic chemicals involved
in breakdown and recycling of large organic molecules
• Three basic functions
1. May fuse with another organelle to activate digestive
enzymes
2. May fuse with another vesicle containing fluid or
solid extracellular materials
3. May break down with cell injury or death causing
autolysis (enzymes destroy cytoplasm)
•
“Suicide packets”
© 2011 Pearson Education, Inc.
The three basic functions of lysosomes
Waste products and debris are ejected from the cell
when the vesicle fuses with the plasma membrane.
Vesicles containing fluids or solids may
form at the surface of the cell.
Extracellular
solid or fluid
Lysosomal enzymes
are activated by
fusion with
another vesicle
or organelle
As digestion
occurs, nutrients
are reabsorbed
for recycling.
Lysosomes
initially contain
inactive
enzymes.
As the materials
or pathogens are
broken down by
lysosomal enzymes,
released nutrients
are absorbed.
Golgi
apparatus
Function 1: A lysosome
may fuse with the membrane of another
organelle, such as a
mitochondrion. This
activates the enzymes
and begins the
digestion of the
lysosomal contents.
Function 2: A lysosome
may also fuse with a
vesicle containing fluid or
solid materials from
outside the cell.
Function 3: The lysosomal membrane
may break down following injury to, or
death of, the cell. The digestive
enzymes become active and then
attack the cytoplasm in a destructive
process known as autolysis. For this
reason, lysosomes are sometimes
called “suicide packets.”
Figure 3.5
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2
Module 3.5: Golgi apparatus
• Membrane flow
• Continuous movement and exchange of
materials between organelles using vesicles
• Can replace parts of cell membrane to allow
cell to grow, mature, or respond to changing
environment
© 2011 Pearson Education, Inc.
Module 3.5 Review
a. List the three major functions of the Golgi
apparatus.
b. The Golgi apparatus produces lysosomes.
What do these lysosomes contain?
c. Describe three functions of lysosomes.
© 2011 Pearson Education, Inc.
Module 3.6: Mitochondria
• Mitochondria (mitos, thread + chondrion,
granule)
• Produce energy (ATP) for cells through the
breakdown of carbohydrates (glucose)
• Vary widely in shape and number
• Red blood cells have none
• Cardiac muscle cells are 30% mitochondria by
volume
Animation: Mitochondria
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The role of mitochondria in the production of the high-energy compound ATP
Although most ATP production
occurs inside mitochodria,
the first steps take place in the
cytosol. In this reaction
sequence, called glycolysis
(glycos, sugar + -lysis, a
loosening), each glucose
molecule is broken down into
two molecules of pyruvate. The
pyruvate molecules are then
absorbed by mitochondria.
Glucose
CYTOPLASM
The energy released
during a series of steps
performs the enzymatic
conversion of ADP to
ATP, which leaves the
mitochondrion.
2 Pyruvate
MITOCHONDRION
Citric acid
cycle
Enzymes and
ADP +
phosphate coenzymes
of cristae
MATRIX
In the mitochondrial matrix, a
CO2 molecule is removed
from each absorbed pyruvate
molecule; the remainder
enters the citric acid cycle,
of TCA (tricarboxylic acid)
cycle, an enzymatic pathway
that systematically breaks
down the absorbed pyruvate
remnant into carbon dioxide
and hydrogen atoms.
The hydrogen atoms are
delivered to enzymes and
coenzymes of the cristae
which catalyze the
synthesis of ATP from
ADP and phosphate. At
the end of this process,
oxygen combines with the
hydrogen atoms to form
water molecules.
Figure 3.6
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2
Module 3.6: Mitochondria
• Mitochondria
• Double membrane
• Outer (surrounds organelle)
• Inner (contains numerous folds called cristae)
• Encloses liquid (matrix)
• Cristae increase surface area for energetic
reactions
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Matrix
A colorized TEM of a mitochondrion
Cristae
Cytoplasm
of cell
TEM x 50,000
Figure 3.6
© 2011 Pearson Education, Inc.
1
Module 3.6: Mitochondria
• Steps of ATP production
1. Glycolysis (glycos, sugar + -lysis, a loosening)
•
Occurs in cytosol
•
1 glucose  2 pyruvate
•
Pyruvate absorbed into mitochondria
2. In mitochondrial matrix
•
CO2 removed from pyruvate
•
Enters citric acid (or TCA, tricarboxylic acid)
cycle
•
Systematically removes CO2 and hydrogen atoms
© 2011 Pearson Education, Inc.
Module 3.6: Mitochondria
• Steps of ATP production (continued)
3. Enzymes and coenzymes use hydrogen atoms
to catalyze ATP from ADP
•
Also forms H2O
4. ATP leaves mitochondrion
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Module 3.6 Review
a. Describe the structure of a mitochondrion.
b. Most of a cell’s ATP is produced within its
mitochondria. What gas do mitochondria
require to produce ATP?
c. What does the presence of many
mitochondria imply about a cell’s energy
requirements?
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Section 2: Nucleus
• Learning Outcomes
• 3.7
Explain the functions of the cell nucleus,
and discuss the nature and importance of
the genetic code.
• 3.8
Summarize the process of protein
synthesis.
• 3.9
Summarize the process of transcription.
• 3.10 Summarize the process of translation.
© 2011 Pearson Education, Inc.
Section 2: Nucleus
• Nucleus
• Usually largest cellular structure
• Control center for cellular operations
• Can direct synthesis of >100,000 different
proteins
• Coded in sequence of nucleotides
• Determines cell structure/function
• Usually only one per cell
• Exceptions:
• Multiple: skeletal muscle cell
• None: mature red blood cells
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Section 2: Nucleus
• The nucleus directs cellular responses to
environmental (ECF) changes
• Short-term adjustments
• Enzyme activity changes
• Long-term adjustments
• Changes in enzymes produced
• Changes in cell structure from changes in
structural proteins
• Often occur as part of growth, development, and
aging
© 2011 Pearson Education, Inc.
EXTRACELLULAR FLUID (ECF)
Plasma membrane
The role of the nucleus in preserving
homeostasis at the cellular level
Changes
in the
composition
of the
ECF
Binding to
membrane
receptors
SHORT-TERM
ADJUSTMENTS
Enzyme
activation or
inactivation
Diffusion
through
membrane
channels
LONG-TERM
ADJUSTMENTS
Binding to nuclear
receptors that alter
genetic activity
DNA in
nucleus
Changes in the biochemical processes
under way in the cell
resulting from the
synthesis of additional
enzymes, fewer
enzymes, or different
enzymes
Changes in the
physical structure of
the cell due to alterations in the rates or
types of structural
proteins synthesized
CYTOPLASM
Figure 3 Section 2
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Module 3.7: Nuclear structure
• Nuclear structures and functions
• Nuclear envelope
• Separates nucleus from cytoplasm
• Double membrane
• Perinuclear space (peri-, around)
• Space between layers
• Nuclear pores
• Allow passage of small molecules and ions
© 2011 Pearson Education, Inc.
Module 3.7: Nuclear structure
• Nuclear structures and functions (continued)
• Nucleoplasm
• Fluid contents of nucleus
• Fine filaments
• Ions
• Enzymes
• RNA and DNA nucleotides
• Small amounts of RNA
• DNA
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Module 3.7: Nuclear structure
• Nuclear structures and functions (continued)
• Nucleoli (singular, nucleolus)
• Transient, clear nuclear organelles
• Composed of:
• RNA
• Enzymes
• Proteins (histones)
• Form around DNA instructions for forming proteins/RNA
• Assemble RNA subunits
• Many found in large, protein-producing cells
• Liver
• Nerve
• Muscle
© 2011 Pearson Education, Inc.
The structure of the nucleus
Perinuclear
space
Nuclear envelope
Nuclear pores
Nucleoplasm
Nucleolus
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Figure 3.7
1
Module 3.7: Nuclear structure
• DNA
• Instructions for protein synthesis
• Strands coiled
• Wrap around histone molecules forming nucleosomes
• Loosely coiled (chromatin) in nondividing cells
• Tightly coiled (chromosomes) in dividing cells
• To begin, two copies of each chromosome held
together at centromere
• 23 paired chromosomes in somatic (general body)
cells
• One each from mother/father
• Carry instructions for proteins and RNA
• Also some regulatory and unknown functions
© 2011 Pearson Education, Inc.
The coiled structure of DNA in the nucleus of a nondividing cell
Chromatin
Nucelosome
Histones
Nucleus of nondividing cell
DNA double
helix
Figure 3.7
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2
The tighter coiling of DNA to form
chromosomes in dividing cells
Centromere
Supercoiled
region
Dividing cell
Visible chromosome
Figure 3.7
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3
Module 3.7 Review
a. What molecule in the nucleus contains
instructions for making proteins?
b. Describe the contents and the structure of the
nucleus.
c. How many chromosomes are contained
within a typical somatic cell?
© 2011 Pearson Education, Inc.
Module 3.8: Protein synthesis
•
DNA
•
•
•
Long parallel chains of nucleotides
Chains held by hydrogen bonds
Four nitrogenous bases
1.
2.
3.
4.
•
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Genetic code (sequence of nucleotides)
•
Triplet code (three nucleotides specify single amino
acid)
© 2011 Pearson Education, Inc.
Figure 3.8
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2
Module 3.8: Protein synthesis
• DNA (continued)
• Gene
• Functional unit of heredity
• All the DNA nucleotides needed to produce a
specific protein
• Size varies (~3003000 nucleotides)
© 2011 Pearson Education, Inc.
Module 3.8: Protein synthesis
• Gene activation
• Removal of histones and DNA uncoiling
• Messenger RNA (mRNA)
• Assembled by enzymes
• Connecting complementary RNA nucleotides
• (A, G, C, U)
• Contains information in triplets (codons)
• Leaves nucleus through pores
• Transfer RNA (tRNA)
• Contains triplets (anticodons) that bind to mRNA codons
• Each type carries a specific amino acid linked to form a
polypeptide
© 2011 Pearson Education, Inc.
Module 3.8: Protein synthesis
Animation: Protein Synthesis: RNA Polymerase
Animation: Protein Synthesis: Transcription and
Translation
© 2011 Pearson Education, Inc.
The key events of protein synthesis
Uncoiling of the portion of DNA molecule
containing an activated gene
DNA triplets are exposed to the nucleoplasms
Paired DNA strands
Enzyme
Assembly of an mRNA strand by enzymes
The mRNA strand containing
the complementary codons
passes through a nuclear pore
and enters the cytoplasm.
Binding of transfer RNA (tRNA) molecules
carrying a specific amino acid
Codon on mRNA
Amino acid
tRNA attaches
to mRNA
Anticodon
mRNA strand
Linking of amino acids to form
a polypeptide
Codon
Polypeptide
methionine-proline-serine-leucine
Figure 3.8
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3
– 6
A summary of how DNA codes for a protein
The DNA
triplets
determine the
sequence of
mRNA codons.
The mRNA
codons
determine
the sequence
of tRNAs.
The sequence of tRNAs
determines the
sequence of amino
acids in the polypeptide
or protein.
Figure 3.8
© 2011 Pearson Education, Inc.
6
Module 3.8 Review
a. List the three types of RNA involved in protein
synthesis.
b. What is a gene?
c. Why is the genetic code described as a triplet
code?
© 2011 Pearson Education, Inc.
Module 3.9: Transcription
• Transcription (“to copy” or “rewrite”)
• Production of RNA from DNA template
• All three types of RNA are formed
• Example:
• mRNA (information for synthesizing proteins)
© 2011 Pearson Education, Inc.
Module 3.9: Transcription
• Steps of transcription
1. Gene activation
• Occurs at control segment (1st segment of gene)
• Template strand (One DNA strand used to
synthesize RNA)
2. RNA polymerase (enzyme)
• Binds to promoter
• Assembles mRNA strand
• Complementary to DNA
• Example: (DNA triplet TAC = mRNA AUG)
• Hydrogen bonds between nucleotides
© 2011 Pearson Education, Inc.
Events in the process of transcription of mRNA
The template
strand is the
DNA strand that
will be used to
synthesize RNA.
The enzyme
RNA polymerase
binds to the
exposed promoter
and, using the
triplets as a guide,
assembles a
strand of mRNA.
Triplet 1
1
Triplet 2
2
Triplet 3
3
Triplet 4
4
Gene
Gene activation, which results in temporary
disruption of the hydrogen bonds between the
nitrogenous bases of the two DNA strands
DNA
Complementary
triplets
The segment
at the start of the
gene is known as
the control
segment.
2
Adenine
Guanine
Cytosine
Uracil (RNA)
Thymine (DNA)
Figure 3.9
© 2011 Pearson Education, Inc.
1
Module 3.9: Transcription
• Steps of transcription (continued)
3. Transcription ends
•
Stop codon reached
•
mRNA detaches
•
Complementary DNA strands reassociate
(hydrogen bonding between complementary
base pairs)
© 2011 Pearson Education, Inc.
Immature mRNA
Events in the process of transcription of mRNA (continued)
Introns
removed
RNA polymerase works only
on RNA nucleotides—it can
attach adenine, guanine,
cytosine, or uracil, but never
thymine. If the DNA triplet is
TAC, the corresponding
mRNA codon will be AUG.
Exons spliced together
to from mature mRNA
The production of functional mRNA
from immature mRNA
mRNA strand
Codon 1
Codon
2
Codon
1
Codon
3
Codon 4
(stop codon)
RNA
nucleotide
RNA
polymerase
Hydrogen bonding between
the nitrogenous bases of
the template strand and
complementary nucleotides
in the nucleoplasm
RNA
polymerase
Conclusion of transcription
when stop codon is reached
Adenine
Guanine
Cytosine
Uracil (RNA)
Thymine (DNA)
Figure 3.9
© 2011 Pearson Education, Inc.
2
– 3
Module 3.9: Transcription
• Immature RNA
• Contains triplets not needed for protein
synthesis
• “Edited” before leaving nucleus through pores
• Introns (removed nonsense regions)
• Exons (remaining coding segments)
• Creates shorter, functional mRNA
• Changing “edits” can produce mRNAs for
different proteins
© 2011 Pearson Education, Inc.
Immature mRNA
Introns
removed
Exons spliced together
to form mature mRNA
The production of functional mRNA
from immature mRNA
Figure 3.9
© 2011 Pearson Education, Inc.
4
Module 3.9 Review
a. Define DNA template strand.
b. What is transcription?
c. What process would be affected if a cell could
not synthesize the enzyme RNA polymerase?
© 2011 Pearson Education, Inc.
Module 3.10: Translation
• Translation (translate nucleic acids to
proteins)
• Uses mRNA created in nucleus
• Leaves via nuclear pores
• Occurs in cytoplasm
Animation: Protein Synthesis:
Translation Initiation
© 2011 Pearson Education, Inc.
Module 3.10: Translation
• Steps of translation
1. mRNA binds to small ribosomal subunit
•
Binding between mRNA and tRNA
•
mRNA codons with tRNA anticodons
2. Small and large ribosomal subunits assemble
around mRNA strand
•
Additional tRNAs arrive
•
More than 20 kinds
•
© 2011 Pearson Education, Inc.
At least one for each amino acid
The process of translation
NUCLEUS
Amino acid
tRNA
Anticodon
tRNA binding sites
Entry of mRNA into cytoplasm
Start codon
mRNA strand
Small
ribosomal
subunit
Adenine
Guanine
Binding of mRNA strand to a small
ribosomal subunit and arrival of the
first tRNA
Large
ribosomal
subunit
Joining of small and large
ribosomal subunits around the
mRNA strand and arrival of
additional tRNAs
Cytosine
Uracil
Figure 3.10
© 2011 Pearson Education, Inc.
1
– 2
Module 3.10: Translation
• Steps of translation (continued)
3. Ribosome attaches to next complementary
tRNA
4. Ribosome links amino acids forming dipeptide
•
More tRNAs arrive and continue forming
polypeptide
5. Stops once stop codon is reached on mRNA
•
Ribosomal subunits detach
•
Leaves intact mRNA and new polypeptide
Animation: Protein Synthesis: Sequence of Amino Acids
in the Newly Synthesized Polypeptide
© 2011 Pearson Education, Inc.
The process of translation (continued)
Small ribosomal
subunit
Peptide
bond
Large
ribosomal
subunit
Completed
polypeptide
Stop
codon
Attachment of tRNA with
anticodon that is complementary
to codon on RNA strand
Formation of a depeptide,
release of first tRNA, and
arrival of another tRNA
Completion of polypeptide and
detachment of ribosomal
subunits
Adenine
Guanine
Cytosine
Uracil
Figure 3.10
© 2011 Pearson Education, Inc.
3
– 5
Module 3.10: Translation
• Translation
• Produces a typical protein in ~20 seconds
• mRNA can interact with other ribosomes and
produce more proteins
• Multiple ribosomes can attached to a single
mRNA strand to quickly produce many proteins
Animation: Transcription Translation
© 2011 Pearson Education, Inc.
Module 3.10 Review
a. What is translation?
b. The nucleotide sequence of three mRNA codons is AUUGCA-CUA. What is the complementary anticodon
sequence for the second codon?
c. During the process of transcription, a nucleotide was
deleted from an mRNA sequence that coded for a protein.
What effect would this deletion have on the amino acid
sequence of the protein?
© 2011 Pearson Education, Inc.
Section 3: Membrane Transport
• Learning Outcomes
• 3.11 Explain the process of diffusion, and
identify its significance to the body.
• 3.12 Explain the process of osmosis, and
identify its significance to the body.
• 3.13 Describe carrier-mediated transport and
its role in the absorption and removal of
specific substances.
• 3.14 Describe vesicular transport as a
mechanism for facilitating the absorption
or removal of specific substances from
cells.
© 2011 Pearson Education, Inc.
Section 3: Membrane Transport
• Plasma membrane
• Acts as a barrier separating cytosol and ECF
• Must still coordinate cellular activity with
extracellular environment
• Permeability (determines which substances can
cross membrane)
• Freely permeable (any substances)
• Selectively permeable (some substances cross)
• Impermeable (none can pass)
• No living cell is impermeable
© 2011 Pearson Education, Inc.
Permeability characteristics of membranes
Freely permeable membranes
Ions
Protein
Selectively permeable membranes
Carbohydrates
Ions
Protein
—
Lipids
Freely permeable membranes
allow any substance to pass without
difficulty.
Carbohydrates
Ions
Protein
—
Water
Impermeable membranes
—
Water
Water
Lipids
Selectively permeable membranes,
such as plasma membranes, permit the
passage of some materials and prevent
the passage of others.
Carbohydrates
Lipids
Nothing can pass through impermeable
membranes. Cells may be impermeable
to specific substances, but no living cell
has an impermeable membrane.
Figure 3 Section 3
© 2011 Pearson Education, Inc.
1
Section 3: Membrane Transport
• Selectively permeable membranes
• Selective based on:
1. Characteristics of material to pass
• Size
• Electrical charge
• Molecular shape
• Lipid solubility
• Other factors
2. Characteristics of membrane
• What lipids and proteins present
• How components are arranged
© 2011 Pearson Education, Inc.
Section 3: Membrane Transport
• Selectively permeable membranes
• Types of membrane transport
1. Passive (do not require ATP)
• Diffusion
• Carrier-mediated transport
2. Active (require ATP)
• Vesicular transport
• Carrier-mediated transport
© 2011 Pearson Education, Inc.
Characteristics of selectively
permeable membranes
EXTRACELLULAR
FLUID
Plasma
membrane
Materials may cross
the plasma membrane
through active or
passive mechanisms.
Passive mechanisms
do not require ATP.
Diffusion is
movement driven
by concentration
differences.
Active mechanisms
require ATP.
Carrier-mediated
transport involves
carrier proteins, and
the movement may
be passive or active.
Vesicular transport
involves the
formation of
intracellular
vesicles; this is an
active process.
CYTOPLASM
Figure 3 Section 3
© 2011 Pearson Education, Inc.
2
Module 3.11: Diffusion
• Diffusion
• Continuous random movement of ions or molecules
in a liquid or gas resulting in even distribution
• Gradient
• Concentration difference or when molecules are not
evenly distributed
• At an even distribution, molecular motion continues
but no net movement
• Slow in air and water but important over small
distances
Animation: Membrane Transport: Diffusion
© 2011 Pearson Education, Inc.
Figure 3.11
© 2011 Pearson Education, Inc.
1
Module 3.11: Diffusion
• In ECF
• Water and solutes diffuse freely
• Across plasma membrane
• Selectively restricted diffusion
• Movement across lipid portion of membrane
• Examples: lipids, lipid-soluble molecules, soluble
gases
• Movement through membrane channel
• Examples: water, small water-soluble molecules,
ions
• Movement using carrier molecules
• Example: large molecules
© 2011 Pearson Education, Inc.
The effects of the plasma membrane, a selectively permeable membrane, on
the diffusion of various substances
EXTRACELLULAR FLUID
Lipids, lipid-soluble molecules,
and soluble gases (O2 and CO2)
can diffuse across the lipid bilayer
of the plasma membrane.
Water, small water-soluble molecules,
and ions diffuse through membrane channels.
Channel
protein
Plasma membrane
Large molecules that cannot fit
through the membrane channels
and cannot diffuse through the
membrane lipids can only cross
the plasma membrane when
transported by a carrier mechanism.
CYTOPLASM
Figure 3.11
© 2011 Pearson Education, Inc.
2
Module 3.11: Diffusion
• Factors that influence diffusion rates:
• Distance (inversely related)
• Molecule size (inversely related)
• Temperature (directly related)
• Gradient size (directly related)
• Electrical forces
• Attraction of opposite charges (+,–)
• Repulsion of like charges (+,+ or –,–)
© 2011 Pearson Education, Inc.
Module 3.11 Review
a. Define diffusion.
b. Identify factors that influence diffusion rates.
c. How would a decrease in the oxygen
concentration in the lungs affect the diffusion
of oxygen into the blood?
© 2011 Pearson Education, Inc.
Module 3.12: Osmosis
• Osmosis (osmos, a push)
• Net diffusion of water across a membrane
• Maintains similar overall solute concentrations between the
cytosol and extracellular fluid
• Osmotic flow
• Movement of water driven by osmosis
• Osmotic pressure
• Indication of force of pure water moving into a solution
with higher solute concentration
• Hydrostatic pressure
• Fluid force
• Can be estimate of osmotic pressure when applied
to stop osmotic flow
© 2011 Pearson Education, Inc.
Osmotic flow, the movement of water driven by osmosis
Volume
increased
Volume
decreased
Original
level
Applied
force
Volumes
equal
Water
molecules
Solute
molecules
Selectively permeable membrane
A selectively permeable membrane
separates these two solutions,
which have different solute
concentrations. Water molecules
(small blue dots) begin to cross
the membrane toward solution B,
the solution with the higher
concentration of solutes (larger
pink circles).
At equilibrium, the solute
concentrations on the two
sides of the membrane are
equal. Note that the volume
of solution B has increased
at the expense of that of
solution A.
Pushing against a fluid generates
hydrostatic pressure. The
osmotic pressure of solution B
is equal to the amount of
hydrostatic pressure, indicated
by the weight, required to stop
the osmotic flow.
Figure 3.12
© 2011 Pearson Education, Inc.
1
Module 3.12: Osmosis
• Osmolarity (osmotic concentration)
• Total solute concentration in an aqueous
solution
• Tonicity
• Effect of osmotic solutions on cell volume
• Three effects
1. Isotonic (iso-, same + tonos, tension)
•
Solution that does not cause osmotic flow
across membrane
© 2011 Pearson Education, Inc.
Module 3.12: Osmosis
• Tonicity
• Three effects (continued)
2. Hypotonic
•
Causes osmotic flow into cell
•
Example: hemolysis (hemo-, blood + lysis,
loosening)
3. Hypertonic
•
Causes osmotic flow out of cell
•
Example: crenation of RBCs
© 2011 Pearson Education, Inc.
Module 3.12: Osmosis
• Importance of tonicity vs. osmolarity: Example
• Administering large fluid volumes to patients with blood loss
or dehydration
• Administered solution has same osmolarity as ICF but
higher concentrations of individual ions/molecules
• Diffusion of solutes may occur across cell
membrane
• Water will follow through osmosis
• Cell volume increases
• Normal saline
• 0.9 percent or 0.9 g/dL of NaCl
• Isotonic with blood
© 2011 Pearson Education, Inc.
Module 3.12 Review
a. Describe osmosis.
b. Contrast the effects of a hypotonic solution
and a hypertonic solution on a red blood cell.
c. Some pediatricians recommend using a 10
percent salt solution to relieve nasal
congestion in infants. Explain the effects this
treatment would have on the cells lining the
nasal cavity. Would it be effective?
© 2011 Pearson Education, Inc.
Module 3.13: Carrier-mediated transport
• Carrier-mediated transport
• Hydrophilic or large molecules transported
across cell membrane by carrier proteins
• Many move specific molecules through the
plasma membrane in only one direction
• Cotransport (>1 substance same direction)
• Countertransport (2 substances in opposite
directions)
• Carrier called exchange pump
© 2011 Pearson Education, Inc.
Module 3.13: Carrier-mediated transport
• Carrier-mediated transport
• Three types
1. Facilitated diffusion
• Requires no ATP (= passive)
• Movement limited by number of available carrier
proteins (= can become saturated)
2. Active transport
• Requires energy molecule or ATP (= active)
• Independent of concentration gradient
• Examples:
• Ion pumps (Na+, K+, Ca2+, and Mg2+)
• Sodium–potassium ATPase
© 2011 Pearson Education, Inc.
Module 3.13: Carrier-mediated transport
Animation: Membrane Transport: Active Transport
Animation: Membrane Transport: Facilitated Diffusion
© 2011 Pearson Education, Inc.
Facilitated diffusion
EXTRACELLULAR
FLUID
Glucose
molecule
Receptor site
Glucose released
into cytoplasm
Carrier
protein
CYTOPLASM
Facilitated diffusion begins when a specific
molecule, such as glucose, binds to a receptor
site on the integral protein.
The shape of the protein then changes, moving
the molecule across the plasma membrane. The
carrier protein then releases the transported
molecule into the cytoplasm. Note that this was
accomplished without ever creating a continuous
open channel between the extracellular fluid and
the cytoplasm.
Figure 3.13
© 2011 Pearson Education, Inc.
1
Active transport
EXTRACELLULAR
FLUID
Sodium–
potassium
exchange
pump
CYTOPLASM
Sodium ion concentrations are
high in the extracellular fluids,
but low in the cytoplasm. The
distribution of potassium in the
body is just the opposite: low in
the extracellular fluids and high
in the cytoplasm. As a result,
sodium ions slowly diffuse into
the cell, and potassium ions
diffuse out through leak
channels. Homeostasis within
the cell depends on the ejection
of sodium ions and the recapture
of lost potassium ions. The
sodium–potassium exchange
pump is a carrier protein called
sodium–potassium ATPase. It
exchanges intracellular sodium
for extracellular potassium.
On average, for each ATP molecule consumed, three sodium ions are ejected and the
cell reclaims two potassium ions. The energy demands are impressive: Sodiumpotassium ATPase may use up to 40 percent of the ATP produced by a resting cell!
Figure 3.13
© 2011 Pearson Education, Inc.
2
Module 3.13: Carrier-mediated transport
• Carrier-mediated transport (continued)
• Three types (continued)
3. Secondary active transport
•
Transport mechanism does not require ATP
•
Cell often needs ATP to maintain homeostasis
associated with transport
© 2011 Pearson Education, Inc.
Secondary active transport
Glucose
molecule
Sodium
ion
+
Na+–K+
pump
CYTOPLASM
A sodium ion and a glucose
molecule bind to receptor
sites on the carrier protein.
+
To preserve homeostasis, the
cell must then expend ATP to
pump the arriving sodium ions
out of the cell by using the
sodium–potassium exchange
pump. It thus “costs” the cell
one ATP for every three
glucose molecules it
transports into the cell.
The carrier protein then changes shape,
opening a path to the cytoplasm and
releasing the transported materials. It
then reassumes its original shape and is
ready to repeat the process.
Figure 3.13
© 2011 Pearson Education, Inc.
3
Module 3.13 Review
a. Describe the process of carrier-mediated
transport.
b. What do the transport processes of facilitated
diffusion and active transport have in common?
c. During digestion, the concentration of hydrogen
ions (H+) in the stomach contents increases to
many times that in cells lining the stomach.
Which transport process could be responsible?
© 2011 Pearson Education, Inc.
Module 3.14: Vesicular transport
• Vesicular transport
• Materials move across cell membrane in small
membranous sacs
• Sacs form at or fuse with plasma membrane
• Two major types (both require ATP)
1. Endocytosis
2. Exocytosis
© 2011 Pearson Education, Inc.
Module 3.14: Vesicular transport
• Vesicular transport (continued)
• Two major types (both require ATP)
1. Endocytosis (into cell using endosomes)
a. Receptor-mediated endocytosis
1) Ligand binds to receptor
2) Plasma membrane folds around receptors
bound to ligands
3) Coated vesicle forms
4) Vesicle fuses with lysosomes
5) Ligands freed and enter cytosol
6) Lysosome detaches from vesicle
7) Vesicle fuses with plasma membrane again
© 2011 Pearson Education, Inc.
Receptor-mediated endocytosis
Receptor-mediated endocytosis begins when materials in the
extracellular fluid bind to receptors on the membrane surface. Most
receptor molecules are glycoproteins, and each binds to a specific
ligand, or target, such as a transport protein or a hormone.
After the vesicle
membrane
detaches, it
returns to the
cell surface,
where its receptors become
available to bind
more ligands.
Ligands binding
to receptors
Exocytosis
Endocytosis
Ligand
receptors
The vesicle
membrane
detaches from
the secondary
lysosome.
The lysosomal
enzymes then
free the ligands
from their
receptors, and
the ligands enter
the cytosol by
diffusion or
active transport.
Ligands
EXTRACELLULAR FLUID
Receptors bound to
ligands cluster together.
Once an area of the
plasma membrane has
become covered with
ligands, it forms
grooves or pockets that
move to one area of the
cell and then pinch off
to form an endosome.
The endosomes
produced in this way
are called coated
vesicles, because
they are “coated” by a
protein-fiber network
on the inner membrane
surface.
Coated
vesicle
CYTOPLASM
The coated vesicles
fuse with lysosomes
filled with digestive
enzymes.
Lysosome
Ligands
removed
Figure 3.14
© 2011 Pearson Education, Inc.
1
Module 3.14: Vesicular transport
• Vesicular transport (continued)
• Two major types (both require ATP)
1. Endocytosis (into cell using endosomes) (continued)
b. Pinocytosis (“cell drinking”)
• Formation of endosomes with ECF
• No receptor proteins involved
c. Phagocytosis (“cell eating”)
• Produces phagosomes containing solids
• Phagocytes or macrophages perform
phagocytosis
2. Exocytosis
• Vesicle discharges materials into ECF
© 2011 Pearson Education, Inc.
Pinocytosis begins with the
formation of deep grooves
or pockets that then pinch
off and enter the cytoplasm.
The steps are similar to
those of receptor-mediated
endocytosis, but they occur
in the absence of ligand
binding.
Plasma membrane
Completed pinosome
Pinocytosis
Color enhanced TEM x 20,000
Figure 3.14
© 2011 Pearson Education, Inc.
2
Bacterium
Pseudopodium
Phagocytosis
Lysosome
Phagocytosis begins when cytoplasmic extensions called pseudopodia
(soo-dō-PŌ-dē-ah; pseduo-, false
podon, foot; singular pseudopodium)
surround the object.
The vesicular events linking
phagocytosis and exocytosis
The pseudopodia then fuse at their
tips to form a phagosome containing
the targeted material.
This vesicle then fuses with many
lysosomes, whereupon its contents
are digested by lysosomal enzymes.
Golgi
apparatus
Released nutrients are absorbed.
Exocytosis
The residue is then ejected from the
cell through exocytosis.
Figure 3.14
© 2011 Pearson Education, Inc.
3
Module 3.14 Review
a. Describe endocytosis.
b. Describe exocytosis.
c. When they encounter bacteria, certain types
of white blood cells engulf the bacteria and
bring them into the cell. What is this process
called?
© 2011 Pearson Education, Inc.
Section 4: Cell Life Cycle
• Learning Outcomes
• 3.15 Describe interphase, and explain its
significance.
• 3.16 Describe the process of mitosis, and the
cell life cycle.
• 3.17 Discuss the relationship between cell
division and cancer.
© 2011 Pearson Education, Inc.
Section 4: Cell Life Cycle
• Cell division
• Production of daughter cells from single cell
• Important in organism development and survival
• Cells have varying life spans and abilities to divide
• Often genetically controlled death occurs (apoptosis)
• Two types
1. Mitosis (2 daughter cells, each with 46 chromosomes)
2. Meiosis (sex cells, each with only 23 chromosomes)
Animation: Cell Life Cycle
© 2011 Pearson Education, Inc.
Section 4: Cell Life Cycle
• Mitosis
• Pair of daughter cells half the size of parent cell
• Grow to size of original cell before dividing
• Identical copies of chromosomes in each
• Ends at complete cell separation (= cytokinesis)
• Followed by nondividing period (= interphase)
• Cell performs normal activities OR
• Prepares to divide again
• Chromosomes duplicated
• Associated proteins synthesized
© 2011 Pearson Education, Inc.
The production of a pair of daughter
cells from a single cell division
Original
cell
Cell
division
Daughter
cells
Figure 3 Section 4
© 2011 Pearson Education, Inc.
1
Module 3.15: Interphase
• Phases
• G0 (performing normal cell functions)
• Examples:
• Skeletal muscle cells (stay in this phase forever)
• Stem cells (never enter G0; divide repeatedly)
• G1 (normal cell function plus growth and
duplication of organelles)
• S (duplication of chromosomes)
• G2 (last minute protein synthesis and centriole
replication)
© 2011 Pearson Education, Inc.
Module 3.15: Interphase
• DNA replication
• Strands unwind
• DNA polymerase binds
• Assembles new DNA strand covalently linking
nucleotides
• Works only in one direction
• One polymerase works continuously along one
strand toward “zipper”
• One polymerase works away from “zipper”
• As “unzipping” occurs, another polymerase
binds closer point of unzipping
• Two new DNA segments bound with ligases
• Two identical DNA strands formed
© 2011 Pearson Education, Inc.
The events in DNA
replication, which
occurs during the
S phase of interphase
DNA replication beings when enzymes unwind the
strands and disrupt the hydrogen bonds between the
bases. As the strands unwind, molecules of DNA
polymerase bind to the exposed nitrogenous bases. This
enzyme (1) promotes bonding between the nitrogenous
bases of the DNA strand and complementary DNA
nucleotides dissolved in the nucleoplasm and (2) links the
nucleotides by covalent bonds.
As the two original stands gradually
separate, DNA polymerase binds to the
strands. DNA polymerase can work in
only one direction along a strand of DNA,
but the two strands in a DNA molecule
are oriented in opposite directions. The
DNA polymerase bound to the upper
strand shown here adds nucleotides to
make a single, continuous complementary
copy that grows toward the “zipper.”
Segment 2
DNA nucleotide
Segment 1
Adenine
Guanine
Cytosine
Thymine
Thus, a second DNA polymerase must bind closer
to the point of unzipping and assemble a complementary copy (segment 2) that grows until it
“bumps into” segment 1 created by the first DNA
polymerase. The two segments are then spliced
together by enzymes called ligases (LĪ-gās-ez;
liga, to tie).
DNA polymerase on the lower strand can
work only away from the zipper. So the
first DNA polymerase to bind to this
strand must add nucleotides and build a
complementary DNA strand moving from
left to right. As the two original strands
continue to unzip, additional nucleotides
are continuously being exposed to the
nucleoplasm. The first DNA polymerase
on this strand cannot go into reverse; it
can only continue to elongate the strand
it already started.
Figure 3.15
© 2011 Pearson Education, Inc.
2
Duplicated DNA double helices
Figure 3.15
© 2011 Pearson Education, Inc.
3
Module 3.15 Review
a. Describe interphase, and identify its stages.
b. What enzymes must be present for DNA
replication to proceed normally?
c. A cell is actively manufacturing enough
organelles to serve two functional cells. This
cell is probably in what phase of interphase?
© 2011 Pearson Education, Inc.
Module 3.16: Mitosis
• Mitosis
• Division and duplication of cell’s nucleus
• Phases
1. Prophase (pro-, before)
•
•
Paired chromosomes tightly coiled
•
Chromatid (each copy)
•
Connected at centromere with raised area
(kinetochore)
Replicated centrioles move to poles
•
Astral rays (extend from centrioles)
•
Spindle fibers (interconnect centriole pairs)
© 2011 Pearson Education, Inc.
The events in mitosis
Chromatids
The centrioles
have replicated,
and the pairs
now move to
opposite sides
of the nucleus.
Centrioles in
centrosome
Nucleus
Interphase, which
precedes mitosis
Microtubules extend outward
from each pair of centrioles:
astral rays extend into the
cytoplasm, whereas spindle
fibers interconnect the
centriole pairs.
The nuclear
membrane
disintegrates
during this period.
Kinetochore
The kinetochore of
each chromatid
becomes attached
to a spindle fiber.
Prophase, the first phase of mitosis
Figure 3.16
© 2011 Pearson Education, Inc.
1
– 2
Module 3.16: Mitosis
• Mitosis (continued)
• Phases (continued)
2. Metaphase (meta, after)
• Chromosomes align at metaphase plate
3. Anaphase (ana-, apart)
• Chromatids separate
• Drawn along spindle apparatus
4. Telophase (telo-, end)
• Cells prepare to enter interphase
• Cytoplasm constricts along metaphase plate
(= cleavage furrow)
• Nuclear membranes re-form
• Chromosomes uncoil
© 2011 Pearson Education, Inc.
The events in mitosis (continued)
The two chromatids are now pulled
apart and drawn to opposite ends of
the cell along the spindle
apparatus (the complex of spindle
fibers). Anaphase ends when the
chromatids arrive near the centrioles
at opposite ends of the cell.
As the chromatids approach
the ends of the spindle
apparatus, the cytoplasm
constricts along the plane of
the metaphase plate, forming
a cleavage furrow.
CYTOKINESIS
Metaphase plate
Metaphase
Anaphase
Telophase, the final
phase of mitosis
Daughter
cells
Cytokinesis
Figure 3.16
© 2011 Pearson Education, Inc.
3
– 6
Module 3.16: Mitosis
• Cytokinesis (cyto-, cell + kinesis, motion)
• Begins with formation of cleavage furrow
• Continues through telophase
• Completion marks end of cell division
© 2011 Pearson Education, Inc.
Module 3.16 Review
a. Define mitosis, and list its four stages.
b. What is a chromatid, and how many would be
present during normal mitosis in a human
cell?
c. What would happen if spindle fibers failed to
form in a cell during mitosis?
© 2011 Pearson Education, Inc.
Module 3.17: Tumors and cancer
• Cancer
• Illness that disrupts normal rates of cell division
• Characterized by permanent DNA sequence
changes (= mutations)
• Most common in tissues with actively dividing
cells
• Examples: skin, intestinal lining
• Compete with normal cells for resources
© 2011 Pearson Education, Inc.
Module 3.17: Tumors and cancer
• Cancerous tumor (neoplasm; mass of cells)
types
1. Benign
•
Remain in original tissue
2. Malignant
•
Accelerated growth due to blood vessel growth
and supply to the area
•
Invasion (cells migrating into surrounding
tissues)
•
Metastasis (formation of secondary tumors)
© 2011 Pearson Education, Inc.
Module 3.17 Review
a. Define metastasis.
b. What is a benign tumor?
c. Define cancer.
© 2011 Pearson Education, Inc.