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Chapter 03
Lecture Outline*
Rod R. Seeley
Idaho State University
Trent D. Stephens
Idaho State University
Philip Tate
Phoenix College
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3-1
Chapter 3
Cell Biology and Genetics
3-2
Basic Structure of the Cell
• Plasma membrane
• Cytoplasm containing organelles
• Nucleus
3-3
Functions of the Cell
• Cell metabolism and energy use
• Synthesis of molecules
• Communication. Cells produce and receive
electrical and chemical signals
• Reproduction and Inheritance. Each cell contains
DNA. Some cells are specialized to gametes for
exchange during sexual intercourse
3-4
Plasma Membrane
• Separation of intracellular vs.
extracellular materials
• Production of charge difference
(membrane potential) across the
membrane by regulation of
intracellular and extracellular ion
concentrations
– Outside of membrane positively
charged compared to inside because
of gathering ions along outside and
inside
• Glycocalyx: combinations of
carbohydrates and lipids
(glycolipids) and proteins
(glycoproteins) on outer surface.
• Fluid-mosaic model
3-5
Membrane Lipids
• Phospholipids and cholesterol predominate
– Phospholipids: bilayer. Polar heads
facing water in the interior and exterior
of the cell (hydrophilic); nonpolar tails
facing each other on the interior of the
membrane (hydrophobic)
– Cholesterol: interspersed among
phospholipids. Amount determines
fluid nature of the membrane
• Fluid nature provides/allows
– Distribution of molecules within the
membrane
– Phospholipids automatically
reassembled if membrane is damaged
– Membranes can fuse with each other
3-6
Membrane Proteins
• Integral or intrinsic
– Extend deeply into membrane,
often extending from one
surface to the other
– Can form channels through the
membrane
• Peripheral or extrinsic
– Attached to integral proteins at
either the inner or outer surfaces
of the lipid bilayer
• Functioning depends on 3-D shape
and chemical characteristics.
Markers, attachment sites,
channels, receptors, enzymes, or
carriers.
3-7
Marker Molecules:
Glycoproteins and Glycolipids
• Allow cells to identify
one another or other
molecules
– Immunity
– Recognition of oocyte
by sperm cell
– Intercellular
communication
3-8
Attachment Proteins
• Cadherins – attach cells
to other cells
• Integrins – integral
proteins that attach to
extracellular molecule
– Sometimes allow
communication due to
contact with intracellular
molecules
3-9
Transport Proteins
• Hydrophilic region faces
inward; charge
determines molecules
that can pass through
• Includes channel
proteins, carrier
proteins, and ATPpowered pumps.
3-10
Channel Proteins
• Nongated ion channels: always
open
– Responsible for the permeability of
the plasma membrane to ions when
the plasma membrane is at rest
• Gated ion channels can be opened
or closed by certain stimuli
– Ligand gated ion channel: open in
response to small molecules that bind
to proteins or glycoproteins
– Voltage-gated ion channel: open
when there is a change in charge
across the plasma membrane
3-11
Carrier Proteins
• Also called transporters
• Integral proteins move ions from
one side of membrane to the
other
– Have specific binding sites
– Protein changes shape to transport
ions or molecules
– Resumes original shape after
transport
3-12
Carrier Proteins (cont.)
• Carrier proteins come in several
forms
– Uniporters – moves one particle
– Symporters – move two particles
in the same direction at the same
time
– Antiporters – move two particles
in opposite directions at the same
time
3-13
ATP-Powered Transport
• Requires ATP. The use of
energy allows the cell to
accumulate substances
• Rate of transport depends on
concentration of substrate
and on concentration of ATP
3-14
Receptor Proteins
• Proteins or glycoproteins in membranes with an exposed
receptor site
• Can attach to specific chemical signal molecules and act
as an intercellular communication system
• Ligand can attach only to cells with that specific receptor
3-15
Receptors Linked to
Channel Proteins
• Receptor molecules linked to channel
proteins
• Attachment of receptor-specific
chemical signals (e.g., acetylcholine) to
receptors causes change in shape of
channel protein
• Channel opens or closes
• Changes permeability of cell to some
substances
– Cystic fibrosis: defect in genes
causes defect(s) in channel proteins
– Drugs used to alter membrane
permeability through attachment to
channel protein-linked receptors
3-16
Receptors Linked to G Protein
Complexes
• Alter activity on inner surface of
plasma membrane
• Leads to intracellular chemical
signals that affect cell function
• Some hormones function in this
way
3-17
Enzymes in the Plasma
Membrane
• Enzymes: some act to catalyze reactions at outer/inner
surface of plasma membrane. Surface cells of small
intestine produce enzymes that digest dipeptides
3-18
Summary of Membrane Proteins
3-19
Movement through the
Plasma Membrane
•
•
•
•
Diffusion
Osmosis
Filtration
Mediated Transport
– Facilitated diffusion
– Active transport
– Secondary active transport
3-20
Diffusion
• Movement of solutes from an area of higher
concentration to lower concentration in solution
– Concentration or density gradient: difference
between two points
– Viscosity: how easily a liquid flows
3-21
Osmosis
• Diffusion of water (solvent) across a
selectively permeable membrane. Water moves
from an area of low concentration of solute to
an area of high concentration of solute
• Osmotic pressure: force required to prevent
water from moving across a membrane by
osmosis
3-22
Osmosis
• Comparative terms used
to describe osmotic
pressures of solutions
– Isosmotic: solutions with
the same concentrations of
solute particles
– Solution with a greater
concentration of solute is
hyperosmotic
– Solution with a lesser
concentration of solute is
hyposmotic
3-23
Osmosis and Cells
• Important because large volume changes caused by water movement
disrupt normal cell function
• Cell shrinkage or swelling
– Isotonic: cell neither shrinks nor swells
– Hypertonic: cell shrinks (crenation)
– Hypotonic: cell swells (lysis)
3-24
Filtration
• Works like a sieve
• Depends on pressure difference on either side
of a partition
• Moves from side of greater pressure to lower
• Example: urine formation in the kidneys.
Water and small molecules move through the
membrane while large molecules remain in the
blood
3-25
Mediated Transport
• Involve carrier proteins or
channels in the cell
membrane
• Characteristics
– Specificity for a single type
of molecule
– Competition among
molecules of similar shape
– Saturation: rate of
transport limited to number
of available carrier proteins
3-26
Saturation of a Carrier Protein
1.
2.
3.
When the concentration of x molecules outside the cell is low, the transport
rate is low because it is limited by the number of molecules available to be
transported.
When more molecules are present outside the cell, as long as enough carrier
proteins are available, more molecules can be transported; thus, the transport
rate increases.
The transport rate is limited by the number of carrier proteins and the rate at
which each carrier protein can transport solutes. When the number of
molecules outside the cell is so large that the carrier proteins are all occupied,
the system is saturated and the transport rate cannot increase.
3-27
Mediated Transport – Facilitated Diffusion
• Facilitated diffusion:
carrier- or channelmediated. Passive.
– Move large, water
soluble molecules or
electrically charged
molecules across the
plasma membrane.
– Amino acids and glucose
in, manufactured proteins
out.
3-28
Mediated Transport – Active Transport
• ATP-Powered Transport
– Requires ATP. The use of energy
allows the cell to accumulate
substances
– Rate of transport depends on
concentration of substrate and on
concentration of ATP
– Example: Na+/K+ exchange
pump that creates electrical
potentials across membranes
3-29
Mediated Transport –
Secondary Active Transport
•
•
•
Ions or molecules move in same
(symport) or different (antiport)
direction.
Is the movement of glucose a symporter
example or an antiporter example?
This example shows cotransport of Na+
and glucose.
1. A sodium-potassium exchange
pump maintains a concentration of
Na that is higher outside the cell
than inside. Active transport.
2. Na moves back into the cell by a
carrier protein that also moves
glucose. The concentration gradient
for Na provides the energy required
to move glucose against its
concentration gradient.
3-30
Endocytosis
• Internalization of substances by formation of a vesicle
• Types
– Phagocytosis (shown)
– Pinocytosis
– Receptor-mediated endocytosis
3-31
Pinocytosis and
Receptor-Mediated Endocytosis
3-32
Exocytosis
• Accumulated vesicle secretions expelled from cell
• Examples
– Secretion of digestive enzymes by pancreas
– Secretion of mucous by salivary glands
– Secretion of milk by mammary glands
3-33
Cytoplasm
• Cellular material outside
nucleus but inside plasma
membrane
• Composed of Cytosol,
Cytoskeleton, Cytoplasmic
Inclusions, Organelles
• Cytosol: fluid portion.
Dissolved molecules (ions
in water) and colloid
(proteins in water)
3-34
Cytoskeleton
• Supports the cell but has to allow for
movements like changes in cell shape
and movements of cilia
– Microtubules: hollow, made of
tubulin.
• Internal scaffold, transport, cell
division
– Microfilaments: actin.
• Structure, support for microvilli,
contractility, movement
– Intermediate filaments:
mechanical strength
• Cytoplasmic inclusions: aggregates
of chemicals such as lipid droplets,
melanin
3-35
Organelles
• Small specialized structures with particular
functions
• Most have membranes that separate interior
of organelles from cytoplasm
• Related to specific structure and function of
the cell
3-36
Nucleus
• Membrane-bound
• Nucleoplasm, nucleolus and nuclear envelope
• Much of the DNA in a cell located here
3-37
Chromosome Structure
• Chromatin: DNA
complexed with proteins
(histones)
• During cell division,
chromatin condenses into
pairs of chromatids
called chromosomes.
Each pair of chromatids is
joined by a centromere
3-38
Ribosomes
• Sites of protein synthesis
• Composed of a large and
a small subunit
• Types
– Free
– Attached (to endoplasmic
reticulum)
3-39
Endoplasmic Reticulum
• Types
– Rough
• Has attached ribosomes
• Proteins produced and modified here
– Smooth
• No attached ribosomes
• Manufactures lipids
• Cisternae: Interior spaces isolated from rest of cytoplasm
3-40
Golgi Apparatus
• Modification,
packaging, distribution
of proteins and lipids
for secretion or internal
use
• Flattened membrane
sacs stacked on each
other
3-41
Function of Golgi Apparatus
3-42
Action of Lysosomes
3-43
Peroxisomes and Proteasomes
• Peroxisomes
– Smaller than lysosomes
– Contain enzymes to break down fatty acids and
amino acids
– Hydrogen peroxide is a by-product of
breakdown
• Proteasomes
– Consist of large protein complexes
– Include several enzymes that break down and
recycle proteins in cell
3-44
Mitochondria
• Major site of ATP synthesis
• Membranes
– Cristae: Infoldings of inner
membrane
– Matrix: Substance located in
space formed by inner
membrane
• Mitochondria increase in
number when cell energy
requirements increase.
• Mitochondria contain DNA
that codes for some of the
proteins needed for
mitochondria production.
3-45
Centrioles and Spindle Fibers
• Located in centrosome:
specialized zone near
nucleus
• Center of microtubule
formation
• Before cell division,
centrioles divide, move to
ends of cell and organize
spindle fibers
3-46
Cilia
• Appendages projecting from cell surfaces
• Capable of movement
• Moves materials over the cell surface
3-47
Flagella
• Similar to cilia but
longer
• Usually only one per
cell
• Move the cell itself in
wave-like fashion
• Example: sperm cell
3-48
Microvilli
•
•
•
•
•
Extension of plasma membrane
Increase the cell surface area
Normally many on each cell
One tenth to one twentieth size of cilia
Do not move
3-49
Genes and Gene Expression
• Gene
– Functional unit of heredity
– Types
• Structural: serve as template for mRNA, code for
amino acid sequences
• Regulatory: control which structural genes
transcribed in given tissue
3-50
Genes and Gene Expression
• Transcription: DNA used to form RNA
• Translation: synthesis of a protein at the ribosomes
using mRNA, tRNA and rRNA
3-51
Transcription
• The strands of DNA are
separated
• RNA polymerase binds at a
promoter region
• RNA polymerase catalyses
the formation of a mRNA
chain using the DNA as a
template and following the
rules of complimentary base
pairing
– A with U
– C with G
• Transcription ends at a
terminator sequence
3-52
Posttranscription Processing
• The mRNA is modified after
transcription and before it
can leave the nucleus
– Intron removal
– Guanosine cap added
– Poly-A tail added
• The mRNA now contains the
genetic code that will be
used to manufacture a
polypeptide
3-53
Translation
• Process that occurs on
ribosomes
• Turns mRNA into a
polypeptide
• Involves rRNA, tRNA, and
mRNA
• tRNA anticodons match with
mRNA codons, and the rRNA
catalyzes the formation of a
peptide bond between the
amino acids at the opposite
end of the tRNA
3-54
Regulation of Protein Synthesis
• All nucleated cells except germ cells have the full
complement of DNA.
• During development, differentiation occurs and some
segments of DNA are turned off in some cells while
those segments remain “on” in other cells.
• During the lifetime of a cell, the rate of protein
synthesis varies depending upon chemical signals that
reach the cell.
– Example: thyroxine from the thyroid causes cells to
increase their metabolic rate. More thyroxine, higher
metabolic rate; less thyroxine, lower metabolic rate.
3-55
Cell Life Cycle
• Interphase: phase between cell
divisions
– Replication of DNA
– Ongoing normal cell activities
• Mitosis: series of events that
leads to the production of two
cells by division of a mother cell
into two daughter cells. Cells are
genetically identical.
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
• Cytokinesis: division of cell
cytoplasm
3-56
Replication of DNA
• DNA strands separate
• The old strands become the templates for the new
(complementary) strands to form
• Two identical DNA molecules are formed by semiconservative
replication
3-57
Mitosis
• Interphase – DNA replication
occurs
• Mitosis
– Prophase – nuclear envelope
disintegrates, chromatin condenses,
spindles attach to kinetochore
– Metaphase – chromosomes are
aligned at the nuclear equator
– Anaphase – spindles separate the
chromatids, cytokinesis begins
– Telophase – chromosomes
decondense, nuclear envelope
reforms, cytokinesis continues
• Cytokinesis – cytoplasmic
division, separate process from
mitosis
3-58
Genetics
• Study of heredity
• Explains how certain characteristics are
passed on to offspring
3-59
Mendalian Genetics
• Genotype: actual set of alleles a person has
for a given trait
• Phenotype: person’s appearance
• Dominant and recessive alleles
– Dominant masks effects of recessive genes
• Sex-linked traits: traits affected by genes
on sex chromosomes
3-60
Mendalian Genetics
• Homozygous: Having two of the same
alleles for a trait.
– Homozygous dominant: AA
– Homozygous recessive: aa
• Heterozygous: Having one dominant and
one recessive allele for a trait
– Aa
3-61
Chromosomes
• Genetics: study of heredity
• DNA: hereditary material of
cells and controls cell activities
• Found in discrete sections
called chromosomes
– Karyotype or display
– Autosomal and sex (X or Y)
– Contain thousands of genes
• Diploid: two copies of
chromosomes
• Haploid: one copy of
chromosomes, only in gametes
• Karyotype: map of
chromosomes
3-62
Inheritance of Sex
3-63
Chromosomes
• Homologous: pairs of
chromosome where one is
from the father and the
other is from the mother
• Locus: the location of a
gene on a chromosome
• Allele: different forms of
the same gene
– Multiple alleles –
sometimes alleles come in
more than just dominant and
recessive forms
3-64
Gene Dominance
• Complete dominance: the dominant allele covers
up the recessive allele and is the only allele expressed
• Codominance: both alleles are expressed equally at
the same time
• Incomplete dominance: the dominant allele and
the recessive allele both are expressed, with the recessive
being at a much lower level
3-65
Other Types of Gene Expression
• Polygenic traits
– Determined by
expression of
multiple genes on
different
chromosomes
– Height, eye and skin
color, intelligence
3-66
Sex-linked Traits
• Affected by areas of
the X and Y
chromosome
• X-linked traits more
often affect males
• Y-linked traits only
affect males
3-67
Meiosis and the
Transmission of Genes
• Meiosis: DNA replication
followed by two cell divisions
• Homologous pairs are
separated
• Resulting gametes (egg,
sperm) unite to form a zygote
• Homologous pairs are
reunited
– New pairs are a mixture of DNA
from two individuals
3-68
Genetic Disorders
• Genetic disorders:
abnormalities in DNA
• Congenital disorders
– Birth defects not
necessarily genetic
– Teratogens: agents that
cause birth defects
• Mutation
– Mutagens: agents that
cause mutations
• Cancer: tumor
resulting from
uncontrolled cell
divisions
– Oncogenes: genes
associated with cancer
– Tumor suppressor
genes
– Carcinogens
– Genetic susceptibility
or predisposition
3-69