Download Chapter 7, Cellular structure and Function

Chapter 7
CELLULAR STRUCTURE AND FUNCTION
Section 1
CELL DISCOVERY AND THEORY
Introduction
 Cells are the simplest collection of matter that can
live.
 Cells were first observed by Robert Hooke in 1665.
 Working with more refined lenses, Antoni van
Leeuwenhoek later described
– blood,
– sperm, and
– organisms living in pond water.
Microscope Technology
INTRODUCTION TO THE CELL
 Difference between Magnification and Resolution
 Magnification is the increase in the apparent size
of an object.
 Resolution is a measure of the clarity of an image.
In other words, it is the ability of an instrument to
show two close objects as separate.
The cell theory
 1- All living cells are composed of one or more cells
 2- Cells are the basic unit of structure and
organization of all living organisms
 3- cells arise only from previously existing cells, with
cells passing copies of their genetic material on to
their daughter cells.
Light microscope
(LM)
Electron Microscope
(EM)
Light passes through a specimen, then
through glass lenses, and finally light is
projected into the viewer’s eye.
EM uses a beam of electrons instead of
light
Specimens can be magnified up to 1000
times
Resolve biological structures as small as
2 nanometers and
Cannot provide the details of a small
cell’s structure.
Magnify up to 100,000 times.
Two Types of EM
1- Scanning electron microscopes
(SEM) study the detailed architecture of
cell surfaces.
2- Transmission electron
microscopes (TEM) study the details of
internal cell structure.
10 m
100 mm
(10 cm)
Length of
some nerve
and muscle
cells
Chicken
egg
10 mm
(1 cm)
Unaided eye
Human height
1m
Frog egg
10 m
1 m
100 nm
Most plant and
animal cells
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosome
10 nm
Proteins
Lipids
1 nm
0.1 nm
Small molecules
Atoms
Electron microscope
100 m
Paramecium
Human egg
Light microscope
1 mm
Basic cell Types
Prokaryotes
Eukaryotes
Have Plasma membrane
Have Plasma membrane
Have DNA coiled into a region
called the nucleoid, but no
membrane surrounds the DNA.
Have DNA bounded in a nucleus
Have cytoplasm
Have Cytoplasm
Have ribosomes
Have ribosomes
No true-bounded organelles
Have number of organelles
Prokaryotes
Eukaryotes
Examples: Bacteria and archaea
Examples: Human, Animals, Plants, Fungi
Unicellular Organisms
Multicellular Organisms
The surface of the prokaryotic cells may:
- Be surrounded by cell wall
- Have a capsule surrounding the cell wall
- Have longer projections called flagella
for movement
- Have short projections, that help attach
to other cells or substrate.
The structures and organelles of eukaryotic
cells perform four basic functions
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1. The nucleus and ribosomes are involved in
the genetic control of the cell.
2. The endoplasmic reticulum, Golgi apparatus,
lysosomes, vacuoles, and peroxisomes are
involved in the manufacture, distribution,
and breakdown of molecules.
3. Mitochondria in all cells and chloroplasts in
plant cells are involved in energy processing.
4. Structural support, movement, and
communication between cells are functions
of the cytoskeleton, plasma membrane, and
cell wall.
Fimbriae
Ribosomes
Nucleoid
Plasma membrane
Cell wall
Bacterial
chromosome
A typical rod-shaped
bacterium
Capsule
Flagella
A TEM of the bacterium
Bacillus coagulans
Origin of cell diversity
 Mitochondria and chloroplasts have
– DNA and
– ribosomes.
 The structure of this DNA and these ribosomes is very similar to that
found in prokaryotic cells.
 The Endosymbiont theory proposes that
– mitochondria and chloroplasts were formerly small prokaryotes and
– they began living within larger cells.
Mitochondrion
Nucleus
Endoplasmic
reticulum
Some
cells
Engulfing
of oxygenusing
prokaryote
Engulfing of
photosynthetic
prokaryote
Chloroplast
Host cell
Mitochondrion
Host cell
Section 2
THE PLASMA MEMBRANE
The small size of cells relates to the need to exchange
materials across the plasma membrane
 As the cell size increases, the surface area to
volume ratio decreases.
 Therefore, in order to build larger organisms, they
must be built up from small cell subunits.
Function of the plasma membrane
– Homeostasis is the process that responsible of
maintaining balance in an organism’s internal
environment
– Plasma membrane is primarily responsible for
homeostasis
– The plasma membrane allows nutrients into the cell and
allows waste and other products leave the cell
– All prokaryotic and eukaryotic cells have a plasma
membrane to separate them from the watery
environments in which they exist
Function of the plasma membrane
– Plasma membrane key property is selective
permeability (allows some substances to pass through
while keeping other out)
Structure of the plasma membrane
 Most molecules in the plasma membrane are
lipids, Lipids are large molecules made up of
glycerol and fatty acids
 The plasma membrane is composed of a
Phospholipid bilayer
– hydrophilic heads (polar) face outward, exposed to
water, and
– hydrophobic tails point inward (non-polar), shielded
from water.
Figure 4.2B
Outside cell
Hydrophilic
heads
Hydrophobic
region of
a protein
Hydrophobic
tails
Phospholipid
Hydrophilic
region of
a protein
Inside cell
Channel
protein
Proteins
Other components of the plasma membrane
 Membrane proteins are either
– attached to the membrane surface or
– embedded in the phospholipid bilayer.
 Some proteins form channels or tunnels that shield
ions and other hydrophilic molecules as they pass
through the hydrophobic center of the membrane
(Transport proteins).
 Other proteins serve as pumps, using energy to
actively transport molecules into or out of the cell.
Fluid mosaic model
 The fluid mosaic model refers to a plasma
membrane with substances that can move around
within the membrane
- Phospholipids can move sideways within the
membrane
- Proteins also move among the phospholipids
- Because there are different substances in the
plasma membrane a pattern or mosaic is created
on the surface
Section 3
STRUCTURES AND ORGANELLES
Cytoplasm and Cytoskeleton
 Cytoplasm
- A semifluid material inside the plasma membrane
- In a prokaryotic cell: all of the chemical processes of
the cell such as breaking down sugar to generate
energy take place in the cytoplasm
- Eukaryotic cells perform these processes within
organelles in the cytoplasm
Cytoplasm and Cytoskeleton
 Cytoskeleton
Cells contain a network of protein fibers, called the
cytoskeleton, which functions in structural support
and cell movement
The cytoskeleton is composed of two kinds of fibers.
1. Microfilaments (actin filaments) support the cell’s shape and are
involved in motility.(The thinnest fiber)
2. Microtubules (made of tubulin) are long, hollow protein cylinders that
form a rigid skeleton for the cell and assist in moving substances
within the cell. (The thickest filaments)
Cell structures
 Ribosomes
- Produce proteins (protein synthesis)
- Are made of two components RNA and protein
- Not bound by a membrane like other organelles are
- Nucleolus is the site of ribosome production
- Some Ribosomes float freely in the cytoplasm(produce
proteins for use within cytoplasm)
- Others are bound to another organelle called the
Endoplasmic Reticulum (RER) They produce proteins that
will be bound within membranes or used by other cells.
Cell structures
Organelles that carry out the genetic control of the
cells Nucleus and Ribosomes
 The Nucleus
- It controls the cell processes.
- Is the cell’s managing structure
- Contains most of the cell’s DNA which stores
information used to make proteins for cell growth,
function and reproduction
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Cell structures
 The Nucleus
- Surrounded by a double membrane called the
nuclear envelope has pores that allow material to
flow in and out of the nucleus
 The nucleolus is
– a prominent structure in the nucleus and
– the site of (ribosomes) ribosomal RNA (rRNA) synthesis
© 2012 Pearson Education, Inc.
Cell structure
 Endoplasmic reticulum
- A membrane system of folded sacs and
interconnected channels that serve as the site of
protein and lipid synthesis
There are two kinds of endoplasmic reticulum—
smooth and rough.
– Smooth ER do not have ribosomes attached.
– Rough ER have ribosomes attached on the outer
surface of their membranes.
Cell structure
 Smooth ER is involved in a variety of diverse metabolic processes.
– Smooth ER produces enzymes important in the synthesis of lipids,
oils, phospholipids, and steroids.
– Other enzymes help process drugs, alcohol, and other potentially
harmful substances.
– Some smooth ER helps store calcium ions.
– Smooth ER in the liver detoxifies harmful substances
 Rough ER makes
– additional membrane for itself and
– proteins destined for secretions.
Cell structure
 The Golgi apparatus
 serves as a molecular warehouse and finishing
factory for products manufactured by the ER.
– Products travel in transport vesicles from the ER to the
Golgi apparatus.
– One side of the Golgi apparatus functions as a receiving
dock for the product and the other as a shipping dock.
– Products are modified as they go from one side of the
Golgi apparatus to the other and travel in vesicles to
other sites.
“Receiving” side
of Golgi
apparatus
Golgi
apparatus
1
Transport
vesicle
from ER
2
Transport
vesicle from
the Golgi
3
4
4
“Shipping”
side of Golgi
apparatus
Golgi apparatus
Organelles That Build Proteins
1. Proteins are assembled on
ribosomes.
2. Some proteins complete their
assembly on the rough
endoplasmic reticulum.
3. Proteins are carried to
the Golgi apparatus in
vesicles.
Organelles That Build Proteins
5. Vesicles are shipped
to their final destination.
4. The Golgi apparatus
sorts and packages
proteins.
Cell structure
 Vacuoles
- membrane-bound organelle
- Temporary storage of materials within the cytoplasm
- A plant vacuole is a sac used to store food, enzymes and
other materials needed by a cell
- Some vacuoles store waste products
- Animal cells usually have no vacuoles , but if they do, these
vacuoles are much smaller than those in plant cell
Cell structure
 A lysosome
is a membranous sac containing digestive enzymes.
– The enzymes and membrane are produced by the ER
and transferred to the Golgi apparatus for processing.
– The membrane serves to safely isolate these potent
(IMPORTANT)enzymes from the rest of the cell.
 Lysosomes help digest food particles engulfed by a cell.
1. A food vacuole binds with a lysosome.
2. The enzymes in the lysosome digest the food.
3. The nutrients are then released into the cell.
Digestive
enzymes
Lysosome
Digestion
Food vacuole
Plasma membrane
Cell structure
 Lysosomes also help remove or recycle damaged
parts of a cell.
1. The damaged organelle is first enclosed in a membrane
vesicle.
2. Then a lysosome
–
fuses with the vesicle,
–
dismantles its contents, and
–
breaks down the damaged organelle.
Lysosome
Digestion
Vesicle containing
damaged mitochondrion
Cell structure
 Centrioles
- Made up of microtubules
- Function during cell division
- Located in the cytoplasm of animal cells
- Plants do not have centrioles
Cell structure
 Mitochondria are organelles that carry out cellular
respiration in nearly all eukaryotic cells.
 Cellular respiration converts the chemical energy in
foods to chemical energy in ATP (Adenosine
triphosphate).
 Highly active cells such as muscle cells can have hundreds
of mitochondria
 Cells that are not active such as fat-storage cells have few
mitochondria
 Mitochondria has its own DNA.
Cell structure
 Mitochondria have two internal compartments.
1. The intermembrane space is the narrow region between
the inner and outer membranes.
2. The mitochondrial matrix contains
– the mitochondrial DNA,
– ribosomes, and
– many enzymes that catalyze some of the reactions of cellular
respiration.
Mitochondrion
Outer
membrane
Intermembrane
space
Inner
membrane
Cristae
Matrix
Cell structure
 Chloroplasts are the photosynthesizing organelles of all photosynthesizing
eukaryotes.
 Photosynthesis is the conversion of light energy from the sun to the chemical
energy of sugar molecules.
 Chloroplasts are partitioned into compartments.
–
Between the outer and inner membrane is a thin intermembrane space.
–
Inside the inner membrane is
– a thick fluid called stroma that contains the chloroplast DNA,
ribosomes, and many enzymes and
– a network of interconnected sacs called thylakoids.
– In some regions, thylakoids are stacked like poker chips. Each stack
is called a granum, where green chlorophyll molecules trap solar
energy
Inner and
outer
membranes
Granum
Chloroplast
Stroma
Thylakoid
Cell structure
 Cilia and flagella
- Cilia are short, numerous projections that look like
hair
- The motion of cilia is similar to the motion of oars in
a rowboat
- Flagella are longer and less numerous than cilia
- These projection move with a whiplike motion
Cilia
4.17 Cilia and flagella move when microtubules
bend
 Both flagella and cilia are made of microtubules
wrapped in an extension of the plasma membrane.
 A ring of nine microtubule doublets surrounds a
central pair of microtubules. This arrangement is
– called the 9 + 2 pattern and
– anchored in a basal body with nine microtubule triplets
arranged in a ring.
Outer microtubule doublet
Central
microtubules
Radial spoke
Dynein proteins
Plasma membrane
Cell structure
 A plant cell, but not an animal cell, has a rigid cell
wall that
– protects and provides skeletal support that helps keep
the plant upright against gravity and
– is primarily composed of cellulose.
 Plant cells have cell junctions called
plasmodesmata that serve in communication
between cells.
Figure 4.21
Plant cell
walls
Vacuole
Plasmodesmata
Primary cell wall
Secondary cell wall
Plasma membrane
Cytoplasm