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Chapter 3: Cell Structure
and Function
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The Cellular Level of
Organization
Living things are constructed of
cells.
Living things may be unicellular or
multicellular.
Cell structure is diverse but all cells
share common characteristics.
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The cell theory states:
1. All organisms are composed of one or
more cells.
2. Cells are the basic unit of structure
and function in organisms.
3. All cells come only from other cells.
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Cells are small so they can exchange
materials with their surroundings.
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Sizes of living things
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Eukaryotic Cells
Eukaryotic cells have a nucleus that
controls the workings of the cell.
All cells are surrounded by a plasma
membrane made of phospholipids
and proteins.
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The plasma membrane regulates what
enters and exits the cell.
Inside the plasma membrane, the
nucleus is surrounded by cytoplasm.
Plant cells have a cell wall in addition to
the plasma membrane.
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Animal and plant cells have organelles.
Organelles compartmentalize functions
within the cell.
The organelles of animal and plant cells
are similar to each other except that
centrioles are present only in animal
cells, and chloroplasts are present only
in plant cells.
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Animal cell anatomy
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Plant cell anatomy
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Structure of the Nucleus
Chromatin: DNA and proteins
Nucleolus: Chromatin and ribosomal
subunits
Nuclear envelope: Double membrane
with pores
Nucleoplasm: semifluid medium inside
the nucleus.
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Nucleus and nuclear
envelope
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Ribosomes
Protein synthesis occurs at tiny
organelles called ribosomes.
Ribosomes are composed of a large
subunit and a small subunit.
Ribosomes can be found alone in
the cytoplasm, in groups called
polyribosomes, or attached to the
endoplasmic reticulum.
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The Endomembrane System
The endomembrane system consists of:
Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Vesicles
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The endoplasmic reticulum
The endoplasmic reticulum (ER) is a
system of membranous channels and
saccules.
Rough ER is studded with ribosomes and
is the site of protein synthesis and
processing.
Smooth ER lacks ribosomes and is the
site of synthesis of phospholipids and
the packaging of proteins into vesicles,
among other functions.
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The endoplasmic reticulum
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The Golgi apparatus
The Golgi apparatus consists of a
stack of curved saccules.
The Golgi apparatus receives protein
and also lipid-filled vesicles from the
ER, packages, processes, and
distributes them within the cell.
This organelle may also be involved in
secretion.
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The Golgi apparatus
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Lysosomes and vacuoles
Lysosomes are vesicles produced by the
Golgi apparatus.
Lysosomes contain hydrolytic enzymes
and are involved in intracellular
digestion.
Vacuoles (large) and vesicles (small) are
membranous sacs in the cell that store
substances.
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Peroxisomes
Peroxisomes are vesicles than contain
enzymes.
The enzymes in these organelles use up
oxygen and produce hydrogen
peroxide.
Peroxisomes are abundant in the liver
where they produce bile salts and
cholesterol and break down fats.
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Energy-Related Organelles
The two energy-related organelles
of eukaryotes are chloroplasts
and mitochondria.
Both organelles house energy in
the form of ATP.
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Chloroplasts
A chloroplast is bounded by two
membranes enclosing a fluid-filled
stroma that contains enzymes.
Membranes inside the stroma are
organized into thylakoids that house
chlorophyll.
Chlorophyll absorbs solar energy and
carbohydrates are made in the stroma.
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Chloroplast structure
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Mitochondria
Mitochondria are found in plant and
animal cells.
Mitochondria are bounded by a
double membrane surrounding
fluid-filled matrix.
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The inner membranes of
mitochondria are cristae.
The matrix contains enzymes that
break down carbohydrates and the
cristae house protein complexes
that produce ATP.
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Mitochondrion structure
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The Cytoskeleton
The eukaryotic cytoskeleton is a network of
filaments and tubules that extends from the
nucleus to the plasma membrane.
The cytoskeleton contains three types of
elements responsible for cell shape,
movement within the cell, and movement of
the cell:
Actin filaments
Microtubules
Intermediate filaments
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Actin filaments occur in bundles
or mesh-like networks.
Actin filaments play a structural
role in intestinal microvilli and
also interact with motor
molecules, such as myosin.
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Actin filaments
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Microtubles are small hollow
cylinders made of the globular
protein tubulin.
Microtubule assembly is controlled
by the microtubule organizing
center, called the centrosome.
Microtubules help maintain the
shape of the cell and act as tracks
along which organelles can move.
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Microtubule structure
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Intermediate filaments are ropelike
assemblies of fibrous
polypeptides that support the
plasma membrane and nuclear
envelope.
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Structure of intermediate
filaments
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Centrioles
Centrioles are short cylinders with
a 9 + 0 pattern of microtubule
triplets.
Centrioles may be involved in
microtubule formation and
disassembly during cell division
and in the organization of cilia
and flagella.
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Centriole structure
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Cilia and flagella
Cilia (small and numerous) and flagella
(large and single) have a 9 + 2
pattern of microtubules and are
involved in cell movement.
Cilia and flagella move when the
microtubule doublets slide past one
another.
Each cilium and flagellum has a basal
body at its base.
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Structure of a flagellum or cilium
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Prokaryotic Cells
Prokaryotic cells include the bacteria and
archaea.
Bacterial cells have these constant features:
Outer Boundary: Cell wall
Plasma membrane
Cytoplasm:
Ribosomes
Thylakoids (Cyanobacteria)
Innumerable enzymes
Nucleoid:
Chromosome (DNA only)
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Bacterial cells may have plasmids,
small accessory rings of DNA.
Some bacteria have a capsule or a
slime layer.
Most bacteria have flagella.
Some also have fimbriae that help
cells attach to surfaces.
Bacteria have a great metabolic
diversity.
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Evolution of the Eukaryotic
Cell
According to the endosymbiotic
hypothesis, eukaryotes arose from a
symbiotic relationship between various
prokaryotes.
- Heterotrophic bacteria became
mitochondria.
- Cyanobacteria became chloroplasts.
- Host cell was a large eukaryotic cell.
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Evolution of the eukaryotic
cell
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