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Chapter 4
Cell Structure and Function
Nucleolus
Nucleus
Nuclear envelope
Rough
endoplasmic
reticulum
Golgi apparatus
Ribosome (attached)
Ribosome (free)
Cell Membrane
Mitochondrion
Smooth
endoplasmic
reticulum
Centrioles
A CELL is . . .
made of MOLECULES
ATOMS  ___________
MOLECULES
ORGANELLES
_______
___________
WHICH IS BIGGER?
Plant
cell
Animal
cell
bacteria
_________ > _____________ > ___________
Note
• The shapes shown on the last slide are
merely a generic version of a plant, animal,
and bacteria cell.
– In other words, not all plants are shaped like a
box and animal cells circular
• That is simply done to show that plants have cell
walls and animal cells do not
– Every type of cell is shaped a particular way to
fit whatever its function may be
ALL LIVING THINGS ARE MADE OF
CELLS
• PROKARYOTES
• Lack nucleus
• Lack membrane
bound organelles
Bacterial Cell
• EUKARYOTES
• Have nucleus
• Have membrane
bound organelles
All cells (both prokaryotic and
eukaryotic) have several basic features in
common
1. Plasma (cell) membrane
2. Chromosomes which carry genes made of DNA
(although the shape of eukaryotic chromosomes
and a prokaryotic chromosome are different)
3. Cytoplasm
4. Cytoskeleton
5. Ribosomes that make proteins (although the
shape of eukaryotic ribosomes and prokaryotic
ribosomes are different)
1. CELL MEMBRANE
(also called plasma membrane)
Made mainly of phospholipids & proteins
Controls what enters and leaves the cell
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
Cell membrane continued PHOSPHOLIPID
• Phospholipid has 2 main regions:
• Head  negative charge, hydrophilic
• 2 fatty acid Tails  nonpolar, hydrophobic
HYDROPHILIC 
HYDROPHOBIC 
Cell membrane continued PHOSPHOLIPID BILAYER
• They form a two-layered sheet called the
phospholipid bilayer.
• Hydrophilic heads face out
• Hydrophobic tails tucked inward.
• Proteins are embedded on the membrane,
or attached to the surface.
Cell membrane continued
• Proteins are embedded on the membrane,
or attached to the surface.
Proteins that stick on the surface = PERIPHERAL
(either inside or outside of cell)
Proteins that stick INTO membrane = Integral
(can go part way in or all the way through)
Cell membrane continued Permeability
• Nonpolar molecules such as O2 and CO2 can
easily pass through the hydrophobic
interior.
• Proteins in the membrane form channels
that allow specific molecules to cross.
Cell membrane continued GLYCOPROTEINS
Recognize
“self”
GLYCOPROTEINS are PROTEINS with
carbohydrates attached.
Play a role in cell-cell interactions.
Cell membrane continued TRANSPORT PROTEINS
help move substances across the
cell membrane
Cell membranes MOVE!
Molecules in cell membranes are
constantly moving and changing
Cell membrane continued WHAT DOES IT DO?
Acts as a boundary
Controls what enters and leaves cell
2. Chromosomes - Genetic
material (DNA)
• Chromatin – thin fibers of DNA and
proteins that look like a diffuse mass.
• As the cell prepares to divide, the DNA is
copied and the chromatin coils up
(becoming visible with a light microscope)
into the structure we know as chromosomes.
3. CYTOPLASM
(Between nucleus and cell membrane)
Organelles suspended
in gel-like goo
ORGANELLEsmall structure with a
specific function (job)
4. CYTOSKELETON
Network of protein fibers, found
throughout the cytoplasm.
Three main types of fibers make up the cytoskeleton:
1. Microfilaments (the thinnest)
2. Microtubules (the thickest)
3. Intermediate filaments (in between)
• Helps cell maintain shape
• Help move organelles around
Cytoskeleton continued Microfilaments
• Solid rods made of the
protein actin, in a twisted
double chain
• Supports the cell’s shape &
involved in cell movement.
– Ex: Actin and another protein
myosin interact to cause
contraction of muscle cells.
Actin subunit
Microfilament
Cytoskeleton continued Microtubules
• Straight hollow tubes made of the
protein tubulin.
• Easily disassembled & subunits
reused elsewhere.
• Give shape and support to the cell
& acts as tracks along which
Nucleus
organelles with motor proteins can
move.
– Ex: lysosomes move along track to
reach a food vacuole.
– Ex: guide chromosomes during cell
division
• The main component of cilia &
flagella
Tubulin subunit
Microtubule
•
Cytoskeleton continued Intermediate
filaments
Made of various proteins,
and has a ropelike structure.
• Reinforce cell shape &
anchors organelles.
– Ex: Nucleus is held in place
by a cage of intermediate
filaments.
– Ex: Our outer layer of skin
consists of dead cells
containing intermediate
filaments made of keratin
proteins.
Nucleus
Intermediate filament
Characteristics of prokaryotic cells that are
not found in eukaryotic cells
1.
2.
3.
4.
5.
Bacterial chromosome – present as a single loop of DNA (eukaryotic
chromosomes come in many pairs which we will discuss in detail later)
Nucleoid – region where the prokaryotic cells DNA is located (not
enclosed by a membrane like eukaryotic cells)
Pili – attachment structures on the surface of some prokaryotes
Cell wall – plants (which are eukaryotic cells) also have cell walls but
they are made of a different structure
Capsule – jellylike outer coating outside of cell wall
Note: Flagella and cilia are also found in animal cells (not plants), but
they are included here because the diagram shows them. Sperm have
flagella, cells in your wind pipe have cilia, and so forth.
• Flagella (long tail like structure) and cilia (many hair like structures) used
for locomotion (some types of eukaryotic cells do have flagella or cilia)
Typical Prokaryotic cell
Fig. 4-3b
Pili
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
Flagella
Nucleoid
• The DNA of a prokaryotic cell is coiled into a region
called the nucleoid.
• Unlike the eukaryotic nucleus, it has no membrane that
surrounds the DNA.
• The DNA of a prokaryote is in a single circular loop. The
DNA of eukaryotes (like you) are in chromosome form
(we’ll discuss this next unit).
• Also, the ribosomes of prokaryotic cells are smaller.
• Antibiotics are designed to target (smaller) ribosomes of
prokaryotic cells (bacteria), interrupting protein synthesis.
– Antibiotics do not harm eukaryotic cells.
Cilia & Flagella
• Both consist of microtubules
wrapped in an extension of the
cell membrane.
• Ring of 9 microtubule
“doublets” surrounds a central
pair of microtubules.
– (called 9 + 2 pattern)
Central
microtubules
Plasma
membrane
Outer microtubule
doublet
• Cilia – short numerous appendages that
propel cell forward.
– Found on cells lining the human windpipe,
which sweeps mucus & trapped debris out of
our lungs.
Cilia
• Flagella – longer, and limited to one or a
few per cell.
– Sperm have flagella for movement.
Flagellum
Bacteria
How did the first eukaryotic cells
form?
• ENDOSYMBIOSIS
Endosymbiosis
• Mitochondria & chloroplasts were formerly small
prokaryotes that began living within larger cells.
• May have occurred as undigested prey or internal
parasites.
• Forming symbiotic relationship.
– Host cell uses nutrients released from photosynthetic
endosymbionts.
– Endosymbionts are provided protection by host cell.
• Over time, they would become more
interdependent, eventually becoming a single
organism.
Evidence of Endosymbiosis
• Mitochondria & chloroplasts both contain
their own DNA & ribosomes.
• Their ribosomes are more similar to
prokaryotic ribosomes.
• Both reproduce by a splitting process
similar to that of prokaryotes.
• Both are surrounded by two membranes.
Fig. 4-16
Mitochondrion
Engulfing of
photosynthetic
prokaryote
Some
cells
Engulfing
of aerobic
prokaryote
Chloroplast
Host cell
Mitochondrion
Host cell
Organelles that are unique amongst
eukaryotes (basically plants and animals)
but not present in prokaryotes (bacteria)
1.
2.
3.
4.
5.
6.
7.
Nucleus
Nucleolus
Endoplasmic reticulum
Golgi Apparatus (also called golgi body)
Mitochondria
Peroxisome
Vacuoles
1. NUCLEUS
• Contains cell’s genetic material (DNA)
• Controls cell’s activity by directing
protein synthesis.
• Largest organelle
in animal cells
1. NUCLEUS
• Surrounded by NUCLEAR ENVELOPE
• It is a double membrane perforated with
protein lined pores.
(also called NUCLEAR MEMBRANE)
1. NUCLEUS
NUCLEAR PORES
• Openings that control the flow of materials into and
out of the nucleus
2. NUCLEOLUS
• Dark spot in nucleus
• Site where ribosomal RNA (rRNA) is synthesized
according to the instructions of DNA.
• Proteins brought in through the nuclear pores are
assembled with the rRNA to build a subunit of
ribosomes.
• These subunits exit through the nuclear pores
where they will be joined to form functional
ribosomes.
Large
Small
subunit
subunit
Diagram of
a ribosome
Another type of RNA
• The nucleus directs protein synthesis with
messenger RNA (mRNA).
• mRNA is a short transcription (copy) of
DNA that exits through the nuclear pores
where it is translated by ribosomes into
amino acid sequences of proteins.

RIBOSOMES for eukaryotes
can be found in several places
Can be attached to:
• Nucleus
• Rough ER
OR
• Free in cytoplasm
3. ENDOPLASMIC
RETICULUM
Network of flattened sacs and tubules
“endoplasmic” –
within the cell
“reticulum” –
little net
Two kinds:
SMOOTH or ROUGH
Smooth ER
• NO ribosomes attached
• Has enzymes for special tasks:
• Example: Cells of ovaries & testes
synthesize the steroid sex hormones.
– Enzymes synthesize lipids
• (oils, phospholipids, & steroids)
Another example (pg.60)
• Liver cells help process drugs and other harmful
substances.
• Cells exposed to drugs cause the amount of smooth
ER (w/ detoxifying enzymes) to increase
• This increases the rate of detoxification.
• Causing increasing tolerance to the drug.
• Now, dose must be increased to be effective.
• Another complication is that enzymes often cannot
distinguish among related drugs.
• So an increase in tolerance in one drug, may cause
one in another drug.
– Ex: barbiturate use can decrease effectiveness of
antibiotics.
Another example (pg.60)
• In muscle cells, smooth ER membrane
pumps calcium ions into the interior of the
ER.
• When a nerve signal stimulates a muscle,
calcium ions rush from the smooth ER into
the cytoplasm….triggering a contraction of
the cell.
Rough ER
• Rough ER membrane
enlarges.
• Phospholipids made by
enzymes of the ER are
inserted into the membrane.
• Some of this membrane is
passed onto other
membranes in vesicles.
Rough ER
4
Ribosome
1
3
2
• Ribosomes attached. (rough)
• These ribosomes make
proteins, which are inserted
into the ER membrane, where
they are modified and
transported to other organelles.
• Example: Insulin. Secreted by
cells in the pancreas.
After leaving the ER, many transport vesicles
travel to the Golgi apparatus…
Transport
vesicle
from ER
Rough ER
Golgi apparatus
4. GOLGI APPARATUS (BODY)
• Discovered by Camillo Golgi with a light
microscope.
• Confirmed later with an electron microscope.
Flattened sacs stacked on top of
each other.
Sacs are NOT interconnected like
ER.
Number of Golgi stacks correlates
with how active the cell is in
secreting proteins.
Electron micrograph
GOLGI APPARATUS (BODY)
•
•
•
•
•
Molecular warehouse & finishing factory.
Receives & modifies products from ER.
One side is receiving dock for transport vesicles
Other side is shipping dock giving off vesicles.
“maturation model” entire sacs mature as they
move from the receiving end to the shipping end,
carrying and modifying their cargo as they go.
• Exiting vesicles move
to the cell membrane for
export form the cell.
5. Mitochondrion
Mitochondria (plural)
• cellular respiration - converts food energy into
a molecule energy.
• ATP (adenosine triphosphate).
– The main energy source for cellular work.
Mitochondrion’s structure
Enclosed by 2 membranes.
The inner membrane is highly folded, and
contains proteins that make ATP.
The folds (cristae) increase membrane
surface area, enhancing ability to
produce ATP.
Has 2 internal compartments
1. Internal membrane space – narrow
region between inner and outer
membrane.
2. Mitochondrial matrix – contains the
mitochondrial DNA, ribosomes, &
enzymes.
Found in plant & animal cells!
MITOCHONDRIA
• You inherit your
mitochondria from
your mother!
WHAT DOES IT DO?
“Powerplant of cell”
Converts glucose to ATP

6. Peroxisome
• Vesicle that neutralizes dangerous oxygen
compounds
– contains catalase that breaks down H2O2
– Detoxification of alcohol
• Also breaks down fatty acids to be used as
fuel.
Zellweger Syndrome
• Defective genes reduce or eliminate the presence
of peroxisomes
• Results in build up of iron and copper in blood and
tissue
• Symptoms include an enlarged liver; facial
deformities, and neurological abnormalities such
as mental retardation and seizures.
• Most infants do not survive past the first 6 months,
and usually succumb to respiratory
distress, gastrointestinal bleeding,
or liver failure.
7. VACUOLES
Membrane sacs used for storage
VACUOLES
• Storage space for WATER,
salts, proteins (enzymes),
carbohydrates, and waste
• Maintains internal pH
•Largest structure in plant cells
•Small in animal cells
•No vacuoles in bacteria cells
Contractile vacuoles
• Paramecium (unicellular organism, protists)
• Collect excess water from cell, and expels it
to the outside of cell.
• Without vacuole, cell fluid would become too
diluted to support life, & cell would
eventually swell & burst.
Contractile
vacuoles
Nucleus
Food Vacuole
• capture and digestion of food particles
• Fuse with lysosomes to digest food And
release nutrients.
• phagocytosis - the ingestion of particulate
matter
Organelles found only in plant
cells
1. Cell wall (prokaryotes also have cell walls
but they’re made of different material.
Animals do not have cell walls)
2. Chloroplast
3. Central Vacuole
1. CELL WALL
Supports and
protects cell
Outside of
cell membrane
Made of carbohydrates & proteins
Plant cell walls are mainly cellulose
2. Chloroplasts
• Photosynthesizing organelles Use energy from sunlight to
make own food (glucose)
Chloroplasts
• Has an inner and outer membrane.
• Inside inner membrane is a thick fluid called stroma.
• Stroma contains the chloroplast DNA & ribosomes.
Chloroplasts
• Thylakoids (a network of connected sacs)
are stacked inside the chloroplast.
• The stacks of thylakoids are called grana
• Grana are the solar power packs – site
where green chlorophyll molecules trap
solar energy.
3. Central vacuole
•
•
•
•
•
Found in plant cells.
Can take up more than half the cells volume
Holds large amounts of water, food & waste
Plays an important role in plant structure.
Vacuoles in flower petals contain pigments
to attract insects!
Organelles found only in animal
cells (not in plants or
prokaryotes)
1. Centrioles
2. Lysosomes – basically the “recycling
center” of the cell
– The most common hypothesis as to why plant
cells do not need lysosomes is that they have a
cell wall that would prevent the majority of
material broken down by lysosomes in animal
cells from entering plant cells
1. Centrioles
Appear during cell
division to guide
chromosomes apart
Centrioles
2. LYSOSOMES
• Membrane bound sacs that contain digestive
enzymes.
• Made by rough ER &
transferred to Golgi body.
Serves as a recycling center. Damaged
organelles are dismantled, releasing
organic molecules for reuse.
* Found in animal cells only!
2. LYSOSOMES
• Protists engulf food particles into
vacuoles…
• White blood cells ingest bacteria into
vacuoles…
• Lysosomes fuse with these vacuoles and
empties its digestive enzymes into them.
Lysosome
Digestive
enzymes
Plasma
membrane
Digestion
Food vacuole
Lysosomal storage disease
• Lack one or more lysosomal enzymes.
• Lysosomes become engorged with
undigested material.
• Example: Tay-Sachs disease
• Lipid digesting enzyme is missing
• Brain cells become impaired by
accumulation of lipids.
• A child with Tay-Sachs disease will die
within a few years.
Apoptosis
• Programmed cell death
• Lysosomes help digest
unwanted cells
• Cells in developing hands and
feet creates the spaces between
fingers & toes.
Apoptosis
Dead cell engulfed
and digested by
adjacent cell
Apoptosis plays a role in:
Embryonic development
Normal body cell maintenance
Immune system responses
Cancer
AIDS infection
Transplant rejection
Cell to cell communication
• The vast majority of eukaryotic organisms
are multicellular
• In order to function properly, these cells
must be able to communicate with one
another and to transmit information back
and forth
Extracellular matrix (ECM) –
Present only in animals
• Helps hold cells together in tissues.
• Protects and supports the plasma membrane.
• Main component: glycoproteins (ex: collagen)
• Integers - membrane proteins that
interconnects the ECM to the cytoskeleton.
Fig. 4-20
Glycoprotein
complex with long
polysaccharide
EXTRACELLULAR FLUID
Collagen fiber
Connecting
glycoprotein
Integrin
Plasma
membrane
Microfilaments
CYTOPLASM
Three types of cell junctions in
animal cells
• Tight junction – membranes of neighboring
cells are very tightly pressed against each
other.
• Prevent leakage of extracellular fluid
–Example: tissue lines the
digestive tract, preventing
the contents from leaking
into surrounding tissues.
Tight
junctions
Three types of cell junctions in
animal cells
• Anchoring junction – functions like rivets,
fastening cells together into strong sheets.
• Common in tissue subject to stretching or
mechanical stress.
– Skin & heart muscle
Anchoring
junction
Three types of cell junctions in
animal cells
• Gap junctions – channels that allow small
molecules to flow through protein lined
pores between neighboring cells.
– Ex: flow of ions through gap junctions in the
cells of heart muscle coordinates their
contraction.
Gap junctions
Fig. 4-21
Tight junctions
Anchoring junction
Gap junctions
Plasma membranes
of adjacent cells
Extracellular matrix
Plasmodesmata – Present only in
plant cells
• Channels between adjacent plant cells, form
a circulatory and communication system
connecting the cells in plant tissue.
• Cell membrane & cytoplasm
extend through the plasmodesmata,
so water and molecules can pass
cell to cell.
Fig. 4-22
Walls
of two
adjacent
plant cells
Vacuole
Plasmodesmata
Primary cell wall
Secondary cell wall
Cytoplasm
Plasma membrane
DIFFERENCES IN ANIMAL CELLS, PLANT CELLS, AND BACTERIA
ANIMAL CELL
PLANT CELL
BACTERIA
Eukaryotes
Eukaryotes
Prokaryotes
Cell membrane
Cell membrane
Cell membrane
Nuclear
membrane
Nuclear membrane NO nuclear membrane
NO cell wall
Cell wall made of
CELLULOSE
Cell wall made of
PEPTIDOGLYCAN
Has ribosomes
Has ribosomes
Has ribosomes
DNA in multiple
chromosomes
DNA in multiple
chromosomes
DNA is a single
circular ring
CYTOSKELETON
CYTOSKELETON
CYTOSKELETON
Small vacuoles
Really big vacuole
NO vacuoles
Has lysosomes
NO lysosomes
NO lysosomes
Has centrioles
NO centrioles
NO centrioles
Has mitochondria
Has mitochondria
No mitochondria
NO chloroplasts
Chloroplasts
NO chloroplasts
SMALLER
SMALL
SMALLEST
USE WORDS FROM THE WORD BANKS TO COMPLETE THE VENN DIAGRAM COMPARISON
Fig. 4-4b
NUCLEUS:
Nuclear envelope
Chromosome
Rough endoplasmic
reticulum
Ribosomes
Nucleolus
Smooth
endoplasmic
reticulum
Golgi
apparatus
CYTOSKELETON:
Central vacuole
Microtubule
Chloroplast
Cell wall
Intermediate
filament
Plasmodesmata
Microfilament
Mitochondrion
Peroxisome
Plasma membrane
Cell wall of
adjacent cell
Fig. 4-4a
NUCLEUS:
Nuclear envelope
Smooth endoplasmic
reticulum
Chromosomes
Nucleolus
Rough
endoplasmic
reticulum
Lysosome
Centriole
Peroxisome
CYTOSKELETON:
Microtubule
Intermediate
filament
Microfilament
Ribosomes
Golgi
apparatus
Plasma membrane
Mitochondrion
Fig. 4-UN3
a.
l.
b.
c.
k.
j.
i.
h.
d.
g.
e.
f.