1. Chapter 4
Cell Structure and Function

2. What Are the Basic Attributes of Cells?
All cells share common features
DNA and RNA
plasma membrane
cytoplasm consists of all the fluid and structures that lie inside the plasma membrane but outside of the nucleus
The fluid portion of the cytoplasm (cytosol) contains water, salts, and organic molecules
Most of the cell’s metabolic activities occur in the cell cytoplasm

3. The Plasma Membrane Functions:
glycoprotein
carbo-
hydrate
extracellular fluid (outside)
cytoplasm (inside)
cholesterol
membrane
protein
channel protein
cytoskeleton
A phospholipid bilayer
helps to isolate the
cell's contents
Proteins help the cell
communicate with
its environment
Functions:
isolates the cell’s contents from the external environment
regulates the exchange of essential substances
allows communication between cells
creates attachments within and between cells
regulates biochemical reactions
Phospholipid bilayer – allows the cell to maintain essential differences in concentrations of material.
Proteins are responsible for exchanging and communicating, controlling reactions, and forming connections.
10,000 membranes stacked atop one another would scarcely equal the thickness of one page.
Membranes vary from one tissue type to another, and their structures can also change dynamically in response to their surroundings.
Fig. 4-2

4. Eukaryotic cells
Plants, animals, protists, and fungi

5. A Generalized Animal Cell
microfilaments
nuclear envelope
nuclear pore
nucleus
chromatin (DNA)
cytosol
nucleolus
micro- (cytoskeleton) tubules
flagellum
basal body
rough
endoplasmic
reticulum
vesicle
intermediate
filaments
(cytoskeleton)
cytoplasm
Golgi
apparatus
Organelles – membrane-enclosed structures, each specialized for a certain function.
centriole
ribosomes
on rough ER
lysosome
smooth
endoplasmic
reticulum
exocytosis of
material from
the cell
mitochondrion
plasma
membrane
Fig. 4-3
free ribosome

6. A Generalized Plant Cell
nuclear envelope
ribosomes
nuclear pore
intermediate
filaments
(cytoskeleton)
nucleus
chromatin
nucleolus
microtubules
(cytoskeleton)
cell walls of adjoining
plant cells
chloroplast
cytoplasm
rough
endoplasmic
reticulum
lysosome
smooth
endoplasmic
reticulum
Golgi apparatus
central
vacuole
vesicle
mitochondrion
cell wall
plasma
membrane
plasmodesmata
Fig. 4-4
cytosol
plastid
free ribosome

7. What Are the Major Features of Eukaryotic Cells?
Cell walls
outer surfaces of plants, fungi, and some protists
Plant cell walls are composed of cellulose
Fungal cell walls are made of chitin
Cell walls are porous, allowing oxygen, carbon dioxide, and water carrying dissolved molecules to flow easily through them
Plasmodesmata - openings that connect adjacent cells in plants
The plasma membrane is located just beneath the cell wall
1. Nonliving, stiff coating secreted outside cell membrane.
2 & 3. some polysaccharides (including prokayrotes) Protists have cellulose, protein, or glassy silica.
4. Protective but also ….

8. What Are the Major Features of Eukaryotic Cells?
microfilaments
intermediate
filaments
microtubules
microtubules (red)
nucleus
microfilaments (blue)
(a) Cytoskeleton
(b) Light micrograph showing the cytoskeleton
Cytoskeleton
provides shape, support, movement, cell division
The cytoskeleton is composed of three types of protein fibers:
microfilaments
intermediate filaments
microtubules
Functions: shape and support (changes cell shape) cells without cell walls
cell movement (cilia & flagella)
organelle movement
guide chromosomes and separate the dividing cell

9. Cytoskeleton
Table 4-2

10. Cilia and Flagella Functions:
0.1 micrometer
cilium
plasma membrane
basal body
section of cilium
central pair of
microtubules
protein
“arms”
Paramecium
Functions:
move the cell through fluid
move fluid past the cell
Both cilia and flagella are slender extensions of the plasma membrane supported by microtubules.
Cilia means eyelash (shorter and numerous)
Flagella means whip (longer, usually only 1 or 2)
Both common in protists.
Both contain a ring of 9 fused pairs of microtubules, with an unfused pair in the center.

11. How Cilia and Flagella Move
cilia lining
trachea
propulsion of fluid
(a) Cilium
power stroke
return stroke
plasma membrane
direction of locomotion
propulsion of fluid
flagellum of
human sperm
Requires energy to continuously undulate
Cilia – energy similar to oars on a rowboat
Flagella – energy compared to a propeller on a motorboat
Paramecium use cilia to swim through water, others use flagella
Cilia used in gills of oysters
In mammals:
Cilia – respiratory tract, female reproductive
Flagella – any sperm
surface of
human egg
cell
(b) Flagellum
continuous propulsion
Fig. 4-7

12. The Nucleus Control center
Nuclear envelope - consists of a double membrane perforated by nuclear pores
Chromatin
Nucleolus
(b) Nucleus of a yeast cell
(a) The nucleus
nuclear
envelope
pores
nucleolus
ribosomes
chromatin
nucleus
nuclear pores with
nuclear pore complex
Stores all information needed to construct the cell and direct the countless chemical reactions for life and reproduction. (make proteins)
Largest organelle
Isolated from the rest of the cell by a …
nuclear pore complex are protein gatekeepers allowing RNA thru for protein synthesis
2. (colored substance) – chromosomes made of DNA
when not dividing – extremely long, thin strands cannot see
3. (little nuclei) Site of ribosome assembly
The nucleolus consists of ribosomal RNA, proteins, ribosomes in various stages of synthesis, and DNA

13. Ribosomes small particle composed of ribosomal RNA and proteins
site of protein synthesis in the cytoplasm
ribosome
mRNA
amino acid
polyribosome
growing
protein
Fig. 4-10

14. Endoplasmic Reticulum
Vesicles are membranous sacs that transport substances
The endoplasmic reticulum (ER) is a series of interconnected membranes that form a labyrinth of interconnected flattened sacs and channels within the cytoplasm
All the proteins and phospholipids of cell membranes are synthesized in the ER
Endomembrane system – loosely connected compartments. Segregate molecules from the surrounding cytosol and ensure orderly process of chemical reactions.
Vesicles – temporary
Reticulum means network

15. Endoplasmic Reticulum
There are two forms of ER:
Smooth endoplasmic reticulum has no ribosomes, detoxifies drugs, and synthesizes lipids like steroid hormones made from cholesterol
Rough endoplasmic reticulum is studded with ribosomes and synthesizes proteins destined for other membranes or for secretion
ribosomes
smooth ER
rough ER
vesicles
Smooth ER – scarce in most cells except liver, mammalian reproductive.
detoxifies alcohol, metabolic wastes like ammonia

16. The Golgi Apparatus
Functions: sorts, chemically alters, and packages important molecules
It synthesizes some polysaccharides used in plant cell walls, such as cellulose and pectin
It packages the finished molecules into vesicles that are then transported to other parts of the cell (lysosomes) or to the plasma membrane for export
Vesicles from the
ER merge with
the Golgi
apparatus
Vesicles carrying
modified protein leave
the Golgi apparatus
Golgi
Named for the Italian cell biologist.

17. Lysosomes Serve as the cell’s digestive system
Golgi apparatus
digestive
enzymes
lysosome
food
vacuoles
The Golgi
apparatus modifies
the enzymes as
they pass through
its compartments
The enzymes
are packaged into
lysosomes, which
bud from the
(extracellular fluid)
Digestive
enzymes are
synthesized on
ribosomes and
travel through
the rough ER
(cytoplasm)
vesicles and travel to
the Golgi apparatus
A lysosome fuses
with a food vacuole,
and the enzymes
digest the food 5 4 3 2 1
Serve as the cell’s digestive system
A lysosome fuses with a food vacuole and digests food into basic nutrients
Digest worn-out organelles
Digest food from individual proteins to microorganisms like bacteria.
Contain enzymes that can break down almost any type of biological molecule.

18. Vacuoles
Serve many functions, including water regulation, support, and storage
Most cells contain one or more
sacs of cell membrane filled with fluid containing various molecules
Many freshwater organisms possess contractile vacuoles composed of collecting ducts, a central reservoir, and a tube leading to a pore in the plasma membrane that carries excess water out of the organism
Some vacuoles are temporary large vesicles (food vacuoles)
Permanent vacuoles in some freshwater protists and in plant cells:

19. Contractile Vacuoles Fig. 4-15 contractile vacuole
Water enters the collecting ducts
and fills the central reservoir
(a) Paramecium
collecting
ducts
central
reservoir
pore
Freshwater constantly leaks into contractile vacuoles through the cell membrane (osmosis).
So much water would cause the organism to burst.
Excrete the water by moving salt into collecting ducts then central reservoir.
The reservoir contracts, expelling
water through the pore
Fig. 4-15
(b) Contractile vacuole

20. Vacuoles Central vacuoles Found in plants Functions:
cytoplasm
(a) Turgor pressure provides support
central vacuole
cell wall
plasma membrane
When water is plentiful, it fills
the central vacuole, pushes
the cytoplasm against the cell
wall, and helps maintain the
cell's shape
When water is scarce, the
central vacuole shrinks and the
cell wall is unsupported
Deprived of the support
from water, the plant
wilts
Water pressure
supports the
leaves of this
impatiens plant
(b) Loss of turgor pressure causes the plant to wilt
Vacuoles
Central vacuoles
Found in plants
Functions:
To maintain water balance
To store hazardous wastes, nutrients, or pigments
To provide turgor pressure on the cytoplasm to keep cells rigid
which occupy three-quarters or more of the volume of many mature plant cells, are used in several ways:
By regulating ion content of cytosol
… As well as substances to deter animals from eating their leaves, nutrients (sugar and amino acids) not immediately needed, blue or purple pigments for the colors of flowers.
Support. Substances attract water into it -> water pressure – turgor pressure
provides support for the non-woody parts of the plant
(when you forget to water your plants)

21. Mitochondria Extract energy from food molecules to make ATP
“Powerhouse” of the cell
Double membrane with cristae
outer
membrane
inner
matrix
cristae
0.2 micrometer
Found in large numbers of cells that are metabolically active (muscle) less in cartilage.

22. Chloroplast Site of photosynthesis Double membrane
The thylakoid membranes contain the green pigment chlorophyll, which capture sunlight and make sugar from CO2 and water (photosynthesis)
outer
membrane
inner
stroma
thylakoid
channel
interconnecting
thylakoids
granum
(stack of thylakoids)
1 micrometer
Plants and some protists.
Stroma – fluid
Thylakoid – a stack of hollow membranous sacs
Chlorophyll captures the energy of sunlight and transfers it to other molecules in the thylakoid membranes. These molecules transfer the energy to ATP which diffuses into the stroma, where their energy is used to drive synthesis of sugar from CO2 and H2O.

23. Plastids Storage Only in plants and photosynthetic protists
starch
globules
plastid
0.5 micrometer
Storage
Only in plants and photosynthetic protists
Double membrane
Storage containers for various molecules, such as pigments or starch
Chloroplasts are highly specialized plastids.
3. Pigments that give ripe fruits their yellow, orange, or red colors.
store photosynthetic products produced during the growing season for over winter
Potatoes are composed almost entirely of cells stuffed with starch-filled plastids

24. Review Questions
Describe the structures and features shared by all cells.
Define organelle.
Which organelles are found in plants not animals?
Describe each major structure and know its function.
DNA, RNA, plasma membrane, cytoplasm
Membrane bound specialized structure in the cytoplasm
Chloroplast, plastids, cell wall, vacuoles

25. prokaryotic cells

26. Prokaryotic Cells Are Simpler Than Eukaryotic Cells
chromosome
(nucleoid region)
cell wall
plasma membrane
ribosomes
capsule
chromosome
(nucleoid region)
(d) Internal structure
pili
(c) Cocci
ribosomes
food granule
prokaryotic
flagellum
(b) Spirilla
capsule or
slime layer
cell wall
plasma membrane
cytoplasm
plasmid (DNA)
photosynthetic
membranes
(a) Generalized prokaryotic cell (bacillus)
(e) Photosynthetic prokaryote
Fig. 4-19

27. What Are the Major Features of Prokaryotic Cells?
Most prokaryotic cells (bacteria) are less than 5 µm long, with a simple internal structure compared to eukaryotic cells
They usually have a stiff cell wall
Prokaryotic cells can take several shapes:
Rod-shaped (bacilli)
Spiral-shaped (spirilla)
Spherical (cocci)
Prokaryotic cells are small and possess specialized surface features
Prokaryotic cells have fewer specialized structures within their cytoplasm (no organelles)
Eukaryotic cells are um
Single celled
2. Antibiotics interfere with cell wall synthesis, causing the bacteria to rupture.

28. What Are the Major Features of Prokaryotic Cells?
Some bacteria and archaea are propelled by flagella
Infectious bacteria may have polysaccharide adhesive capsules and slime layers on their surfaces
Pili are protein projections in some bacteria that further enhance adhesion
In the central region of the cell is an area called the nucleoid, which is separate from the cytoplasm
Within the nucleoid is a single, circular chromosome of DNA
Small rings of DNA (plasmids) are located in the cytoplasm
None have cilia.
Flagella is structured differently from eukaryotes.
Capsules and slime layers are similar except that capsules are more organized structurally so more difficult to remove. Allows them to stick to surfaces, protect, and prevent drying out.
Pili (hairs) from cell wall.
attachment pili: short and abundant
sex pili: few and long. Binds to a nearby bacterium of the same type and draws them together to exchange DNA.
4. Also has some RNA and protein
The single DNA carries essential genetic info
Plasmids carry genes that give the cell special properties (like inactivating antibodics)

29. What Are the Major Features of Prokaryotic Cells?
No nuclear membrane or membrane-bound organelles
Some have internal membranes used to capture light
Extensive cytoskeleton
The cytoplasm may contain
food granules
ribosomes
2. Some bacteria use membranes to organize enzymes for reactions. Lined up in order. Example …
3. Proteins differ but play similar roles
4. Food granules – store energy-rich molecules (glycogen)
Ribosomes – protein synthesis but smaller and different RNA and proteins.

30. Review Questions
Explain the major differences between prokaryotic and eukaryotic cells.
Describe the structure and function of the major surface features of bacteria.
Describe the internal features of bacteria.

31. A Protein Is Manufactured and Exported
Vesicles merge with the
plasma membrane and
release antibodies into the
extracellular fluid
Vesicles fuse with the
Golgi apparatus, and
carbohydrates are added
as the protein passes
through the compartments
The protein is
packaged into vesicles
and travels to the Golgi
apparatus
Antibody protein is
synthesized on ribosomes
and is transported into
channels of the rough ER
Completed glycoprotein
antibodies are packaged
into vesicles on the opposite
side of the Golgi apparatus
(extracellular fluid)
(cytoplasm)
vesicles
Golgi apparatus
forming
vesicle 5 4 3 2 1
Fig. 4-13