Cells are small to maintain a high surface area to volume ratio which allows for efficient exchange of substances. There are two main types of cells - prokaryotic cells which are smaller and lack organelles, and eukaryotic cells which are larger and have membrane-bound organelles that perform specialized functions. Key organelles in eukaryotic cells include the nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, cytoskeleton, and vacuoles.

1. Chapter 5 - Cells

2. Cells
Cells are small
(mostly)
Exceptions: Bird eggs,
neurons, some algae,
and bacteria cells

3. Why are Cells Small?
Cells are small because a high surface area-to-
volume ratio is essential.
Volume determines the amount of chemical
activity in the cell per unit time.
Surface area determines the amount of
substances that can pass the cell boundary per
unit time.

4. As the Cell Gets Larger the
SA:V Ratio Decreases

5. Plasma Membrane (Chapter 6)
The plasma membrane
is the outer surface of
every cell, and has more
or less the same
structure in all cells.
It is made of a
phospholipid bilayer
with proteins and other
molecules embedded.

6. Two Types of Cells
Prokaryotic and Eukaryotic
Bacteria and Archaea are prokaryotes.
Eukarya are eukayotes.

7. Prokaryotes
Very small
Individuals are single cells,
but often found in chains or
clusters.
Prokaryotes are very
successful—they can live on
a diversity of energy sources Image Credit--JEFF JOHNSON Hybrid Medical
Animation
and some can tolerate
extreme conditions.

8. All Prokaryotes:
Are enclosed by a plasma
membrane
The DNA is contained in
the nucleoid
Cytoplasm consists of
cytosol (water and
dissolved material) and
suspended particles
Ribosomes— sites of
protein synthesis (Free)

9. Specialized Prokaryotic
Structures
Rigid cell wall outside the
plasma membrane.
Some bacteria have an
additional outer
membrane.
Some bacteria have a
slimy capsule of
polysaccharides.

10. Specialized Prokaryotic
Structures
Inner Membrane
Photosynthesis
Other
Energy- Related
Functions
Usually Highly Folded
WHY?

11. Specialized Prokaryotic
Structures
Flagella
Used for Movement
Flagella move like a
“cork-screw”
Pili
Hairlike structures
Food/ Protection/ Mating
(sex pili)/ Adhere to Cells
Cytoskeleton
Some rod-shaped bacteria
have a cytoskeleton made
of the protein actin.

12. Eukaryotes
Eukaryotic cells are up to ten times larger than
prokaryotes.
Eukaryotic cells have membrane-enclosed
compartments called organelles.
Each organelle has a specific role in cell functioning.
Compartmentalization allowed eukaryotic cells to
specialize and form the tissues and organs of
multicellular organisms.

13. Eukaryotes

14. Eukaryotes

15. All Eukaryotes:
Plasma Membrane
Cytoplasm/Cytosol
Ribisomes
Ribosomes consist of ribosomal RNA
(rRNA) and more than 50 different protein
molecules.
“Free” or “Bound” Ribosomes

16. All Eukaryotes:
Nucleus
Usually the largest organelle.
Contains the DNA
Site of DNA replication
Site where gene transcription is turned on or off
Assembly of ribosomes begins in a region called
the nucleolus

17. Nucleus
Nuclear Envelope
- Double membrane
Nuclear Pores
Nucleoplasm
Chromatin
(Chromosomes)
- DNA and proteins

18. All Eukaryotes:
Endomembrane System
Plasma Membrane
Nuclear Envelope
Endoplasmic
Reticulum
Golgi Apparatus
Lysosome

19. Endoplasmic Reticulum (ER)
Network of interconnected (single)
membranes in the cytoplasm; has large
surface area.

20. Rough ER (RER)
Ribosomes are attached.
Single Membrane
Newly made proteins enter the RER
lumen where they are modified and
folded.

21. Smooth ER (SER)
More tubular, no ribosomes
Chemically modifies small molecules
such as drugs and pesticides
Hydrolysis of glycogen in animal cells
Synthesis of lipids and steroids

22. Golgi Apparatus
Composed of flattened sacs (cisternae)
and small membrane-enclosed
vesicles.
Receives proteins from the RER—can
further modify them
Concentrates, packages, sorts proteins
In plant cells, polysaccharides for cell
walls are synthesized here

24. How do Proteins get from one
Organelle to Another?
Vesicles
Localization Sequences
Short (~20 a.a.) polypeptides linked to
the C or N terminous of a protein
Allow a protein to cross a specific type of
membrane

25. Lysosomes
Primary lysosomes originate from the
Golgi apparatus.
They contain digestive enzymes—
macromolecules are hydrolyzed into
monomers.

26. Phagocytosis / Secondary Lysosomes
Food molecules enter the
cell by phagocytosis—a
phagosome is formed.
Phagosomes fuse with
primary lysosomes to form
secondary lysosomes.
Enzymes in the secondary
lysosome hydrolyze the
food molecules.

27. All Eukaryotes:
Mitochondria
Cellular Respiration
Convert potential energy of fuel molecules to
into a form the cell can use
Fuel Molecules + ADP + O2  Energy (ATP) + CO2
Most O2 in eukaryotic organisms is used up by
mitochondria

28. Mitochondria Structure
Mitochondria have two
membranes.
The inner membrane folds
inward to form cristae.
This creates a large
surface area for proteins
involved in cellular
respiration reactions.
The mitochondrial matrix
contains enzymes, DNA,
and ribosomes.

29. Specialized Eukaryotic Structures: Plastids
Plants/ Some Protists
Chloroplast
Site of photosynthesis—light
energy is converted to the
energy of chemical bonds
Chloroplasts have a double
membrane
Leucoplast
Store starches and fats
Chromoplast
Contain red, orange, and
yellow
pigments (gives color to
flowers)

30. Chloroplast
Grana
are stacks of thylakoids—made
of circular compartments of the
inner membrane.
Thylakoids
contain chlorophyll and other
pigments that harvest light
energy for photosynthesis.
Stroma
fluid in which grana are
suspended. The stroma
contains DNA and ribosomes.

31. Specialized Eukaryotic Structures only
found in Plants / Protists
Peroxisomes
Collect and break down toxic byproducts
of metabolism such as H2O2, using
specialized enzymes
Glyoxysomes
Only in plants—lipids are converted to
carbohydrates for growth

32. Specialized Eukaryotic Structures only
found in Plants / Protists
Vacuoles
Store waste products and toxic compounds; some
may deter herbivores
Provide structure for plant cells; water enters the
vacuole by osmosis, creating turgor pressure
Store anthocyanins (pink and blue pigments) in
flowers and fruits; the colors attract pollinators
Vacuoles in seeds have digestive enzymes to
hydrolyze stored food for early growth
Freshwater protists may have contractile vacuoles to
expel excess water.

33. Specialized Eukaryotic
Structures: Cytoskeleton
Supports and maintains cell shape
Holds organelles in position
Moves organelles
Involved in cytoplasmic streaming
Interacts with extracellular structures to
hold cell in place

34. Components of the
Cytoskeleton
Microfilaments  Intermediate filaments  Microtubules

35. Specialized Eukaryotic
Structures: Flagella and Cilia
Cilia
short, usually many
present, move with stiff
power stroke and flexible
recovery stroke
Flagella
Longer, usually one or two
present, movement is
snakelike

36. Extracellular Structures
Outside the Plasma Membrane
Cell Walls (Plants/Protists)
Extracellular Matrix (Animals)

37. Plant Cell Walls
Cellulose fibers are embedded in other
complex polysaccharides and proteins.
Adjacent plant cells are connected by
plasma membrane-lined channels called
plasmodesmata.

38. Extracellular Matrix
Composed of fibrous proteins such as
collagen, gel- like glycoproteins, and other
proteins.

39. Extracellular Matrix
• Holds cells together in tissues
• Contributes to properties of bone,
cartilage, skin, etc.
• Filters materials passing between
different tissues
• Orients cell movements in development
and tissue repair
• Plays a role in chemical signaling