Biology 12 PowerPoint for Section 3-3 and 3-4

2. UNIT A: Cell Biology
Chapter 2: The Molecules of Cells
Chapter 3: Cell Structure and Function:
Sections 3.3, 3.4
Chapter 4: DNA Structure and Gene
Expression
Chapter 5: Metabolism: Energy and
Enzymes
Chapter 6: Cellular Respiration
Chapter 7: Photosynthesis

3. UNIT A Chapter 3: Cell Structure and Function
Chapter 3: Cell Structure and Function
In this chapter, you will learn about how cell structures have critical
roles to play in the health of an organism.
What other cellular organelles
have a similar function to the
lysosome?
Why doesn’t the cell “clean
up” the faulty lysosomes?
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4. UNIT A Chapter 3: Cell Structure and Function Section 3.3
3.3 The Cytoskeleton
The proteins of the cytoskeleton interconnect and extend
from the nucleus to the plasma membrane.
•The cytoskeleton allows eukaryotic cells to maintain their
shape and the organelles to move
•Three components of the cytoskeleton network are actin
filaments, intermediate filaments, and microtubules
A B C
TO PREVIOUS SLIDE From Figure 3.12 The Cytoskeleton. Fibroblasts contain (A) actin
filaments, (B) intermediate filaments, and (C) microtubules.

5. UNIT A Chapter 3: Cell Structure and Function Section 3.3
Actin Filaments
• Long, extremely thin (~ 7 nm diameter), flexible fibres that
occur as bundles or mesh-like networks
• Each filament contains two chains of globular actin
monomers twisted about each other in a helix
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From Figure 3.12 The Cytoskeleton. a. Left to right: Fibroblasts in animal tissue
contain actin filaments. The drawing shows that actin filaments are composed of a
twisted double chain of actin subunits. The giant cells of the green alga Chara rely on
actin filaments to move organelles from one end of the cell to another.

6. UNIT A Chapter 3: Cell Structure and Function Section 3.3
Actin Filaments: Structure and Movement
• Actin filaments play a structural role by forming dense,
complex webs under the surface of the plasma membrane.
They are also in microvilli, which project from intestinal
cells, and pseudopods, which are extensions that allow
some cells to move.
• Actin filaments play a role in movement by associating
with motor molecules, which are proteins that attach,
detach, and reattach farther along the actin filament
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In muscle cells, myosin is a motor molecule. The head interacts with ATP
and actin and the tail interacts with the membrane. Myosin pulls actin
filaments along, using ATP for energy.

7. UNIT A Chapter 3: Cell Structure and Function Section 3.3
Intermediate Filaments
• Intermediate in size between actin filaments and
microtubules (8−10 nm diameter)
• A rope-like assembly of fibrous polypeptides
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From Figure 3.12 The Cytoskeleton. b. Left to right: Fibroblasts in animal tissue contain
intermediate filaments. The drawing shows that fibrous proteins account for the ropelike
structure of intermediate filaments. Hair is strengthened by the presence of intermediate
filaments.

8. UNIT A Chapter 3: Cell Structure and Function Section 3.3
Microtubules
• Small, hollow cylinders about 25 nm in diameter and 0.2
to 25 μm in length
• Composed of 13 rows of alpha and beta tubulin dimers,
surrounding an empty core
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From Figure 3.12 The Cytoskeleton. c. Left to right: Fibroblasts in animal tissue contain
microtubules. The drawing shows that microtubules are hollow tubes composed of tubulin
subunits. The skin cells of a chameleon rely on microtubules to move pigment granules
around so they can take on the colour of their environment.

9. UNIT A Chapter 3: Cell Structure and Function Section 3.3
Microtubule Assembly
In most eukaryotic cells, the centrosome contains a
microtubule organizing centre, which regulates microtubule
assembly. Microtubules radiate from the centrosome.
• Microtubules help maintain the shape of the cell
• Microtubules act as tracks that organelles move along,
with the aid of motor molecules (kinesin and dynein)
Before cell division, microtubules disassemble then
reassemble into a spindle, which attaches to chromosomes
for proper distribution and participates in dividing the cell.
After cell division, the spindle disassembles and microtubules
reassemble into their former arrangement.
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10. UNIT A Chapter 3: Cell Structure and Function Section 3.3
Centrioles
In animal cells, a centrosome contains two centrioles lying at
right angles to each other.
•Centrioles are short cylinders of microtubules in a 9 + 0
pattern of triplets ( a ring of nine sets of microtubule triplets)
•Centrioles replicate before cell division and each pair becomes
part of a centrosome. The centrosomes move apart at cell
division.
Figure 3.13 Centrioles In a nondividing
animal cell, a single pair of centrioles lies
in the centrosome located just outside
the nucleus.
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11. UNIT A Chapter 3: Cell Structure and Function Section 3.3
Cilia and Flagella
Cilia and flagella are hair-like
extensions that move.
•They provide movement for
some cells
•Both consist of membrane-bound
cylinders composed of a 9
+ 2 pattern of microtubules (nine
microtubule doublets in a circle
around two central microtubules)
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From Figure 3.14 Structure of a
flagellum or cilium

12. UNIT A Chapter 3: Cell Structure and Function Section 3.3
Cilia and Flagella
• Cilia and flagella move
when the microtubule
doublets move past each
other
• The protein dynein acts as
a motor molecule
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From Figure 3.14 Side arm motor
molecules of dynein are involved in
movement of flagella and cilia.

13. UNIT A Chapter 3: Cell Structure and Function Section 3.3
Check Your Progress
1. Identify the structural makeup of actin filaments,
intermediate filaments, and microtubules.
2. Describe the structures of cilia, flagella, and
centrioles.
3. Explain how cilia and flagella move.
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14. UNIT A Chapter 3: Cell Structure and Function Section 3.3
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15. UNIT A Chapter 3: Cell Structure and Function Section 3.4
3.4 Plasma Membrane Structure and Function
The plasma membrane regulates entrance and exit of substances
from the cell to help maintain homeostasis.
The fluid-mosaic model of the plasma membrane structure:
•Phospholipids form a bilayer, with the hydrophilic polar heads
facing inside and outside of the cell and hydrophobic tails facing
each other
•Peripheral proteins are partially embedded on one side of the
membrane
•Integral proteins span the entire membrane and may protrude
into one or both sides; they move laterally
•Steroids, glycolipids, and glycoproteins are also present
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16. UNIT A Chapter 3: Cell Structure and Function Section 3.4
TO PREVIOUS SLIDE Figure 3.15 Fluid-mosaic model of plasma membrane structure.

17. UNIT A Chapter 3: Cell Structure and Function Section 3.4
Functions of the Membrane Proteins
Plasma membranes of different cell types have unique
combinations of proteins. Generally,
•Peripheral proteins play a structural role by helping to
stabilize and shape the plasma membrane
•Integral proteins determine a membrane’s specific functions.
The following are types of integral proteins:
• channel proteins
• carrier proteins
• cell recognition proteins
• receptor proteins
• enzymatic proteins
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18. UNIT A Chapter 3: Cell Structure and Function Section 3.4
Functions of the Membrane Proteins
Channel proteins are
involved in the passage of
molecules through the cell
membrane by forming a
channel.
Carrier proteins are
involved in the passage of
molecules through the cell
membrane by combining
with the substance.
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From Figure 3.16 Examples of membrane
protein diversity.

19. UNIT A Chapter 3: Cell Structure and Function Section 3.4
Functions of the Membrane Proteins
Cell recognition proteins are
glycoproteins involved in cell
recognition of pathogens.
Receptor proteins bind
specific molecules, which
causes a cell response.
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From Figure 3.16 Examples of membrane
protein diversity.

20. UNIT A Chapter 3: Cell Structure and Function Section 3.4
Functions of the Membrane Proteins
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Enzymatic proteins
catalyze cell reactions.
From Figure 3.16 Examples of
membrane protein diversity.

21. UNIT A Chapter 3: Cell Structure and Function Section 3.4
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Check Your Progress
1. Describe the role of proteins, steroids, and
phospholipids in the fluid-mosaic model.
2. Distinguish between the roles of the various
integral proteins in the plasma membrane.

22. UNIT A Chapter 3: Cell Structure and Function Section 3.4
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