1. Chapter 3
Cells

2. Introduction:
A. The human body consists of 75 trillion cells that vary considerably in shape and size yet have much in common.
B. Differences in cell shape make different functions possible.

3. Composite Cell:
A. A composite cell includes many different cell structures.
B. A cell consists of three main parts-- the nucleus, the cytoplasm, and the cell membrane.
C. Within the cytoplasm are specialized organelles that perform specific functions for the cell.

4. Phospholipid bilayer
Flagellum
Nucleus
Nuclear envelope
Chromatin
Nucleolus
Ribosomes
Microtubules
Cell membrane
Centrioles
Mitochondrion
Rough
endoplasmic
reticulum
Microvilli
Secretory
vesicles
Cilia
Golgi
apparatus
Microtubule
Microtubules
Smooth
endoplasmic
reticulum L
ysosomes

5. A. Cell Membrane: (plasma membrane)
1. The cell membrane regulates the movement of substances in and out of the cell, participates in signal transduction, and helps cells adhere to other cells.
2. General Characteristics
a. The cell membrane is extremely thin and selectively permeable.
b. It has a complex surface with adaptations to increase surface area.

6. Extracellular side
of membrane
Extracellular side
of membrane
Carbohydrate
Fibrous proteins
Double
layer (bilayer)
of phospholipid
molecules
Phospholipid bilayer
Cholesterol
molecules
Globular
protein
Hydrophobic
fatty acid
“tail”
Cytoplasmic side
of membrane
Hydrophilic
phosphate
“head”

7. 3. Cell Membrane Structure: a
3. Cell Membrane Structure: a. The basic framework of the cell membrane consists of a double layer (bilayer) of phospholipids, with fatty acid tails turned inward. b. Molecules that are soluble in lipids (gases, steroid hormones) can pass through the lipid.

8. c. Embedded cholesterol molecules strengthen the membrane and help make the membrane less permeable to water-soluble substances. d. Many types of proteins are found in the cell membrane, including transmembrane proteins and peripheral membrane proteins.

9. e. Membrane proteins perform a variety of functions and vary in shape.
f. Some proteins function as receptors on the cell surface, starting signal transduction.
g. Other proteins aid the passage of molecules and ions.

10. h. Proteins protruding into the cell
h. Proteins protruding into the cell anchor supportive rods and tubules.
i. Still other proteins have carbohydrates attached (glycoproteins); these complexes are used in cell identification. Membrane proteins called cellular adhesion molecules (CAMs) help determine one cell’s interactions with others.

11. B. Cytoplasm:
1. The cytoplasm consists of a clear liquid (cytosol), a supportive cytoskeleton, and
networks of membranes and organelles.
a. Endoplasmic reticulum is made up of membranes, flattened sacs, and vesicles, and provides a tubular transport system inside the cell.
i. With ribosomes, endoplasmic reticulum (ER) is rough ER, and functions in protein synthesis.
ii. Without ribosomes, it is smooth ER, and functions in lipid synthesis.

12. b. Ribosomes are found with ER and. are scattered throughout the
b. Ribosomes are found with ER and are scattered throughout the cytoplasm. They are composed of protein and RNA and provide a structural support for the RNA molecules that come together in protein synthesis. Clusters of ribosomes in the cytoplasm are called polysomes.

13. Fig03.04 ER membrane Ribosomes (a) Membranes Membranes Ribosomes (b)
© Don Fawcett/Photo Researchers
(a)
Membranes
Membranes
Ribosomes
(b)
(c)

14. c. The Golgi apparatus is composed of
c. The Golgi apparatus is composed of flattened sacs, and refines, packages, modifies, and delivers proteins.
i. Vesicles formed on ER travel to the Golgi apparatus which modifies their contents chemically.
ii. The vesicle may then move to the cell membrane and secrete its contents to the outside (exocytosis).
iii. Vesicles form a “delivery service,” carrying chemicals throughout the cell.

15. Fig03.05 Nuclear envelope Nucleus Cytosol Rough endoplasmic reticulum
Golgi
apparatus
Transport
vesicle
Secretion
© Gordon Leedale/Biophoto Associates
(a)
(b)
Cell membrane

16. ii. Very active cells contain thousands of mitochondria.
d. Mitochondria are the powerhouses of the cell and contain enzymes needed for aerobic respiration.
i. The inner membrane of the mitochondrion is folded into cristae which hold the enzymes needed in energy transformations to make ATP.
ii. Very active cells contain thousands of mitochondria.

17. Inner membrane Cristae Outer membrane (a) (b) Fig03.06
©Gordon Leedale/Biophoto Associates
(a)
(b)

18. e. Lysosomes are the "garbage. disposals" of the cell and contain
e. Lysosomes are the "garbage disposals" of the cell and contain digestive enzymes to break up old cell components and bacteria.
f. Peroxisomes contain enzymes that function in the synthesis of bile acids, breakdown of lipids, degradation of rare biochemicals, and detoxification of alcohol.

19. g. Microfilaments and microtubules are thin, threadlike structures that serve as the cytoskeleton of the cell. i. Microfilaments, made of actin, cause various cellular movements. ii. Microtubules, made of the globular protein tubulin, are attached in a spiral to form a long tube. iii. Microfilaments group together to form myofibrils.

20. up of two hollow cylinders called centrioles that function in the
h. The centrosome is a structure made
up of two hollow cylinders called
centrioles that function in the
separation of chromosomes during cell
division.
i. Cilia and flagella are motile
extensions from the cell; shorter
cilia are abundant on the free
surfaces of certain epithelial cells
(respiratory linings, for example), and
a lengthy flagellum can be found on
sperm cells.
j. Vesicles form from part of the cell
membrane or the Golgi and store
materials.

21. (longitudinal section)
Fig03.08
Centriole
(cross section)
Centriole
(longitudinal section)
©Don W. Fawcett/Visuals Unlimited
(a)
(b)

22. Fig03.09a
Cilia
©Oliver Meckes/Photo Researchers
(a)

23. Fig03.09b
Flagellum
©Manfred Kage/Peter Arnold/Photolibrary
(b)

24. C. Cell Nucleus: 1. The fairly large nucleus is bounded by a double-layered nuclear envelope containing relatively large nuclear pores that allow the passage of certain substances. a. The nucleolus is composed of RNA and protein and is the site of ribosome production. b. Chromatin consists of loosely coiled fibers of protein and DNA. Condensed DNA is referred to as chromosomes.

25. Fig03.10 Nuclear envelope Nucleus Nucleolus Chromatin Nuclear pores
©Stephen L. Wolfe
(a)
(b)

26. Movements Through Cell Membranes
A. The cell membrane controls what passes through it.
B. Mechanisms of movement across the membrane may be passive, requiring no energy from the cell (diffusion, facilitated diffusion, osmosis, and filtration) or active mechanisms, requiring cellular energy (active transport, endocytosis, and exocytosis).

27. C. Passive Mechanisms 1. Diffusion a
C. Passive Mechanisms 1. Diffusion a. Diffusion is caused by the random motion of molecules and involves the movement of molecules from an area of greater concentration to one of lesser concentration until equilibrium is reached. b. Diffusion enables oxygen and carbon dioxide molecules to be exchanged between the air and the blood in the lungs, and between blood and tissue cells.

28. Permeable membrane Solute molecule Water molecule A B A B A B (1) (2)
Fig03.12
Permeable
membrane
Solute molecule
Water molecule A B A B A B
(1)
(2)
(3)
Time

29. Fig03.13
High O2
Low O2
High CO2
Low CO2

30. 2. Facilitated Diffusion a
2. Facilitated Diffusion a. Facilitated diffusion uses membrane proteins that function as carriers to move molecules (such as glucose) across the cell membrane. b. The number of carrier molecules in the cell membrane limits the rate of this process.

31. Region of higher concentration Transported substance Region of lower
Fig03.14
Region of higher
concentration
Transported
substance
Region of lower
concentration
Protein carrier
molecule
Cell
membrane

32. 3. Osmosis
a. Osmosis is a special case of diffusion in which water moves from an area of greater water concentration (where there is less osmotic pressure) across a selectively permeable membrane to an area of lower water concentration (where there is greater osmotic pressure).

33. Selectively permeable membrane Protein molecule Water molecule A A B B
Fig03.15
Selectively
permeable
membrane
Protein molecule
Water molecule A A B B 1 2
Time

34. b. Osmotic pressure is the ability of. osmosis to lift a volume of
b. Osmotic pressure is the ability of osmosis to lift a volume of water.
c. A solution with the same osmotic pressure as body fluids is called isotonic; one with higher osmotic pressure than body fluids is hypertonic; one with lower osmotic pressure is hypotonic.

35. Fig03.16a

36. Fig03.16b

37. Fig03.16c

38. 4. Filtration
a. Because of hydrostatic pressure, molecules can be forced through membranes by the process of filtration. Blood pressure is a type of hydrostatic pressure.

39. Blood pressure Blood flow Capillary wall Tissue fluid Larger molecules
Fig03.17
Capillary wall
Tissue fluid
Blood
pressure
Blood
flow
Larger molecules
Smaller molecules

40. D. Active Mechanisms 1. Active Transport a
D. Active Mechanisms 1. Active Transport a. Active transport uses ATP to move molecules from areas of low concentration to areas of high concentration through carrier molecules in cell membranes. b. As much as 40% of a cell's energy supply may be used to fuel this process.

41. c. The union of the specific. particle to be transported with
c. The union of the specific particle to be transported with its carrier protein triggers the release of cellular energy (ATP), which in turn alters the shape of the carrier protein, releasing the particle to the other side of the membrane.
d. Particles that are actively transported include sugars, amino acids, and sodium, potassium, calcium, and hydrogen ions, as well as nutrient molecules in the intestines.

42. Fig03.18 Carrier protein Binding site Region of higher concentration
Cell membrane
Region of lower
concentration
Phospholipid
molecules
Transported
particle
(a)
Carrier protein
with altered shape
Cellular
energy
(b)

43. b. Exocytosis is the reverse of endocytosis.
2. Endocytosis and Exocytosis
a. In endocytosis, molecules that are too large to be transported by other means are conveyed inside a vesicle that forms from a section of the cell membrane.
b. Exocytosis is the reverse of endocytosis.

44. i. Pinocytosis is in which cells engulf liquids.
c. Three various forms of endocytosis:
i. Pinocytosis is in which cells engulf liquids.
ii. Phagocytosis is in which the cell takes in larger particles, such as a white blood cell engulfing a bacterium.
iii. Receptor-mediated endocytosis allows the cell to take in very specific molecules (ligands) that pair up with specific receptors on the cell surface.

45. Cell membrane Particle Phagocytized particle Vesicle Nucleus Nucleolus
Fig03.19
Cell
membrane
Particle
Phagocytized
particle
Vesicle
Nucleus
Nucleolus

46. Fig03.20
Molecules
outside cell
Receptor-ligand
combination
Vesicle
Receptor
protein
Cell
membrane
Cell
membrane
indenting
Cytoplasm
(a)
(b)
(c)
(d)

47. The Cell Cycle
A. The series of changes a cell undergoes from the time it is formed until it reproduces is called the cell cycle.
B. The cell cycle consists of interphase, mitosis, cytokinesis, and differentiation.
C. The cell cycle is controlled by special protein checkpoints. Most cells do not divide continually. Cells have a maximum number of times they can divide because of built-in “clocks” (telomeres) on the tips of chromosomes.

48. D. Interphase
1. Interphase is a period of great metabolic activity in which the cell grows and synthesizes new molecules and organelles.
2. During the S phase of interphase, the DNA of the cell is replicated in preparation for cell division.
3. During the G1 and G2 phases of interphase, the cell grows and other structures are duplicated.

49. E. Cell Division 1. In one type of cell division, meiosis, four cells (sperm or ova) are produced, each of which contains half of the parent cell’s genetic information. 2. Mitosis is a carefully orchestrated division of the nucleus of the cell that results in each daughter cell receiving an exact copy of the mother cell's genetic material. Cytokinesis is the division of the cytoplasm.

50. 3. Mitosis is described as a series of four
3. Mitosis is described as a series of four stages, but the process is actually continuous.
a. Prophase, the first stage of mitosis, results in the DNA condensing into chromosomes, centrioles migrating to the poles, microtubules of the cytoskeleton reorganizing into spindle fibers, and the disappearance of the nuclear membrane.

51. b. Metaphase occurs as spindle fibers attach to centromeres on the chromosomes and the chromosomes align midway between centrioles. c. Anaphase occurs as the spindle fibers contract and pull the sister chromatids toward the centrioles. d. Telophase, the final stage of mitosis, begins when the chromosomes have completed their migrations, the nuclear envelope reappears, and the chromosomes begin to unwind.

52. Fig03.22 Late Interphase Cell has passed the restriction checkpoint
and completed DNA
replication, as well as
replication of centrioles
and mitochondria, and
synthesis of extra
membrane.
Early Interphase
of daughter cells—
a time of normal cell
growth and function.
(a)
Restriction
checkpoint
Nuclear
envelope
©Ed Reschke
Chromatin
fibers
Centrioles
Cleavage
furrow
©Ed Reschke
Prophase
Chromosomes condense and
become visible. Nuclear
envelope and nucleolus
disperse. Spindle apparatus
forms.
Microtubules
(e)
(b)
Centromere
Spindle fiber
Late Prophase
Sister
chromatids
Chromosomes
Nuclear
envelopes
©Ed Reschke
Telophase and Cytokinesis
Nuclear envelopes begin to
reassemble around two daughter
nuclei. Chromosomes decondense.
Spindle disappears. Division of
wo cells.
(d)
(c)
Mitosis
Cytokinesis G 1
phase
©Ed Reschke
©Ed Reschke
S phase
Interphase
Anaphase.
Sister chromatids separate to
opposite poles of cell. Events
begin which lead to cytokinesis.
Metaphase
Chromosomes align along
equator, or metaphase plate
of cell. G 2
phase

53. F. Cytoplasmic Division (Cytokinesis)
1. Cytokinesis begins during anaphase of mitosis and continues as a contractile ring pinches (cleavage furrow) the two new cells apart.
2. The two daughter cells may have varying amounts of cytoplasm and organelles, but they share identical genetic information.

54. G. Cell Differentiation 1
G. Cell Differentiation 1. The process by which cells develop into different types of cells with specialized functions is called differentiation. 2. Cell differentiation reflects genetic control of the nucleus as certain genes are turned on while others are turned off. 3. Stem cells retain the ability to divide without specialization. 4. Progenitor cells are daughters of stem cells that are partially specialized.

55. Fig03.23 Sperm Sebaceous Egg gland cell Progenitor cell
Fertilized
egg
Skin cell
Stem cell
Progenitor
cell
Progenitor
cell
Stem cell
Neuron
Progenitor
cell
Progenitor
cell
Progenitor
cell
Astrocyte
Progenitor
cell
Progenitor
cells
Progenitor
cells
Bone cell
Connective tissue cell
One or more steps
Self-renewal
Blood cells and platelets

56. H. Cell Death
1. Apoptosis is a form of cell death that is a normal part of development.