1. Ch. 7-8 Review Lecture

2. 1. Why are phospholipids considered amphipathic molecules?

3. Phospholipids are the most abundant lipid in the plasma membrane
Concept 7.1: Cellular membranes are fluid mosaics of lipids and proteins
Phospholipids are the most abundant lipid in the plasma membrane
Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions
The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it
For the Cell Biology Video Structure of the Cell Membrane, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. 2. Explain the role of cholesterol in the fluid mosaic model of cell membranes.

5. Fig. 7-5
Lateral movement
(~107 times per second)
Flip-flop
(~ once per month)
(a) Movement of phospholipids
Fluid
Viscous
Unsaturated hydrocarbon
tails with kinks
Saturated hydro-
carbon tails
(b) Membrane fluidity
Figure 7.5 The fluidity of membranes
Cholesterol
(c) Cholesterol within the animal cell membrane

6. 3. List four functions of membrane proteins and give an example of each.

7. Six major functions of membrane proteins:
Signaling molecule
Enzymes
Receptor
ATP
Signal transduction
(a) Transport
(b) Enzymatic activity
(c) Signal transduction
Glyco-
protein
(d) Cell-cell recognition
(e) Intercellular joining
(f) Attachment to
the cytoskeleton
and extracellular
matrix (ECM)
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8. 4. Define selectively permeability and explain how that serves a function in cell activity.

9. The Permeability of the Lipid Bilayer
Hydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly
Polar molecules, such as sugars, do not cross the membrane easily
This makes the membrane selectively permeable
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10. 5. Differentiate between channel and carrier proteins
5. Differentiate between channel and carrier proteins. Give an example of each.

11. Transport Proteins
Cell membranes are permeable to a variety of polar molecules.
Transport proteins allow passage of hydrophilic substances across the membrane
Some transport proteins, called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel
Channel proteins called aquaporins facilitate the passage of water
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12. A transport protein is specific for the substance it moves
Other transport proteins, called carrier proteins, bind to molecules and change shape to shuttle them across the membrane
A transport protein is specific for the substance it moves
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

13. Fig. 7-12
Figure 7.12 Osmosis

14. 6. Compare and contrast hypertonic, hypotonic, and isotonic in terms of solutes.

15. Water Balance of Cells Without Walls
Osmosis is the diffusion of water across a selectively permeable membrane
Tonicity is the ability of a solution to cause a cell to gain or lose water
Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water
Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water
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16. 7. Explain the differences between plant and animal cells when placed in varying tonicities.

17. Fig. 7-13
Figure 7.13 The water balance of living cells

18. 8. Describe three two types of facilitated diffusion and its function in the cell.

19. Facilitated Diffusion: Passive Transport Aided by Proteins
In facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membrane
Channel proteins provide corridors that allow a specific molecule or ion to cross the membrane
Channel proteins include
Aquaporins, for facilitated diffusion of water
Ion channels (gated channels) that open or close in response to a chemical/physical stimulus
For the Cell Biology Video Water Movement through an Aquaporin, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

20. 9. Describe the action of the sodium/potassium pump.

21. 1 2 3 6 5 4 EXTRACELLULAR FLUID [Na+] high Na+ [K+] low Na+ Na+ Na+
Fig
EXTRACELLULAR
FLUID
[Na+] high
Na+
[K+] low
Na+
Na+
Na+
Na+
Na+
Na+
Na+
[Na+] low
ATP P
Na+ P
CYTOPLASM
[K+] high
ADP 1 2 3 K+
Figure 7.16, 1–6 The sodium-potassium pump: a specific case of active transport K+ K+ K+ K+ P K+ P 6 5 4

22. Facilitated diffusion
Fig. 7-17
Passive transport
Active transport
ATP
Diffusion
Facilitated diffusion
Figure 7.17 Review: passive and active transport

23. 10. Describe the action of the co-transport model for glucose.

24. – + H+ ATP H+ – + H+ H+ – + H+ H+ – + H+ H+ – + – + Diffusion of H+
Fig. 7-19 – + H+
ATP H+ – +
Proton pump H+ H+ – + H+ H+ – + H+
Diffusion
of H+
Sucrose-H+
cotransporter
Figure 7.19 Cotransport: active transport driven by a concentration gradient H+ –
Sucrose + – +
Sucrose

25. 11. Differentiate between pinocytosis and phagocytosis.

26. Animation: Exocytosis and Endocytosis Introduction
In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane
Endocytosis is a reversal of exocytosis, involving different proteins
There are three types of endocytosis:
Phagocytosis (“cellular eating”)
Pinocytosis (“cellular drinking”)
Receptor-mediated endocytosis
Animation: Exocytosis and Endocytosis Introduction
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

27. Environment: 0.01 M sucrose “Cell” 0.01 M glucose 0.01 M fructose
Fig. 7-UN3
Environment:
0.01 M sucrose
0.01 M glucose
0.01 M fructose
“Cell”
0.03 M sucrose
0.02 M glucose

28. 12. Differentiate between catabolic and anabolic pathways
12. Differentiate between catabolic and anabolic pathways. Give examples of each.

29. The synthesis of protein from amino acids is an example of anabolism
Catabolic pathways release energy by breaking down complex molecules into simpler compounds
Cellular respiration, the breakdown of glucose in the presence of oxygen, is an example of a pathway of catabolism
Anabolic pathways consume energy to build complex molecules from simpler ones
The synthesis of protein from amino acids is an example of anabolism
Bioenergetics is the study of how organisms manage their energy resources
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

30. 13. Define the first two laws of thermodynamics and how they are related.

31. The First Law of Thermodynamics
According to the first law of thermodynamics, the energy of the universe is constant:
– Energy can be transferred and transformed, but it cannot be created or destroyed
The first law is also called the principle of conservation of energy
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

32. The Second Law of Thermodynamics
During every energy transfer or transformation, some energy is unusable, and is often lost as heat
According to the second law of thermodynamics:
– Every energy transfer or transformation increases the entropy (disorder) of the universe
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

33. 14. Defines Gibbs Free Energy equation and how it applies to biology.

34. Free-Energy Change, G
The change in free energy (∆G) during a process is related to the change in enthalpy, or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin (T):
∆G = ∆H – T∆S
Only processes with a negative ∆G are spontaneous
Spontaneous processes can be harnessed to perform work
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35. 15. Differentiate between endergonic and exergonic reactions.

36. Free Energy and Metabolism
The concept of free energy can be applied to the chemistry of life’s processes
There are 2 metabolic reaction types:
1. An exergonic reaction proceeds with a net release of free energy and is spontaneous
2. An endergonic reaction absorbs (stores) free energy from its surroundings and is nonspontaneous
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

37. Progress of the reaction
Fig. 8-6a
Reactants
Amount of
energy
released
(∆G < 0)
Free energy
Energy
Products
Figure 8.6a Free energy changes (ΔG) in exergonic and endergonic reactions
Progress of the reaction
(a) Exergonic reaction: energy released

38. Progress of the reaction
Fig. 8-6b
Products
Amount of
energy
required
(∆G > 0)
Energy
Free energy
Reactants
Figure 8.6b Free energy changes (ΔG) in exergonic and endergonic reactions
Progress of the reaction
(b) Endergonic reaction: energy required

39. 16. What are the three types of cellular work?

40. How ATP Performs Work
The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP
ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant
The recipient molecule is now phosphorylated
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41. The Regeneration of ATP
ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP)
The energy to phosphorylate ADP comes from catabolic reactions in the cell
The chemical potential energy temporarily stored in ATP drives most cellular work
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

42. 17. Describe the role of enzymes in the cell.

43. Progress of the reaction
Fig. 8-14 A B C D
Transition state A B EA C D
Free energy
Reactants A B
Figure 8.14 Energy profile of an exergonic reaction
∆G < O C D
Products
Progress of the reaction

44. Progress of the reaction
Fig. 8-15
Course of
reaction
without
enzyme EA
without
enzyme
EA with
enzyme
is lower
Reactants
Free energy
Course of
reaction
with enzyme
∆G is unaffected
by enzyme
Figure 8.15 The effect of an enzyme on activation energy
Products
Progress of the reaction

45. 18. Explain the active site/substrate interaction for enzymes, and how they are affected by pH and temperature.

46. Fig. 8-17 Substrates enter active site; enzyme
changes shape such that its active site
enfolds the substrates (induced fit). 1
Substrates held in
active site by weak
interactions, such as
hydrogen bonds and
ionic bonds. 2
Substrates
Enzyme-substrate
complex
Active site can lower EA
and speed up a reaction. 3
Active
site is
available
for two new
substrate
molecules. 6
Figure 8.17 The active site and catalytic cycle of an enzyme
Enzyme 5
Products are
released.
Substrates are
converted to
products. 4
Products

47. Fig. 8-18 Optimal temperature for typical human enzyme
enzyme of thermophilic
(heat-tolerant)
bacteria
Rate of reaction 20 40 60 80
100
Temperature (ºC)
(a) Optimal temperature for two enzymes
Optimal pH for pepsin
(stomach enzyme)
Optimal pH
for trypsin
(intestinal
enzyme)
Figure 8.18 Environmental factors affecting enzyme activity
Rate of reaction 1 2 3 4 5 6 7 8 9 10 pH
(b) Optimal pH for two enzymes

48. 19. Describe two ways do decrease the effectiveness of enzymes.

49. Fig. 8-19 Substrate Active site Competitive inhibitor Enzyme
Figure 8.19 Inhibition of enzyme activity
Noncompetitive inhibitor
(a) Normal binding
(b) Competitive inhibition
(c) Noncompetitive inhibition

50. 20. Define allosteric regulation. Describe cooperativity.

51. Allosteric Regulation of Enzymes
Allosteric regulation may either inhibit or stimulate an enzyme’s activity
Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site
Most allosterically regulated enzymes are made from polypeptide subunits
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

52. Allosteric Activation and Inhibition
Each enzyme has active and inactive forms
The binding of an activator stabilizes the active form of the enzyme
The binding of an inhibitor stabilizes the inactive form of the enzyme
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53. Cooperativity is a form of allosteric regulation that can amplify enzyme activity
In cooperativity, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

54. 21. Define how an enzyme might utilize negative feedback systems.

55. Feedback Inhibition
In feedback inhibition, the end product of a metabolic pathway shuts down the pathway
Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings