Question: 1. How does the fluid mosaic model fit our understanding of membrane structure?

Question:1. How does the fluid mosaic model fit our understanding of membrane structure? 

1. Fluid mosaic refers to the different types of lipid within the membrane and the tendency for the membrane to melt given a high enough temperature. 
2. The fluid refers to the presence of water surrounding the membrane and mosaic refers to the presence of both saturated and unsaturated fats. 
3. The fluid refers to the ability of ions and other molecules to flow across the membrane and mosaic refers to the diversity of molecules that can cross. 
4. The fluid refers to the ability of lipid to move freely within a flexible membrane and mosaic refers the presence of a variety of different types of protein and other components within the membrane. 

2. Which of the following statements about membrane structure is true? 

1. Cholesterol molecules extend across the lipid bilayer, so that their charged ends can interact with water. 
2. Glycolipids are only found on the cytoplasmic side. 
3. Peripheral proteins are usually found only on the cell surface, not the cytoplasmic side of the membrane. 
4. Lipids move readily within one side of the bilayer, but rarely flip from one side to the other. 

3. You are a scientist and are studying the plasma membrane of bacteria. You leave the bacteria growing in a water bath overnight at 23oC but the electricity goes out after you leave and the temperature drops to 15oC . When you get back several hours later, what will you expect to see when you analyze the bacterial membrane? 

A. The loss of sterols from the membrane. B. Higher levels of saturated fats.

C. Lower levels of saturated fats.

D. Higher levels of trans fats. 

4. Which of the following molecules is likely to move most quickly across the membrane by simple diffusion and why? 

A. Cl- because it is negatively charged. 

1. Na+ because it is small. 
2. O2 because it is non polar 
3. Glucose because it is polar 
4. There would be no difference in the rate of diffusion across the membrane for these molecules. 

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Biol1000 Fall 2013 - Test 2 

5. You are working with two artificial membranes in the lab. They are both identical in terms of lipid content except that lipid A has three times more cholesterol content than lipid B. As you increase the temperature, which of the two will melt first? 

1. Lipid A will melt first as the cholesterol will tend to prevent the fatty acid tails from aligning and packing tightly. 
2. Lipid A will melt first as the cholesterol will align with the unsaturated fats but not the saturated fats. 
3. Lipid A will melt last as the cholesterol will interact with the fatty acid tails and restrict phospholipid movement. 
4. Lipid A and Lipid B will melt at about the same temperature as cholesterol content does not affect membrane fluidity. 

6. A cell is placed in a solution of growth medium that has a solute concentration of 3.0 mM. The internal solute concentration of the cell is 0.2 mM. Which of the following statements is true? 

1. The growth medium is hypertonic compared to the cytoplasm and the cell will shrink. 
2. The growth medium is hypotonic compared to the cytoplasm and the cell will swell. 
3. The growth medium is isotonic compared to the cytoplasm and the cell will shrink. 
4. The growth medium is hypertonic compared to the cytoplasm and the cell will swell. 
5. None of the above. 

7. Through the process of endocytosis, some cells internalize (engulf) about 100% of their plasma membrane in approximately 30 minutes. The cell surface to volume ratio of these cells never change. How is this possible? 

1. The plasma membrane is not included in cell surface to volume measurements. 
2. Exocytosis replaces the internalized plasma membrane at a rate equal to membrane removal. 
3. Phospholipids are removed from the plasma membrane to maintain surface area to volume ratios. 
4. Expansion of the endomembrane area, due to fusing of endocytotic vesicles, makes up for the reduction in plasma membrane surface area. 

8. Lactose is moved into E. coli using a H+/lactose symporter. Based on your knowledge of symporters, what is the role of H+?

1. It is moving into the cell against its concentration gradient. 
2. It is binding to the transport protein to open the gated lactose channel. 
3. It is moving out of the cell against its concentration gradient.
4. It is binding to lactose and changing its conformation. The lactose/H+ complex then binds the receptor site on the transport protein. 
5. It is moving into the cell along its concentration gradient.

9. In question #8 above, what type of transport is this? 

A. primary active transport

B. secondary active transport

C. facilitated diffusion

D. transport via a gated ion channel 

10. Which of the following includes all others presented below? 

12. Some viruses inject their DNA into cells, but others are taken in whole by cells. How are they likely to be transported into the cell? 

14. How do enzymes work? 

1. They can change the shape of a substrate to make it more reactive. 
2. They provide the free energy required to catalyse a reaction. 
3. They decrease the potential energy of the reactants to increase the rate of reaction. 
4. They convert endergonic reactions to exergonic reactions. 

15. The enzyme tyrosine kinase modifies the amino acid tyrosine. What is it likely doing? 

A. Removing tyrosine from proteins.

B. Adding tyrosine to proteins.

C. Breaking the peptide bond wherever a tyrosine residue is found. D. Phosphorylating tyrosine. 

16. Is the following reaction spontaneous? 

A ÄG= 14.0 B 

A. Yes as the reactants are at a lower free energy than the products. 

B. Yes as the products are at a lower free energy than the reactants. 

C. No as the reactants are at a lower free energy than the products. 

D. No as the products are at a lower free energy than the reactants. 

17. During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the G for the new reaction? 

20. Side A of a membrane contains 0.05 μM of sodium. Side B of this membrane contains 0.05 μM of sodium. Diffusion of sodium across the membrane occurs via an open channel. Based on this information predict the direction of movement of sodium. 

A. Sodium will move from Side A to Side B

B. Sodium will move from Side B to Side A

C. There will be no movement of sodium across the membrane. D. Sodium will move in both directions at equal rates. 

21. Succinate dehydrogenase catalyzes the conversion of succinate to fumarate in the Citric Acid Cycle. The reaction is inhibited by malonic acid, which structurally resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the concentration of succinate relative to malonic acid reduces the inhibitory effect of malonic acid. Based on this information, which of the following is correct? 

A. Malonic acid is a non-competitive inhibitor. B. Malonic acid is a competitive inhibitor.

C. Succinate is a non-competitive inhibitor. D. Succinate is a competitive inhibitor. 

22. What is meant by signal amplification during cell signaling? 

1. There are multiple steps involving enzymes, each of which can activate multiple substrate molecules. 
2. The first messenger activates the production of effector molecules which accumulate within the cell. 
3. One signaling molecule can phosphorylate several receptors, activating all of them and increasing the signal to the cell. 
4. Often an activated receptor can in turn activate other receptors, much like the opening of gated ion channels during the nerve impulse. 

23. How does the receptor for a signal transduction pathway get the message from the outside to the inside of the cell? 

1. Receptors are integral membrane transport proteins that move the signal in by symport. 
2. Receptors and signal molecules are internalized by endocytosis.
3. Receptors are cleaved by enzyme activity to release the second messenger. 
4. Receptors undergo conformational change that activates the cytoplasmic side of the receptor. 

24. Where are receptors for steroid hormones found? 

A. On the cell surface.

B. Coupled to G-proteins.

C. In the cytoplasm.

D. Embedded in the membrane of smooth ER. 

26. A growth hormone acts via a G protein coupled receptor signal transduction pathway that involves cyclic AMP. A drug has been found that blocks the ability of cells to respond to this hormone. Experimental investigation reveals that cyclic AMP is still being produced in drug treated cells when hormone is present. What is the best hypothesis to explain this observation? 

A. The drug binds and inhibits the effector.

B. The drug binds and inhibits a protein kinase.

C. The drug binds and inhibits the insulin receptor.

D. All of these are equally good explanations given the above information. 

27. How is fermentation different from cellular respiration? 

A. It skips glycolysis, thereby missing out on the ATP generated by ATP synthase. B. It does not use pyruvate as a substrate.

C. It does not use the electron transport chain to convert NADH to NAD+

D. It stops oxidation of glucose after the citric acid cycle. 

28. When NAD+ is converted to NADH 

A. It is oxidized.

B. It is reduced.

C. It is phosphorylated. 

29. Where is the pH highest in the mitochondrion? 

A. The inter membrane space. B. The stroma

C. The matrix

D. The thykaloid lumen 

30. How does the electron transport chain in cellular respiration differ from the electron transport chain in photosynthesis? 

1. In respiration water is formed from oxygen whereas in photosynthesis oxygen is formed from carbon dioxide. 
2. In respiration the electrons flow from high to low energy, whereas in photosynthesis the electrons flow from low to high energy. 
3. In respiration the final electron acceptor is oxygen whereas in photosynthesis the final electron acceptor is ferrodoxin. 
4. In respiration the source of electrons is an activated carrier molecule whereas in photosynthesis the final product is an activated carrier molecule. 

31. What is an important role of photosystem II? 

1. It absorbs light energy to generate high energy electrons for the electron transport chain. 
2. It uses light energy to pull electrons off of oxygen. 
3. It absorbs light using chlorophyll then uses the energy to power the flow of electrons through ATP synthase. 
4. It receives electrons from photosystem I then passes them to the electron transport chain. 

32. A plant cell experiences a shift from linear to cyclic electron transport. This is likely because 

A. oxygen levels are low B. NADH levels are low C. NADP+ levels are low D. ATP levels are high 

33. You are working on a genetically altered plant and note that, although it is getting plenty of water and sunlight, it is failing to thrive. You suspect it's a problem with the chloroplasts so you run an analysis and you realize that oxygen is being made but carbon dioxide use is low. What do you conclude? 

A. Rubisco activity is being inhibited.

B. Pyruvate dehydrogenase is inhibited.

C. Photosystem I activity is overstimulated. D. Photosystem II has been shut down. 

34. What's the difference between oxidative phosphorylation and substrate level phosphorylation? 

1. Oxidative phosphorylation uses inorganic phosphate; substrate level phosphorylation uses phosphate attached to another molecule. 
2. Oxidative phosphorylation uses electrons derived from oxygen; substrate level phosphorylation does not. 
3. Substrate level phosphorylation is driven by the proton motive force; oxidative phosphorylation uses the energy of ATP. 
4. Substrate level phosphorylation involves ATP synthase; oxidative phosphorylation does not. 

35. What do respiration and photosynthesis have in common? 

A. Oxygen is required for both.

B. G3P is produced.

C. NADH and FADH2 are involved.

D. Both are exergonic reactions that occur spontaneously.