Cell Biology Exam #2-Spring 2007

Name______________________

MULTIPLE CHOICE. Choose the best answer (2 points each).

1) Which of the following factors would tend to increase membrane fluidity? 1) ___E____

A) a greater proportion of saturated phospholipids

B) a lower temperature

C) a relatively high protein content in the membrane

D) a greater proportion of relatively large glycolipids compared to lipids having smaller molecular masses

E) a greater proportion of unsaturated phospholipids

2) Which of the following types of molecules are the major structural components of the cell membrane? 2) _____A__

A) phospholipids and proteins

B) glycoproteins and cholesterol

C) nucleic acids and proteins

D) phospholipids and cellulose

E) proteins and cellulose

3) What is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold? 3) ___B____

A) by decreasing the number of hydrophobic proteins in the membrane

B) by increasing the percentage of unsaturated phospholipids in the membrane

C) by increasing the percentage of cholesterol molecules in the membrane

D) A and B only

E) A, B, and C

4) Which of the following is a characteristic feature of a carrier protein in a plasma membrane? 4) ___A____

A) It exhibits a specificity for a particular type of molecule.

B) It requires the expenditure of cellular energy to function.

C) It works against diffusion.

D) It has few, if any, hydrophobic amino acids.

E) It is a peripheral membrane protein.

5) Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are 5) ___A____

A) hypertonic to fresh water but hypotonic to the salt solution.

B) isotonic with fresh water but hypotonic to the salt solution.

C) hypertonic to both fresh water and the salt solution.

D) hypotonic to both fresh water and the salt solution.

E) hypotonic to fresh water but hypertonic to the salt solution.

Refer to Figure 7.3 to answer the following questions.

The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same.

Figure 7.3

6) If you examine side A after 3 days, you should find 6) ___A____

A) a decrease in the concentration of NaCl and a decrease in the water level.

B) no change in the concentration of NaCl and glucose and an increase in the water level.

C) a decrease in the concentration of NaCl and glucose and an increase in the water level.

D) a decrease in the concentration of NaCl, an increase in water level, and no change in the concentration of glucose.

E) no net change in the system.

7) You are working on a team that is designing a new drug. In order for this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would not be a factor that determines whether the molecule enters the cell? 7) ___D____

A) size of the drug molecule

B) similarity of the drug molecule to other molecules transported by the target cells

C) charge on the drug molecule

D) lipid composition of the target cells' plasma membrane

E) polarity of the drug molecule

8) Carrier molecules in the membrane and metabolic energy are required for 8) __A_____

A) active transport.

B) facilitated diffusion.

C) osmosis.

D) B and C only

E) A, B, and C

9) All of the following processes take material into cells except 9) _______

A) carrier-facilitated diffusion.

B) endocytosis.

C) pinocytosis.

D) exocytosis.

E) active transport.

10) What is the cause of familial hypercholesterolemia? 10) __D____

A) poor attachment of the cholesterol to the extracellular matrix of cells

B) a poorly formed lipid bilayer that cannot incorporate cholesterol into cell membranes

C) a general lack of glycolipids in the blood cell membranes

D) inhibition of the cholesterol active transport system in red blood cells

E) defective LDL receptors on the cell membranes

11) If an enzyme solution is saturated with substrate, the most effective way to obtain an even faster yield of products is to 11) ___E___

A) add a noncompetitive inhibitor.

B) heat the solution to 90°C.

C) add an allosteric inhibitor.

D) add more of the enzyme.

E) add more substrate.

12) What is the change in free energy of a system at chemical equilibrium? 12) __D____

A) slightly decreasing

B) slightly increasing

C) greatly decreasing

D) no net change

E) greatly increasing

13) Which of the following is true for all exergonic reactions? 13) __B____

A) The reactions are nonspontaneous.

B) The reaction proceeds with a net release of free energy.

C) A net input of energy from the surroundings is required for the reactions to proceed.

D) The products have more total energy than the reactants.

E) Some reactants will be converted to products.

14) Which of the following reactions is most likely to be coupled to the reaction ATP + O →ADP + (ΔG = -7.3 kcal/mol)? 14) __B____

A) DP → D + (ΔG = -10 kcal/mol)

B) E + → EP (ΔG = +5 kcal/mol)

C) B + → BP (ΔG = +8 kcal/mol)

D) A + → AP (ΔG = +10 kcal/mol)

E) CP → C + (ΔG = -4 kcal/mol)

15) Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's 15) _D_____

A) entropy.

B) free-energy content.

C) heat content.

D) activation energy.

E) endothermic level.

16) Which of the following statements regarding enzymes is true? 16) _A___

A) Enzymes increase the rate of a reaction.

B) Enzymes prevent changes in substrate concentrations.

C) Enzymes are permanently altered by the reactions they catalyze.

D) Enzymes change the direction of chemical reactions.

E) Enzymes decrease the free energy change of a reaction.

17) According to the induced fit hypothesis of enzyme catalysis, which of the following is correct? 17) _A_____

A) The binding of the substrate changes the shape of the enzyme's active site.

B) The binding of the substrate depends on the shape of the active site.

C) The active site creates a microenvironment ideal for the reaction.

D) Some enzymes change their structure when activators bind to the enzyme.

E) A competitive inhibitor can outcompete the substrate for the active site.

18) Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? 18) __E____

A) allosteric inhibition

B) saturation of the enzyme activity

C) denaturization of the enzyme

D) insufficient cofactors

E) competitive inhibition

19) What is a nonprotein "helper" of an enzyme molecule called? 19) __C___

A) accessory enzyme

B) enzyme activator

C) coenzyme

D) functional group

E) allosteric group

The next questions are based on the following information.

A series of enzymes catalyze the reaction X→Y→Z→A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme.

20) Substance A functions as 20) C ______

A) a competitive inhibitor.

B) the substrate.

C) an allosteric inhibitor.

D) an intermediate.

E) a coenzyme.

21) Which metabolic pathway is common to both fermentation and cellular respiration? 21) _A_____

A) glycolysis

B) the citric acid cycle

C) reduction of pyruvate to lactate

D) the electron transport chain

E) synthesis of acetyl CoA from pyruvate

22) The final electron acceptor of the electron transport chain that functions in oxidative phosphorylation is 22) B______

A) pyruvate.

B) oxygen.

C) ADP.

D) water.

E) .

23) Most from the catabolic breakdown of glucose is released during 23) ___C___

A) glycolysis.

B) electron transport.

C) the Kreb's cycle.

D) oxidative phosphorylation.

E) lactate fermentation.

24) Which of the following statements about NA is false? 24) __D____

A) NA is reduced by the action of dehydrogenases.

B) NA can receive electrons for use in oxidative phosphorylation.

C) In the absence of NA, glycolysis cannot function.

D) NA has more chemical energy than NADH.

E) NA is reduced to NADH during both glycolysis and the citric acid cycle.

25) Which process in eukaryotic cells will proceed normally whether oxygen () is present or absent? 25) _B_____

A) electron transport

B) glycolysis

C) oxidative phosphorylation

D) chemiosmosis

E) the citric acid cycle

26) All of the following are functions of the Kreb's cycle except 26) _A_____

A) adding electrons and protons to oxygen, forming water.

B) production of NADH.

C) release of carbon dioxide.

D) production of ATP.

E) production of FAD.

27) For each molecule of glucose that is metabolized by glycolysis and the Kreb's cycle, what is the total number of NADH + FADH₂ molecules produced? 27) __C____

A) 10 B) 4 C) 12 D) 5 E) 6

28) Cellular respiration harvests the most chemical energy from which of the following? 28) __D____

A) transferring electrons from organic molecules to pyruvate

B) substrate-level phosphorylation

C) generating carbon dioxide and oxygen in the electron transport chain

D) oxidative phosphorylation

E) converting oxygen to ATP

29) Inside an active mitochondrion, most electrons follow which pathway? 29) __B____

A) electron transport chain → Kreb's cycle → ATP → oxygen

B) Kreb's cycle → NADH → electron transport chain → oxygen

C) Kreb's cycle → FAD → electron transport chain → ATP

D) glycolysis → NADH → oxidative phosphorylation → ATP → oxygen

E) pyruvate → Kreb's cycle → ATP → NADH → oxygen

30) How many molecules of carbon dioxide (CO₂) would be released from the complete aerobic respiration of a molecule of sucrose (C₁₂H₂₂ O₁₁), a disaccharide? 30) __D____

A) 3 B) 2 C) 6 D) 12 E) 38

31. (4 points each) Agree or disagree with the following statements. In either case, fully defend you position.

A. Conformational changes in the sodium/potassium ATPase are critical in the ability of this protein to carry out its function.

Agree-There are several conformational changes that make the pump work and several are driven by the phosphorylation/dephosphorylation of the Atpase protein. Examples include: When the pump is phosphorylated, the shape changes so that it opens to the outside and the shape of the sodium binding sites change so sodium can no longer bind.  This pumps sodium out of the cell.  When the pump is dephosphorylated, it open to the inside of the cell and changes the shape of the potassium binding site so potassium can no longer bind.  This releases potassium into the cell.

B. If you administered a drug to a cell that inhibited the process of exocytosis but not the process of endocytosis, the drug would kill the cell.

Agree-All of the plasma membrane would eventually become part of the endomembrane system (the plasma membrane would disappear).  Plasma membranes would be lost by endocytosis but not returned by exoocytosis.  In order for the endomembrane system and the plasma membrane to maintain their normal size, there has to be an equilibrium between the rates of exocytosis and endocytosis.

C. It is important to the survival of the cell that its catabolic pathways are arranged in such a way that the product of one reaction is used as a substrate of the next reaction.

delta G=0 at equilibrium.  If the cell lets its catabolic pathways reach equilibrium, delta G=0 and no work can be done.  By arranging the pathways in a sequence where the product of one reaction is the substrate of the next, the pathways are kept from reaching equilibrium so work can be done.

D. Cellular respiration might have evolved in such a way that it produced only 4 ATP/glucose rather than 36, if cells had had an unlimited supply of oxidized NAD to use during cellular metabolism.

Agree-If there were an unlimited supplied of NAD+, there would be no need for a means to recycle NADH. Thus, no need for an electron transport system which produces 32 of the 36 ATP.

E. The final steps of alcoholic fermentation (conversion of pyruvate into ethanol) and the electron transport system occur in the cell for the same reason. 

Agree- the purpose of both is to recycle the reduced form of the coenzymes back into the oxidized forms.  Without the oxidized forms of the coenzymes, the reactions that require them will stop.

32. (8 points) Describe how the cell produces 36 ATP/glucose during cellular respiration. In your description, tell where (glycolysis, Kreb’s cycle, or electron transport system) and how (oxidative phosphorylation or substrate level phosphorylation) the ATP is made. Describe the role that reduced NAD and FAD and the electron transport system play in producing this 36 ATP.

glycolysis-                              

2 ATP used

4 ATP formed

net 2ATP formed

2 NADH formed

Kreb’s cycle

2 ATP formed

8 NADH formed

2 FADH2 formed

ETS-

Each NADH from Kreb’s cycle oxidized give 3 ATP=24 ATP

Each FADH2 from Kreb’s cycle oxidized give 2 ATP=4 ATP

Each NADH from glycolysis converted in to FADH=4 ATP

Total=32 ATP

Grand total =36 ATP

33. (6 points) Using diagrams and accompanying explanations, describe the structure of the cell membrane (what molecules it's made up of and how they arranged) according to the fluid mosaic model.   How does the structure of the cell membrane relate to its function?

The diagram and explanations should show the following elements:

Phospholipid bilayer, lipids and proteins able to move laterally within the bilayer, integral proteins, peripheral proteins, cholesterol, gylcoproteins, the membrane being bifacial (different on the outer and inner surfaces).

The Singer-Nicholson model explains how membranes are fluid (allowing endo and exocytosis), explains the need for transport proteins for substances that are not nonpolar, and illustrates the involvement of membrane proteins in phenomena like cell-cell recognition.

34. (6 points) On the surface, life seems to be a contradiction of the Second Law of Thermodynamics. Explain why. Explain how life is able to exist despite the natural tendency of matter as described by the Second Law of Thermodynamics.

The Second Law says that all matter tends to spontaneously assume the maximum state of entropy. However, cell’s are systems of low entropy, thus seeming to contradict the Second Law. Cells maintain their organization by expending energy (ATP) to maintain their low state of entropy. The system (the cell) maintains its low state of entropy by increasing the entropy of its surroundings.