CELL BIO--Chapter 2

Indicate if each of the following descriptions matches lipids (1), nucleic acids (2), polysaccharides (3), or proteins (4). (nucleic acids) Their monomers contain phosphorus and nitrogen. ( proteins) They constitute almost half of the cell's dry mass. (lipids) They are the main constituent of all cellular membranes. (lipids) They are largely hydrophobic and can store energy.

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Weak noncovalent attractions in the cell can be very strong in a nonaqueous environment. Some of these attractions are as strong as covalent interactions in a vacuum (their bond energy is approximately 340 kJ/mole), but become more than twenty-five times weaker (their bond energy becomes approximately 13 kJ/mole) in water. What type of attraction shows this phenomenon? A. Electrostatic attractions B. Hydrogen bonds C. van der Waals attractions D. Hydrophobic force E. All of the above

A. Electrostatic attractions (The probing of the charged ions by water molecules greatly reduces the bond energy of ionic bonds (electrostatic interactions) in aqueous solutions. Hydrogen bonds are also weakened in water, but they are not that strong in a vacuum to begin with)

Which of the following statements is true regarding reactions involving oxidation and reduction? A. The carbon atom is more oxidized in formaldehyde (CH2O) than in methanol (CH3OH). B. Oxidation of food in all organisms requires oxygen. C. A molecule is oxidized if it gains an electron (plus a proton) in a reaction. D. A dehydrogenation reaction is a reduction. E. In an organic molecule, the number of C-H bonds increases as a result of oxidation

A. The carbon atom is more oxidized in formaldehyde (CH2O) than in methanol (CH3OH).

Fill in the blank in the following paragraph. "During intense 'anaerobic' physical exercise, the high energy demand in the muscle cells leads to an accumulation of lactic acid in these cells and their surrounding tissues. Similarly, the yeast Saccharomyces cerevisiae can produce ethanol when grown anaerobically. The lactate or ethanol production takes place in a process called ..."

FERMENTATION

What are the molecules that normally supply carbon and oxygen atoms, respectively, for the citric acid cycle? A. Oxaloacetate, oxaloacetate B. Acetyl CoA, O2 C. Oxaloacetate, O2 D. Acetyl CoA, H2O E. Pyruvate, pyruvate

D. Acetyl CoA, H2O

Which of the following chemicals do you NOT expect to be readily dissolved in water? A. Uric acid B. Hexane C. Glycerol D. Ethanol E. Potassium chloride

B. Hexane **hydrocarbon!!

Arsenate is a toxic ion that can interfere with both glycolysis and oxidative phosphorylation. Arsenate resembles Pi (inorganic phosphate) and can replace it in many enzymatic reactions. One such reaction is catalyzed by glyceraldehyde 3-phosphate dehydrogenase in step 6 of glycolysis. Upon completion of the reaction, instead of the normal product, 1,3-bisphosphoglycerate, the mixed anhydride 1-arsenato-3-phosphoglycerate is formed; this undergoes rapid spontaneous hydrolysis into arsenate plus 3-phosphoglycerate, the latter being a normal product of step 7 in glycolysis. What would be the effect of arsenate poisoning in glycolysis? A. It results in more ATP and NADH molecules generated for every glucose molecule. B. It results in fewer ATP molecules generated per glucose molecule, but NADH generation is not directly affected. C. It brings glycolysis to an abrupt stop. D. It results in fewer ATP and NADH molecules generated per glucose molecule. E. It does not affect the number of ATP or NADH molecules generated per glucose molecule.

B. It results in fewer ATP molecules generated per glucose molecule, but NADH generation is not directly affected.

Which of the following represents an "activated" carrier molecule? A. AMP B. NADH C. NAD+ D. NADP+ E. CoA

B. NADH

A cellular enzyme catalyzes the catabolic reaction shown below. Its coenzyme is shown in the box. Which of the following is correct regarding this reaction? A. The substrate is reduced in this reaction and the coenzyme is converted from state 1 to state 2. B. The substrate is oxidized in this reaction and the coenzyme is converted from state 1 to state 2. C. The substrate is reduced in this reaction and the coenzyme is converted from state 2 to state 1. D. The substrate is oxidized in this reaction and the coenzyme is converted from state 2 to state 1.

B. The substrate is oxidized in this reaction and the coenzyme is converted from state 1 to state 2.

Sort the following from a low to a high contribution to the total mass of an E. coli bacterium. Your answer would be a four-letter string composed of letters A to D only, e.g. DCBA. (A) Water (B) Sugars (C) Proteins (D) Nucleic acids

BDCA [Water accounts for about 70% of the total mass in a typical cell. In the remaining "dry mass," proteins constitute about half, the nucleic acids RNA and DNA are next, and polysaccharides (and their sugar monomers) are still less abundant.]

The amino acid serine has an amino group, a carboxyl group, and a hydroxyl group. Which of the following better represents the structure of this amino acid at neutral pH?

C [The amino and carboxyl groups are common to all amino acids. The serine side chain contains a hydroxyl group.]

In an enzymatic reaction involving NADH or NADPH, reduction of a substrate accompanies the oxidation of these carrier molecules to NAD+ or NADP+, respectively. What else typically happens in such a reaction? A. A molecule of water is released to the solution upon completion of the reaction. B. A proton is released during the oxidation of the carriers. C. A proton is taken up by the substrate that is being reduced. D. A proton is taken up by the carrier molecule that is being oxidized. E. A phosphate group is transferred to the substrate.

C. A proton is taken up by the substrate that is being reduced.

The three families of cellular macromolecules are polymerized and depolymerized by a general mechanism involving water. Each of them has a set of monomers whose polymerization changes the total free energy of the system. Which of the following statements is true regarding these macromolecules? A. Each polymerization step requires free-energy input and proceeds by the consumption of one water molecule. B. Each depolymerization step requires free-energy input and proceeds by the consumption of one water molecule. C. Each polymerization step requires free-energy input and proceeds by the release of one water molecule. D. Each depolymerization step requires free-energy input and proceeds by the release of one water molecule

C. Each polymerization step requires free-energy input and proceeds by the release of one water molecule. (the addition of each monomer to the growing polymer is a condensation reaction that is accompanied by the release of one water molecule. The opposite reaction (depolymerization) involves hydrolysis and consumes one water molecule.)

Which of the following correctly summarizes the overall process of photosynthesis? A. CO2 + O2 → H2O + sugars B. CH2O + CO2 + O2 → H2O + sugars C. CO2 + H2O → H2 + CO2 D. CO2 + H2O → O2 + sugars

D. CO2 + H2O → O2 + sugars

Imagine the reaction A → B with a negative ΔG value under experimental conditions. Which of the following statements is true about this reaction? A. The reaction is energetically unfavorable. B. The reaction proceeds spontaneously and rapidly under these conditions. C. Increasing the concentration of B molecules would increase the ΔG value (toward more positive values). D. The reaction would result in a net decrease in the entropy (disorder) of the universe. E. The reaction cannot proceed unless it is coupled to another reaction with a positive value of ΔG.

C. Increasing the concentration of B molecules would increase the ΔG value (toward more positive values). [The negative ΔG value indicates that the reaction is favorable under these conditions and would increase the entropy of the universe. However, unless we know the steps of the reaction, the ΔG value cannot predict the reaction rate, because the latter depends on the activation-energy barrier. Finally, the ΔG value changes as the concentrations of reactants and products change. As the products accumulate, the reaction will eventually reach an equilibrium, where ΔG is equal to zero]

The bond energies associated with noncovalent attractions in the cell are too weak to resist disruption by thermal motion. However, cellular macromolecules can interact specifically AND strongly with each other (or fold by themselves) merely via such interactions. How is this possible? A. The bond energies increase radically when two interacting molecules approach each other. B. The interacting molecules also fortify their binding via covalent bonds to keep them from dissociation. C. Many weak bonds together in a complementary geometry can afford a strong binding. D. The cell lowers its internal temperature to reduce thermal motion of molecules and enhance the weak attractions

C. Many weak bonds together in a complementary geometry can afford a strong binding.

Which of the following elements is NOT normally found in cells? A. Copper B. Iron C. Silver D. Cobalt E. Zinc

C. Silver

Which of the following statements is true regarding cellular metabolism? A. A living organism decreases the entropy in its surroundings. B. During catabolism, heat is generated, and the cell uses this heat to perform work during anabolism. C. The heat released by an animal cell as part of its metabolic processes comes from the bond energies in the foodstuffs that are consumed by the animal. D. Living organisms defy the second law of thermodynamics, but still obey the first law

C. The heat released by an animal cell as part of its metabolic processes comes from the bond energies in the foodstuffs that are consumed by the animal.

In the following diagram showing the distribution of thermal energy in a population of substrate molecules, the energy thresholds indicated by numbers represent ... A. the activation energy at high and low temperature. B. the reaction rate at high and low pH. C. the activation energy with and without an enzyme. D. the reaction rate at high and low substrate concentrations. E. the activation energy at high and low substrate concentrations.

C. the activation energy with and without an enzyme.

Sort the following molecules from a low to high rate of diffusion inside the cytosol. Your answer would be a four-letter string composed of letters A to D only, e.g. ADCB. (A) Myoglobin (a protein) (B) Glycine (an amino acid) (C) Ribosome (a protein-RNA complex) (D) CO2

CABD [In general, larger molecules diffuse more slowly compared to smaller molecules.]

Which of the following is true regarding a fatty acid molecule in water? A. It is positively charged at physiological pH, but can become neutral when the pH is high enough. B. It is positively charged at physiological pH, but can become neutral when the pH is low enough. C. It is negatively charged at physiological pH, but can become neutral when the pH is high enough. D. It is negatively charged at physiological pH, but can become neutral when the pH is low enough. E. It is not charged at physiological pH.

D. It is negatively charged at physiological pH, but can become neutral when the pH is low enough. [Due to the presence of the carboxyl group, a fatty acid molecule carries a negative charge at neutral pH. However, lowering the pH can reverse the ionization of this group to the neutral (protonated) state]

ATP is the main energy currency in cells, and it can especially be used to drive condensation reactions that produce macromolecular polymers. How does ATP normally catalyze the condensation reaction, which by itself is energetically unfavorable? A. It transfers its terminal phosphate to an enzyme and is released as ADP. B. It transfers its two terminal phosphates to an enzyme, and is released as AMP. C. It covalently attaches to both of the substrates. D. It transfers either one or two terminal phosphate(s) to one of the substrates and is released as either ADP or AMP. E. It covalently attaches to the enzyme, forming an enzyme-AMP adduct.

D. It transfers either one or two terminal phosphate(s) to one of the substrates and is released as either ADP or AMP. [By transferring either a phosphate group or a pyrophosphate group to a hydroxyl group on one of the monomers involved in the polymerization, ATP "activates" the monomer, making the overall reaction favorable]

The substrate for the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase is glyceraldehyde 3-phosphate (with one phosphate group) while its product is 1,3-bisphosphoglycerate (with two phosphate groups). Where does the extra phosphate group come from? A. From combining two molecules of the substrate B. ATP C. Fructose 1,6-bisphosphate D. Pi E. NADH

D. Pi [In step 6 of glycolysis, this enzyme couples the oxidation of the substrate with the production of NADH, as well as incorporation of inorganic phosphate. The Pi is then transferred to ADP to generate ATP in step 7]

What is the end product of glycolysis in the cytoplasm of eukaryotic cells? How many carbon atoms does the molecule have? A. Acetyl CoA; it has two carbon atoms attached to coenzyme A B. Phosphoenolpyruvate; it has three carbon atoms C. Glucose 6-phosphate; it has six carbon atoms D. Pyruvate; it has three carbon atoms E. Glyceraldehyde 3-phosphate; it has three carbon atoms

D. Pyruvate; it has three carbon atoms [In glycolysis, two pyruvate molecules (each with three carbon atoms) are produced from each molecule of glucose (with six carbon atoms). 1 glucose--> 2 pyruvates (with 3 Cs)]

What is the reaction performed on the molecule labeled as substrate in the following diagram? What is the name of the activated carrier?

D. This is a carboxylation reaction and the activated carrier is carboxylated biotin.

Under anaerobic conditions, glycolysis provides most of the ATP that the cell needs. In animal cells, pyruvate, the end product of glycolysis, is converted to lactic acid by lactate dehydrogenase, as shown below: CH3(CO)COO- + X →CH3(CHOH)COO- + Y What is the correct carrier pair (in place of X and Y) in this reaction? A. X is (ADP + Pi), and Y is (ATP) B. X is (NADP+), and Y is (NADPH + H+) C. X is (NAD+), and Y is (NADH + H+) D. X is (NADH + H+), and Y is (NAD+) E. X is (NADP++ H+), and Y is (NADPH)

D. X is (NADH + H+), and Y is (NAD+) [Under anaerobic conditions, NAD+ can be recycled in this reaction (in which pyruvate is reduced), so that glycolysis can continue in the absence of oxidative phosphorylation]

Sort the following molecules (A to E) based on the oxidation of the carbon atom, from higher to lower oxidation states. Your answer would be a five-letter string composed of letters A to E only, e.g. ADCBE. Put the letter corresponding to the highest oxidation level on the left.

DAECB CO2, formic acid, formaldehyde, methanol, methane [As a general rule, in organic molecules, a lower number of C-H bonds corresponds to more oxidized carbon atoms]

Sort the following molecules based on the amount of energy that is released when their phosphate bond is hydrolyzed as indicated. Your answer would be a four-letter string composed of letters A to D only, e.g. ADCB. Put the molecule with the highest amount of hydrolysis energy on the left. (A) ATP when hydrolyzed to ADP (B) Glucose 6-phosphate when hydrolyzed to glucose (C) 1,3-bisphosphoglycerate when hydrolyzed to 3-phosphoglycerate (D) Phosphoenolpyruvate when hydrolyzed to pyruvate

DCAB

Steps 6 and 7 of glycolysis are catalyzed by the enzymes glyceraldehyde 3-phosphate dehydrogenase and phosphoglycerate kinase, respectively. Together, they ... A. result in the oxidation of an aldehyde to a carboxylic acid. B. produce both ATP and NADH. C. couple the oxidation of a C-H bond to the activation of carrier molecules. D. catalyze the only glycolytic reactions that create a high-energy phosphate linkage directly from inorganic phosphate. E. All of the above.

E. All of the above.

Enzymes are the cell's catalyst crew. They make the life of the cell possible by carrying out various reactions with astounding performance. Which of the following is NOT true regarding cellular enzymes? A. Enzymes lower the activation energy of the reactions that they catalyze. B. Enzymes can specifically drive substrate along certain reaction pathways. C. Enzymes can push energetically unfavorable reactions forward by coupling them to energetically favorable reactions. D. Enzymes are proteins, but RNA catalysts, called ribozymes, also exist. E. Enzymes can change the equilibrium point for reactions that they catalyze.

E. Enzymes can change the equilibrium point for reactions that they catalyze.

Despite their overall similarity, NADH and NADPH are not used indiscriminately by the cell. What are the distinctive features of these two carrier molecules? A. NADPH has an extra phosphate near its nicotinamide ring, giving it distinct electron-transfer properties. B. In the cell, NADH is usually in excess over NAD+, but NADP+ is usually in excess over NADPH. C. NADH is normally involved in anabolic reactions, whereas NADPH is normally involved in catabolism. D. Both NADPH and NADH are recognized by the same enzymes with similar affinities, since the extra phosphate group in NADPH is not involved in such recognition. E. In the cell, NADH is found mostly in the form that acts as an oxidizing agent, whereas NADPH is found mostly in the form that acts as a reducing agent.

E. In the cell, NADH is found mostly in the form that acts as an oxidizing agent, whereas NADPH is found mostly in the form that acts as a reducing agent.

Which of the following is true regarding energy production and storage in plants and animals? A. Plant and animal cells make starch for long-term energy storage. B. Most of the ATP in a plant cell has been generated in the chloroplast and transported to other parts of the cell. C. Oxidation of one gram of starch releases more energy than oxidation of fat, but since starch absorbs a lot of water, it is not as efficient as fat in energy storage. D. Animals, but not plants, can store fats in the form of triacylglycerol (triglyceride). E. Plant seeds often contain large amounts of fats and starch.

E. Plant seeds often contain large amounts of fats and starch.

Macromolecules in the cell can be made from their monomers using one of two polymerization schemes. One is called head polymerization, in which the reactive bond required for polymerization is carried on the end of the growing polymer. In contrast, in tail polymerization, the reactive bond is carried by each monomer for its own incorporation. In the figure, indicate the polymerization scheme and the type of macromolecule. A. Head polymerization of a protein B. Tail polymerization of a protein C. Head polymerization of a polysaccharide D. Head polymerization of a nucleic acid E. Tail polymerization of a nucleic acid

E. Tail polymerization of a nucleic acid

A hydrophobic molecule is typically ... A. able to form hydrogen bonds with itself but not with water. B. able to form hydrogen bonds with water. C. charged. D. hard to dissolve in a solvent. E. incapable of interacting favorably with water

E. incapable of interacting favorably with water

Indicate true (T) and false (F) statements below regarding the cellular metabolism of nucleotides and amino acids. ( ) Nitrogen fixation occurs in the mitochondria in most animal cells to generate amino acids. ( ) All 20 natural amino acids must be provided in our diet and are therefore "essential." ( ) There are NO essential nucleotides that must be provided in the diet. ( ) Catabolism of amino acids in our body leads to the production of urea which is excreted.

FFTT [All known nitrogen-fixing cells are prokaryotic microorganisms. Animals rely on their dietary intake of protein and nucleic acids as sources of useful nitrogen. However, only 9 of the 20 amino acids that make up proteins and none of the nucleotides that make up nucleic acids are essential; the remainder can be synthesized from other ingredients in the diet. When amino acids in our body are degraded, their nitrogen atoms eventually appear in urea molecules which are excreted.]

Indicate true (T) and false (F) statements below regarding glycolysis. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTT. ( ) Molecular oxygen is used in glycolysis to oxidize glucose. ( ) Along the glycolytic pathway, ATP is both consumed and generated. ( ) In the course of glycolysis, one molecule of NADH is formed per molecule of glucose. ( ) Following the production of one molecule of fructose 1,6-bisphosphate, the rest of the glycolytic pathway generates four molecules of ATP.

FTFT [During the stepwise oxidation of glucose in the course of glycolysis, two molecules of ATP are used to make fructose 1,6-bisphosphate, which is then cleaved and eventually converted to two molecules of pyruvate, generating four molecules of ATP and two molecules of NADH.]

For each of the following pairs, indicate whether they interact via hydrogen bonds (H) or ionic bonds (I), or do not favorably interact (N). Your answer would be a four-letter string composed of letters H, I, and N only, e.g. HNNI. ( ) ATP and Mg2+ ( ) Urea and water ( ) Glucose and the enzyme hexokinase (which uses glucose as a substrate) ( ) A phospholipid tail and inorganic phosphate

IHHN ( I ): ATP and Mg2+ ATP is negatively charged and can form ionic bonds with magnesium ions. ( H): Urea and water Urea is highly soluble in water due to its hydrogen-bonding capacity. Similarly, interaction of a polar molecule like glucose with the active site of an enzyme can be mediated by hydrogen bonds and other noncovalent (or even covalent) bonds. ( N ): A phospholipid tail and inorganic phosphatehe fatty acid tails in phospholipids are hydrophobic and do not favorably interact with negatively charged phosphate molecules.

Indicate whether each of the following descriptions matches glycolysis (G) or the Krebs cycle (K). Your answer would be a four-letter string composed of letters G and K only, e.g. GGGK. ( ) It oxidizes acetyl CoA to CO2. ( ) In eukaryotic cells, it is carried out in the cytosol. ( ) It produces FADH2. ( ) α-Ketoglutarate, one of its intermediates, is used to synthesize the amino acid glutamic acid.

KGKK

Indicate true (T) and false (F) statements below regarding fatty acid metabolism. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTT. ( ) Most animals derive their energy from fatty acids between meals. ( ) Fatty acids are converted to acetyl CoA in the cytosol, which is then transported into mitochondria for further oxidation. ( ) Fatty acids are stored in fat droplets in the form of triacylglycerols. ( ) The breakdown of fatty acids into each acetyl CoA unit requires the hydrolysis of two ATP molecules.

TFTF

Indicate whether each of the following molecules is an intermediate in glycolysis (G) or in the tricarboxylic acid cycle (T). Your answer would be a four-letter string composed of letters G and T only, e.g. GGTT. ( ) Fumarate ( ) Malate ( ) Phosphoenolpyruvate ( ) Succinate

TTGT [Phosphoenolpyruvate is converted to pyruvate in the last step of glycolysis. Succinate, fumarate, and malate are three consecutive citric acid cycle intermediates leading to the regeneration of oxaloacetate.]