Microbial Metabolism Questions and Answers

Q: The FADH2 formed during the TCA cycle enters the electron transport system at which site?

Correct answer: coenzyme QFADH2 is bound to succinate dehydrogenase, which sits in the membrane as Complex II and passes its electrons straight to coenzyme Q - entering the chain below NADH dehydrogenase. It therefore bypasses one proton-pumping site, which is why FADH2 yields about 2 ATP against NADH’s 3.

Q: Which of the following is true of passive transport?

Correct answer: it requires a gradientPassive transport is driven by the concentration or electrochemical gradient and by nothing else - no ATP, no carrier necessarily - so it stops when the gradient is gone. Endocytosis is an active, energy-consuming process, and passive transport moves solutes as well as water.

Q: Radioisotopes are frequently used in the study of cells. Assume a culture of E. coli is grown in a culture medium containing radioactive phosphorous. At the end of 48 hours, it is expected to find the radioactive label located in

Correct answer: all of thesePhosphorus is a constituent of many cell components, so a 32P label turns up in all of them: in nucleic acids through the phosphate backbone of RNA and DNA, in phospholipids of the membranes, and in enzymes both as phosphorylated residues and through cofactors such as ATP, NAD and FAD.

Q: Phosphate deregulated mutants are

Correct answer: less sensitive to phosphate regulationA deregulated mutant has lost some part of the control circuit, so its secondary metabolism is less sensitive to repression by phosphate and continues to make product where the wild type would stop. This is why such mutants are selected for industrial production strains.

Q: The enzyme catalase protects a cell by breaking down ________.

Correct answer: hydrogen peroxideCatalase converts hydrogen peroxide into water and oxygen, which is why a drop of peroxide bubbles on a catalase-positive colony. Superoxide dismutase handles the separate task of converting superoxide radicals into peroxide and oxygen.

Q: An organism that can synthesize all its required organic components from CO2 using energy from the sun is a:

Correct answer: photoautotrophThe name states both halves: photo- for light as the energy source, autotroph for CO2 as the carbon source. Plants, algae and cyanobacteria are photoautotrophs. A photoheterotroph uses light but needs organic carbon; a chemoautotroph fixes CO2 using energy from inorganic chemical oxidations.

Q: The chlorophyll molecules used by eucaryotes and cyanobacteria absorb radiant energy in the____________portion(s) of the visible spectrum.

Correct answer: red and blueChlorophyll absorbs strongly in the blue (around 430 nm) and the red (around 660 nm), and reflects the middle of the spectrum - which is why plants and cyanobacteria look green. The wavelengths a pigment reflects are precisely the ones it cannot use.

Q: The nitrogen bases in DNA are bonded to the

Correct answer: deoxyriboseThe base is joined to the 1’ carbon of the deoxyribose by an N-glycosidic bond. The phosphate attaches to the sugar too, at the 5’ and 3’ carbons, so the sugar is the hub of the nucleotide: base on one side, backbone on the other.

Q: The base pairs are held together primarily by

Correct answer: hydrogen bondsThe two strands are held to each other by hydrogen bonds between the paired bases, reinforced by the stacking of the flat rings. Individually these bonds are weak, which is what lets helicase separate the strands; collectively, over thousands of pairs, they hold the duplex firmly. The covalent bonds run along each backbone, not across between them.

51.

The FADH2 formed during the TCA cycle enters the electron transport system at which site?

A.NADH dehydrogenase
B.cytochrome
C.coenzyme Q
D.ATP synthase

Answer: C

Correct answer: coenzyme Q

FADH₂ is bound to succinate dehydrogenase, which sits in the membrane as Complex II and passes its electrons straight to coenzyme Q - entering the chain below NADH dehydrogenase. It therefore bypasses one proton-pumping site, which is why FADH₂ yields about 2 ATP against NADH’s 3.

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52.

Which of the following is true of passive transport?

A.it requires a gradient
B.it uses the cell wall
C.it includes endocytosis
D.it only moves water

Answer: A

Correct answer: it requires a gradient

Passive transport is driven by the concentration or electrochemical gradient and by nothing else - no ATP, no carrier necessarily - so it stops when the gradient is gone. Endocytosis is an active, energy-consuming process, and passive transport moves solutes as well as water.

Discuss in Forum

53.

Radioisotopes are frequently used in the study of cells. Assume a culture of E. coli is grown in a culture medium containing radioactive phosphorous. At the end of 48 hours, it is expected to find the radioactive label located in

A.enzymes
B.RNA
C.phospholipids
D.all of these

Answer: D

Correct answer: all of these

Phosphorus is a constituent of many cell components, so a ³²P label turns up in all of them: in nucleic acids through the phosphate backbone of RNA and DNA, in phospholipids of the membranes, and in enzymes both as phosphorylated residues and through cofactors such as ATP, NAD and FAD.

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54.

Why must the lagging strand of DNA be replicated in short pieces?

A.because of limited space
B.otherwise, the helix will become distorted
C.the DNA polymerase can synthesize in only one direction
D.to make proofreading of code easier

Answer: C

Correct answer: the DNA polymerase can synthesize in only one direction

DNA polymerase can add nucleotides only to a free 3’-OH, so it works 5’→3’ and nothing else. On the lagging strand that direction runs away from the advancing fork, so synthesis has to be done in short bursts - the Okazaki fragments - each begun near the fork and extended backwards, and afterwards joined by ligase.

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55.

Phosphate deregulated mutants are

A.less sensitive to phosphate regulation
B.moderately sensitive to phosphate regulation
C.highly sensitive to phosphate regulation
D.none of these

Answer: A

Correct answer: less sensitive to phosphate regulation

A deregulated mutant has lost some part of the control circuit, so its secondary metabolism is less sensitive to repression by phosphate and continues to make product where the wild type would stop. This is why such mutants are selected for industrial production strains.

Discuss in Forum

56.

The enzyme catalase protects a cell by breaking down ________.

A.superoxide radicals
B.hydrogen peroxide
C.hydroxyl radicals
D.singlet oxygen

Answer: C

Correct answer: hydrogen peroxide

Catalase converts hydrogen peroxide into water and oxygen, which is why a drop of peroxide bubbles on a catalase-positive colony. Superoxide dismutase handles the separate task of converting superoxide radicals into peroxide and oxygen.

Discuss in Forum

57.

An organism that can synthesize all its required organic components from CO2 using energy from the sun is a:

A.photoautotroph
B.photoheterotroph
C.chemoautotroph
D.chemoheterotroph

Answer: A

Correct answer: photoautotroph

The name states both halves: photo- for light as the energy source, autotroph for CO₂ as the carbon source. Plants, algae and cyanobacteria are photoautotrophs. A photoheterotroph uses light but needs organic carbon; a chemoautotroph fixes CO₂ using energy from inorganic chemical oxidations.

Discuss in Forum

58.

The chlorophyll molecules used by eucaryotes and cyanobacteria absorb radiant energy in the____________portion(s) of the visible spectrum.

A.red
B.green
C.red and blue
D.green and ultraviolet

Answer: C

Correct answer: red and blue

Chlorophyll absorbs strongly in the blue (around 430 nm) and the red (around 660 nm), and reflects the middle of the spectrum - which is why plants and cyanobacteria look green. The wavelengths a pigment reflects are precisely the ones it cannot use.

Discuss in Forum

59.

The nitrogen bases in DNA are bonded to the

A.phosphate
B.deoxyribose
C.ribose
D.hydrogen

Answer: B

Correct answer: deoxyribose

The base is joined to the 1’ carbon of the deoxyribose by an N-glycosidic bond. The phosphate attaches to the sugar too, at the 5’ and 3’ carbons, so the sugar is the hub of the nucleotide: base on one side, backbone on the other.

Discuss in Forum

60.

The base pairs are held together primarily by

A.covalent bonds
B.hydrogen bonds
C.ionic bonds
D.gyrases

Answer: B

Correct answer: hydrogen bonds

The two strands are held to each other by hydrogen bonds between the paired bases, reinforced by the stacking of the flat rings. Individually these bonds are weak, which is what lets helicase separate the strands; collectively, over thousands of pairs, they hold the duplex firmly. The covalent bonds run along each backbone, not across between them.

Discuss in Forum

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