Microbial Metabolism Questions and Answers

Q: The phosphate inhibition in the clavine formation with Claviceps SD58, can be counteracted by the addition of

Correct answer: tryptophanTryptophan is the precursor of the clavine alkaloids and also an inducer of the pathway, so supplying it counteracts the repression that phosphate imposes on Claviceps SD58. It is a useful illustration that a precursor can act as a regulatory signal as well as a substrate.

Q: The reaction, where small precursor molecules are assembled into larger organic molecules is referred to as

Correct answer: anabolismAnabolism is biosynthesis - small precursors assembled into larger molecules such as proteins, nucleic acids and polysaccharides. It consumes the ATP and reducing power that catabolism produces.

Q: The source of the necessary elements of life is:

Correct answer: an inorganic environmental reservoirEvery element in a living thing comes ultimately from an inorganic reservoir - the atmosphere, the oceans, the rocks and soil - and returns to it. The sun supplies energy, not matter, which is why energy flows through an ecosystem while elements cycle round it.

Q: Entner - Doudoroff pathway is not found in

Correct answer: eukaryotesThe Entner-Doudoroff pathway is a prokaryotic route, present in aerobes and anaerobes alike, and essentially absent from eukaryotes, which use glycolysis instead.

Q: Aerobic catabolism of glucose yields how much energy (ATP synthesized) relative to glucose fermentation?

Correct answer: More than 10 times as muchFermentation yields about 2 ATP per glucose, aerobic respiration around 38 - roughly nineteen times as much. The difference is that fermentation stops at an organic end product still holding most of the energy, while respiration oxidises the substrate all the way to CO2 and water.

Q: For each glucose molecule broken down, there are______________number of reduced coenzymes to be oxidized.

Correct answer: 12Per glucose, complete oxidation yields 10 NADH - 2 from glycolysis, 2 from pyruvate dehydrogenase and 6 from the TCA cycle - and 2 FADH2, making 12 reduced coenzymes in all. Each is then reoxidised by the electron transport chain.

Q: The compound that enters the TCA cycle is

Correct answer: acetyl coenzyme AGlycolysis ends at pyruvate, which is not itself an intermediate of the cycle. The link reaction - pyruvate dehydrogenase - removes a carbon as CO2, reduces NAD+ and attaches the remaining two-carbon acetyl group to coenzyme A. It is that acetyl-CoA which condenses with oxaloacetate to form citrate and so enters the cycle.

Q: What is the smallest unit of heredity?

Correct answer: geneA gene is the smallest unit of heredity - the stretch of DNA that specifies one product and is inherited as a unit. A chromosome carries many genes; a codon is three bases within one; a nucleotide is a single chemical building block and carries no heritable information alone.

Q: If radioactive bicarbonate was supplied to bacterial cells, which were actively synthesizing fatty acids, it is expected to find the bulk of the radioactivity in

Correct answer: cellular bicarbonateThe CO2 fixed by acetyl-CoA carboxylase to make malonyl-CoA is released again at each condensation step of fatty acid synthesis. So the labelled carbon passes through the pathway and returns to the cellular bicarbonate pool rather than being built into the fatty acid chain, which is assembled entirely from acetyl units.

Q: What serves as the terminal electron acceptor in aerobic respiration ?

Correct answer: OxygenOxygen accepts the electrons at the end of the chain and is reduced to water. Anaerobic respiration substitutes another inorganic acceptor such as nitrate or sulphate, and because these have lower reduction potentials they yield less energy.

101.

The phosphate inhibition in the clavine formation with Claviceps SD58, can be counteracted by the addition of

A.alanine
B.methionine
C.tryptophan
D.lysine

Answer: C

Correct answer: tryptophan

Tryptophan is the precursor of the clavine alkaloids and also an inducer of the pathway, so supplying it counteracts the repression that phosphate imposes on Claviceps SD58. It is a useful illustration that a precursor can act as a regulatory signal as well as a substrate.

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102.

The reaction, where small precursor molecules are assembled into larger organic molecules is referred to as

A.anabolism
B.catabolism
C.metabolism
D.any of these

Answer: A

Correct answer: anabolism

Anabolism is biosynthesis - small precursors assembled into larger molecules such as proteins, nucleic acids and polysaccharides. It consumes the ATP and reducing power that catabolism produces.

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103.

The source of the necessary elements of life is:

A.an inorganic environmental reservoir
B.the sun
C.rocks
D.the air

Answer: A

Correct answer: an inorganic environmental reservoir

Every element in a living thing comes ultimately from an inorganic reservoir - the atmosphere, the oceans, the rocks and soil - and returns to it. The sun supplies energy, not matter, which is why energy flows through an ecosystem while elements cycle round it.

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104.

Entner - Doudoroff pathway is not found in

A.aerobic prokaryotes
B.anaerobic prokaryotes
C.Both (a) and (b)
D.eukaryotes

Answer: D

Correct answer: eukaryotes

The Entner-Doudoroff pathway is a prokaryotic route, present in aerobes and anaerobes alike, and essentially absent from eukaryotes, which use glycolysis instead.

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105.

Aerobic catabolism of glucose yields how much energy (ATP synthesized) relative to glucose fermentation?

A.Slightly less
B.About the same
C.Twice as much
D.More than 10 times as much

Answer: D

Correct answer: More than 10 times as much

Fermentation yields about 2 ATP per glucose, aerobic respiration around 38 - roughly nineteen times as much. The difference is that fermentation stops at an organic end product still holding most of the energy, while respiration oxidises the substrate all the way to CO₂ and water.

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106.

For each glucose molecule broken down, there are______________number of reduced coenzymes to be oxidized.

A.12
B.8
C.6
D.4

Answer: A

Correct answer: 12

Per glucose, complete oxidation yields 10 NADH - 2 from glycolysis, 2 from pyruvate dehydrogenase and 6 from the TCA cycle - and 2 FADH₂, making 12 reduced coenzymes in all. Each is then reoxidised by the electron transport chain.

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107.

The compound that enters the TCA cycle is

A.citric acid
B.oxaloacetic acid
C.pyruvic acid
D.acetyl coenzyme A

Answer: C

Correct answer: acetyl coenzyme A

Glycolysis ends at pyruvate, which is not itself an intermediate of the cycle. The link reaction - pyruvate dehydrogenase - removes a carbon as CO₂, reduces NAD⁺ and attaches the remaining two-carbon acetyl group to coenzyme A. It is that acetyl-CoA which condenses with oxaloacetate to form citrate and so enters the cycle.

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108.

What is the smallest unit of heredity?

A.chromosome
B.gene
C.codon
D.nucleotide

Answer: B

Correct answer: gene

A gene is the smallest unit of heredity - the stretch of DNA that specifies one product and is inherited as a unit. A chromosome carries many genes; a codon is three bases within one; a nucleotide is a single chemical building block and carries no heritable information alone.

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109.

If radioactive bicarbonate was supplied to bacterial cells, which were actively synthesizing fatty acids, it is expected to find the bulk of the radioactivity in

A.cellular bicarbonate
B.the fatty acids
C.the cytoplasmic membrane
D.nucleic acids

Answer: A

Correct answer: cellular bicarbonate

The CO₂ fixed by acetyl-CoA carboxylase to make malonyl-CoA is released again at each condensation step of fatty acid synthesis. So the labelled carbon passes through the pathway and returns to the cellular bicarbonate pool rather than being built into the fatty acid chain, which is assembled entirely from acetyl units.

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110.

What serves as the terminal electron acceptor in aerobic respiration ?

A.Nitrate
B.Sulphate
C.Oxygen
D.Pyruvate

Answer: D

Correct answer: Oxygen

Oxygen accepts the electrons at the end of the chain and is reduced to water. Anaerobic respiration substitutes another inorganic acceptor such as nitrate or sulphate, and because these have lower reduction potentials they yield less energy.

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