The reactions of the cell that are carried out for capturing energy are called
Answer: A
Correct answer: catabolism
Catabolism is the degradative half of metabolism: larger molecules are broken down, and the energy released is captured as ATP and reducing power. Anabolism is the building half, which spends that energy. Metabolism is the two together.
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The relationship between an oxidation-reduction potential difference and the standard free energy change is (where n is the number of moles of electron transferred, F= Faraday's constant and E°= standard oxidation-reduction potential difference)
Answer: A
Correct answer: ΔG° = -nFE°
The relation between redox potential and free energy is
\[ \Delta G^{\circ} = -nFE^{\circ} \]The minus sign is the point: a positive potential difference - electrons falling to a more electropositive acceptor - gives a negative \(\Delta G\), that is a spontaneous, energy-releasing reaction. \(n\) is the number of moles of electrons and \(F\) the Faraday constant, 96.5 kJ per volt per mole.
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DAHP synthetase catalyzes the condensation of
Answer: C
Correct answer: both (a) and (b)
DAHP synthetase catalyses the first step of the shikimate pathway, condensing erythrose-4-phosphate from the pentose phosphate pathway with phosphoenolpyruvate from glycolysis. The product, DAHP, leads on to chorismate and thence to the aromatic amino acids - phenylalanine among them, which is a product of the pathway rather than a substrate of this step.
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Exergonic reactions
Answer: A
Correct answer: release potential energy
An exergonic reaction has a negative \(\Delta G\): the products hold less free energy than the reactants, so energy is released and the reaction proceeds spontaneously. Endergonic reactions consume energy and must be coupled to an exergonic one to go at all.
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A product or products of glycolysis is/are
Answer: D
Correct answer: both a and b
Glycolysis yields a net 2 ATP, and also 2 molecules of water, released by enolase when 2-phosphoglycerate is dehydrated to phosphoenolpyruvate. Its other products are 2 NADH and 2 pyruvate. No CO2 is released - that comes later, at pyruvate dehydrogenase and in the TCA cycle.
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TCA cycle functions in
Answer: C
Correct answer: amphibolic reactions
The TCA cycle is amphibolic: it works in both directions of metabolism. It oxidises acetyl-CoA for energy (catabolic), and its intermediates are drawn off as precursors - oxaloacetate and α-ketoglutarate for amino acids, succinyl-CoA for porphyrins (anabolic). Anaplerotic reactions exist precisely to replace what is withdrawn.
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Ribosomal RNA _______
Answer: A
Correct answer: contributes to the structure of ribosomes
Ribosomal RNA is a structural and catalytic component of the ribosome: with the ribosomal proteins it forms the two subunits, and it is the rRNA itself, not any protein, that catalyses peptide bond formation. Carrying the code from DNA is the job of mRNA, and matching codons to amino acids that of tRNA.
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An obligate aerobe is an organism that ________.
Answer: D
Correct answer: requires oxygen for growth
An obligate aerobe depends on oxygen as its terminal electron acceptor and cannot grow without it. Mycobacterium tuberculosis is a familiar example, and in a thioglycolate tube such organisms form a band at the oxygen-rich surface.
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High energy transfer compounds are capable of
Answer: B
Correct answer: transferring large amounts of free energy
A high-energy transfer compound - ATP is the type case - holds a bond whose hydrolysis releases a large amount of free energy, and is positioned in the middle of the energy scale so that it can pass that energy on to a reaction that needs it. Its usefulness lies in the transfer, not in the storage: ATP is turned over constantly rather than accumulated.
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A pathogen would most accurately be described as a:
Answer: A
Correct answer: parasite
A pathogen lives at its host’s expense and causes harm, which is the definition of a parasite. A commensal benefits without harming, a symbiont in the mutualistic sense benefits both partners, and a saprobe lives on dead organic matter.
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