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Ch. 5 - Microbial Metabolism
Tortora - Microbiology: An Introduction 14th Edition
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
All textbooksTortora 14th EditionCh. 5 - Microbial MetabolismProblem 1
Chapter 5, Problem 1

Which substance in the following reaction is being reduced?
Chemical reaction showing acetaldehyde converted to ethanol with NADH oxidized to NAD⁺ and H⁺ involved.
a. Acetaldehyde
b. NADH
c. Ethanol
d. NAD+

Verified step by step guidance
1
Identify the reactants and products involved in the reaction. Typically, in biochemical redox reactions involving NADH and NAD⁺, one molecule is oxidized and the other is reduced.
Recall the definitions: Reduction is the gain of electrons (or hydrogen atoms), and oxidation is the loss of electrons (or hydrogen atoms).
Determine which substance gains electrons or hydrogen atoms during the reaction. NADH usually acts as an electron donor (reducing agent), and NAD⁺ acts as an electron acceptor (oxidizing agent).
Look at the transformation of acetaldehyde and ethanol. Acetaldehyde can be reduced to ethanol by gaining hydrogen atoms, while ethanol can be oxidized to acetaldehyde by losing hydrogen atoms.
Conclude which substance is reduced by identifying the molecule that gains hydrogen atoms or electrons in the reaction, based on the roles of NADH/NAD⁺ and the conversion between acetaldehyde and ethanol.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Oxidation-Reduction (Redox) Reactions

Redox reactions involve the transfer of electrons between molecules, where one substance is oxidized (loses electrons) and another is reduced (gains electrons). Identifying which molecule gains electrons helps determine the reduced substance.
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Role of NAD⁺/NADH in Cellular Reactions

NAD⁺ acts as an electron acceptor, becoming reduced to NADH by gaining electrons. Conversely, NADH can donate electrons and be oxidized back to NAD⁺. Understanding this cycle is key to identifying which molecule is reduced or oxidized.
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Reduction of Carbonyl Compounds to Alcohols

In biochemical reactions, aldehydes like acetaldehyde can be reduced to alcohols such as ethanol by gaining electrons (usually from NADH). Recognizing this transformation helps pinpoint the reduced substance in the reaction.
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Related Practice
Textbook Question

Which of the following reactions produces the most molecules of ATP during aerobic metabolism?

a. Glucose → Glucose 6-phosphate

b. Phosphoenolpyruvic acid → Pyruvic acid

c. Glucose → Pyruvic acid

d. Acetyl CoA → CO2 + H2O

e. Succinic acid → Fumaric acid

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Textbook Question

Using the following diagrams, show each of the following:

a. where the substrate will bind

b. where the competitive inhibitor will bind

c. where the noncompetitive inhibitor will bind

d. which of the four elements could be the inhibitor in feedback inhibition

e. What effect will the reactions in (a), (b), and (c) have?

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Textbook Question

Use the following diagrams (a), (b), and (c) for the question.

<IMAGE>


Name pathways diagrammed in parts (a), (b), and (c) of the figure.

a. Show where glycerol is catabolized and where fatty acids are catabolized.

b. Show where glutamic acid (an amino acid) is catabolized:

<IMAGE>

c. Show how these pathways are related.

d. Where is ATP required in pathways (a) and (b)?

e. Where is CO₂ released in pathways (b) and (c)?

f. Show where a long-chain hydrocarbon such as petroleum is catabolized.

g. Where is NADH (or FADH₂ or NADPH) used and produced in these pathways?

h. Identify four places where anabolic and catabolic pathways are integrated.

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