12. Microbial Metabolism

Why must NADH be reoxidized? How does this happen in an organism that uses respiration? Fermentation?

All cells require a source of ___________ for redox reactions.

When glucose donates electrons to NAD⁺ creating NADH, the glucose molecule becomes:

a) Hydrolyzed.

b) Oxidized.

c) Neutral.

d) Reduced.

Label each reactant and product in the reactions as reduced or oxidized (X is a theoretical molecule or atom).

Most oxidation reactions in bacteria involve the _______.

a. Removal of hydrogen ions and electrons

b. Removal of oxygen

c. Addition of hydrogen ions and electrons

d. Addition of hydrogen ions

Define oxidation-reduction, and differentiate the following terms:

a. Aerobic and anaerobic respiration

b. Respiration and fermentation

c. Cyclic and noncyclic photophosphorylation

Which of the following reactions is an oxidation carried out by A. ferrooxidans?

a. Fe²⁺ → Fe³⁺

b. Fe³⁺ → Fe²⁺

c. CuS→ CuSO₄

d. Fe⁰ → Cu⁰

e. None of the above

In the sulfur cycle, microbes degrade organic sulfur compounds, such as (a) _________________, to release H₂S, which can be oxidized by Acidithiobacillus to (b) _________________. This ion can be assimilated into amino acids by (c) _________________ or reduced by Desulfovibrio to (d) _________________. H₂S is used by photoautotrophic bacteria as an electron donor to synthesize (e) _________________. The sulfur-containing by-product of this metabolism is (f) _________________.

Which electron carrier is not matched with its correct function.

Redox reactions ______.

a. Transfer energy

b. Transfer electrons

c. Involve oxidation and reduction

d. Are involved in all of the above

Use this pathway schematic to answer questions a through d.

a. Which enzyme carries out a redox reaction? In this reaction, what is being reduced and what is being oxidized?

b. Which enzyme would be the most likely to be regulated by feedback inhibition?

c. What is the end product of this pathway?

d. Which enzyme carries out substrate-level phosphorylation?

A reduced molecule ______.

a. Has gained electrons

b. Has become more positive in charge

c. Has lost electrons

d. Is an electron donor

An electron carrier before it harvests energy from glucose molecules in a series of gradual steps is:

a) Pyruvate.

b) AMP.

c) ATP.

d) NAD⁺.

e) NADH.

Which substance in the following reaction is being reduced?

a. Acetaldehyde

b. NADH

c. Ethanol

d. NAD⁺

NADH is commonly used as an electron carrier during the breaking down of complex molecules like glucose in cellular respiration. NADPH is also a common electron carrier. However, NADPH is used to build complex molecules like glucose in a process called: