7.E: Microbial Metabolism (Exercises)

7.1: Fermentation

Fermentation uses an organic molecule as a final electron acceptor to regenerate NAD⁺ from NADH so that glycolysis can continue. Fermentation does not involve an electron transport system, and no ATP is made by the fermentation process directly. Fermenters make very little ATP—only two ATP molecules per glucose molecule during glycolysis. Microbial fermentation processes have been used for the production of foods and pharmaceuticals, and for the identification of microbes.

Multiple Choice

Which of the following is the purpose of fermentation?

1. to make ATP
2. to make carbon molecule intermediates for anabolism
3. to make NADH
4. to make NAD⁺

Answer

D

Which molecule typically serves as the final electron acceptor during fermentation?

1. oxygen
2. NAD⁺
3. pyruvate
4. CO₂

Answer

C

Which fermentation product is important for making bread rise?

1. ethanol
2. CO₂
3. lactic acid
4. hydrogen gas

Answer

B

Which of the following is not a commercially important fermentation product?

1. ethanol
2. pyruvate
3. butanol
4. penicillin

Answer

B

Fill in the Blank

The microbe responsible for ethanol fermentation for the purpose of producing alcoholic beverages is ________.

Answer

yeast (Saccharomyces cerevisiae)

________ results in the production of a mixture of fermentation products, including lactic acid, ethanol and/or acetic acid, and CO₂.

Answer

Heterolactic fermentation

Fermenting organisms make ATP through the process of ________.

Answer

glycolysis

Matching

Match the fermentation pathway with the correct commercial product it is used to produce:

___acetone-butanol-ethanol fermentation	a. bread
___alcohol fermentation	b. pharmaceuticals
___lactic acid fermentation	c. Swiss cheese
___mixed acid fermentation	d. yogurt
___propionic acid fermentation	e. industrial solvents

Answer

e; 2. a; 3. d; 4. b; 5. c

Short Answer

Why are some microbes, including Streptococcus spp., unable to perform aerobic respiration, even in the presence of oxygen?

How can fermentation be used to differentiate various types of microbes?

Critical Thinking

The bacterium E. coli is capable of performing aerobic respiration, anaerobic respiration, and fermentation. When would it perform each process and why? How is ATP made in each case?

7.2: Catabolism of Lipids and Proteins

Collectively, microbes have the ability to degrade a wide variety of carbon sources besides carbohydrates, including lipids and proteins. The catabolic pathways for all of these molecules eventually connect into glycolysis and the Krebs cycle. Several types of lipids can be microbially degraded. Triglycerides are degraded by extracellular lipases, releasing fatty acids from the glycerol backbone. Phospholipids are degraded by phospholipases, releasing fatty acids and phosphorylated head groups.

Multiple Choice

Which of the following molecules is not produced during the breakdown of phospholipids?

1. glucose
2. glycerol
3. acetyl groups
4. fatty acids

Answer

A

Caseinase is which type of enzyme?

1. phospholipase
2. lipase
3. extracellular protease
4. intracellular protease

Answer

C

Which of the following is the first step in triglyceride degradation?

1. removal of fatty acids
2. β-oxidation
3. breakage of fused rings
4. formation of smaller peptides

Answer

A

Fill in the Blank

The process by which two-carbon units are sequentially removed from fatty acids, producing acetyl-CoA, FADH₂, and NADH is called ________.

Answer

β-oxidation

The NADH and FADH₂ produced during β-oxidation are used to make ________.

Answer

ATP by oxidative phosphorylation

________ is a type of medium used to detect the production of an extracellular protease called caseinase.

Answer

Skim milk agar

Short Answer

How are the products of lipid and protein degradation connected to glucose metabolism pathways?

What is the general strategy used by microbes for the degradation of macromolecules?

Critical Thinking

Do you think that β-oxidation can occur in an organism incapable of cellular respiration? Why or why not?

7.3: Photosynthesis and the Importance of Light

Heterotrophic organisms ranging from E. coli to humans rely on the chemical energy found mainly in carbohydrate molecules. Many of these carbohydrates are produced by photosynthesis, the biochemical process by which phototrophic organisms convert solar energy (sunlight) into chemical energy. Although photosynthesis is most commonly associated with plants, microbial photosynthesis is also a significant supplier of chemical energy, fueling many diverse ecosystems.

Multiple Choice

During the light-dependent reactions, which molecule loses an electron?

1. a light-harvesting pigment molecule
2. a reaction center pigment molecule
3. NADPH
4. 3-phosphoglycerate

Answer

B

In prokaryotes, in which direction are hydrogen ions pumped by the electron transport system of photosynthetic membranes?

1. to the outside of the plasma membrane
2. to the inside (cytoplasm) of the cell
3. to the stroma
4. to the intermembrane space of the chloroplast

Answer

A

Which of the following does not occur during cyclic photophosphorylation in cyanobacteria?

1. electron transport through an ETS
2. photosystem I use
3. ATP synthesis
4. NADPH formation

Answer

D

Which are two products of the light-dependent reactions are ________.

1. glucose and NADPH
2. NADPH and ATP
3. glyceraldehyde 3-phosphate and CO₂
4. glucose and oxygen

Answer

B

True/False

Photosynthesis always results in the formation of oxygen.

Answer

False

Fill in the Blank

The enzyme responsible for CO₂ fixation during the Calvin cycle is called ________.

Answer

ribulose bisphosphate carboxylase (RuBisCO)

The types of pigment molecules found in plants, algae, and cyanobacteria are ________ and ________.

Answer

chlorophylls and carotenoids

Short Answer

Why would an organism perform cyclic phosphorylation instead of noncyclic phosphorylation?

What is the function of photosynthetic pigments in the light-harvesting complex?

Critical Thinking

Is life dependent on the carbon fixation that occurs during the light-independent reactions of photosynthesis? Explain.