7.E: Microbial Metabolism (Exercises)
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8.1: Energy, Matter, and Enzymes
Cellular processes such as the building or breaking down of complex molecules occur through series of stepwise, interconnected chemical reactions called metabolic pathways. The term anabolism refers to those endergonic metabolic pathways involved in biosynthesis, converting simple molecular building blocks into more complex molecules, and fueled by the use of cellular energy.
Multiple Choice
Which of the following is an organism that obtains its energy from the transfer of electrons originating from chemical compounds and its carbon from an inorganic source?
- chemoautotroph
- chemoheterotroph
- photoheterotroph
- photoautotroph
- Answer
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A
Which of the following molecules is reduced?
- NAD +
- FAD
- O 2
- NADPH
- Answer
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D
Enzymes work by which of the following?
- increasing the activation energy
- reducing the activation energy
- making exergonic reactions endergonic
- making endergonic reactions exergonic
- Answer
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B
To which of the following does a competitive inhibitor most structurally resemble?
- the active site
- the allosteric site
- the substrate
- a coenzyme
- Answer
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C
Which of the following are organic molecules that help enzymes work correctly?
- cofactors
- coenzymes
- holoenzymes
- apoenzymes
- Answer
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B
Fill in the Blank
Processes in which cellular energy is used to make complex molecules from simpler ones are described as ________.
- Answer
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anabolic
The loss of an electron from a molecule is called ________.
- Answer
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oxidation
The part of an enzyme to which a substrate binds is called the ________.
- Answer
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active site
True/False
Competitive inhibitors bind to allosteric sites.
- Answer
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False
Short Answer
In cells, can an oxidation reaction happen in the absence of a reduction reaction? Explain.
What is the function of molecules like NAD + /NADH and FAD/FADH 2 in cells?
8.2: Catabolism of Carbohydrates
Glycolysis is the first step in the breakdown of glucose, resulting in the formation of ATP, which is produced by substrate-level phosphorylation; NADH; and two pyruvate molecules. Glycolysis does not use oxygen and is not oxygen dependent. After glycolysis, a three-carbon pyruvate is decarboxylated to form a two-carbon acetyl group, coupled with the formation of NADH. The acetyl group is attached to a large carrier compound called coenzyme A.
Multiple Choice
During which of the following is ATP not made by substrate-level phosphorylation?
- Embden-Meyerhof pathway
- Transition reaction
- Krebs cycle
- Entner-Doudoroff pathway
- Answer
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B
Which of the following products is made during Embden-Meyerhof glycolysis?
- NAD +
- pyruvate
- CO 2
- two-carbon acetyl
- Answer
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B
During the catabolism of glucose, which of the following is produced only in the Krebs cycle?
- ATP
- NADH
- NADPH
- FADH 2
- Answer
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D
Which of the following is not a name for the cycle resulting in the conversion of a two-carbon acetyl to one ATP, two CO 2 , one FADH 2 , and three NADH molecules?
- Krebs cycle
- tricarboxylic acid cycle
- Calvin cycle
- citric acid cycle
- Answer
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C
True/False
Glycolysis requires oxygen or another inorganic final electron acceptor to proceed.
- Answer
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False
Fill in the Blank
Per turn of the Krebs cycle, one acetyl is oxidized, forming ____ CO 2 , ____ ATP, ____ NADH, and ____ FADH 2 molecules.
- Answer
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2; 1; 3; 1
Most commonly, glycolysis occurs by the ________ pathway.
- Answer
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Embden-Meyerhof
Short Answer
What is substrate-level phosphorylation? When does it occur during the breakdown of glucose to CO 2 ?
Why is the Krebs cycle important in both catabolism and anabolism?
Critical Thinking
What would be the consequences to a cell of having a mutation that knocks out coenzyme A synthesis?
8.3: Cellular Respiration
Cellular respiration begins when electrons are transferred from NADH and FADH 2 —through a series of chemical reactions to a final inorganic electron acceptor (either oxygen in aerobic respiration or non-oxygen inorganic molecules in anaerobic respiration). These electron transfers take place on the inner part of the cell membrane of prokaryotic cells or in specialized protein complexes in the inner membrane of the mitochondria of eukaryotic cells.
Multiple Choice
Which is the location of electron transports systems in prokaryotes?
- the outer mitochondrial membrane
- the cytoplasm
- the inner mitochondrial membrane
- the cytoplasmic membrane
- Answer
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D
Which is the source of the energy used to make ATP by oxidative phosphorylation?
- oxygen
- high-energy phosphate bonds
- the proton motive force
- P i
- Answer
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C
A cell might perform anaerobic respiration for which of the following reasons?
- It lacks glucose for degradation.
- It lacks the transition reaction to convert pyruvate to acetyl-CoA.
- It lacks Krebs cycle enzymes for processing acetyl-CoA to CO 2 .
- It lacks a cytochrome oxidase for passing electrons to oxygen.
- Answer
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D
In prokaryotes, which of the following is true?
- As electrons are transferred through an ETS, H + is pumped out of the cell.
- As electrons are transferred through an ETS, H + is pumped into the cell.
- As protons are transferred through an ETS, electrons are pumped out of the cell.
- As protons are transferred through an ETS, electrons are pumped into the cell.
- Answer
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A
Which of the following is not an electron carrier within an electron transport system?
- flavoprotein
- ATP synthase
- ubiquinone
- cytochrome oxidase
- Answer
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B
Fill in the Blank
The final ETS complex used in aerobic respiration that transfers energy-depleted electrons to oxygen to form H 2 O is called ________.
- Answer
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cytochrome oxidase
The passage of hydrogen ions through ________ down their electrochemical gradient harnesses the energy needed for ATP synthesis by oxidative phosphorylation.
- Answer
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ATP synthase
True/False
All organisms that use aerobic cellular respiration have cytochrome oxidase.
- Answer
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True
Short Answer
What is the relationship between chemiosmosis and the proton motive force?
How does oxidative phosphorylation differ from substrate-level phosphorylation?
How does the location of ATP synthase differ between prokaryotes and eukaryotes? Where do protons accumulate as a result of the ETS in each cell type?
8.4: 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?
- to make ATP
- to make carbon molecule intermediates for anabolism
- to make NADH
- to make NAD +
- Answer
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D
Which molecule typically serves as the final electron acceptor during fermentation?
- oxygen
- NAD +
- pyruvate
- CO 2
- Answer
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C
Which fermentation product is important for making bread rise?
- ethanol
- CO 2
- lactic acid
- hydrogen gas
- Answer
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B
Which of the following is not a commercially important fermentation product?
- ethanol
- pyruvate
- butanol
- penicillin
- Answer
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B
Fill in the Blank
The microbe responsible for ethanol fermentation for the purpose of producing alcoholic beverages is ________.
- Answer
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yeast ( Saccharomyces cerevisiae )
________ results in the production of a mixture of fermentation products, including lactic acid, ethanol and/or acetic acid, and CO 2 .
- Answer
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Heterolactic fermentation
Fermenting organisms make ATP through the process of ________.
- Answer
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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
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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?
8.5: 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?
- glucose
- glycerol
- acetyl groups
- fatty acids
- Answer
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A
Caseinase is which type of enzyme?
- phospholipase
- lipase
- extracellular protease
- intracellular protease
- Answer
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C
Which of the following is the first step in triglyceride degradation?
- removal of fatty acids
- β-oxidation
- breakage of fused rings
- formation of smaller peptides
- Answer
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A
Fill in the Blank
The process by which two-carbon units are sequentially removed from fatty acids, producing acetyl-CoA, FADH 2 , and NADH is called ________.
- Answer
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β-oxidation
The NADH and FADH 2 produced during β-oxidation are used to make ________.
- Answer
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ATP by oxidative phosphorylation
________ is a type of medium used to detect the production of an extracellular protease called caseinase.
- Answer
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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?
8.6: 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?
- a light-harvesting pigment molecule
- a reaction center pigment molecule
- NADPH
- 3-phosphoglycerate
- Answer
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B
In prokaryotes, in which direction are hydrogen ions pumped by the electron transport system of photosynthetic membranes?
- to the outside of the plasma membrane
- to the inside (cytoplasm) of the cell
- to the stroma
- to the intermembrane space of the chloroplast
- Answer
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A
Which of the following does not occur during cyclic photophosphorylation in cyanobacteria?
- electron transport through an ETS
- photosystem I use
- ATP synthesis
- NADPH formation
- Answer
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D
Which are two products of the light-dependent reactions are ________.
- glucose and NADPH
- NADPH and ATP
- glyceraldehyde 3-phosphate and CO 2
- glucose and oxygen
- Answer
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B
True/False
Photosynthesis always results in the formation of oxygen.
- Answer
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False
Fill in the Blank
The enzyme responsible for CO 2 fixation during the Calvin cycle is called ________.
- Answer
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ribulose bisphosphate carboxylase (RuBisCO)
The types of pigment molecules found in plants, algae, and cyanobacteria are ________ and ________.
- Answer
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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.
8.7: Biogeochemical Cycles
Energy flows directionally through ecosystems, entering as sunlight for phototrophs or as inorganic molecules for chemoautotrophs. The six most common elements associated with organic molecules—carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—take a variety of chemical forms and may exist for long periods in the atmosphere, on land, in water, or beneath earth’s surface.
Multiple Choice
Which of the following is the group of archaea that can use CO 2 as their final electron acceptor during anaerobic respiration, producing CH 4 ?
- methylotrophs
- methanotrophs
- methanogens
- anoxygenic photosynthesizers
- Answer
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C
Which of the following processes is not involved in the conversion of organic nitrogen to nitrogen gas?
- nitrogen fixation
- ammonification
- nitrification
- denitrification
- Answer
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A
Which of the following processes produces hydrogen sulfide?
- anoxygenic photosynthesis
- oxygenic photosynthesis
- anaerobic respiration
- chemoautrophy
- Answer
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C
The biogeochemical cycle of which of the following elements is based on changes in solubility rather than redox chemistry?
- carbon
- sulfur
- nitrogen
- phosphorus
- Answer
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D
Fill in the Blank
The molecule central to the carbon cycle that is exchanged within and between ecosystems, being produced by heterotrophs and used by autotrophs, is ________.
- Answer
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carbon dioxide
The use of microbes to remove pollutants from a contaminated system is called ________.
- Answer
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bioremediation
True/False
There are many naturally occurring microbes that have the ability to degrade several of the compounds found in oil.
- Answer
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True
Short Answer
Why must autotrophic organisms also respire or ferment in addition to fixing CO 2 ?
How can human activity lead to eutrophication?
Critical Thinking
In considering the symbiotic relationship between Rhizobium species and their plant hosts, what metabolic activity does each organism perform that benefits the other member of the pair?