6.E: Microbial Metabolism (Exercises)
6.1: 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
-
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
-
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?
6.2: 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
-
2; 1; 3; 1
Most commonly, glycolysis occurs by the ________ pathway.
- Answer
-
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?
6.3: 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
-
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
-
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?