Question 1

Briefly describe the reductive acetyl-CoA pathway. What is its relevance for methanogens?

Accepted Answer

The reductive acetyl-CoA pathway seems to be the most ancient CO₂ fixation and biomass assimilation; for example, in methanogens, up to 5% of the CO₂ they absorb is used in biosynthesis. It consists in the formation of an acetyl group using two CO₂ molecules converging from two different pathways. Formate is produced by reduction of CO₂ and transfer to tetrahydrofolate (THF), thus forming a C1 unit. The C1 unit is reduced to a methyl group, -CH₃. In methanogens, methane is formed from this C1 unit for energy gain. The methyl group can be fixed into biomass after being transferred to a tetrapyrrole (called TB and related to vitamin B₁₂). The second CO₂ molecule becomes $ \mathrm{CO}_{3}^{-} $ via carbon dioxide dehydrogenase $ \mathrm{CO}_{3}^{-} $. is condensed with coenzyme A and the methyl group carried by TB to form acetyl-CoA.

Question 2

Which of the following statements concerning glyceraldehyde-3-phosphate is FALSE?

Accepted Answer

A)  One G3P is produced by everything three turns of the cycle. 
B)  Two molecules of G3P condense to form a six-carbon sugar. 
C)  One more G3P condenses with a sugar to form a larger molecule used for biosynthesis. 
D)  PGA is reduced to G3P after the PGA moves out of the carboxysome. 
E)  G3P is reoxidized to carbon dioxide so that the cycle continues. 
A)  One G3P is produced by everything three turns of the cycle. 
B)  Two molecules of G3P condense to form a six-carbon sugar. 
C)  One more G3P condenses with a sugar to form a larger molecule used for biosynthesis. 
D)  PGA is reduced to G3P after the PGA moves out of the carboxysome. 
E)  G3P is reoxidized to carbon dioxide so that the cycle continues. E

Question 3

What is the health risk of having nitrates in drinking water? What conditions favor the accumulation of nitrates and nitrites in bodies of water?

Accepted Answer

In natural environments most nitrogen sources are subject to competition from dissimilatory metabolism. Fertilizers contain nitrogen as NH₄⁺, which can leach from agricultural soils to bodies of water where it can be oxidized to nitrate and nitrite by lithotrophs, a process known as nitrification. Nitrites can combine with hemoglobin, rendering it incapable of taking up oxygen. When infants drink water with high nitrate content, they become ill with "blue baby" syndrome, as nitrate becomes nitrite in the digestive system.

Question 4

The cell diagrammed below provides an overview of some regulation of the Calvin cycle. Which of the following is NOT involved in this regulation?  
a. Several different transport mechanisms are used for $ \mathrm{CO}_{2} $ and $ \mathrm{HCO}_{3}^{-}- $.
b. $ \mathrm{CO}_{2} $ and $ \mathrm{HCO}_{3}^{-}{ }^{-} $are sequestered inside a carboxysome.
c. Rubisco is sequestered inside a carboxysome.
d. Carbonic anhydrase is used to convert $ \mathrm{CO}_{2} $ to $ \mathrm{HCO}_{3}{ }^{-} $and thus trap it.
e. Proteins are used to block light and thus the light reactions.

Accepted Answer

The answer of The cell diagrammed below provides an overview...

Question 5

In anaplerotic reactions

Accepted Answer

A)  intermediates in a pathway are regenerated. 
B)  nutrients are imported from the environment. 
C)  molecules targeted for breakdown are salvaged for anabolism. 
D)  the reactions are thermodynamically impossible. 
E)  large amounts of ATP are generated. 
A)  intermediates in a pathway are regenerated. 
B)  nutrients are imported from the environment. 
C)  molecules targeted for breakdown are salvaged for anabolism. 
D)  the reactions are thermodynamically impossible. 
E)  large amounts of ATP are generated.

Question 6

Which of the following molecules CANNOT freely cross biological membranes?

Accepted Answer

A)  O2 
B)  CO2 
C)  NH4+ 
D)  N2 
E)  H2 
A)  O2 
B)  CO2 
C)  NH4+ 
D)  N2 
E)  H2

Question 7

All microorganisms require all of the following for biosynthetic purposes EXCEPT

Accepted Answer

A)  phosphorous. 
B)  reduction. 
C)  energy. 
D)  carbon. 
E)  nitrogen gas. 
A)  phosphorous. 
B)  reduction. 
C)  energy. 
D)  carbon. 
E)  nitrogen gas.

Question 8

Describe the 3-hydroxypropionate cycle; give examples of microorganisms that use this CO₂ fixation mechanism.

Accepted Answer

@#LAT-DLM& as @#LAT-DLM& condenses with acetyl-CoA to form m

Question 9

How is fatty acid biosynthesis regulated in bacteria?

Accepted Answer

Because fatty acid biosynthesis consumes

Question 10

Which of the following are unique in that they fix CO₂ as their sole carbon source?

Accepted Answer

A)  organotrophs and iron oxidizers 
B)  photoheterotrophs and chemiolithotrophs 
C)  photoautotrophs and lithotrophs 
D)  heterotrophs and methanogens 
E)  methanogens and photoheterotrophs 
A)  organotrophs and iron oxidizers 
B)  photoheterotrophs and chemiolithotrophs 
C)  photoautotrophs and lithotrophs 
D)  heterotrophs and methanogens 
E)  methanogens and photoheterotrophs

Question 11

Chorismate is used in a branched pathway to synthesize

Accepted Answer

A)  fatty acids. 
B)  polyketide antibiotics 
C)  purines and pyrimidines 
D)  aromatic amino acids 
E)  tetrapyrroles 
A)  fatty acids. 
B)  polyketide antibiotics 
C)  purines and pyrimidines 
D)  aromatic amino acids 
E)  tetrapyrroles

Question 12

Briefly describe how NH₄⁺ is assimilated into biomass by bacteria.

Accepted Answer

The assimilable ammonium ion (NH₄⁺) is p

Question 13

Cyanobacteria are believed to generate the majority of oxygen gas in Earth's atmosphere. What allows them to produce oxygen?

Accepted Answer

A)  photosynthesis in which H2S is the electron source 
B)  photosynthesis in which water photolysis produces H+, e-, and O2 
C)  bacteriorhodopsin-based photosynthesis 
D)  being near the surface of a pond where more oxygen is available 
E)  possession of a variety of chlorophylls to absorb a wide range of wavelengths of light 
A)  photosynthesis in which H2S is the electron source 
B)  photosynthesis in which water photolysis produces H+, e-, and O2 
C)  bacteriorhodopsin-based photosynthesis 
D)  being near the surface of a pond where more oxygen is available 
E)  possession of a variety of chlorophylls to absorb a wide range of wavelengths of light

Question 14

Based on the number of enzymes involved in its biosynthesis, which of the following is the most complex amino acid specified by the genetic code?

Accepted Answer

A)  tryptophan 
B)  tyrosine 
C)  phenylalanine 
D)  leucine 
E)  isoleucine 
A)  tryptophan 
B)  tyrosine 
C)  phenylalanine 
D)  leucine 
E)  isoleucine

Question 15

Certain amino acids are more energetically expensive than others (tryptophan versus glutamate). Thus, when proteins are moved to the cell surface, extended outside the surface, or secreted out of the cell, there is a potential harm. Why is this potentially harmful, and what adaptations do bacteria have for this potential loss? Give an example.

Accepted Answer

With more "expensive" amino acids, more

Question 16

Which molecules use 5-phosphoribosyl-1-pyrophosphate (PRPP) in their biosynthesis?

Accepted Answer

A)  amino acids 
B)  nucleotides 
C)  fatty acids 
D)  tetrapyrrole 
E)  nonribosomal peptide antibiotics 
A)  amino acids 
B)  nucleotides 
C)  fatty acids 
D)  tetrapyrrole 
E)  nonribosomal peptide antibiotics

Question 17

How do ammonium and oxygen regulate the expression of nitrogen fixation genes?

Accepted Answer

An operon (nifHDKTY) encodes the nitroge

Question 18

It is thought that the Calvin cycle appeared after the divergence of the three domains of life. What supports this hypothesis?

Accepted Answer

The full Calvin cycle is only found in b

Question 19

Gene expression of nitrogenase through NtrC is downregulated in high concentrations of

Accepted Answer

A)  carbon dioxide. 
B)  nitrogen. 
C)  nitrate. 
D)  ammonium. 
E)  FeMo protein. 
A)  carbon dioxide. 
B)  nitrogen. 
C)  nitrate. 
D)  ammonium. 
E)  FeMo protein.

Question 20

Which of the following is the reducing agent in the saturation step of polyketide biosynthesis?

Accepted Answer

A)  NADH 
B)  NADPH 
C)  ferredoxin 
D)  H2 
E)  O2 
A)  NADH 
B)  NADPH 
C)  ferredoxin 
D)  H2 
E)  O2

Exam 15: Biosynthesis

Briefly describe the reductive acetyl-CoA pathway. What is its relevance for methanogens?

Which of the following statements concerning glyceraldehyde-3-phosphate is FALSE?

What is the health risk of having nitrates in drinking water? What conditions favor the accumulation of nitrates and nitrites in bodies of water?

In anaplerotic reactions

Which of the following molecules CANNOT freely cross biological membranes?

All microorganisms require all of the following for biosynthetic purposes EXCEPT

Describe the 3-hydroxypropionate cycle; give examples of microorganisms that use this CO₂ fixation mechanism.

How is fatty acid biosynthesis regulated in bacteria?

Which of the following are unique in that they fix CO₂ as their sole carbon source?

Chorismate is used in a branched pathway to synthesize

Briefly describe how NH₄⁺ is assimilated into biomass by bacteria.

Cyanobacteria are believed to generate the majority of oxygen gas in Earth's atmosphere. What allows them to produce oxygen?

Based on the number of enzymes involved in its biosynthesis, which of the following is the most complex amino acid specified by the genetic code?

Which molecules use 5-phosphoribosyl-1-pyrophosphate (PRPP) in their biosynthesis?

How do ammonium and oxygen regulate the expression of nitrogen fixation genes?

It is thought that the Calvin cycle appeared after the divergence of the three domains of life. What supports this hypothesis?

Gene expression of nitrogenase through NtrC is downregulated in high concentrations of

Which of the following is the reducing agent in the saturation step of polyketide biosynthesis?

Microbial Life: Origin and Discovery

Observing the Microbial Cell

Cell Structure and Function

Bacterial Culture, Growth, and Development

Environmental Influences and Control of Microbial Growth

Viruses

Genomes and Chromosomes

Transcription, Translation, and Bioinformatics

Gene Transfer, Mutations, and Genome Evolution

Molecular Regulation

Viral Molecular Biology

Biotechniques and Synthetic Biology

Energetics and Catabolism

Electron Flow in Organotrophy, Lithotrophy, and Phototrophy

Food and Industrial Microbiology

Origins and Evolution

Bacterial Diversity

Archaeal Diversity

Eukaryotic Diversity

Microbial Ecology

Microbes in Global Elemental Cycles

Human Microbiota and Innate Immunity

The Adaptive Immune Response

Microbial Pathogenesis

Microbial Diseases

Antimicrobial Therapy

Clinical Microbiology and Epidemiology

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