Question 1

During aerobic cellular respiration, which molecule acts as the terminal electron acceptor in the electron transport chain, and what is the main consequence of this choice for ATP yield?

Accepted Answer

Oxygen ($$\mathrm{O_2$}$$); it enables the maximum ATP production through oxidative phosphorylation.

Question 2

Which of the following best describes the difference between substrate-level phosphorylation and oxidative phosphorylation in terms of ATP production?

Accepted Answer

Substrate-level phosphorylation directly transfers a phosphate group to ADP from a phosphorylated intermediate, while oxidative phosphorylation uses a proton gradient generated by the electron transport chain to drive ATP synthesis.

Question 3

A bacterial cell is exposed to a competitive inhibitor that binds to the active site of an enzyme. What is the most likely immediate effect on the enzyme's activity?

Accepted Answer

The enzyme's activity will decrease because the inhibitor prevents substrate binding at the active site.

Question 4

During glycolysis, how many net ATP molecules are produced per molecule of glucose, and by what mechanism?

Accepted Answer

2 net ATP by substrate-level phosphorylation

Question 5

Which of the following statements about fermentation is correct?

Accepted Answer

Fermentation regenerates NAD$$^+$$ from NADH, allowing glycolysis to continue in the absence of oxygen.

Question 6

In the light-dependent reactions of photosynthesis in eukaryotes, what is the role of water ($$\mathrm{H_2O}$$), and what is the terminal electron acceptor?

Accepted Answer

Water donates electrons to Photosystem II, and NADP$$^+ is $$the terminal electron acceptor, forming NADPH.

Question 7

How many turns of the Calvin cycle are required to produce one molecule of glucose, and what is the direct product of the cycle?

Accepted Answer

Six turns; the direct product is glyceraldehyde-3-phosphate (G3P)

Question 8

Which of the following best explains why photorespiration occurs in plants?

Accepted Answer

Rubisco incorporates oxygen instead of carbon dioxide into ribulose-1,5-bisphosphate, leading to a wasteful pathway that does not produce ATP or sugar.

Question 9

Which type of bond holds the two DNA strands together in the double helix, and how many hydrogen bonds are formed between adenine and thymine?

Accepted Answer

Hydrogen bonds; two bonds between adenine and thymine

Question 10

Which of the following statements correctly describes the difference between prokaryotic and eukaryotic DNA organization?

Accepted Answer

Prokaryotic DNA is typically circular and found in the nucleoid, while eukaryotic DNA is linear and organized into chromosomes within a nucleus.

Question 11

During DNA replication, which enzyme is responsible for synthesizing the RNA primer, and in which direction does DNA synthesis occur?

Accepted Answer

Primase; DNA synthesis occurs in the 5' to 3' direction

Question 12

What is meant by 'semi-conservative' replication of DNA?

Accepted Answer

Each new DNA molecule consists of one parental strand and one newly synthesized strand.

Question 13

Which of the following best describes the difference between the leading and lagging strands during DNA replication?

Accepted Answer

The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments called Okazaki fragments.

Question 14

In prokaryotic transcription, what is the function of the promoter region?

Accepted Answer

It is the binding site for RNA polymerase to initiate transcription.

Question 15

Which of the following statements about translation is correct?

Accepted Answer

The Shine-Dalgarno sequence in prokaryotic mRNA helps align the ribosome with the start codon.

Question 16

How many codons are there in the genetic code, and how many code for amino acids?

Accepted Answer

There are 64 codons, of which 61 code for amino acids.

Question 17

Which of the following best describes a missense mutation?

Accepted Answer

A point mutation that results in a codon coding for a different amino acid.

Question 18

Which of the following is NOT a method of horizontal gene transfer in prokaryotes?

Accepted Answer

Transcription

Question 19

Which of the following best describes the genome of a typical virus?

Accepted Answer

It can be DNA or RNA, single-stranded or double-stranded, linear or circular.

Question 20

What is a prion, and what is significant about its pathogenicity?

Accepted Answer

A prion is a misfolded protein that can induce misfolding in normal proteins, causing neurodegenerative diseases without containing nucleic acids.

MCB 2010 Exam Two Study Guide – Step-by-Step Microbiology Guidance

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