MCB 250 MOLECULAR GENETRICS EXAM
WITH VERIFIED QUESTIONS AND ANSWERS ||
GUARANTEED PASS || LATEST VERSION 2026
Part 1: DNA & RNA Structure (Questions 1–25)
1. Q: What are the six primary chemical elements of life?
A: Carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.
2. Q: What is the peak absorbance wavelength for DNA?
A: 260 nm.
3. Q: Which amino acid(s) absorb light at 280 nm?
A: Tryptophan and tyrosine (and to a lesser extent, phenylalanine).
4. Q: What is the structure of B-form DNA?
A: A right-handed double helix with approximately 10 base pairs per
turn, a major groove of ~22 Å, and a minor groove of ~12 Å.
5. Q: How does increasing salt content affect the melting temperature (Tm)
of DNA?
A: Increasing salt concentration stabilizes the DNA duplex by
neutralizing the negative charge of the phosphate backbone, thereby
increasing the Tm.
6. Q: What is Chargaff's rule?
A: In double-stranded DNA, the amount of adenine equals thymine
(A=T), and the amount of guanine equals cytosine (G=C).
7. Q: What type of bond connects nucleotides in a DNA strand?
A: Phosphodiester bonds.
8. Q: What is the difference between a nucleoside and a nucleotide?
A: A nucleoside consists of a nitrogenous base and a sugar; a nucleotide
is a nucleoside with one or more phosphate groups attached.
,9. Q: What is the difference between the major and minor grooves in DNA?
A: The major groove is wider and exposes more chemical information for
protein binding; the minor groove is narrower and less accessible.
10.Q: What are the stabilizing properties of B-form DNA?
A: Base stacking, hydrogen bonding between complementary bases, and
the hydrophobic effect.
11.Q: What is the role of the 2'-OH group in RNA?
A: It makes RNA more reactive and less stable than DNA, contributing to
RNA's shorter half-life.
12.Q: What are the three main types of RNA?
A: Messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA
(tRNA).
13.Q: What is the difference between prokaryotic and eukaryotic
transcription and translation?
A: In prokaryotes, transcription and translation occur simultaneously in
the cytoplasm. In eukaryotes, transcription occurs in the nucleus, and
translation occurs in the cytoplasm, so they do not occur simultaneously.
14.Q: What is the central dogma of molecular biology?
A: DNA → RNA → Protein.
15.Q: What is the difference between a purine and a pyrimidine?
A: Purines (adenine, guanine) have a two-ring structure; pyrimidines
(cytosine, thymine, uracil) have a single-ring structure.
16.Q: What is the role of the phosphate backbone in DNA?
A: It provides structural support and a negative charge that allows
interaction with proteins and cations.
17.Q: What is the significance of the AT-rich region in DNA?
A: It is easier to unwind because A-T base pairs have only two hydrogen
bonds, compared to three in G-C pairs.
18.Q: What are the non-covalent bonds that contribute to protein structure?
A: Hydrogen bonds, ionic bonds, van der Waals interactions, and
hydrophobic interactions.
19.Q: What is the universal tree of life based on?
A: Comparisons of ribosomal small subunit RNAs.
20.Q: What is the difference between the "tree of life" based on rRNA and
other genes?
, A: rRNA genes are highly conserved and provide a reliable measure of
evolutionary relationships.
21.Q: What is the role of the 9-bp DnaA box?
A: It is the binding site for DnaA-ATP at the origin of replication (oriC)
in E. coli.
22.Q: What is the "DNA unwinding element" (DUE)?
A: An AT-rich region adjacent to the DnaA boxes that is opened by
DnaA-ATP to create single-stranded DNA.
23.Q: What is the role of DnaC?
A: DnaC is a helicase loader that helps load DnaB (helicase) onto the
single-stranded DNA.
24.Q: What is the function of primase (DnaG)?
A: It synthesizes short RNA primers on each strand to provide a 3'-OH
for DNA polymerase.
25.Q: What is the sliding clamp (β clamp)?
A: It loads DNA polymerase III onto the DNA to start elongation.
Part 2: DNA Replication (Questions 26–50)
26.Q: What is the function of DnaA in E. coli?
A: DnaA initiates DNA replication by binding to the 9-bp DnaA boxes in
oriC.
27.Q: What ligands must be bound to DnaA for it to be active?
A: DnaA must be bound to ATP (not ADP) to be active.
28.Q: What is the consequence of over-initiation of DNA replication?
A: Multiple replication forks start before the previous round finishes,
leading to DNA over-replication, genomic instability, chromosome
breakage, and cell death.
29.Q: What is the consequence of under-initiation of DNA replication?
A: The chromosome is not fully replicated before cell division, so
daughter cells may receive incomplete genomes, which is lethal.
30.Q: What is the "end replication problem" in eukaryotic DNA replication?
A: DNA polymerases require a 3'-OH primer and can only add
nucleotides in the 5'→3' direction, so the ends of linear chromosomes
cannot be fully replicated.
WITH VERIFIED QUESTIONS AND ANSWERS ||
GUARANTEED PASS || LATEST VERSION 2026
Part 1: DNA & RNA Structure (Questions 1–25)
1. Q: What are the six primary chemical elements of life?
A: Carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.
2. Q: What is the peak absorbance wavelength for DNA?
A: 260 nm.
3. Q: Which amino acid(s) absorb light at 280 nm?
A: Tryptophan and tyrosine (and to a lesser extent, phenylalanine).
4. Q: What is the structure of B-form DNA?
A: A right-handed double helix with approximately 10 base pairs per
turn, a major groove of ~22 Å, and a minor groove of ~12 Å.
5. Q: How does increasing salt content affect the melting temperature (Tm)
of DNA?
A: Increasing salt concentration stabilizes the DNA duplex by
neutralizing the negative charge of the phosphate backbone, thereby
increasing the Tm.
6. Q: What is Chargaff's rule?
A: In double-stranded DNA, the amount of adenine equals thymine
(A=T), and the amount of guanine equals cytosine (G=C).
7. Q: What type of bond connects nucleotides in a DNA strand?
A: Phosphodiester bonds.
8. Q: What is the difference between a nucleoside and a nucleotide?
A: A nucleoside consists of a nitrogenous base and a sugar; a nucleotide
is a nucleoside with one or more phosphate groups attached.
,9. Q: What is the difference between the major and minor grooves in DNA?
A: The major groove is wider and exposes more chemical information for
protein binding; the minor groove is narrower and less accessible.
10.Q: What are the stabilizing properties of B-form DNA?
A: Base stacking, hydrogen bonding between complementary bases, and
the hydrophobic effect.
11.Q: What is the role of the 2'-OH group in RNA?
A: It makes RNA more reactive and less stable than DNA, contributing to
RNA's shorter half-life.
12.Q: What are the three main types of RNA?
A: Messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA
(tRNA).
13.Q: What is the difference between prokaryotic and eukaryotic
transcription and translation?
A: In prokaryotes, transcription and translation occur simultaneously in
the cytoplasm. In eukaryotes, transcription occurs in the nucleus, and
translation occurs in the cytoplasm, so they do not occur simultaneously.
14.Q: What is the central dogma of molecular biology?
A: DNA → RNA → Protein.
15.Q: What is the difference between a purine and a pyrimidine?
A: Purines (adenine, guanine) have a two-ring structure; pyrimidines
(cytosine, thymine, uracil) have a single-ring structure.
16.Q: What is the role of the phosphate backbone in DNA?
A: It provides structural support and a negative charge that allows
interaction with proteins and cations.
17.Q: What is the significance of the AT-rich region in DNA?
A: It is easier to unwind because A-T base pairs have only two hydrogen
bonds, compared to three in G-C pairs.
18.Q: What are the non-covalent bonds that contribute to protein structure?
A: Hydrogen bonds, ionic bonds, van der Waals interactions, and
hydrophobic interactions.
19.Q: What is the universal tree of life based on?
A: Comparisons of ribosomal small subunit RNAs.
20.Q: What is the difference between the "tree of life" based on rRNA and
other genes?
, A: rRNA genes are highly conserved and provide a reliable measure of
evolutionary relationships.
21.Q: What is the role of the 9-bp DnaA box?
A: It is the binding site for DnaA-ATP at the origin of replication (oriC)
in E. coli.
22.Q: What is the "DNA unwinding element" (DUE)?
A: An AT-rich region adjacent to the DnaA boxes that is opened by
DnaA-ATP to create single-stranded DNA.
23.Q: What is the role of DnaC?
A: DnaC is a helicase loader that helps load DnaB (helicase) onto the
single-stranded DNA.
24.Q: What is the function of primase (DnaG)?
A: It synthesizes short RNA primers on each strand to provide a 3'-OH
for DNA polymerase.
25.Q: What is the sliding clamp (β clamp)?
A: It loads DNA polymerase III onto the DNA to start elongation.
Part 2: DNA Replication (Questions 26–50)
26.Q: What is the function of DnaA in E. coli?
A: DnaA initiates DNA replication by binding to the 9-bp DnaA boxes in
oriC.
27.Q: What ligands must be bound to DnaA for it to be active?
A: DnaA must be bound to ATP (not ADP) to be active.
28.Q: What is the consequence of over-initiation of DNA replication?
A: Multiple replication forks start before the previous round finishes,
leading to DNA over-replication, genomic instability, chromosome
breakage, and cell death.
29.Q: What is the consequence of under-initiation of DNA replication?
A: The chromosome is not fully replicated before cell division, so
daughter cells may receive incomplete genomes, which is lethal.
30.Q: What is the "end replication problem" in eukaryotic DNA replication?
A: DNA polymerases require a 3'-OH primer and can only add
nucleotides in the 5'→3' direction, so the ends of linear chromosomes
cannot be fully replicated.
