Nucleotide/DNA damage-repair

Which of the following correctly distinguishes a nucleotide from a nucleoside?
A) Nucleotide lacks phosphate groups
B) Nucleoside contains phosphate groups
C) Nucleotide contains phosphate groups, sugar, and base
D) Nucleoside contains phosphate, sugar, and base

Nucleotide contains phosphate groups, sugar, and base

PRPP serves as a donor of which components in nucleotide synthesis?
A) Ribose only
B) Phosphate only
C) Both ribose and phosphate
D) Nitrogenous base

Both ribose and phosphate

The first purine nucleotide formed during de novo synthesis is:
A) AMP
B) GMP
C) IMP
D) UMP

IMP

Which amino acids contribute nitrogen atoms to purine and pyrimidine rings?
A) Lys, Arg, His
B) Gln, Asp, Gly
C) Ser, Thr, Tyr
D) Ala, Val, Leu

Gln, Asp, Gly

1. Hyperuricemia can lead to:
   A) Anemia
   B) Gout
   C) Diabetes
   D) Hypertension

Gout

Allopurinol acts by inhibiting:
A) Xanthine oxidase competitively
B) Uric acid excretion
C) DNA polymerase
D) Thymidylate synthase

Xanthine oxidase competitively

Probenecid’s mechanism of action involves:
A) Inhibiting xanthine oxidase
B) Preventing uric acid reabsorption in kidneys
C) Converting uric acid to allantoin
D) Blocking purine salvage pathway

Preventing uric acid reabsorption in kidneys

Which enzyme is inhibited by 5-Fluorouracil?
A) Dihydrofolate reductase
B) Thymidylate synthase
C) DNA polymerase
D) Xanthine oxidase

Thymidylate synthase

Methotrexate inhibits:
A) Thymidylate synthase
B) Dihydrofolate reductase
C) DNA ligase
D) RNA polymerase

Dihydrofolate reductase

DNA replication is described as:
A) Conservative
B) Semi-conservative
C) Dispersive
D) Random

Semi-conservative

Complementary base pairing in DNA pairs:
A) A with C, G with T
B) A with T, G with C
C) A with G, T with C
D) A with U, G with C

A with T, G with C

DNA replication proceeds in which direction?
A) 3’ to 5’
B) 5’ to 3’
C) Both directions simultaneously
D) Randomly

5’ to 3’

The origin of replication (ORC) in eukaryotes:
A) Is a single site per chromosome
B) Has multiple sites per genome
C) Does not exist
D) Only found in prokaryotes

Is a single site per chromosome

Okazaki fragments are synthesized on the:
A) Leading strand continuously
B) Lagging strand discontinuously
C) Leading strand discontinuously
D) Lagging strand continuously

Lagging strand discontinuously

Helicase functions to:
A) Synthesize new DNA strands
B) Unwind the DNA double helix
C) Remove RNA primers
D) Join Okazaki fragments

Unwind the DNA double helix

DNA topoisomerase I relieves torsional strain by:
A) Breaking both DNA strands
B) Nicking one DNA strand
C) Synthesizing RNA primers
D) Ligating DNA fragments

Nicking one DNA strand

Which protein coats single-stranded DNA to prevent reannealing?
A) DNA polymerase
B) Single-strand binding protein (SSB)
C) Primase
D) Ligase

Single-strand binding protein (SSB)

DNA polymerase requires what to initiate DNA synthesis?
A) DNA primer
B) RNA primer
C) Protein primer
D) No primer needed

RNA primer

The sliding clamp function is to:
A) Initiate replication
B) Keep DNA polymerase attached for processivity
C) Remove RNA primers
D) Cut DNA strands

Keep DNA polymerase attached for processivity

During replication, histones must be:
A) Permanently removed
B) Dislodged temporarily ahead of replication fork
C) Not affected
D) Degraded

Dislodged temporarily ahead of replication fork

Telomerase adds repetitive sequences to:
A) The leading strand end
B) The lagging strand end
C) Both ends equally
D) Mitochondrial DNA

The lagging strand end

Telomere shortening is associated with:
A) Increased cell proliferation
B) Cell senescence and aging
C) Cancer prevention exclusively
D) DNA repair

Cell senescence and aging

Reactivation of telomerase in somatic cells is linked to:
A) Normal aging
B) Unregulated cell growth and cancer
C) Apoptosis
D) DNA methylation

Unregulated cell growth and cancer

Compared to prokaryotic replication, eukaryotic replication is:
A) Faster due to fewer origins
B) Slower due to chromatin complexity
C) Identical in speed
D) Independent of helicase

Slower due to chromatin complexity

The G1 phase is characterized by:
A) DNA replication
B) RNA and protein synthesis and organelle duplication
C) Chromosome segregation
D) Cytokinesis

RNA and protein synthesis and organelle duplication

Cells in G0 phase are:
A) Actively dividing
B) Temporarily or permanently non-dividing
C) Undergoing mitosis
D) Synthesizing DNA

Temporarily or permanently non-dividing

The S phase duration is approximately:
A) 1 hour
B) 6 hours
C) 12 hours
D) 24 hours

6 hours

Cyclin D/CDK4 complex regulates progression through:
A) G2 phase
B) G1 restriction point
C) M phase
D) S phase

G1 restriction point

The M checkpoint ensures:
A) DNA has been replicated
B) Chromosomes are aligned and attached to spindle
C) Growth factors are present
D) DNA damage is repaired

Chromosomes are aligned and attached to spindle

Retinoblastoma protein (RB) controls transition from:
A) G2 to M phase
B) G1 to S phase
C) S to G2 phase
D) M to G1 phase

G1 to S phase

When RB is phosphorylated, it:
A) Binds E2F tightly
B) Releases E2F allowing S phase progression
C) Stops cell cycle at G1
D) Activates p53

Releases E2F allowing S phase progression

p53 tumor suppressor protein functions to:
A) Promote cell cycle progression
B) Detect DNA damage and halt cell cycle
C) Activate cyclins
D) Repair DNA directly

Detect DNA damage and halt cell cycle

Mutation in p53 often results in:
A) Enhanced DNA repair
B) Uncontrolled cell proliferation
C) Cell cycle arrest
D) Apoptosis activation

Uncontrolled cell proliferation

Synonymous mutations:
A) Change amino acid sequence
B) Do not change amino acid sequence
C) Introduce stop codons
D) Cause frameshifts

Do not change amino acid sequence

Frameshift mutations result from:
A) Base substitutions
B) Insertions or deletions of bases
C) UV-induced thymine dimers
D) DNA crosslinks

Insertions or deletions of bases

Spontaneous deamination converts cytosine into:
A) Uracil
B) Adenine
C) Guanine
D) Hypoxanthine

Uracil

Alkylating agents cause DNA damage by:
A) Forming thymine dimers
B) Adding covalent adducts to DNA bases
C) Causing strand breaks only
D) Removing bases

Adding covalent adducts to DNA bases

Thymine dimers caused by UV light:
A) Are easily bypassed by DNA polymerase
B) Distort the DNA helix and block replication
C) Result in synonymous mutations
D) Are repaired by mismatch repair

Distort the DNA helix and block replication

Direct reversal repair mechanisms:
A) Require a template strand
B) Use photolyase to reverse thymine dimers
C) Always involve excision of damaged bases
D) Occur only in mammals

Use photolyase to reverse thymine dimers

Base excision repair (BER) involves:
A) Removal of bulky lesions
B) Removal of damaged bases by glycosylases
C) Repair of double strand breaks
D) Fixing mismatches during replication

Removal of damaged bases by glycosylases

Nucleotide excision repair (NER) removes:
A) Small base modifications
B) Bulky helix-distorting lesions
C) Double strand breaks
D) RNA primers

Bulky helix-distorting lesions

DNA mismatch repair (MMR) is most active during:
A) G1 phase
B) S phase
C) M phase
D) G0 phase

S phase

Homologous recombination repairs:
A) Single strand breaks
B) Double strand breaks using sister chromatid template
C) Mismatched bases
D) Thymine dimers

Double strand breaks using sister chromatid template

Non-homologous end joining (NHEJ):
A) Uses a homologous template
B) Is error-prone and fast
C) Occurs mainly in S phase
D) Requires long homology regions

Is error-prone and fast

Microhomology-mediated end joining (MMEJ) is:
A) More accurate than NHEJ
B) More error prone and uses short homologies
C) Active only in G1 phase
D) The same as homologous recombination

More error prone and uses short homologies

Apoptosis differs from necrosis because it:
A) Causes inflammation
B) Is an accidental cell death
C) Is programmed and regulated without inflammation
D) Results in cell swelling

Is programmed and regulated without inflammation

Caspases are:
A) DNA repair enzymes
B) Intracellular proteases activated during apoptosis
C) Membrane receptors
D) Transcription factors

intracellular proteases activated during apoptosis

One hallmark of apoptosis is:
A) Cell membrane rupture
B) Chromatin condensation and DNA fragmentation
C) Cell swelling
D) Release of cellular contents causing inflammation

Chromatin condensation and DNA fragmentation

The intrinsic apoptotic pathway is triggered by:
A) Death ligands like TNF
B) Withdrawal of growth factors or DNA damage
C) External toxins only
D) Viral infection exclusively

Withdrawal of growth factors or DNA damage

During apoptosis, phosphatidylserine exposure on the outer leaflet of the plasma membrane:
A) Triggers inflammation
B) Acts as a signal for macrophage engulfment
C) Causes cell lysis
D) Prevents phagocytosis

Acts as a signal for macrophage engulfment