GEN2MHG – Molecular Genetics (Lectures 1–2)

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Question-and-Answer style flashcards covering foundational concepts from GEN2MHG Molecular Genetics lectures 1–2, including Mendelian genetics, DNA/RNA structure, chromatin organization, cell division, DNA replication machinery, telomere biology, extra-nuclear genomes, and key terminology.

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57 Terms

1
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Which scientist’s pea experiments led to the laws of segregation and independent assortment?

Gregor Mendel

2
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According to Mendel, what happens to alleles during gamete formation?

They segregate so that each gamete carries only one allele for each gene.

3
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In Avery, MacLeod & McCarty’s 1944 experiment, which molecule transformed avirulent bacteria into virulent forms?

DNA

4
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What four key properties must genetic material exhibit?

Replication, information storage, expression, and ability to generate inherited variability.

5
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What repeating units make up DNA and RNA?

Nucleotides

6
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What three components form a nucleotide?

A pentose sugar, a phosphate group, and a nitrogenous base.

7
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What is a nucleoside?

A base attached to a sugar (no phosphate).

8
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Name the two purine bases in nucleic acids.

Adenine and guanine

9
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Name the two pyrimidine bases in DNA.

Thymine and cytosine

10
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How many hydrogen bonds connect G-C base pairs?

Three

11
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Which base replaces thymine in RNA?

Uracil

12
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What rule states that %A = %T and %G = % C in double-stranded DNA?

Chargaff’s rule

13
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Why does DNA with high G-C content melt at higher temperatures?

G-C pairs have three hydrogen bonds, requiring more energy to separate.

14
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Why is RNA usually single-stranded?

The extra 2′-OH on ribose destabilises long double helices, promoting intramolecular folding instead.

15
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Define plasmid.

A small, extra-chromosomal, circular DNA molecule that replicates independently of the host chromosome.

16
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What proteins package eukaryotic DNA into nucleosomes?

Histones

17
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What term describes DNA plus its associated proteins in eukaryotes?

Chromatin

18
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During which cell-cycle phase is DNA replicated?

S phase of interphase

19
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List the four basic stages of mitosis in order.

Prophase, metaphase, anaphase, telophase (followed by cytokinesis).

20
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What unique process during meiosis creates recombinant chromosomes?

Crossing-over (homologous recombination).

21
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What enzyme unwinds the DNA double helix ahead of the replication fork?

Helicase

22
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Which enzyme relieves torsional strain by cutting and resealing DNA?

DNA gyrase (a topoisomerase).

23
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DNA synthesis always proceeds in which direction?

5′ → 3′

24
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Why is an RNA primer needed for DNA replication?

DNA polymerase can only extend an existing 3′-OH end; it cannot start de novo.

25
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What are the short DNA fragments synthesized on the lagging strand called?

Okazaki fragments

26
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Which strand is synthesized continuously during replication?

The leading strand

27
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What enzyme seals nicks between Okazaki fragments?

DNA ligase

28
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Describe the proofreading function of DNA polymerase.

Its 3′→5′ exonuclease removes mismatched nucleotides, then synthesis resumes, increasing fidelity ~100-fold.

29
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What is the "end-replication problem"?

DNA polymerase cannot fully replicate the 3′ ends of linear lagging strands, leading to progressive telomere shortening.

30
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What sequence is repeated many times in human telomeres?

TTAGGG

31
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Which enzyme extends telomeres in germ and stem cells?

Telomerase

32
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What is cellular senescence?

A permanent growth arrest that occurs when telomeres become critically short after many divisions.

33
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How is mitochondrial DNA inherited in humans?

Maternally, because sperm contribute virtually no mitochondria to the zygote.

34
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Give one reason mitochondrial DNA accumulates mutations faster than nuclear DNA.

It is exposed to high reactive oxygen species and lacks protective histone packaging.

35
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What theory explains the bacterial origin of mitochondria and chloroplasts?

Endosymbiotic theory

36
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What term describes DNA segments that can move to new genomic locations?

Transposons (transposable elements)

37
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Which chromosome region attaches to spindle fibres during cell division?

Centromere

38
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Define nucleosome.

About 147 bp of DNA wrapped around an octamer of core histones.

39
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Approximately what percentage of the human genome encodes proteins?

1–2 percent

40
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What are VNTRs and STRs examples of?

Variable, short repetitive DNA sequences used in forensics and genetics.

41
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In prokaryotes, where is the chromosome located given absence of a nucleus?

In the nucleoid region

42
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Why are bacterial genomes transcription-ready without extensive packaging changes?

They are not tightly wrapped in chromatin like eukaryotic DNA.

43
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What are sister chromatids?

Identical copies of a chromosome joined at the centromere after DNA replication.

44
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What does "semi-conservative" replication mean?

Each daughter DNA molecule contains one parental strand and one newly synthesized strand.

45
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Which proteins prevent single-stranded DNA from re-annealing during replication?

Single-stranded binding proteins (SSBPs)

46
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What is the role of the sliding clamp (β-clamp) in replication?

It keeps DNA polymerase attached to the template, increasing processivity.

47
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Define cytokinesis.

Division of the cytoplasm, producing two separate daughter cells after mitosis.

48
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What percentage of bacterial genomes is coding versus non-coding?

About 85–90 % is coding.

49
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Which nucleic acid bases are connected by two hydrogen bonds?

Adenine–thymine in DNA and adenine–uracil in RNA

50
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What type of viral genomes can exist?

DNA or RNA, single- or double-stranded, circular or linear.

51
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Why do plasmid vectors often carry antibiotic-resistance genes?

To allow selection of cells that have taken up the plasmid by growing them on antibiotic media.

52
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During which mitotic stage do sister chromatids separate?

Anaphase

53
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What is "open" chromatin?

Less condensed chromatin accessible to transcription and replication machinery.

54
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Name two stages unique to meiosis but absent in mitosis.

Reductional division (meiosis I) and equational division (meiosis II) producing haploid gametes.

55
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How many times can typical human somatic cells divide before senescence?

Approximately 45–65 times (Hayflick limit).

56
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Why is telomerase reactivation considered a hallmark of cancer?

It prevents telomere shortening, giving cancer cells replicative immortality.

57
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What is the main structural difference between ribose and deoxyribose?

Ribose has a 2′-OH group; deoxyribose lacks it (has H instead).