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MED-109 Biology II > Topic 3: molecular basis of inheritance > Flashcards

Topic 3: molecular basis of inheritance Flashcards

1
Q

Describe the structure of DNA

A
  • 2 antiparallel sugar-phosphate backbones
  • Nitogenous base pairs = AT + CG
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2
Q

What is Chargaff’s rule?

A
  • Equal number of AT + GC bases
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3
Q

How many H bonds between the bases?

A
  • AT = 2
  • CG = 3
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4
Q

Describe the structure of DNA nucelotide

A
  • Nitrogenous base
  • Pentose sugar
  • Phosphate group
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5
Q

Describe the phosphodiester bond

A
  • Between 3’ OH group of sugar molecule + 5’ phosphate group = sugar phosphate backbone
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6
Q

Describe bacterial chromosomes

A
  • Double stranded circular DNA + small proteins
  • Super coiled in nucliod
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7
Q

Describe eukaryotic chromosomes

A
  • Double stranded linear DNA + histone proteins
  • In nucleus
  • Chromatin = DNA + histones
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8
Q

Give the levels of chromatin packing in eukaryotic chromosomes

A

1) Double helix = 2nm
2) Nucleosomes = 10nm
3) 30 nm fiber
4) Looped domain = 300nm
5) Chromatid = 700nm
6) Replicated chromosome = 1400nm

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9
Q

Describe the structure of the nucleosome

A
  • Octamer
  • Consists of 8 histones
  • (H2A + H2B + H3 + H2)2
  • ds DNA = 168 base pairs
  • H1 histone = located between nucleosomes = stabilizes interactions between DNA + nucleosomal histones
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10
Q

Describe the structure of chromatin

A

1) Euchromatin: loosely packed = active
- Enables replication + transcription
- Enables gene expression
2) Heterochromatin: highly concentrated = inactive
- Inhibits replication + transcription + gene expression

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11
Q

Describe changes to chromatin during cell cycle

A

1) Interphase = euchromatin = gene expression
- 10 nm - 30 nm fiber
2) Mitosis = heterochromatin = inhibition
- Exception = centromeres + telomeres = always highly condensed hetrochromatin during whole cell cycle

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12
Q

Define epigenetics

A
  • Study of traits NOT caused by change in DNA sequence BUT in gene expression
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13
Q

Types of histone modification

A
  • Histone acetylation
  • Histone deacetylation
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14
Q

Describe histone acetylation

A
  • Converts heterochromatin > euchromatin = activates
  • Loss of charge = acetylation weakens interaction with DNA
  • Enables gene expression
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15
Q

Describe histone deacetylation

A
  • Converts to heterochromatin = deactivates
  • Restores charge = strengthens interaction with DNA
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16
Q

Give the enzymes involved in histone modification

A
  • HAT = histone acetyl-transferase = activate
  • HDAC - histone deacetylase = inactivates
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17
Q

Describe the semiconservative model of replication

A
  • Double helix replicates each daugher = have 1 old each + 1 new synthesized strand
  • DNA replication = fast + highly accurate
18
Q

Define bidirectional replication

A
  • Replication in both direction from each origin until whole molecule copied
19
Q

Define replication fork

A
  • Y-shaped region at end of each replication bubble = new DNA strand elongates
20
Q

Define helicase

A
  • Enzyme untwists double helix at replication forks
21
Q

Define single strand binding protein

A
  • Stabilizes single-stranded DNA until it can be used as template
22
Q

Define topoisomerase

A
  • Corrects overwinding in replication forks by breaking + swiveling + rejoining DNA strands
23
Q

What are the limitations of DNA polymerases?

A
  • Only add nucleotides to pre-existing nucleotide chain
  • Cannot initiate synthesis of chain
  • Requires primer + DNA template
  • Only add nucleotides from 5’-3’
24
Q

Describe the function of primase

A
  • Synthesizes short RNA primer from scratch using parental DNA as template
  • Free 3’ side = acts as starting point for synthesis of new DNA by polymerase
25
What is nucleoside triphosphate?
- Each nucleotide added to growing DNA comes from NTP
26
What is azido deoxy thymidine?
- Blocks replication due to modified 3' OH group - Anti-retroviral drug
27
Describe lagging strand syntheis
1) Primase synthesizes short RNA primers 2) DNA polymerase III = synthesizes Okazaki fragment = adds DNA nucleotide to each primer 5' - 3' 3) DNA polymerase I = degrades RNA primers + replaces with DNA nucleotides 4) DNA ligase joins DNA fragments to Okazaki fragments
28
Describe repliation on the ends of DNA
- Due to polymerase limitation = no way to complete 5' ends - Replication produces shorter DNA = problem for only eukaryotic linear NOT prokaryotic circular
29
Describe telomeres + function
- Ends of eukaryotic chromosomes + repetitive sequence bound to proteins - Role = protect chromosomal end = erosion + degradation + recombination - Postpone shortening of molecules + erosion - Postponsing shortening = connected to aging
30
Describe the end-replication problem
- No Okazaki fragments for replication of 3' - 3' projections at ends - Every DNA replication = small regionof telomere cannot be replaced = each cell division some base pairs lost
31
Define telomerase
- Enzyme conserves telomere length - Replication capacity depends on length of telomeres
32
What is the role of telomere shortening?
- Protects cells from carcinogenesis = limits number of cell divisions = Hayflicks limit
33
Define senescence
- Permanent cell cycle arrest after cell reachs number of cell divisions
34
Describe the regulation of telomerase activity
- Active in germ cell = if chromosomes become shorter every cell cycle = essentila genes would go missing from gametes they produce - Inactive in most somatic = except stem cell + hair cell + lympocytes - Abnormally active in cancer cells = allows cancer to persist
35
Explain proof reading
- Replication errors occur during DNA replication = base pairing - Proof reading corrects - Polymerase proofread new DNA + replaces an mismatched nuceotides - Polymerase = 3'-5' exonuclease activity mediates proofreading during replication
36
Give exogenous DNA damage
- Chemicals = cigarette smoke - Radiation = UV/X-ray
37
Give the DNA repair mechanisms for single strand breaks
1) Mismatch repair 2) Base excision repair 3) Nucleotide excision repair
38
Describe MMR
- Corrects remaining base pairing errors in DNA replication - Occurs immediately after DNA replication
39
Describe BER
- Removes damages bases = small non-helix distorting base lesions
40
Describe NER
- Removes bulky DNA lesions = thymine dimer caused by UV - Nuclease cuts out + replaces
41
Give an example of an inherited DNA repair disorder
- Xeroderma pigmentosum = impaired NER
42
Describe xeroderma pigmentosum
- Autosomal recessive - Mutation encoded = NER repair enzyme responsible for repairing UV damage - UV = produced thymine dimers in DNA - No DNA repair - Susceptible to skin cancer

MED-109 Biology II (6 decks)

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