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Nucleic Acids > Genome > Flashcards

Genome Flashcards

1
Q

The human genome contains _ nucleotides packaged into _ chromosomes

A

3.2 x 10^9

24

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2
Q

Diameter of the nucleus

A

~6 micrometres

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3
Q

Chromatin

A

DNA and its associated proteins

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4
Q

What causes DNA to bind to histones

A
  • ionic bonding
  • DNA is neg charged due to phosphates
  • histones are pos charged due to high lys arg content
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5
Q

Nucleosome

A

-148 bp of DNA wound in sequence around histone octamer

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6
Q

Linker DNA

A

54bp DNA segment that joines nucleosomes together

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7
Q

Experimental evidence for nucleosomes

A
  1. ‘Beads on a string’ appearance of chromatin in EMs

2. Micrococcal nuclease digestion of chromatin

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8
Q

What determines nucleosome position on DNA

A
  1. DNA flexibility

2. Nearby bound proteins

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9
Q

Nuclear matrix

A

insoluble network of non-histone proteins which forms a scaffold onto which specific DNA sequences attach to form long loops

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10
Q

Euchromatin

A

Loosely packed form of DNA containing genes that are actively transcribed
(92% of genome)

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11
Q

Heterochromatin

A

Very tightly packed DNA that is inaccessible to polymerases, thus is not actively transcribed

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12
Q

Chromatin remodelling complexes

A

Large protein complexes that modify nucleosome structure using ATP, leaving DNA less tightly bound to histone proteins

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13
Q

Euchromatin packing ratio

A

750

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14
Q

Heterochromatin packing ratio

A

20,000 - 50,000

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15
Q

Evidence for the association between chromosome decondensation and transcription

A

When nuclei are digested with DNase I, regions more prone to cleavage are those near actively transcribed genes

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16
Q

Proteins that make up the histone octamer

A

H2A
H2B
H3
H4

17
Q

First level of DNA packing

A

Nucleosomes

18
Q

Second level of DNA packing

A

30nm fibre

19
Q

30nm fibre

A

structure formed when histone H1 pulls the nucleosomes together into a regular repeating array

20
Q

Two ways the nucleosomes structure is altered to allow DNA access

A
  1. Chromatin-remodelling complexes

2. Modification of histone tails

21
Q

Histone tail modification

A
  • acetyl, phosphate or methyl groups are added to the tails
  • histone stabilisation isn’t altered but overall 30nm fibre is
  • modified histone will recruit and bind different proteins causing different effects
22
Q

Heterochromatin is mostly found….

A

around the centromere and telomeres (mammals)

23
Q

Chromatin assembly factor

A

adds the new H3 and H4 tetramers to the newly synthesised DNA

24
Q

Five histone modification enzymes

A
  1. Histone acetyltransferase
  2. Histone deacetylase
  3. Methyltransferase
  4. Kinase
  5. Ubiquitin transferase
25
Q

How does histone acetlyation affect DNA?

A
  • modifies the transcription of DNA
  • HATs make DNA more accessible
  • HDACs make DNA less accessible
26
Q

Transcriptional activators

A
  • hyperacetylate histones near the activator binding site by interacting with HATs
  • facilitate promoter-TF interaction
27
Q

Transcriptional repressors

A
  • deacetylate histonesnear the repressor binding site by interacting with HDACs
  • inhibit promoter-TF interaction
28
Q

Centromere

A
  • Part of DNA linking sister chromatids

- site of assembly of the kinetochore

29
Q

Kinetochore

A

set of proteins at the centromere that provide a site of attachment for the spindle fibres

30
Q

Replication origin

A
  • First point of opening of the double helix during replication
  • A-T rich and with unique short repeating sequences that multimeric origin binding proteins recognise
31
Q

Telomeres

A
  • end structures of eukaryotic chromos
  • G rich and with unique short repeating species-specific sequences (TTAGGG in humans)
  • forms 15 residue 3’-terminal overhangs which are looped back into stable t-loops
32
Q

Two roles of telomeres

A
  1. Stabilise chromo ends

2. Prevent loss of genetic info after each replication

33
Q

Two diseases involving abnormal telomeres

A
  1. Down’s syndrome: shorter telomeres, accelerated ageing, x3 rate telomere shortening
  2. Dyskeratosis congenita (DKC): telomerase mutation, short telomeres in stem cells
34
Q

SIR protein chromatin modification

A

bind to H3/H4 tails thus deacetylating them and inactivating transcription

35
Q

Three examples where DNA methylation is

associated with transcriptional silencing

A
  1. X-xhromosome inactivation
  2. Genomic imprinting
  3. Repression of transposable element proliferation

Nucleic Acids (4 decks)

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