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Animal Physiology > BLGY2296 Epigenetics > Flashcards

BLGY2296 Epigenetics Flashcards

1
Q

What is epigenetics?

A

The study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself (the concept that the function of a piece of DNA is determined by factors other than its nucleotide sequence alone)

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2
Q

Alternation in gene expression can be due to what?

A

1) Mutation of gene DNA sequence
2) Alteration of methylation status
3) Alteration in underlying chromatin organisation

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3
Q

What is chromatin?

A

A complex of DNA and protein that makes up the chromosomes

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4
Q

What does the chromosomal organisation mediate?

A
  • compaction of genetic material
  • efficient transmission to daughter cells upon cell division
  • protection from DNA damage (because the DNA is wrapped up)
  • regulation of DNA accessibility (regulates recombination)
  • regulation of gene transcription
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5
Q

What does a tetrahymena macronucleus contain?

A

Thousands of short linear chromosomes (therefore lots of telomeres)

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6
Q

Eukaryotes have what shaped chromosomes?

A

Linear (so need a mechanism to replicate the ends of the DNA)

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7
Q

Prokaryotes have what shaped chromosomes?

A

Circular (so need a mechanism to separate DNA strands)

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8
Q

What are chromatids?

A

A chromatid is one-half of two identical copies of a replicated chromosome

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9
Q

Which is the largest human chromosome?

A

1 (10um)

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10
Q

Which is the smallest human chromosome?

A

21 (2um)

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11
Q

How many autosomes do humans have?

A

22 pairs

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12
Q

What is the human chromosome with the lowest density?

A

4 (8 genes/Mb)

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13
Q

What is the human chromosome with the highest density?

A

19 (27 genes/Mb)

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14
Q

In what stage of the cell cycle are chromosomes decondensed?

A

Interphase

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15
Q

What stage of interphase is DNA replicated?

A

S phase

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16
Q

What happens in the M phase of interphase?

A

Cell division - mitosis

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17
Q

What stage of interphase are all the compounds required for DNA synthesis synthesized?

A

G1 phase

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18
Q

What stage of interphase do the cells prepare for mitosis?

A

G2 phase

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19
Q

True of false? Different chromosomes occupy the same territories in the nucleus?

A

False- they occupy different territories in the nucleus

20
Q

What is a centromere?

A

The point on a chromosome by which it is attached to a spindle fibre during cell division, it contains highly repetitive DNA

21
Q

What is a kinetochore?

A

A large protein complex which bones to the centromere and attaches to microtubules (has a role in separating the chromosomes to opposite poles during the metaphase)

22
Q

What is heterochromatin?

A

Highly repetative DNA that is tightly packed and so not accessible to DNA polymerase. It is found at the centromeres

23
Q

What are telomeres?

A

Specialized structures at the ends of chromosomes essential for chromosome integrity (the rate at which chromosomes are changed), repetitive DNA, well conserved

24
Q

Which structure prevents chromosomes binding to each other, re-combing or degrading?

A

Telomeres

25
Q

What is the well conserved sequence of the telomeres?

A

TTAGGG - form t-loops (bind specific proteins e.g. shelterin)

26
Q

Extraction of nuclei using salt of physiological ionic strength (150um) produces a chromatin fibre of what length?

A

30nm

27
Q

Extraction of nuclei using lower salt concentrations produces what length of fibre?

A

10nm (beads on a string)

28
Q

DNA is packaged into what?

A

Nucleosomes

29
Q

Are histone core proteins highly conserved?

A

Yes

30
Q

How many times is DNA wrapped around a histone core particle?

A

Twice

31
Q

How many nucleotides long is a histone core particle?

A

147 nucleotides

32
Q

Micrococcal nuclease (MNase)cleaves chromatin where?

A

In the linker between the nucleosome cores

33
Q

What can be used to extract proteins from nucleosome beads?

A

High salt concentration

34
Q

Each nucleosome contains how many copies of core histones?

A

Two

35
Q

What are the core histones?

A

H2A, H2B, H3, H4

36
Q

What is the linker histone?

A

H1

37
Q

Are histones very acidic or very basic?

A

Very basic (rich basic tail)

38
Q

What percentage of the mass of core histones are composed of lysine and arginine residues?

A

20-25%

39
Q

The histone fold domain is made up of what?

A

Three alpha helices that form a Z shape

40
Q

The interactions between histones mediated by the histone core fold forms which heterodimers?

A

H2A-H2B (dimer) and H3-H4 (tetramer)

41
Q

Does the H2A-H2B dimer or the H3-H4 tetramer interact with DNA?

A

H3-H4 tetramer

42
Q

True of false the histone tails protrude from the nucleosome?

A

True - can be cleaved of by protease (doesn’t affect the structure of the nucleosome)

43
Q

Which interaction is the weakest and the first to be disrupted when the nucleosome unfolds in vivo?

A

H2B-H4

44
Q

Histones form what type of interactions?

A

Charge interactions (not basic interactions)

45
Q

Where are the AT rich regions found when the nucleosomes bind to DNA?

A

On the inside

Animal Physiology (5 decks)

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