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biochem > TMC 3- Chromatin structure > Flashcards

TMC 3- Chromatin structure Flashcards

1
Q

hat does DNA in eukaryotes predominantly exist as

A

Chromatin

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2
Q

length of DNA in the human nucleus,

A

2 m

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3
Q

number of histones in a nucleosome

A

8 (histone octamer)

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4
Q

how many core histones – what are they

A

4 core and 1 linker
Core - H2A, H2B, H3+H4
Linker - H1

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5
Q

Linker histone

A

H1

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6
Q

nucleosome

A

formed by ~146bp of DNA + histone octamer

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7
Q

what are the dimers formed in an octamer

A

H2A & H2B
H3 & H4

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8
Q

Where does H1 histone bind and function

A

binds to the linker DNA and induces tighter DNA
wrapping around the nucleosome and compacts DNA further

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9
Q

chromatin.

A

The complex of nucleosomes, H1 transcription factors and other proteins is called chromatin.

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10
Q

2 main functions of chromatin

A

1) compaction and organisation of DNA
2) regulation of gene expression.

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11
Q

nucleosome structure

A
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12
Q

what is a major protein in the scaffold.

A

Topoisomerase II

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13
Q

Chromatin organisation

A

DNA coiled around histones giving beads on string structure – 10 nm fibres
Beads on string structure can be condensed into 30nm fibres
This compacts the DNA 40x
Chromatin– the 10nm and 30nm fibres together w/ their associated proteins is called chromatin
Chromatin organised in loops around a protein scaffold
Topoisomerase II is a major protein in the scaffold
During mitosis and meiosis DNA further compacts into chromosomes about 10,000-20,000 x

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14
Q

what is a nucleosome bead made of

A
  • Histone octamer:
    –> 2 H2A (histone 2A)
    –> 2 H2B
    –> 2 H3
    –> 2 H4
  • DNA coiled around it
    *** Linker histone - H1 IS NOT PART OF THE BEAD BUT IS A KEY COMPONENT OF CHROMATIN
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15
Q

Is H1 histone a part of the nucleosome bead

A

no.
but is a key component of chromatin
it binds to the bead wround the DNA enters and exits
**H1 can stabilize both nucleosome structure and higher-order chromatin architecture

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16
Q

charge on histones

A

+ve
(also v. abundant and highly conserved)

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17
Q

What part of the histone differs btwn each one
and can be modified extensively

A

The N-terminal tail

an N terminal tail that differs between the
histones - this tail is exposed on the histones and
can be modified extensively

18
Q

what is the histone fold region made up of

A

three alpha helical regions

a common histone fold region made up of three
alpha helical regions

19
Q

what do histones contain?

A

an N-terminal tail (differs btwn histoned - can be highly modified)
A common histone fold region
A relatively short C-terminal tail

20
Q

similarities and diff btwn histone structures

A

The main bodies (histone fold) of the core histones – similar structure – 3 alpha helical regions and 2 short loops
N-terminal tails of histones differ from each other – can be modified extensively

21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
21
Q

main N-terminal tail modifications that occur are?

A
  1. Lysines (K) can be acetylated, methylated (addition of 1-3 methyl groups), sumolayted (addition of string of specific amino acids), ubiquinated (addition of a different string of amino
    acid) and ribosylated (addition of a ribose sugar).
  2. Arginines can be methylated (addition of 1-2 methyl groups)
  3. Serines (S) and threonines (T) can be
    phosphorylated.
22
Q

What modifications can be added to the tails of histones? Where are they added?

A

acetylation (a negatively charged acetyl group is added) – Lysines
methylation (addition of 1-3 methyl groups)– Lysines + Arginines
sumoylation (addition of string of specific amino acids) – Lysines
ribosylation (addition of ribose sugar)
– Lysines
phosphorylation (– Lysines + Serines (S) and threonines (T)
ubiquinated (addition of a different string of amino acid) – Lysine

23
Q

What amino acids can typically be modified in the histones tails?

A

Lysine, Arginines, Serines and Threonines

Lysine - all
Argnines - methylation
Serines + Threonines - phosphorylation

24
Q

Variation in compaction of chromatin

A

The compaction of chromatin varies from loosely packed nucleosomes to compacted to extremely compacted.

Loosely compacted chromatin is ~10nm in diameter and is called the
10nm fibre.

Compacted chromatin is ~30nm in diameter and is called the 30nm
fibre.

25
Q

Diameter of chromatin in interphase

A

10nm and 30 nm fibers exist in this phase

26
Q

Explain what is meant by the phrase “chromatin states are dynamic”?

A

Chromatin states are dynamic and sections of chromatin are regularly
remodelled from 10nm fibre to 30nm fibre and visa versa.
That is – The chromatin 10nm fibre can condense to the 30nm fibre and visa
versa.

27
Q

What is euchromatin? what is heterochromatin? what is the difference between them?

A

Euchromatin – 10 nm fibre – open chromatin – DNA in the 10nm fibre is relatively accessible to enzymes and factors in transcription of DNA

Heterochromatin – 30nm fibre – closed chromatin – The DNA in the 30nm fibre is quite inaccessible (closed) to the
enzymes and factors involved in transcribing DNA

biochem (10 decks)

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