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Genes and Heredity > Chromosome Structure and Chromatin > Flashcards

Chromosome Structure and Chromatin Flashcards

1
Q

What is the spacing between base pairs on DNA?

A

3.4 Angstroms

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2
Q

How many base pairs are there in the human genome?

A

3.2 billion

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3
Q

How many protein coding genes are present in the human genome?

A

~ 22000

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4
Q

What is the simplest level of DNA organisation?

A

Chromatin in a double stranded helix.

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5
Q

What makes up the nucleosome?

A

DNA complexed with histones

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6
Q

What is the chromatasome?

A

The nucleosome and H1 histone protein

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7
Q

How is the nucleosome arranged?

A

It is folded up to produce a 30nm fibre with a loop of length 300 nm. The 300nm fibre is compressed to 250nm and becomes a chromatid.

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8
Q

How are chromosomes arranged at metaphase?

A

Highly condensed.

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9
Q

How are chromosomes arranged in interphase?

A

Chromosomes are less distinct with variable levels of compaction depending on activity and function of particular regions.

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10
Q

What is euchromatin?

A

Chromatin that is highly de-compacted and is potentially active active in gene expression.

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11
Q

What is heterochromatin?

A

Highly compacted chromatin that’s transcriptionally inactive.

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12
Q

What is the function of heterochromatin that contains very few genes?

A

To form key structures such as centromeres or telomeres.

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13
Q

What do the beads of the beads on a string analogy represent?

A

Nucleosomes

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14
Q

What does the string of the beads on a string analogy represent?

A

DNA

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15
Q

What are the histones in a nucleosome?

A

H2A, H2B, H3 and H4

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16
Q

What is condensation?

A

A series of higher order structures adopted by chromatin.

17
Q

What are territories?

A

Areas that individual chromosomes concentrate in.

18
Q

Where does euchromatin concentrate?

A

In the middle of the nucleus

19
Q

Where does heterochromatin concentrate?

A

In the periphery of the nucleus.

20
Q

Why is regulating DNA accessibility helpful?

A

As it regulates gene expression.

21
Q

Why is gene expression regulated?

A

To ensure correct timing and location of protein production.

22
Q

What is chromatin remodelling?

A

Alteration of chromatin structures to increase DNA accessibility.

23
Q

What is chromatin remodelling required for?

A

Transcription.

24
Q

What is the function of histone modifying proteins?

A

To modify chromatin structure and ATP dependent chromatin remodelling complexes to permit DNA replication and transcription.

25
Q

What is the charge on a histone?

A

It has a positively charged tail at the N terminus.

26
Q

How do histone acetyltransferases change the chemical nature of histones?

A

By adding acetyl groups to lysine residues on histones making them neutral.

27
Q

What is the function of HDACs?

A

To remove acetyl groups from lysine residues.

28
Q

How does the function of HATs activate transcription?

A

By opening the nucleosome which increases DNA accessibility, facilitating transcription factor binding and recruiting chromatin remodellers.

29
Q

How are HDACs involved in cancer?

A

Some cancers are caused by tumour suppressors that have been excessively deacetylated.

30
Q

What are the mechanisms used to increase local access to DNA?

A
  • nucleosome sliding
  • nucleosome displacement
  • partial histone displacement
  • replacement of octamer subunits with histone variants.
31
Q

What is epigenetics?

A

The study of changes in gene expression prompted without changes in the DNA sequence.

32
Q

What catalyses methylation of cytosine?

A

DNA methyltransferase

33
Q

What catalyses the removal of a methyl group from cytosine?

A

Demethylase

34
Q

Why are heavily methylated genes inactive?

A

As they attract proteins that repress transcription.

Genes and Heredity (6 decks)

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