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Fundamentals of Life Science > Histones and DNA packaging > Flashcards

Histones and DNA packaging Flashcards

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Biology 101 flashcards
1
Q

What size is one complete turn of DNA?

A

10 bases

3.4nm long

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2
Q

How much DNA is there in a human diploid cell?

A

~2m

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3
Q

What is the composition of chromatin?

A

DNA
RNA
Proteins

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4
Q

What is chromatin?

A

What chromosomes are made of

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5
Q

What are histones?

A

Proteins found in chromatin
They are the most common nuclear protein
Account for almost half of nuclear protein

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6
Q

Describe the basic features of histones

A

Small molecular weight

Positively charged

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7
Q

Name the core histones

A

H2A
H2B
H3
H4

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8
Q

Name the linker histone

A

H1

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9
Q

What is the width of double stranded DNA?

A

2nm

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10
Q

What is the basic unit of chromatin?

A

A nucleosome

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11
Q

How much DNA is in one nucleosome?

A

200bp

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12
Q

How many turns of DNA make one nucleosome?

A

1.8 (2)

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13
Q

List the components of a nucleosome

A 
200bp of DNA
2x H2A
2x H2B
2x H3
2x H4
H1
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14
Q

How do H3 and H4 interact?

A

They form a heterodimer called the histone handshake motif

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15
Q

What is formed from the H3/H4 heterodimer?

A

A tetramer that is horse shoe like in structure

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16
Q

How do H2A and H2B interact?

A

They form a dimer

17
Q

Where does the H2A/H2B dimer go?

A

One goes below and one goes above the H3/H4 tetramer

18
Q

What would happen if a histone was altered?

A

The DNA packaging around the octamer would be altered

19
Q

Name four variations of H2A

A

H2A.Z
macroH2A
H2A.Bbd
H2A.X

20
Q

Compare H2A and H2A.Z

A

H2A.Z has 60% identity to H2A
It alters the stability between H2A and H2B
Alters interaction between the dimer and tetramer
Alters the canonical nucleosome
Associated with transcriptionally active chromatin

21
Q

What is the role of histone variants?

A

Differentiates chromatin at centromeres, active genes and heterochromatin

22
Q

What does H3.3 do?

A

It marks actively transcribed loci by replication independent nucleosome activity

23
Q

What is level two of chromatin structure?

A

The 10nm fibre
“beads on a string”
Packing ratio: 6-7

24
Q

What is level three of chromatin structure?

A

The 30nm solenoid
Further coiling of the 10nm fibre
Packing ratio: ~40

25
Q

What is H1s role in the solenoid?

A

It forms the centre of the rings of the 10nm fibre

26
Q

How many nucleosomes make a 30nm solenoid?

A

6

27
Q

What is the fourth level of chromatin structure?

A

Loops of 60-100kb of DNA tethered by non histone scaffold proteins
Packing ratio: 680

28
Q

What is level five of chromatin structure?

A

700nM fibre
Coiled coil
Condensed fibre
Packing ratio: 10^4

29
Q

What is level six of chromatin structure?

A

A metaphase chromosome

30
Q

What is the packing ratio?

A

How much smaller the folded version is than the extended length of DNA

31
Q

Describe the metaphase chromosome

A

Telomeres at each end
A centromere
Sections of heterochromatin and euchromatin

32
Q

Where is the centromere?

A

At the primary constriction

33
Q

What is the purpose of the centromere?

A

Site that spindles attach to

Chromosome segregation occurs here

34
Q

What are the two types of chromatin?

A

Heterochromatin

Euchromatin

35
Q

Describe heterochromatin

A

Highly condensed
Transcriptionally inactive
Repetitive DNA sequences

36
Q

What is constitutive heterochromatin?

A

All cells of a given species package the same regions of DNA into constitutive heterochromatin
Genes contained within constitutive heterochromatin will be poorly expressed

37
Q

What is facultative heterochromatin?

A

DNA packaged into facultative heterochromatin is not consistent throughout the cells of a species
Facultative heterochromatin is regulated and associated with morphogenesis and differentiation
In different cells it may be packaged in euchromatin

38
Q

When is heterochromatin replicated?

A

Late in the S phase

39
Q

Describe euchromatin

A

More open configuration
Replicated early in S phase
Contains both transcriptionally active and inactive genes

Fundamentals of Life Science (24 decks)

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