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Human Molecular B > Lecture 2 - Eukaryotic Chromosome > Flashcards

Lecture 2 - Eukaryotic Chromosome Flashcards

1
Q

Approx ? Of DNA in a single human cell?

A

1.8m

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2
Q

What is the compaction needed just to fit into the nucleus is approx how many times?

A

180,000

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3
Q

What is the role of packaging DNA?

A

Protects from damage and to regulate DNA metabolism

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4
Q

Where can evidence of DNA packaging be found?

A

Electron microscopy DNA in non-diving cells forms chromatin: compaction DNA during mitosis forms chromosomes

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5
Q

What is the chromatin structure?

A

Chromatin has a fundamental subunit structure - present in virtually all eukaryotic organisms Several levels of organisation are found to form chromosomes Levels vary depending on whether a cell is in interphase or undergoing mitosis or meiosis

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6
Q

What is nucleosome?

A

A repeating unit of chromosome

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7
Q

Each nucleoside compromises .. molecules each of … core histones

A

2 molecules 4 core histones

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8
Q

Each core histone dimer has … DNA binding surface that organise … DNA turns

A

6 core histones 3 DNA turns

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9
Q

The histone octamer organises … of DNA in … helical turn of DNA

A

145bp and 1 3/4

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10
Q

How much DNA is packaged in a disc of 6x11nm?

A

48nm

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11
Q

How are nucleosomes prepared?

A

Individual nucleosomes may be prepared by limited digestion of chromatin with micrococcal nuclease followed by separation of the particles on sucrose gradients

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12
Q

Mono nucleosome

A

200bp

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13
Q

Trimmed nucleosome

A

165 bp

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14
Q

Core particles

A

146 bp

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15
Q

What are histones?

A

Highly conserved small basic proteins

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16
Q

How are histone readily solubilised from chromatin by dilute acid ?

A

Arctic acid or HCL Rich in positively charged arginine and lysine

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17
Q

What are species of histones ?

A

There are 5 species designated H1 to H4 H5 is a type of H1 Histone H2A, H2B, H3 and H4 form
Various aggregates

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18
Q

A particular aggregate forms the core structure of the nucleosome in the .. fibril?

A

11 fibril

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19
Q

Which histone is not present in the nucleosome?

A

H1 (H5)

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20
Q

Which histones have variable regions?

A

H1 (2), H2A (2), H2B (1)

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21
Q

Which histones preferentially aggregate to form tetramers ?

A

H3 and H4 Tetramers contain 2 molecules of each histone

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22
Q

Which histones also aggregate but in stages?

A

H2A and H2B

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23
Q

What does the size of aggregate depend on?

A

Initial concentration of 2 histones

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24
Q

What are the 5 different inteactions of histones with DNA ?

A
  1. Helix dipoles from alpha-helices in H2B, H3 and H4 cause a net positive charge to accumulate at point of interaction with negatively charged phosphates of DNA 2. h-bonds between DNA backbone and the amjne group on the main chain of histone proteins 3. Non polar interaction between histones and deoxyribose on DNA 4. Salt link and hydrogen bond between side chains of basic amino acids lysine and arginine and phosphate oxygen on DNA 5. Non-specific minor groove insertions of the H3 and H2B N terminal tails into 2 minor grooves each on the DNA
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25
Q

What removes histones?

A

2M Nacl

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26
Q

What structure does 30 fibre have?

A

Solenoid

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27
Q

What is 30nm solenoid fibre AkA?

A

Heterochromatin

28
Q

What is 11nm beads on string AKA?

A

Euchromatin

29
Q

What are the features of Euchromatin?

A

Extended structure Active genes

30
Q

What are the features of heterochromatin?

A

Highly condensed Inactive genes

31
Q

What is the first level of organisation?

A

11nm fibril

32
Q

In the 11nm fibril, how many number of np of ds DNA wrapped…around on the outside of a flat cyclindridal disc of small BASIC protein?

A

147 bp and 1.67 turns

33
Q

What is spacer or linker DNA?

A

Each nucleosome is joined to its neighbour by the DNA which runs the length of the chromosome The short length of DNA joining any two nucleosomes is termed spacer or linker

34
Q

What is the length of spacer DNA?

A

Around 50bp

35
Q

What is the packing ration of the 11nm fibril?

A

6 A 6 fold reduction in total length

36
Q

What comprises of the 11nm fibril?

A

Euchromatin and heterochromatin

37
Q

When is the 11nm present ?

A

Interface Meiotic/mitotic division

38
Q

What is the transcriptonally active form of chromatin?

A

11nm fibril

39
Q

How can chromatin be assembled into 11nm fibril?

A

In vitro on mixing, in low salt, DNA and 4 pairs of histones (H2A,H2B, H3, H4)

40
Q

What is the 2nd level of organisation?

A

30nm fibril

41
Q

What does the 30nm fibril form?

A

Left handed solenoid helix

42
Q

How many nucleosomes per turn in the left handed solenoid helix of the 30nm fibril?

A

6

43
Q

What is the packing ration of the 30nm fibril?

A

400

44
Q

What is required for the condensation in the 30nm fibril?

A

Histone H1

45
Q

When is the 30nm fibril present?

A

Interphase

Mitotic/meiotic division

46
Q

When is the 30nm fibril inactive?

A

RNA synthesis (transcription)

47
Q

How can chromatin be assembled into a 30nm fibril?

A

High salt solution mixing DNA and ALL histone species, including histone H1

48
Q

What is the 3rd level of organisation?

A

Loops, coils and rosettes

49
Q

What is loops?

A

75kb of DNA

50
Q

What is rosette?

A

Around 6 loops

51
Q

What is coils?

A

Around 30 rosettes

52
Q

Looping and cooling the chromatin results in a reduction in total length to: … in heterochromatin ?

A

Ca 10,000

53
Q

What are probably involved in condensation?

A

Specific packaging proteins

54
Q

What are not present in Euchromatin?

A

Rosettes and coils

55
Q

What is the 4th level of organisation?

A

Chromatids

56
Q

When is chromatin maximally condensed?

A

Mitosis

57
Q

What is the packing ratio in mitosis?

A

> 10,000

58
Q

What is the length of chromosomal DNA at mitosis?

A

~5 micrometer

59
Q

In a single human chromosome DNA ranges in size from … (smallest) to … (largest)

A

1) 50 x 10^6 2) 250 x 10^6 bp

60
Q

What is the full length of DNA in a chromosome of stretched?

A

1.7cm - 8.5cm

61
Q

What is deproteination?

A

Chromatin DNA make loop to and from the central scaffold

62
Q

What is the scaffold?

A

A network of proteins that cross-tie DNA loops

63
Q

Topoisomerase II and Protein SC2 (XCAP C/E)

A

Major component Both proteins are required for chromosome assembly

64
Q

What is SAR?

A

Scaffold attachment regions Protein bind to SAR in chromosomal DNA

65
Q

What is SAR?

A

Highly AT-rich DNA ~ 1 - 2 kB in size

66
Q

What is the role of SAR?

A

SAR define the bases of the DNA loop Participate in chromosome assembly and structural maintenance

Human Molecular B (13 decks)

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