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Biomed > BB1720 DNA packaging > Flashcards

BB1720 DNA packaging Flashcards

1
Q

How much DNA is in a human cell?

A

6 billion base pairs
0.6 billion turns
each turn is 3.4nm
= 2m

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2
Q

How is DNA packaged in the cell?

A
  • by histones/non histone chromosomal proteins that bind and fold DNA
  • occurs in chromosomes
  • nucleosomes begin the process
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3
Q

What do histones do?

A

short regions of DNA wrap around histones to form chromatin

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4
Q

role of non histone proteins?

A

support DNA structure

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5
Q

what is a chromosome?

A

long linear DNA molecule associated with proteins

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6
Q

how is a nucleosome formed?

A

when 8 separate histone protein sub units attach to the DNA molecule
functional unit of DNA packaging

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7
Q

which proteins are involved in the formation of the nucleosome?

A

102-135 amino acids that interact with DNA
2x H2A, H2B, H3 and H4

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8
Q

what is the difference between H2A H2B H3 and H4?

A

H2A, H2B, H3 and H4 form the octamer
they are part of a histone family
similar structures and amino acid sequences
varients of histones with roles in gene regulation

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9
Q

How much and how far does DNA wrap around the histone?

A

146bp
1.65x

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10
Q

How does the nucleosome form the chromosome?

A
  • adjacent nucleosomes connect via spacer DNA
  • histone 1 attaches and stacks two nucleosomes to form a chromatosome
  • DNA wraps around the histone and compresses the structure
  • the string of beads coil and nucleosomes stack to form a chromatin fibre
  • chromatin fibre is condensed and folded by addition of scaffold proteins
  • all join and form a mitotic chromosome
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11
Q

How are chromosomes in non dividing cells organised?

A
  • very fine and tangled
  • DNA packed in folded chromatin fibres
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12
Q

how does the cell access tightly packed DNA to make proteins?

A
  • scaffold proteins
  • 30nm chromatin loop fibre attaches to central scaffold
  • similar loop and scaffold structures occur in interphase but not visible
  • lampbrush chromosomes
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13
Q

what are lampbrush chromosomes?

A
  • transcriptionally active chromosomes found in the germinal vesicle of large oocytes of many animals
  • the cells are in prophase of first meiotic division
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14
Q

what happens to chromosomes after DNA replication?

A

more condensed

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15
Q

non dividing cells in interphase

A

certain insects have visible chromosomes during interphase

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16
Q

what does it mean if there is a break in dna pattern

A

translation and trascription are occuring

17
Q

what are the different types of chromatin in interphase?

A

euchromatin
heterochromatin

18
Q

features of euchromatin?

A

less condensed
doesnt strongly stain
major genes involved in transcription
unmodified by enzymes

19
Q

features of heterochromatin?

A

highly condensed
visible by light microscope in eukaryotes
gene activity suppressed
modified by enzymes

20
Q

where are chromosomes contained in eukaryotes

A

the nucleus

21
Q

what happens to chromosomes during interphase?

A

highly organised
regulated

22
Q

why is the rate of transcription lower in the presence of histones?

A

machinary cannot access DNA

23
Q

why are chromosomes not visible during interphase?

A

cell has a relaxed structure
no access to cell

24
Q

How many types of histone molecules are commonly found in eukaryotic cells?

A

5

25
Q

which charge amino acids do histones contain?

A

Histones have a high content of positively charged amino acids.

26
Q

what is the association of DNA and histone is mainly mediated by?

A

hydrogen bonds

27
Q

whats the features of histone H1 DNA packaging

A

H1 binding gives nucleosome a defined angle
H1 binds to two DNA helices at once
H1 induces compaction (“30 nm fibre”)
H1 stabilises higher-order chromatin structures

28
Q

what is the state of chromosomes in interphase cells?

A

not highly compacted and are clearly visible

29
Q

Transcription and other aspects of nucleic acid metabolism are?

A

active in euchromatin
repressed in heterochromatin

30
Q

A picture in which all of the homologous chromosomes of an organism have been stained and organised is called?

A

karyogram

31
Q

how are chromosomes in the nucleus are highly organised?

A

all chromosomes are in defined locations in the nucleus

32
Q

what is a core nucleosome is composed of?

A

two copies each of histone H2A, H2B, H3 and H4 and 146 bp of DNA

33
Q

how does in vitro, the rate of transcription from DNA differ depending on histones?

A

is lower when histones are present than when histones are absent

Biomed (57 decks)

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