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BIOCHEMISTRY > Chromosome, DNA replication and gene expression in eukaryotes > Flashcards

Chromosome, DNA replication and gene expression in eukaryotes Flashcards

1
Q

What is chromatin?

A

DNA condensed and wrap around Histones

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2
Q

How many different types of Histones are there?

A

4

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3
Q

What is nucleosome?

A

complex when DNA wrapped around octamer of histones

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4
Q

What is structure of chromatin?

A

helical array of 6 nucleosomes per turn of helix

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5
Q

What is 4 stages of eukaryotic cell cycle?

A

1) S phase- DNA synthesis and replication
2) G2- synthesis of proteins for mitosis
3) Mitosis (PMAT)
3) G1- check DNA, protein/ Organelles made

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6
Q

What is PMAT?

A

1) prophase
2) Metaphase
3) Anaphase
4) Telophase

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7
Q

How are eukaryote chromosomes replicated?

A

G rich end of chromosome called Telomeres

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8
Q

Where is eukaryote chromosome replication observed?

A

In lagging strand where okazaki fragments

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9
Q

What is telomerase?

A

a reverse transcriptase, makes DNA from RNA template

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10
Q

What are stages of chromosome telomere replication?

A

1) RNA primer removed from 5’ end of lagging strand
2) Telomerase bind to overhanging DNA and adds Bases
3) telomerase moves down from 5’ to 3’ end of single strand dna
4) primase and ligase synthesise lagging strand in 5’ to 3’

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11
Q

What is telomerase complementary to?

A

G rich section of telomere

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12
Q

When does telomerase operate?

A

foetal development
sperm/egg cells
cancer cells
not found in somatic body cells

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13
Q

What is overall transcription/translation in eukaryotes?

A

Transcription in nucleus then mRNA out into cytoplasm to ribosome

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14
Q

What is eukaryote start signal?

A

AUG binded to anticodon on tRNA with Methionine

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15
Q

Do eukaryotes have initiation factors?

A

yes

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16
Q

how many RNA polymerases for eukaryotic transcription?

A

3 RNA POLYMERASES (1-3)

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17
Q

What are promoter sequences in eukaryotic transcript./

A

DNA region that initiate it e.g CAAT and GC box

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18
Q

What is the initiation sequence for RNA polymerase 2?

A

TATA box

19
Q

What is needed for transcription initiation?

A

promoter sequence

Transcription factors

20
Q

What does RNA polymerase do??

A

mRNA synthesis

21
Q

What is the basal transcription factor

A

CTD= all basal factors + DNA polymerase2 TAT complex

22
Q

What can basal factors do?

A

need to be activated to inc/decrease rate of transcription

23
Q

What regulates gene expression?

A

Chromatin remodelling
Enhancers
Modification

24
Q

What is chromatin remodelling

A

acylate or deacylated histones

25
Q

What does histone acetyltransferase do? (HAT)

A

acetylate histones so make DNA more accessible to transcription factors so incr. transcription

26
Q

What does Histone deacetylase (HDAC) do?

A

deacetylates histones so strengthen DNA with histones so down regulate transcription

27
Q

What do enhancers do?

A

short sequence DNA that cause transcription

28
Q

What do enhancers bind to?

A

activators then co activators attached to transcriptional factor

29
Q

What is DNA modification?

A

DNA methylation- methyl added to DNA

30
Q

How is DNA methylated ?

A

via DNA methyltransferase

31
Q

What is gene splicing?

A

mRNA introns removed (non coding) , interferon proteins don’t contain introns

32
Q

What does gene splicing involve?

A

snRNPs (Small Nuclear Ribonucleoprotein)

33
Q

What do several snRNPs form?

A

spliceosome

34
Q

Splicing mechanism steps?

A
  • 2 snRNP bind to 5’ and 3’ site separately
  • then preassembled 3rd, 4th, 5th snRNP complex bind to intron region and cleave it from exons
  • spliceosome falls and exons now joined
35
Q

What are splicing defects?

A

mutation of 1 base in intron so new 3’ splice site

36
Q

What’s an example of splice defect?

A

Thalessemia blood disorder- red blood cell abnormlaity

37
Q

What is alternative splicing?

A

protein diversity as protein spliced in several ways to create isoforms of protein

38
Q

Is alternative splicing in prokaryotes?

A

no

39
Q

What are post transcriptional modifications of mRNA?

A

5’ CAP

Poly A tail at 3’ end

40
Q

What is the addition of 5’cap and 3’ poly A tail for?

A

protect mRNA from degradation by ribonucleases

41
Q

What does 5’ cap do?

A

stabilise mRNA so transported out of nucleus

42
Q

What does 3’ Poly A tail do?

A
  • buffer for exonucleases
  • stabilise mRNA
  • enhance translation
  • determines half life of mRNA
43
Q

how is 3’ poly tail added?

A

cleavage signal

- poly A polymerase added adenine nucleotides

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