Lecture 15 Flashcards

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1
Q

Discovery of mRNA

A

DNA is in the nucleus

protein synthesis occurs in ribosomes, in the cytoplasm

ribosomes have RNA and protein

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2
Q

Difficulties of perspective

A

some proposals: DNA were 3D structural moulds for protein synthesis

ribosomes were gene-specific, specificity conferred by RNA

genetic code was not yet determined

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3
Q

Brenner, Jacob and Meselson

A

used again the T4/E coli infection system,

T4 infection means the injection of phage DNA and synthesis of phage proteins to produce new viral particles

it was known that a burst in RNA production occurred shortly after infection but what was that RNA. A structural component for new gene-specific ribosomes or messenger

They labelled all E coli ribosomes with 15N and 13C

the infected with T4 and removed 15N and 13C from the medium

so ribosomes assembled before infection were heavy, new ribosomes were light

then they added 32p to label newly synthesised RNA and saw to which ribosomes it went

new RNA goes to pre-existing ribosomes to make protein

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4
Q

RNA polymerase

A

pries DNA strands apart
reads sequence by base-pairing
uses the base uracil instead of thymine
polymerises ribonucleotides 5’–>3’
does not need a primer
is a multiprotein gene

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5
Q

Promoter

A

DNA sequence where RNA polymerised binds

it directs the initiation of transcription

can overlap a few tens of nucleotides with the transcription unit

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6
Q

Transcription unit

A

DNA sequence that is copied into RNA

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7
Q

Terminator

A

DNA sequence that signals for the RNA polymerse to detach from DNA

directs the termination of transcription

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8
Q

Initiation of transcription

A

RNA polymerase starts at the promoter

As RNA polymerase moves along the DNA it untwists the double helix 10 20 bases at a time

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9
Q

Elongation of transcription

A

5’–>3’
transcription progresses at a rate of around 60nt/s in E coli

a gene can be transcribed simultaneously by several RNA polymerase

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10
Q

Termination of transcription

A

the mechanisms of termination are different in bacteria and eukaryotes

in bacteria the polymer stops transcription at the end of the terminator region and the mRNA can be translated without further modification

splicing in eukaryotes

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11
Q

Regulation of gene expression

A

proteins fulfil many functions- some are needed all the time but some should only be used when necessary

therefore genes need to be turned on and off again
- positive and negative regulation

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12
Q
A
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13
Q
A
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14
Q
A
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15
Q

Brenner, Jacob and Meselson

A

used the T4/E coli infection system

it was known that a burst in RNA production occurred shortly after infection

they labelled all E coli ribosomes with 15N and 13C

then infected with T4 and removed 15N and 13C from the medium

so ribosomes assembled before infection were heavy but after were light

they added 32P to level newly synthesised RNA, and saw to which ribosomes went

new RNA goes to pre-existing ribosomes

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16
Q

T4 infection

A

T4 infection means the injection of phage DNA and synthesis of phage proteins to produce new viral particles

17
Q

RNA polymerase as an RNA synthesis catalyst

A
  • pries DNA strands apart
  • reads sequence by base pairing
  • uses uracil
  • polymerises ribonucleotides 5’->3’
  • does not need a primer
  • it is a multi protein complex
18
Q

Promoter

A

DNA sequence where RNA polymerase binds

it directs the initiation of transcription

can overlap a few tens of nucleotides with the transcription unit

19
Q

transcription unit

A

DNA sequence that is copied into RNA

19
Q

terminator

A

DNA sequence that signals for the RNA polymerase to detach from DNA

directs the termination of transcription

19
Q

initiation of transcription

A

RNA polymerase starts at the promoter
as RNA polymerase moves along the DNA it untwists the double helix 10-20 bases at a time

19
Q

Termination of transcription

A

the mechanism of termination are different in bacteria and eukaryotes

in bacteria- polymerase stops transcription at the end of the terminator and mRNA can be translated without further modification

19
Q

Elongation of transcription

A

5’–>3’
transcription progresses at a rate of around 60nt/s in E coli

A gene can be transcribed simultaneously by several RNA polymerases

19
Q

Regulation of gene expression

A

proteins fulfil many functions- some are needed all the time but some should only be used when necessary

therefore genes need to be turned on and off again
- positive and negative regulation
it starts at the first step: transcription

20
Q

The PaJaMo experiment

A

they were wondering about how the synthesis of beta galactosidase was inducible by the presence of lactose

they considered two mutants
-lacZ (cannot synthesis any BG)
-lacI: cannot present the synthesis of low levels of BG in absence of lactose

20
Q

How can you go from constitutive to inducible synthesis?

A

they decided to look at the kinetics of beta gal synthesis
- for that they need to create cells that had no beta-galactosidase in them and then initiate both beta-gal function and lacI function

  • used bacterial conjugation (DNA exchange between bacterial cells) to follow trait inheritance
20
Q

PaJaMo experiment
- strains

A

F+ harbouring the F factor and sensitive to both streptomycin and phage T6

F- can act as a receptor during conjugation, resistant to both Sm and T6

21
Q
A
22
Q
A