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micr335 section b > lecture 6 > Flashcards

lecture 6 Flashcards

1
Q

what is the function of ribosomes?

A

translation
- about 50,000 per cell (depending on the growth rate)

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2
Q

what is the average size of a bacterial protein?

A

~300 amino acids

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3
Q

is mRNA or the coded protein bigger?

A

mRNA

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4
Q

why do bacteria lack a membrane enclosed nucleus?

A

They have to respond to changes very quickly
- the ribosomes can readily access mRNA once it is made

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5
Q

what are the advanges to bacteria having no membrane enclosed nucleus?

A

-prevents accumulation of non-functional transcripts in the cytoplasm
- avoids the formation of RNA-DNA loops
- Regulation of transcription pausing by translation: gene regulatory mechanism

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6
Q

what is the structure of the bacterial ribosome?

A

a large multi protein complex (70S)
- two subunits; 30S (small), 50S (large)
RNA and protein

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7
Q

how is RNA stabilised?

A

by alot of small proteins

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8
Q

what is the difference between bacterial and mammalian ribosome structure?

A

mammalian ribosome is slightly larger

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9
Q

what are the steps involved in bacterial translation?

A
  • initiation
  • elongation
  • termination
  • recycling of the ribosomes
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10
Q

what stabilises RNA?

A

a lot of small proteins

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11
Q

what are the tRNA binding sites on the ribosome?

A

A, P, E

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12
Q

what is the function of the A tRNA binding site?

A

aminoacyl-tRNA enters the ribosome

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13
Q

what is the function of the P tRNA binding site?

A

hold tRNA carrying the nascent chain

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14
Q

what is the function of the E tRNA binding site?

A

tRNA dissociated from the ribosome

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15
Q

how is the ribosomes polysome arranged?

A

to avoid direct collision during elongation
- the ribosomes can communicate within the cell to stop them from bumping into each other

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16
Q

how is transcription regulated by the rate of translation?

A

Global rates of transcription and translation is influenced by nutrient availability and growth rate

  • transcription can be interruped by pauses
17
Q

what is direct coupling in transcription pausing?

A

an mRNA hairpin programed pause
- causes transcription to be paused of stoped

the hairpin is an mRNA secondary structure

18
Q

how is an mRNA hairpin pause releated?

A

by translation
- the ribosome pulls the mRNA from transcription and detangles to mRNA secondary structure (hairpin)

19
Q

how is bacterial transcription regulated by leader regions in direct coupling?

A

Charged tRNA is abundant
leads to
Rapid translation
leads to
Formation of a terminator loop

charged tRNA is deficient
leads to
Slow translation
leads to
Formation of an anti-terminator loop

20
Q

what is the structure of the Expressome?

A
  • ribosome and RNAP are bridged by dedicated transcription factors
  • NusG has domains specific for the two interactions
  • RNAP binds to the 30S head domain
  • RNAP Beta’ subunit zinc finger domain (ZF) is closest to the ribosome surface
  • NusA is rotated in expressome compared with paused elongating RNAP
21
Q

what is the expressome structure in situ with Cryo-ET imaging?

A

in-cell architecture of a transcripting and translating expressome: abundance, structural variability, mobility, functional analysis

22
Q

what are the effects of the drugs on the expressome?

A
  • translation inhibito
  • Transcription inhibitor
23
Q

how are ribosomes profiled?

A
  • deep sequencing of ribosome- protected mRNA fragments
  • Genome-wide investigation of translation
  • Monotoring protein translation in different conditions
24
Q

what is the function of tunning the synthesis of protein products?

A

majority of multiprotein complexes: a single polycistronic mRNA
- gene order does not explain differential synthesis rates
- synthesis rates are generally determined by the frequnecy of translation initiation

Proportional synthesis: tuning synthesis rates to the subunti stoichiometry (acheived through translational control (not transcriptional control)

25
Q

what is the function of most bacterial proteins?

A

dedicated to translation

26
Q

what is the relationship between transcription and translation?

A

Functionally coupled

27
Q

what tunes protein synthesis?

A

translational control

28
Q

what is the expressome?

A

A macromolecular structure

29
Q

what is the central dogma?

A

DNA->RNA->protein

30
Q

how is the bacterial genome compacted?

A

In a hierarchical manner

31
Q

what are responsible for dsDNA modelling?

A

Nucleosome associated proteins

32
Q

how is gene expression regulated?

A

in response to environmental conditions

33
Q

what steps in the gene expression pathway can be regulated?

A

All steps
- transcription initiation
- mRNA stability
- translation

34
Q

where is RNAP conserved?

A

RNAP general architecture and catalytic function is conserved across the three domains of life

35
Q

what are the steps in transcription?

A

Initiation, Elongation, Termination

36
Q

what is the function of sigma factors?

A

sigma factors are necessary for the recognition of promoters by RNAP holoenzyme

37
Q

what is sigma 70?

A

the housekeeping factor

38
Q

what are the alternative sigma factor families?

A

sigma70
sigma54

39
Q

at what level do activators and repressors work?

A

on a DNA level

micr335 section b (4 decks)

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