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Microbiology 265 > Transcription and Translation > Flashcards

Transcription and Translation Flashcards

1
Q

What are the 4 types of RNA?

A

mRNA
rRNA
tRNA
ncRNA

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2
Q

What is the structure and lifetime of mRNA?

A

Unstructured

Short-lived (minutes)

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3
Q

What is the structure and lifetime of rRNA?

A

Highly structured

Long-lived

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4
Q

What is the structure and lifetime of tRNA?

A

Identical structures

Long-lived

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5
Q

What is the structure of tRNA?

A

They are identical structures
There is an amino acid attachment site
Anti-codon

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6
Q

What is tRNA aminoacylation?

A

Amino acids are added based on the anticodon

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7
Q

What is rRNA structure?

A

70s structure to 30s and 50s
30s structure to 16s
50s structure to 23s and 5s

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8
Q

What do most bacterial RNA polymerases have?

A

A core enzyme composed of 5 chains that catalyze RNA synthesis

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9
Q

What are sigma factors?

A

Have no catalytic activity but help the core enzyme recognize the start of genes

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10
Q

What is a holoenzyme?

A

A core enzyme + the sigma factor

Only the holoenzyme can begin transcription

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11
Q

What do sigma factors do?

A

Help RNA polymerase bind to the promotor

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12
Q

What is the promotor?

A

The site where RNA polymerase binds to initiate transcription

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13
Q

Are promotors transcribed?

A

No

They have specific sequences before the transcription starting point and a Pribnow box which contains consensus sequence

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14
Q

What is the transcription bubble?

A

Moves with the polymerase as it transcribes mRNA from the template strand
Within the bubble a temporary RNA:DNA hybrid is formed

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15
Q

When does termination occur?

A

When core RNA polymerase dissociates from template DNA

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16
Q

Where do DNA sequences mark the end of the gene?

A

In the trailer and the terminator

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17
Q

What do some terminators require?

A

The rho factor for termination

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18
Q

What are you left with after transcription?

A

Leaves you with free mRNA

19
Q

Are there 5’ caps or long poly-A tails in bacteria?

A

No

20
Q

What is a gene?

A

The basic unit of genetic information

21
Q

What is a locus?

A

Position on a genome

22
Q

What is a gene cluster?

A

Cluster of gene encoding proteins involved in the biosynthesis of one structure

23
Q

What is an operon?

A

Cotranscribed

One mRNA for all the genes

24
Q

How do you tell if something is an operon?

A

Through experimentation

25
Q

What is a start codon?

A

Start site for translation
Begins with DNA sequence 3’-TAC-5’
Produces codon AUG

26
Q

What is a stop codon?

A

Coding region ends with a stop codon
UAA, UAG, UGA
Do not encode amino acids

27
Q

What is code degeneracy?

A

Up to 6 different codons can code for a single amino acid

28
Q

What is codon usage bias?

A

There are fewer tRNAs in the tRNA pool for some codons which slows down translations at these sites

29
Q

What is 3rd base pair wobble?

A

Loose base pairing in the 3rd position of the codon

Eliminates the need for unique tRNA for each codon

30
Q

What are reading frames?

A

Specifies where the codons are

The ribosome binding site is always 6-7 bp upstream of the start of the codon

31
Q

What is tRNA aminoacylation?

A

Amino acids are added based on the anticodon
Attached via the carboxyl group
Requires ATP hydrolysis

32
Q

What are the steps of translation initiation?

A
  1. Binding of mRNA to 30S subunit
  2. Binding of initiator tRNA to complex
  3. Hydrolysis of GTP by initiation factors to bring 50S subunit
33
Q

What sites does an intact ribosome contain?

A 
A site (amino acid)
P site (peptide)
E site (exit)
34
Q

What is the elongation cycle?

A

Sequential addition of amino acids to growing peptide

35
Q

What are the 3 phases of elongation?

A

Aminoacyl-tRNA binding
Transpeptidation reaction
Translocation

36
Q

What does the peptidyl (P) site do?

A

Binds initiator tRNA or tRNA attached to the growing polypeptide

37
Q

What does the aminoacyl (A) site do?

A

Binds incoming aminoacyl-tRNA

38
Q

What does the exit (E) site do?

A

Briefly binds empty tRNA before it leaves ribosome

39
Q

What is aminoacyl-tRNA binding?

A

Aminoacyl-tRNA enters the ribosome
Based on codon
Requires EF-Tu and GTP hydrolysis

40
Q

What is transpeptidation?

A

Formation of the peptide bond
Catalyzed by peptidyl transferase activity of 23S rRNA
Amino groups on the A site amino acid performs a nucleophilic attack on the carboxyl group of the C-terminal amino acid on the P site of tRNA

41
Q

What are the 3 simultaneous events in translocation?

A

Peptidyl-tRNA moves from A site to P site
The ribosome moves down one codon
Empty tRNA moves to E site and dissociates

42
Q

What does translocation require?

A

Requires EF-G (translocase) and GTP hydrolysis

43
Q

What is termination?

A

Takes place at any of the 3 nonsense codons
Has release factors
Requires GTP hydrolysis
Ribosome dissociates into 30S and 50S components

44
Q

What are release factors?

A

Aid in recognition of stop codons
3 RFs function in prokaryotes
Only 1 RF active in eukaryotes

Microbiology 265 (26 decks)

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