Transcription and Translation Flashcards by Celina MacLeod

What are the 4 types of RNA?

mRNA
rRNA
tRNA
ncRNA

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What is the structure and lifetime of mRNA?

Unstructured

Short-lived (minutes)

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What is the structure and lifetime of rRNA?

Highly structured

Long-lived

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What is the structure and lifetime of tRNA?

Identical structures

Long-lived

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What is the structure of tRNA?

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

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What is tRNA aminoacylation?

Amino acids are added based on the anticodon

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What is rRNA structure?

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

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What do most bacterial RNA polymerases have?

A core enzyme composed of 5 chains that catalyze RNA synthesis

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What are sigma factors?

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

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What is a holoenzyme?

A core enzyme + the sigma factor

Only the holoenzyme can begin transcription

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What do sigma factors do?

Help RNA polymerase bind to the promotor

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What is the promotor?

The site where RNA polymerase binds to initiate transcription

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Are promotors transcribed?

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

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What is the transcription bubble?

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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When does termination occur?

When core RNA polymerase dissociates from template DNA

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Where do DNA sequences mark the end of the gene?

In the trailer and the terminator

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What do some terminators require?

The rho factor for termination

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What are you left with after transcription?

Leaves you with free mRNA

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

What is a gene?

The basic unit of genetic information

What is a locus?

Position on a genome

What is a gene cluster?

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

What is an operon?

Cotranscribed

One mRNA for all the genes

How do you tell if something is an operon?

Through experimentation

What is a start codon?

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

What is a stop codon?

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

What is code degeneracy?

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

What is codon usage bias?

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

What is 3rd base pair wobble?

Loose base pairing in the 3rd position of the codon | Eliminates the need for unique tRNA for each codon

What are reading frames?

Specifies where the codons are | The ribosome binding site is always 6-7 bp upstream of the start of the codon

What is tRNA aminoacylation?

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

What are the steps of translation initiation?

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

What sites does an intact ribosome contain?

``` A site (amino acid) P site (peptide) E site (exit) ```

What is the elongation cycle?

Sequential addition of amino acids to growing peptide

What are the 3 phases of elongation?

Aminoacyl-tRNA binding Transpeptidation reaction Translocation

What does the peptidyl (P) site do?

Binds initiator tRNA or tRNA attached to the growing polypeptide

What does the aminoacyl (A) site do?

Binds incoming aminoacyl-tRNA

What does the exit (E) site do?

Briefly binds empty tRNA before it leaves ribosome

What is aminoacyl-tRNA binding?

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

What is transpeptidation?

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

What are the 3 simultaneous events in translocation?

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

What does translocation require?

Requires EF-G (translocase) and GTP hydrolysis

What is termination?

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

What are release factors?

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