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SL12002 - Cell Biology > Lecture 5 - Translation > Flashcards

Lecture 5 - Translation Flashcards

1
Q

What does Degenerate code mean

A

Multiple codons encode for the same amino acid

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2
Q

What is the only start codon in Eukaryotes

A

Methionine AUG

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3
Q

What do prokaryotes also use as start codons alongside methionine

A

GUG and UUG

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4
Q

What are the 3 kinds of RNA

A

mRNA,
rRNA,
tRNA

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5
Q

How is Ribosomal RNA processed

A

Synthesised by pol I

Not translated into protein

Processed by cleavage and chemical modifications into final form

Packaged with proteins in the nucleolus

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6
Q

What is snoRNAs

A

Small nucleolar RNA
60-300 nucleotides
Involved in processing rRNA
Many come from introns of protein-coding genes

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7
Q

What is tRNA

A

RNA with complex secondary structure
Transcribed by RNA pol III
Anticodons bind to mRNA codons
Charged with 1 AA each

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8
Q

What is aminoacylation

A

Aminoacylation is a two-step process in which amino acids are first activated by ATP, forming an intermediate aminoacyl adenylate, and then transferred to the 3′-end of tRNA to form the aminoacyl-tRNA end-product by ARS (Aminoacyl-tRNA synthetases)

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9
Q

What is the translation pre-initiation complex

A

Met-tRNA binds small ribosomal subunit

With eIF2 (eukaryotic initiation factor 2) + GTP

40S complex (S = sedimentation coefficient)

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10
Q

Describe the process for mRNA binding to 40S complex

A

eIF4 proteins binds the mRNA cap

mRNA folded on itself through interaction between polyA tail binding protein and eIF4 complex

eIF4 complex binds to eIF2 in the 40S subunit

43S complex

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11
Q

How is the large ribosomal subunit recruited

A

ATP hydrolysis powers scanning

GTP hydrolysis leads to release of eIF proteins and binding of Met-tRNA to large subunit

Met-tRNA is in the middle of three tRNA binding pockets

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12
Q

What are the Large ribosomal subunit tRNA binding sites

A

A site - Aminoacyl-tRNA
P site - Peptidyl-tRNA
E site - empty or exit

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13
Q

What is EF1(alpha)

A

aa-tRNA binds its codon to A site, then EF1alpha

Elongation factor 1 alpha is powered by GTP hydrolysis

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14
Q

How does conformational change occur in translation

A

GTP hydrolysis brings amino acids together

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15
Q

Describe transpeptidation

A

Ribozyme catalyses formation of the peptide bond between two amino acids

Peptidyl transferase transfers the peptide onto the growing chain

Amino acid dissociates from tRNA in the P site

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16
Q

Describe translocation in translation

A

tRNA with polypeptide chain moves into P site

Empty tRNA moves into the E site and is released

Powered by GTP hydrolysis - breaking the bond between 2nd and 3rd phosphate group of GTP –> GDP

17
Q

Describe how termination occur

A

Release factor protein complex binds a STOP codon (eRF1 subunit)

No more peptide bonds can be formed

GTP hydrolysis (eRF3 subunit) –> complex falls apart, releasing the new polypeptide

18
Q

What is wobble base-pairing

A

Base pairing is loose in the third position of tRNA-mRNA interaction

Accounts for redundancy in last letter of codons in genetic code on 5’ wobble position on tRNA (3’ mRNA)

19
Q

What is a neutral or silent mutation

A

does not affect protein sequence

20
Q

What is a neutral amino acid substitution

A

change does not affect protein function

21
Q

What is a Ribonucleoprotein

A

RNA + protein complexes

22
Q

What is a brief summary of translation

A

tRNAs are ‘charged’ with one amino acid each

tRNA anticodon bind mRNA codon

Met-tRNA is initiator

Translation PIC = Met-tRNA, eIF2, GTP, small ribosomal subunit

eIF4 complex brings mRNA to PIC

Large ribosomal subunit arrives last

Conformational changes driven by energy from GTP hydrolysis moves tRNA through A, P, and E sites

rRNA ribozyme catalyses peptide bonds in ribosome

eRF1 binds STOP codon, terminates polypeptide chain

Polyribosomes in the cytosol or tethered to ER

SL12002 - Cell Biology (13 decks)

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