RR11

Question 1

What are 3 critical RNAs in protein synthesis?

Answer 1

• tRNA
• rRNA (80% of total cellular RNA)
• mRNA

Question 2

How are pre-rRNA transcription units arranged?

Answer 2

In repetitive clusters, creating a membraneless nucleolus, this is where rRNA is made

Question 3

What are th differences between bacterial ribosome and eukaryotic ribosome?

Answer 3

• In bacteria, 23S,16S and 50S give rise to two structires, coming together to form a complete 70S ribosome
• In eukaryotes, 60S and 40S come together to make 80S ribosome, eukaryotes have an additional RNA in it’s large subunit

Question 4

Explain rRNA structure and how it is highly conserved?

Answer 4

• Folds into conserved stem-loops
  we see that is in eukaryotes and prokaryotes, indicating how this structure is critical

Question 5

Explain the processing of pre-tRNAs and how they “prepare” for translation

Answer 5

1) 5’ sequence is removed
2) Section of sequene is removed form loop
3) CCA is added to 3’ end
4) Modification of internal bases

The anticodon is critical for decoding of mRNA

Question 6

What are aminoacyl-tRNA synthetases

Answer 6

Bind/charge tRNA to correct amino acid
Bind 2 substrates by froming ester bond between carboxy on a.a. and hydroxyl on tRNA nucleotide

Question 7

What does it mean for codes to be “degenerate”?

Answer 7

• Amino acid can bind to more than one unique tRNA
• A single tRNA can bind to more than one single codon
• tRNAs will be bound to their amino acid and charged to be used in protein synthesis
  Several codes can result in same thing

Question 8

What are the two type of tRNAmet?

Answer 8

• Initiator tRNAmet (tRNAimet) - ONLY for initiation of polypeptide chain
• Normal tRNAmet - used whenever methionine comes up

Question 9

How do we distinguish the two types of tRNAmet?

Answer 9

• In prokaryotes, tRNAimet has a formyl group to show it’s an initiatior
• In eukaryotes, tRNAimet is structurally different - binds to P site specifically

Question 10

Explain the assembly of the pre-initiation complex in translation - what is the name of the complex created?

Answer 10

• EIF2 aids in binding of GTP with tRNAmet
• Complex binds to small ribosomal subunit, also bound by other initiation factors (creates 43S pre-initiation complex)

Question 11

How does tRNAimet and EIF2 react to bad conditions?

Answer 11

• Bad conditions cause phosphorylation that blocks EIF2 from tRNAmet, blocking synthesis

Question 12

What do we need for efficient translational initiation of mRNA?

Answer 12

Need a 5’cap - enhances synthesis
- specifically, a 7mGDPcap is related to increased translational efficiency, but no correlation with uncapped transcripts

Question 13

What does eIF4 in general do?

Answer 13

• Interacts with cap, bringing down whole complex to 5’ end of an mRNA to be translated
• too much eIF4 causes protein overexpression, which is associated with tumour formation
• eIF4g brings small ribosomal subunit to where it needs to work, and forms a loop (pre-initiation complex +eIF4 with mRNA)

Question 14

What does eIF4B do?

Answer 14

Works to enhance eIF4 activity

Question 15

What does eIF4A do?

Answer 15

Works as an RNA helicase

Question 16

What does eIF4E do?

Answer 16

Binds the 5’ cap of mRNA

Question 17

What does eIF4G do?

Answer 17

binds PAPBC and eIF3

Question 18

What is the scanning complex - what does it do?

Answer 18

eIFs + 40S and 80S ribosomes, and tRNA (including tRNAimet) make up the structure
It moves along mRNA, and first stops when it reaches the start codon

Question 19

When happens when we get to the start codon?

Answer 19

• Instantaneously - we get the 48S initiation complex (as soon as scanning complex hits AUG)
• This changes the conformational change that permits association of large subunit
• All other initiation factors are released - 80S ribosome
• tRNAimet stays interacting with AUG in the Psite, leaving the A site vacant