Ribosomes and Protein Synthesis

Question 1

What signals for protein synthesis on RNA

Answer 1

AUG start codon

UAG stop

Question 2

Molecules involved in Ribosome binding mRNA

Answer 2

cap binding complex on mRNA:
-recruits ribosome
Initiation factors:
-escorts small subunits of RNA AND...
Met-tRNA

Question 3

eIF4E Cap Binding Complex

Answer 3

• made of EIF:A, G,E
• recruits ribosome
• unwinds 2ndary RNA structure
• LIMITING SUBUNIT.

Question 4

Describe EIF E , A, and G

Answer 4

E: limiting subunit. binds to M7G-Cap (elevated in cancers)

A: helicase

G: scaffolding, binds to PABP

Question 5

EIFE and weak RNA

Answer 5

EIFE is necessary to protect “ weak” RNA so it can be translated

-Often targeted

Question 6

Strong RNA vs Weak RNA

Answer 6

Strong: less secondary structure

Weak: high secondary structure, relies on EIFE
–>involved in promoting cancer

Question 7

3 Ribosomal Assembly sites:

Answer 7

A: Aminoacyl tRNA Site -tRNA waits to be translated here. tRNA’s anti-codon is reading codon on mRNA

P: Peptidyl Site -(translation site) peptydyl tRNA is currently being translated

E: Exit site, tRNA that was in P site is now here naked before leaving

Question 8

Why is the 3’ end of tRNA important? Modified bases?

Answer 8

It is the acceptor site where a 3’ ester bond is formed between the tRNA and Amino Acid.

this 3’ Ester bond btwn tRNA and AA is later used to create peptide bond

Modified bases: these are how Ribosome recognizes it

Question 9

eIF2

Answer 9

escorts met-tRNA to ribosome

leaves once AUG is recognized, combining large and small subunit, and elongation commences

Question 10

eIF1 and eif3

Answer 10

binds ribosomal small unit and interact with cap binding complex to bring ribosome to mRNA

Question 11

How is AUG recognized?

Answer 11

16s rRNA in small subunit recognize specific conserved sequence (kozak) before AUG

Question 12

PABP

Answer 12

poly A binding protein binds to EIF G and improves translation (ONLY IN EUKARYOTES)

Question 13

EF2

Answer 13

G-protein that hydrolyzes one GTP to move Ribosome down one codon

-Inhibited by Diptheria and Exotoxin A

Question 14

EF1

Answer 14

escorts tRNA with amino acids to A site

Question 15

RF (release factor)

Answer 15

Binds to A site. Causes tRNA to release protein. Encourages ribosome to disassemble.

Question 16

What happens when proteins accumulate in ER?

Answer 16

PERK phosporylates eIF2 (what brings met tRNA to connect cap and ribo small subunit). Stops protein synthesis except for stress response proteins (like for apoptosis)

OR

eIF4E is inhibited by 4E-BP

Question 17

microRNA Translation regulation

Answer 17

Post-transcriptional gene silencing (PTGS):

21-22 nucleotide noncoding RNAS
-Regulate gene expression and/or destabilize target mRNAs

• -> does this by basepairing with target mRNAS.
• Brings in RISC ->complex that leads to mRNA degredation (very specific)
• how to target specific genes!