translation

Question 1

Name 6 Differences between eukaryotic and prokaryotic translation.

Answer 1

1. Eukaryotic 80S ribosome is bigger than prokaryotic 70S ribosome.
2. Eukaryotic mRNA usually encodes for just 1 protein, prokaryotic mRNA can potentially encode for more than 1.
3. Eukaryotic translation initiation begins at the 5’ cap since there is just one start site. Prokaryotic translation initiation begins at the start site following the Shine-Dalgarno sequence since there can be multiple start sites.
4. Eukaryotic first amino acid is Met, prokaryotic is fMet.
5. Eukaryotic mRNA forms a circle by having 5’ Cap connect to Poly(A) tail. Prokaryotic does not.
6. Eukaryotic translation only has 1 release factor. Prokaryotic has 2.

Question 2

Name the components of the prokaryotic ribosome.

Answer 2

1. Entire thing: 70S ribosome complex
2. Large subunit: 50S subunit made up of:
   
   1. 23S RNA - The peptidyl-transferase center is located here, which catalyzes teh formation of peptide bonds.
   2. 5S RNA
3. Small Subunit: 30S subunit
   
   1. 16S RNA: associates with the Shine-Dalgarno sequence, which moves the start codon and anti-codon into position with each other to begin protein synthesis.

Question 3

Name the components of the Eukaryotic ribosome

Answer 3

1. Whole thing: 80S ribosome complex
2. Large subunit: 60S subunit made up of:
   
   1. 5S RNA: homologous to prokaryotic 5S RNA
   2. 28S RNA: homologous to prokaryotic 23S RNA
   3. 5.8S RNA: homologous to 5’ end of prokaryotic 23S RNA.
3. Small Subunit: 40S subunit
   
   1. 18S RNA: homologous to 16S RNA in prokaryotes.

Question 4

Draw prokaryotic initiation

Answer 4

Question 5

Draw prokaryotic elongation

Answer 5

1. EF-Tu-GTP brings new aminoacyl-tRNA to A site
   
   1. leaves as EF-Tu-GDP and is regenerates by EF-Ts
2. Peptide bond formation
   
   1. old amino acid transfered to C side of new one on new tRNA
   2. catalized by Peptidyl transferase
3. Translocation of mRNA
   
   1. EF-G uses hydrolysis of GTP to move mRNA by 3 base pairs forward through ribosome
4. tRNA in exit site dissociates.

Question 6

Draw prokaryotic termination

Answer 6

Question 7

Name the prokaryotic release factors and their function

Answer 7

• RF1 - Recognizes UAA or UAG stop codons
  
  • catalyzes hydrolytic cleavage of ester linkage holding polypeptide chain to tRNA in P site.
• RF2 - Recognizes UAA or UGA stop codons
  
  • does same thing as RF1, just with different codon.
• RF3
  
  • catalyzes release of RF1 or RF2 from ribosome upon release of newly synthesized protein.
  • Ribosome Release factor (RRF)
  • causes dissociation of entire 70S complex.

Question 8

Name the Eukaryotic inititation factors and their function.

Answer 8

Initiation Factors

1. eIF-2
   
   1. associates with 40S ribosome and Met-tRNA_i to form the 43S preinititation complex (PIC).
2. eIF-4E
   
   1. Binds to 5’ cap of mRNA
   2. helps PIC bind to mRNA
   3. Linked by eIF-4G to PABPI to make mRNA circular.
3. eIF-4G
   
   1. Links eIF-4E to poly(A) binding protein I (PABPI) at the Poly(A) tail to make circular mRNA.

Question 9

Name the eukaryotic elongation factors and their function

Answer 9

• EF1-alpha - homologous to EF-Tu
  
  • delivers aminoacyl-tRNA to A site
• EF1-By (beta-gamma) - homologous to EF-Ts
  
  • catalyzes exchange of GTP for bound GDP
• EF2 - homologous to EF-G
  
  • mediates GTP-driven translocation, moving mRNA through ribosome.

Question 10

Name the eukaryotic release factors and their function

Answer 10

• eRF-1 - only 1 release factor for eukaryotes
  
  • binds to all stop codons.
• eRF-3
  
  • accelerates the activity of eRF-1

Question 11

Draw eukaryotic initiation

Answer 11

Question 12

Draw eukaryotic circularization

Answer 12

Question 13

Draw diagram of translation cycle in prokaryotes and eukaryotes

Answer 13