Translation/Post Translational Modifications

Question 1

Translation steps (3)

Answer 1

1.) Initiation
2.) Elongation
3.) Termination

Question 2

Initiation

Answer 2

Translation begins when mRNA binds with tRNA methionine (Start Codon)
Occurs at P-site

Question 3

Elongation
What is it?
What are the three steps of Elongation?

Answer 3

AA’s added to the C-terminus of growing peptide chain @ P-site

1.) Codon recognition
P-Site
2.) Peptide bond formation
Single AA @ A-Site; polypeptide chain @ P-Site forms a peptide bond with single AA at A-site
->entire polypeptide chain transfers to A-site upon bond formation.
3.) Translocation
empty tRNA moved to E site (exit site)
A site tRNA moves to p-site
Ribosome ready for next amino acyl tRNA

Question 4

Termination

Answer 4

1.) Elongation continues until stop codon in mRNA reaches A site
2.) Release factor promotes hydrolysis
3.) Ribosomal subunits/ other components dissociate

Question 5

Clicker:

During a normal translation cycle, where would you expect to find a
tRNA attached to a single amino acid?

Answer 5

A-Site

*Unless its methionine (start codon) tRNA attached to a single AA attaches to A-Site

Question 6

Clicker
Translate the following mRNA strand into protein.
Ensure you label the directionality of the polypeptide.

5’-AUG CUA AGU UUU GCA UGA-3’

Answer 6

N-MLSFA-C
UGA = Stop codon, so its not included in peptide chain

Question 7

Polyribosomes

Answer 7

mass produced polypeptide that synthesize single mRNA simultaneously

-> Important because mRNA is short lived in the cytoplasm (faster degradation compared to DNA due to hydroxyl group at C-3 instead of C-2)-> Greater steric hindrance: Less stable

Question 8

Clicker!
Consider the following two peptides:

Protein A
N-Met-Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val-Leu-Leu-Phe-Phe-C
Protein B
N-Met-Leu-Leu-Phe-Phe-Lys-Asp-Glu-Leu-C

How many codons comprised the mRNA molecules that were translated
into Protein A and B?

A. A = 13, B = 9
B. A = 14, B = 10
C. A = 12, B = 8
D. A = 15, B = 11

Answer 8

B.) A=14, B=10
(remember to count stop codons even though they aren’t visible in peptide sequence!)

Question 9

Where does polypeptide synthesis begin?

Answer 9

Cytosol (liquid of the cell membrane)

Question 10

Post-Translational Modifications (PTMs)

Answer 10

Chemical changes that occur after the protein has been produced

-alters protein conformation

Question 11

What is NOT a post-translational modification (PTM) of a protein?

a.) Glycosylation
b.) Phosphorylation
c.) Dephosphorylation
d.) Degradation
e.) Methylation

Answer 11

d.) degradation