Week 9 - The regulation of gene translation

Question 1

Why is it important to control translation

Answer 1

Protein synthesis through DNA translation requires a large proportion of energy hence it must be tightly regulated to ensure that the proteins were synthesized correctly

Question 2

What is the rate limiting step in translation

Answer 2

the binding to the mRNA (translation initiation)

Question 3

What are the processes which regulate gene transcription

Answer 3

1. Regulation of Transcription
2. mRNA turnover
3. Translation initiation
4. Protein degradation

Question 4

What is the difference between eukaryotic and prokaryotic mRNA turnover

Answer 4

The half-life of bacterial mRNAs is typically a few minutes = less translational regulation

The half-life of eukaryotic mRNAs is usually several hours = more translational regulation

Question 5

Why does prokaryotes have a short mRNA half life while eukaryotes have a longer one

Answer 5

bacteria living in highly unstable and constantly changing environments where as the cellular environment of eukaryotes are very stable as its regulated by homeostasis.

Question 6

What molecules degrade mRNA

Answer 6

• miRNA (microRNA)
  -siRNA (small interfering RNA)

Question 7

What is miRNA made up of

Answer 7

• single stranded RNA
• pairing nucleotides don’t need to be perfectly complementary to mRNA

Question 8

How do miRNA degrade mRNA

Answer 8

miRNAs bind to a specific sequence at the 3’ end of their target mRNA to signal mRNA degradation and to repression translation from occuring

Question 9

What is siRNA comprised of

Answer 9

• double stranded RNA (from 1 RNA strand or 2)
• binds perfectly to its mRNA
• requires binding to the RISC complex

Question 10

How does siRNA silence mRNA

Answer 10

1. An endoribonuclease named Dicer binds to the double stranded RNA and claves (cuts) it into smaller fragments, some of which become siRNA.
   2.Additional proteins combine to form RNA induced silencing complex (RISC)
2. RISC binds to specific mRNAs by complementary binding the mRNA which will then be degraded and thus translation inhibited.

Question 11

How does translation initiation regulate gene translation

Answer 11

Involves the sites along the mRNA which contain binding sites for proteins which can promote but usually inhibit translation

Question 12

How does post translational modification occur

Answer 12

Ubiquitin = addition of ubiquitin (Ub) to target proteins

Question 13

Explain the process of ubiquitin

Answer 13

1. Ubiquitin tags are added to a target protein by ubiquitin ligase (ubiquination)
2. Proteasomes take in the tagged proteins and cut them up into pieces

Question 14

What are methods of post translational modification/regulation

Answer 14

• ubiquitination
• phosphorylation
• methylation
• acetylation