Protien Synthesis

Question 1

What are ribosomes (ribonucleoprotein) composed of?

Answer 1

• rRNA

- Proteins

Question 2

What 2 populations of ribosomes are involved in protein synthesis?

Answer 2

• Bound to the endoplasmic reticulum

- Free within the cytosol

Question 3

Where on the ribosome does protein synthesis occur?

Answer 3

The cleft between the small and large subunit

Question 4

What is the most common RNA and why?

Answer 4

• ribosomal RNA

- As protien synthesis occurs rapidly, protein turnover occurs rapidly so the cell still needs lots of ribosomes

Question 5

What 2 subunits are mammalian ribosomes made of ?

Answer 5

40s and 60s = 80s ribosome

Question 6

What are the 2 subunits in prokaryotic RNA?

Answer 6

40s and 30s = 70s ribosome

Question 7

What is the site located on the LARGE subunit of mammalian ribosomes ?

Answer 7

P site = peptide binding site

Question 8

What is the site located on the SMALL subunit of mammilian ribosomes?

Answer 8

• E site = exit site

- A site = aminoacyl tRNA binding site

Question 9

What are the untranslated regions on mRNA (UTR)?

Answer 9

• Are found on the end of the coding region
• Can be 3’ or 5’
• Are coded by exons
• Mutations here can also cause genetic diseases

Question 10

Wha are the three stages of protein synthesis?

Answer 10

1. Initiation
2. Elongation
3. Termination

Question 11

What are initiation factors (EF+number)?

Answer 11

Are proteins that bind to a small subunit of ribosome during the initiation of translation - can also interact with depressors to slow down or prevent translation.

Question 12

What are elongation factors (ELF + number)?

Answer 12

Protiens that function at the ribosome to facilitate translational elongation from the first to last peptide bond of a growing polypeptide.

Question 13

Describe the process in initiation

Answer 13

1- multiple initiation factors bing to the cap and poly A tail of mRNA
2- one initiation factor binds to met-tRNAi
3- Small ribosomal subunit scans to find start codon - uses energy (ATP hydrolysis)
4- met-tRNA occupies p site
5- Large ribosomal subunit joins complex - processes is catalysed by release of energy from GTP and dissociation of some initiation factors
6- 2nd aminoacyl tRNA enters A site with elongation factor 1 (ELF1)
7- 1st peptide bond forms and 80s translocates

Question 14

Describe the steps involved in elongation of translation

Answer 14

1. Amino acid + ATP + tRNA = Aminoacyl tRNA + AMP + PPI
2. Amino acyl tRNA synthase forms tRNA
3. Aminoacyl tRNA binds to site A - where ELF1 and GTP hydrolysis occurs
4. Peptadile transferase causes the amino acid of the new tRNA molecule to form a peptide bond with the previous tRNA molecule amino acid
5. This causes the RNA small subunit to move forward one codon and allows the previous tRNA molecules to leave - a new tRNA binding site brines free and this binding site uses energy from GTP
6. Translocation hydrolysis EF2 and GTP - allowing the larger subunit to move one codon along - initiation of trannclation occurs many times.

Question 15

Describe the steps involved in termination of translation

Answer 15

1. A release factor binds to stop codon using GTP
2. Hydrolysis of terminal peptidyl tRNA and release of polypeptide chain
3. Ribosomes are reused

Question 16

What antibiotics are used on the large ribosomal subunit?

Answer 16

• Chloramphenicol inhibits peptidyl transferase activity

- Erythromycin inhibits translocation

Question 17

What antibiotics are used on the small ribosomal subunit?

Answer 17

• Streptomycin inhibits the initiation misreading genetic code
• Tetracyclines inhibits of tRNA molecules from binding to ribosome