Lecture 7 - Protein Synthesis

Question 1

UTRs - Untranslated regions (4)

Answer 1

Do not code for anything.
5’ UTR determines the rate at which the protein is synthesised.
3’ UTR tends to affect the stability of the RNA (how long it stays in cell before degrading).
Together these UTR’s determine how much protein is made, as it determines the speed at which is made and the longevity of the message.

Question 2

Genetic code (3)

Answer 2

Triple codons = 64 codons = 20 amino acids.
Redundancy with more than one codon for the same amino acid (degenerate code).
Highly conserved.

Question 3

Ribosomes (4)

Answer 3

Made from rRNA and protein.
Protein synthesis occurs at cleft between large (60S) and small (40S) subunit = 80S.
40 S = 18S rRNA (1900 nucleotides) and 33 proteins.
60S = 5S, 5.8S and 28S (120, 160nd 4700 nucleotides and 49 proteins).
Formed in the initiation stage of protein synthesis.
Add 20 amino chains to polypeptide chain per second.

Question 4

Ribosomes can be found (2)

Answer 4

Free in cytosol.

Bound to ER.

Question 5

80S eukaryotic ribosome (3)

Answer 5

3 parts.
Exit.
Peptidyl binding site.
Aminoacyl tRNA binding site.

Question 6

RNA type

Answer 6

rRNA = 80-85%
tRNA = 10-15%
mRNA = 2-5%

Question 7

Bacterial ribosome (4)

Answer 7

Ribosome: 70 S.
Large/Small subunit: 50S & 30S.
Large subunit components: 23S & 5S RNA, 31 proteins.
Small subunit RNA: 16S, 21 proteins.

Question 8

Eukaryotic ribosome (4)

Answer 8

Ribosome: 80 S
Large/Small subunit: 60S & 40S.
Large subunit components: 28S, 5.8S & 5S RNA, 49 proteins.
Small subunit RNA: 18S, 33 proteins.

Question 9

Drugs/Cellular target in bacteria/Effect on protein synthesis (15)

Answer 9

Streptomycin - Small RS - Inhibition of initiation misreading of genetic code.
Tetracyclines - Small RS - Inhibition of aminoacyl tRNA binding to ribosome.
Chloramphenicol - Large RS - Inhibition of peptidyl transferase activity.
Erythromycin - Large RS - Inhibition of translocation.
Neomycins - Multiple sites - Several effects.

Question 10

Drug example for eukaryotic ribosome (2)

Answer 10

Cycloheximide – Inhibits eukaryotic ribosomes.

Question 11

Limitations of antibiotics on protein synthesis (2)

Answer 11

Antibiotics have no action on viruses (which use the hosts protein synthesis for viral replication).
Antibiotics are not given for viral infections due to bacterial resistance.

Question 12

How can bacteria develop drug resistance? (2)

Answer 12

Changing the ribosome (alteration of target site where antibiotics binds).
Destroying the antibiotic through enzymes (or converting to inactive form).

Question 13

Mitochondria and Ribosomes (3)

Answer 13

Mitochondria ribosomes are very similar to prokaryotic ribosomes.
Antibiotics that prevent bacterial protein synthesis will also have an impact on mitochondrial protein synthesis. So long term, antibiotics can impair energy production.

Question 14

Energetically expensive

Answer 14

Charging tRNAs with amino acids = 1 ATP/ aa.
Initiation of polypeptide synthesis = GTP + nATP.
Elongation of the polypeptide = 2GTP /aa.
Termination of polypeptide synthesis = GTP.