Bio 4 - Protein Synthesis

Question 1

What composes the 3’ end of a tRNA molecule?

Answer 1

A Hydroxyl group, ending with the sequence CCA.

Question 2

At which part of the tRNA does Aminoacyl tRNA synthetase work in order to “charge” the tRNA?

Answer 2

It works at the 3’ end.

Question 3

Where do tRNA and mRNA come together to build polypeptides?

Answer 3

In the ribosome.

Question 4

Where are ribosomes synthesized?

Answer 4

Ribosomal subunits are made in the nucleus, then transported into the cytoplasm.

Question 5

What are the 2 subunits of ribosomes in Eukaryotes?

Answer 5

60S and 40S. They come together to form 80S ribosome.

Question 6

What are the 2 subunits of ribosomes in Prokaryotes?

Answer 6

50S and 30S to form 70S ribosomes. Inside the 50S subunit, there is a 23S part.

Question 7

What are the 3 phases of protein synthesis inside the ribosome?

Answer 7

Initiation, elongation, termination.

Question 8

Describe initiation in the protein synthesis step in Prokaryotes.

Answer 8

Begins with initiation factor 2 (IF-2). It binds to 30S, then binds to methionine tRNA (the one with a start codon). Then 50S comes, hydrolyzes the GTP on the IF-2, releasing energy to attach to the 30S, kicking the IF-2 and combining to make a 70S. Lastly, the tRNA with methionine (start codon) attaches to the P site.

Question 9

What are the 3 sites of the ribosome complex where the tRNA can combine?

Answer 9

A site (where incoming aminoacyl tRNA binds), P site (where the polypeptide tRNA binds, where the growing polypeptide chain is found), E site (where the now empty tRNA is moved so it can exit the ribosomal unit). The fist tRNA (the one containing the start codon) is in the P site.

Question 10

Describe the elongation process in protein synthesis in the ribosome.

Answer 10

The tRNA containing the next codon binds to the A site with the help of the Elongation factors (EF). Then, Peptidyltransferase, fond in the 50S, transfer the peptide that is bound to tRNA in the P site, to the peptide that is attached to the tRNA in the A site. Then translocation happens (shifts both tRNAs into the next sites). The empty tRNA that is now in the E site gets kicked off.

Question 11

What is the elongation factor found in prokaryotes?

Answer 11

Elongation facto G.

Question 12

What is the elongation factor found in eukaryotes?

Answer 12

Elongation factor 2.

Question 13

Which bacteria toxins inhibit Elongation factor 2?

Answer 13

Diphtheria toxin. Exotoxin A.

Question 14

Describe termination process in protein synthesis in ribosomes.

Answer 14

Once it reaches a Stop codon (UAG,UAA, or UGA) in the mRNA sequence, a protein called Release Factor, binds to the stop codon, hydrolyzing GTP, releasing the polypeptide chain and the ribosome complex falls apart.

Question 15

How do aminoglycosides work?

Answer 15

It binds to the 30S ribosomes, so it can inhibit bacterial protein synthesis before initiation.

Question 16

How does Linezolid work?

Answer 16

Binds to 50S before initiation.

Question 17

How does Chloramphenicol work?

Answer 17

It binds to the 50S that inhibits the peptidyltransferase part, the 23s rRNA.

Question 18

How do macrolides (Erythromycin, Azithromycin) work?

Answer 18

They bind to the 50S, inhibiting the Translocation step.

Question 19

How does Clindamycin work?

Answer 19

Binds to the 50S, inhibiting the Translocation step.

Question 20

How does Lincomycin work?

Answer 20

Binds to the 50S, inhibiting the Translocation step.

Question 21

How does Streptogramins work?

Answer 21

Binds to the 50S, inhibiting the Translocation step.

Question 22

What are the 6 antibiotics that target the 50s subunit?

Answer 22

Chloramphenicol. Linezolid. Macrolides. Clindamycin. Lincomycin. Streptogramins.

Question 23

What are the 2 antibiotics that target 30S subunit?

Answer 23

Tetracyclines. Aminoglycosides.

Question 24

How do tetracyclines work?

Answer 24

Bind to the 30S, after 50s has been bound, preventing tRNA getting into the A site.

Question 25

What are the Post-translational modifications that can occur?

Answer 25

Trimming (N-terminal or C-terminal). Covalent modification (Glycosylation, Hydroxylation, Phosphorylation).

Question 26

What does it mean when they refer to the primary structure of the polypeptide?

Answer 26

The specific sequence of amino acids.

Question 27

What does it mean when they refer to the secondary structure of the polypeptide?

Answer 27

When they fold into alpha helix or beta pleated sheets.

Question 28

What extracellular proteins do Fibroblasts make?

Answer 28

Collagen. Fibrillin. Elastin.

Question 29

What extracellular proteins do Hepatocytes make?

Answer 29

Albumin. Hormone binding globulin. Ferritin. Haptoglobin. Coagulation factors. Fibrinogen.

Question 30

What extracellular proteins do Plasma cells make?

Answer 30

Immunoglobulins.

Question 31

What enzyme matches amino acids to tRNA?

Answer 31

Aminoacyl-tRNA synthetase.

Question 32

Which antibiotics target 30S? Which ones target 50S?

Answer 32

[buy AT 30, CCELLS at 50]
Aminoglycosides, Tetracyclines target 30S. Chloramphenicol, Clindamycin, Erythromycin (macrolides), Lincomyzin, Linezolid, Streptogramins target 50.

Question 33

What do we need to attach to each tRNA in order to start building polypeptides?

Answer 33

We need to attach an amino acid to each tRNA molecule, AKA “Charge the tRNA”, done by Aminoacyl tRNA synthetase (requires ATP).