Protein Synthesis

Question 1

Explain the flow of genetic info

Answer 1

Transcription -> Pre mRNA -> Capping / PolyA tail / Splicing -> Mature mRNA

Question 2

How does the cell know when to undergo translation?

Answer 2

mRNA is exported out the nucleus and recognised by the ribosome for translation

Question 3

Describe the structure of eukaryotic mRNA

Answer 3

5' capped end 
followed by 5' UTR 
Coding region in the middle 
3' UTR 
3' polyAdenylated tract

Question 4

What are the consequences of mRNA modification errors?

Answer 4

Protein is unable to leave the cell and is degraded

Question 5

What does the coding region consist of?

Answer 5

Exons

including the initiaton codon

Question 6

What is the initiation codon?

Answer 6

AUG methionine

Question 7

How many bases are read at a time by the ribosome?

Answer 7

3 bases / 1 codon

Question 8

How are the amino acids assembled at the ribosome?

Answer 8

Complementary anitcodon to mRNA codon on tRNA
Amino acids on 3’ end of tRNA
form peptide bonds

Question 9

What is the role of the 5’ UTR?

Answer 9

Determines rate of protein synthesis

Question 10

What is the significance of the 3’ UTR ?

Answer 10

Affects stability

Question 11

Explain what it means when we describe the genetic code as universal?

Answer 11

More than one codon can code for the same amino acid

Question 12

Describe the consequences of a transcription / translation error

Answer 12

Unable to fold protein correctly, structure changes = non functional

Question 13

What are ribosomes composed of?

Answer 13

rRNA and ribonucleoprotein complexes (protein)

Question 14

What are the 2 types of ribosome?

Answer 14

• ribosomes free in cytosol

- ribosomes bound to ER

Question 15

Where does protein synthesis occur?

Answer 15

At a cleft between a large and small ribosomal subunit

Question 16

At what rate does a ribosome add amino acids to form a

protein?

Answer 16

20 amino acids per second

Question 17

Why are so many ribosomes required?

Answer 17

To maintain high speed of translation to fulfill cells needs

Question 18

List the different types of RNA and their approximate % cellular abundance

Answer 18

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

Question 19

Which size ribosomal subunits do mamallian ribosomes consist of?

Answer 19

40s (small) and 60s (large)

Question 20

Collectively what size are mamallian ribosomes?

Answer 20

80s

Question 21

What are the 3 stages of translation?

Answer 21

1. Initiation
2. Elongation
3. Termination

Question 22

Describe in detail what occurs during Initiation of translation?

Answer 22

1. mRNA in cytoplasm
2. EiF1 and Eif3 bind to 40s subunit, separating it from 60s
3. EiF2 binds to tRNA
4. 40s binds to tRNA
5. EiF1,2, and 3 form 48 pre initiation complex
6. EiF4 binds to 5’ cap
7. Complex scans for AUG start codon
8. 60s joins 40s at start codon
9. All EiF’s are released

Question 23

Does protein synthesis require energy?

Answer 23

YES, it is energetically expensive

Question 24

How much energy is consumed during inititation?

Answer 24

2 GTP molecules and nATP

Question 25

Outline the Elongation process of translation

Answer 25

1. Initiator tRNA in P site 2. Complementary anticodon in A site 3. Due to close proximity of amino acids, peptide bonds form 4. Ribosome moves 1 codon along 5. Empty/used tRNA moves to E site and is released 6. Other tRNA (prev. in A site) moves to P site and holds chain 7. => peptidyl RNA

Question 26

How much energy does elongation of the polypeptide require?

Answer 26

2 GTP molecules and amino acids

Question 27

How does Termination of translation occur?

Answer 27

1. UAG stop codon in A site 2. No complementary anticodon to UAG stop codon 3. Release factor recognises stop codon 4. Hydrolysis of terminal peptidyl tRNA 5. Polypeptide released

Question 28

How much energy is required to charge tRNA molecules with amino acids?

Answer 28

1 ATP molecule each and amino acids

Question 29

What energy is used in termination of translation?

Answer 29

1 GTP molecule

Question 30

What is the size of prokaryotic ribosomes?

Answer 30

70s ribosomes | - 50s and 30s subunits

Question 31

Compare the differences in ribosomes between prokaryotes and eukaryotes

Answer 31

Prokaryotic - 23 and 5s large RNA subunits - 31 large subunit proteins - 16s small RNA subunits - 21 small subunit proteins Eukaryotic - 28, 5.8 and 5s large RNA subunits - 49 large subunit proteins - 18s small RNA subunits - 33 small subunit proteins

Question 32

How can the difference in ribosomes between prokaryotes and eukaryotes be beneficial to us?

Answer 32

Can use antibiotics to inhibit protein synthesis in bacterial ribosomes ONLY, to prevent disease

Question 33

Give an example of an antibiotic that targets bacterial protein synthesis

Answer 33

Streptomycin - inhibits initiation process in protien synthesis