The genetic code and RNA in translation

Question 1

Why should the genetic code be studied (in terms of vaccines)?

Answer 1

Traditional vaccines take years to develop as they require growing weakened viruses.

mRNA vaccines are created in record time using principles of genetic code.

Question 2

Describe the process of 2020 COVID-19 pandemic vaccine creating.

Answer 2

SARS-CoV-2 carries genetic instructions in the form of RNA so scientists rapidly sequenced viral RNA to identify part of the code for the viruses spike protein.

Used universal genetic code to create synthetic mRNA.

Question 3

What happened when mRNA was injected into a person’s body?

Answer 3

Entered cells and was translated so ribosomes produced the viral spike protein.

Spike protein is detected by the immune system and antibodies are produced against the virus.

Question 4

What happens when a person now comes into contact with the actual virus?

Answer 4

Antibodies stop virus replicating by binding to it.

Question 5

In 1961, Leslie Barnett, Francis Crick, Sydney Brenner and Richard Tobin wrote a paper on how the genetic code was deciphered.

Describe the experiment they did.

Answer 5

Background information:
Bacteriophage T4 infects E.coli.
A mutation in the r2 region of the bacteriophage genome makes large, distinctive plaques compared to normal (wild type) bacteriophage plaques.

Experiment:
Proflavin (planar molecule) intercalates (slides in) between the DNA base pairs to insert a single extra base or delete a single base.
Brought mutations together by recombination (exchange of genetic material between different bacteriophages).

Crick’s frame shift mutants:
No mutation = not mutant
Insertion = mutant
Insertion and deletion = not mutant
Double insertion = mutant
Triple insertion = not mutant

Question 6

In 1968, what did Gobind Khorana win the Nobel Prize for?

Answer 6

Research showing order of nucleotides in nucleic acids carry genetic code of cell and control cell’s synthesis of proteins.

(First person to synthesise an artificial gene in the laboratory).

Question 7

Explain why the genetic code is degenerate.

Answer 7

More than one triplet codes for the same amino acid.

4^3 = 64 possible triplets if 3 nucleotides code for an amino acid

20 types of amino acids in proteins.

Question 8

Explain why the genetic code is non-overlapping.

Answer 8

Single base mutations only ever affect one amino acid, not the rest of the sequence.

Each triplet is read separately to the one before and after it.

Question 9

How is the genetic code of mRNA read?

Answer 9

In sets of 3 nucleotides = codons.

Question 10

In 1968 why did Marshall Nirenberg, Har Gobind and Robert Holley win the Nobel Prize?

Answer 10

Deciphered genetic code with biochemical experiments.

Holley = described tRNAs.

Question 11

Describe degeneracy in terms of tRNA.

Answer 11

Some amino acids have more than one tRNA.

Question 12

What is a stop codon? How many are there?

Answer 12

Halt protein synthesis in DNA and mRNA because they don’t code for amino acids.

3

Question 13

A single letter code for amino acids means protein sequences can be analysed digitally in…

Answer 13

bioinformatics

Question 14

Why is the genetic code nearly universal (the same codons code for the same amino acids in most living things)?

Answer 14

Many variations are known in mitochondria and some in nuclear genomes.

Question 15

What is the structure of tRNA?

Answer 15

A cloverleaf shape with an attached amino acid and anticodon loop.

Question 16

What is meant by the ‘wobble’ position?

Answer 16

Some tRNAs can tolerate a mismatch at the third codon position.

Question 17

What is the genetic code translated by?

Answer 17

Aminoacyl-tRNA synthetases and tRNAs.

Question 18

What does aminoacyl-tRNA synthetase do?

Answer 18

‘charging’ - helps join tRNA to amino acid

Question 19

Give the reaction that happens when a high energy bond is formed between tRNA and its amino acid.

Answer 19

ATP –> AMP + 2Pi

AMP = adenosine monophosphate

Question 20

Why is there a synthetase enzyme for each type of amino acid?

Answer 20

Due to (tRNA and) amino acids to fitting in active sites.

Question 21

Describe the structure of a ribosome.

Answer 21

Large complex of 4 RNAs and > 80 proteins:

Large subunit has a larger molecular weight = 2800000 g/mol and made of 49 proteins with 3 RNA molecules.

Small subunit has a smaller molecular weight = 1400000 g/mol and made of 33 proteins with 1 RNA molecule.

Question 22

What is the A-site of an aminoacyl-tRNA synthetase?

Answer 22

Aminoacyl-tRNA site (to accept incoming tRNA).

Question 23

What is the P-site of an aminoacyl-tRNA synthetase?

Answer 23

Peptidyl-tRNA site (holds tRNA linked to growing polypeptide chain).

Question 24

What is the E site of an of an aminoacyl-tRNA synthetase?

Answer 24

Exit site.

Question 25

Describe the process of initiation in translation.

Answer 25

mRNA binds to small ribosomal subunit with translation initiation factors and initiator tRNA bound.

Small ribosomal subunit moves along mRNA in search of AUG/GUG/UUG start codon.

Translation initiation factors dissociate and large ribosomal subunit binds.

Charged tRNA binds to a site and first peptide bond forms between Met and amino acid.

Question 26

Describe the process of elongation in translation.

Answer 26

Newly bound charged tRNA binds to next site and new peptide bond forms with previous amino acid.

Large subunit translocates (moves).

tRNA ejected and small subunit translocates.

Question 27

Draw the general structure of an amino acid.

Answer 27

Summary sheet.

Question 28

What is the N-terminus of a ploypeptide?

Answer 28

Free amine group at the end.

Question 29

What is the C-terminus of a polypeptide?

Answer 29

Free carboxyl group at the end.

Question 30

Describe the process of termination in translation.

Answer 30

Stop codon UAG/UAA/UGA reached.

Release factor binds to A-site.

(Water is required to) release polypeptide chain.

Ribosome dissociates and components disintegrate.

mRNA can be translated multiple times.