The Genetic Code

Question 1

What is the central dogma

Answer 1

DNA -> RNA -> Protein

Question 2

What was beadle & Tatum discovery, and explain

Answer 2

‘One gene, one enzyme’

• generated 3 mutants in a fungi
• mutants couldn’t grow without specific vitamins
• reproduced them sexually and offspring inherited mutations
• proved genes controlled biochemical reactions

Question 3

Explain how the tobacco mosaic virus proved codons don’t overlap

Answer 3

Tobacco mosaic virus

• treated it with nitrous acid, leading to a point mutation
• compared protein produced with normal protein
• mutant protein amino sequence contained a change in only one amino acid

Question 4

How did Crick, Barnett, Brenner and Watts-Tobin prove that codons are triplets

Answer 4

• used mutagens that insert or delete
• reverted the phage T4 point mutants with rounds of point mutagenesis
• observed that insertions could be reversed with deletions vice versa

Question 5

6 features of the genetic code

Answer 5

Continuous
No-overlapping
Degenerate
Unambiguous
Start and stop codons 
Universal

Question 6

Which direction do codons read in

Answer 6

5’ —> 3’ region

Question 7

What is the start codon

Answer 7

AUG

Question 8

What is the basic mRNA structure

Answer 8

5’ Untranslated region… ORF… 3’ untranslated region

Question 9

Why is the wobble effect allowed/ why does it work

Answer 9

The pairings are essential for secondary structure of many rNAs but some organisms do not have tRNA for all synonym codons

Question 10

What does it mean when you say mutations are either spontaneous or induced

Answer 10

Spontaneous = caused by replication errors 
Induced = caused by external agents eg chemical, physical or biological

Question 11

Name the types of point mutation

Answer 11

Substitution
Insertion
Deletion
Indel (deletion and insertion)

Question 12

What are the 2 base substitutions

Answer 12

Transition - replace purines with purines and pyramidine s with pyrimidines
Transversion - replaces purines with pyrimidines, vice versa

Question 13

Effect of missense mutations

Answer 13

Base change leads to codon for a different amino acid.

Can change protein 3D structure and function.

Question 14

Effect of nonsense mutation

Answer 14

Premature termination of a protein.
Terminal truncation.
Severe consequences to function.

Question 15

Effect of indels

Answer 15

They produce frame shift.
Adding or removing changes sequence of amino acids.
Leads to possible premature termination (terminal truncation)

Question 16

The 2 types of mutation types by lineage

Answer 16

Germ line mutations - transmitted to the offspring

Somatic mutations - arise in non-germ cells, not passed to offspring - lead to mosaicism