Molecular Genetics

Question 1

Describe the basic composition of a nucleotide.

Answer 1

pentose sugar, phosphate group and nitrogenous base.

Question 2

Name the key differences between an RNA and DNA nucleotide.

Answer 2

RNA nitrogenous bases include uracil in place of thymine.
pentose sugar is deoxyribose in DNA vs ribose in RNA

Question 3

What type of bond links nucleotides?

Answer 3

Phosphodiester.

Question 4

Describe the structure of the double helix.

Answer 4

Hydrophobic nitrogenous bases face internally, phosphate groups on the outside forming phosphate-sugar backbone, hydrogen bonding holds the two strands together.

Question 4

Define semi-conservative replication of DNA.

Answer 4

Each original strand is the template for a new strand (each new helix will contain one of the original strands).

Question 5

Explain the roles of the enzymes topoisomerase and helicase in DNA replication.

Answer 5

topoisomerase unwinds the double helix.
helicase unzips the double strand.

Question 6

Explain the roles of DNA polymerases and ligases in DNA replication.

Answer 6

DNA polymerase adds new complimentary bases to the DNA template strand.
DNA ligase links the nucleotides in the new strand together.

Question 7

Outline the 3 stages of a PCR.

Answer 7

1. Denaturing. Heat sample to 95C to break bonds in the double strand.
2. Annealing. Cool to ~60C allowing primers to bind to DNA.
3. Extension. Heat to 72C, optimal temp. for DNA polymerase (Taq).

Question 8

Which are spliced during transcription - introns or exons?

Answer 8

Introns.

Question 9

Transcription is..?

Answer 9

Synthesis of mRNA strand complimentary to a DNA template in the 5’ to 3’ direction.

Question 10

Translation is…?

Answer 10

Synthesis of a protein from mRNA code, using ribosomes and specialized RNA (ribosomal and transfer).

Question 11

Define point mutations.

Answer 11

A mutation (genetic polymorphism) in the genome in which 1 nucleotide is substituted.

Question 12

Explain how the different types of point mutations can have varying degrees of influence on the proteome.

Answer 12

Silent = no effect due to degenerate code.
Nonsense = no protein synthesised as new triplet becomes a stop codon that terminates translation.
Missense = different amino acid translated & incorporated into protein. Can be conservative (protein still functions as normal) or non-conservative (significant changes).

Question 13

Give one example of a known non-conservative missense mutation and explain its effects.

Answer 13

Sickle-cell anemia. Point mutation to DNA sequence for red blood cells causes haemoglobin structure to change. Originated in the Green Sahara 7,300ya.

Question 14

Organisms with duplicate numbers of chromosomes due to mutation are called?

Answer 14

Polyploidy.