Composition of DNA

Question 1

Trait

Answer 1

An observable characteristic of an organism.

Question 2

Phenotype

Answer 2

May refer to a single trait or more commonly a group of traits.

Question 3

Genotype

Answer 3

The genetic make up of a cell

Question 4

What is DNA made up of?

Answer 4

Nitrogen-containing bases: purines and pyrimidines

Question 5

Functions of nucleotides

Answer 5

• Hydrolytic removal of the terminal phosphatase can release energy.
• Can also act as carriers of other chemical groups
• Can act as signalling molecules (cyclic AMP)

Question 6

Watson-Crick double helix structure

Answer 6

• Double stranded, right-handed, antiparallel helix
• Two anti-parallel helical chains coil around a common axis
• Sugar-phosphate “backbone” runs on outside, bases inside
• Bases lie perpendicular to common axis
• Bases on inside form hydrogen bonds

Question 7

Chargaff’s Rule

Answer 7

DNA from any species should a have a 1:1 stoichiometric ratio of pyrimidine and purine bases and, more specifically, that the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine

Question 8

If DNA helix not stable..

Answer 8

• Hydrogen bonds are relatively weak (5% of a covalent bond) and reversible.
• Increased flexibility of the double helix.
• Allows several cellular functions to occur, including DNA replication.

Question 9

Name the 3 types of double helix structures

Answer 9

• A-form right-handed
• B-form right-handed
• Z-form right-handed

Question 10

Difference between DNA and RNA

Answer 10

DNA: double helix, C.G.A.Thymine.
RNA: helix, C.G.A.Uracil

Question 11

Gene

Answer 11

A unit of inheritance that carries a characteristic from a parent to a child

Question 12

Genome

Answer 12

collective name given to all the genes of an organism

Question 13

Locus

Answer 13

position of a gene on a chromosome

Question 14

Chromosomes

Answer 14

discrete unit of the genome carrying many genes.

Question 15

Mutation

Answer 15

any change in a DNA sequence away from normal.
This implies there is a normal allele that is prevalent in the population and that the mutation changes this to a rare and abnormal variant.

Question 16

Polymorphism

Answer 16

a DNA sequence variation that is common in the population. In this case no single allele is regarded as the standard sequence.

Question 17

Substitution

Answer 17

One base is incorrectly added during replication and replaces the pair in the corresponding position on
the complementary strand

Question 18

Insertion

Answer 18

One or more extra nucleotides are inserted into replicating DNA, often resulting in a frameshift

Question 19

Deletion

Answer 19

One or more nucleotides is “skipped” during replication or otherwise excised, often resulting in a frameshift

Question 20

Name 3 point mutations that can occur in DNA

Answer 20

• Mutation
• Substitution
• Deletion