5. DNA Replication

Question 1

Describe the process of DNA replication.

Answer 1

1. Hydrogen bonds between bases break and double helix unwinds
2. Free DNA nucleotides line up against their complementary bases on both strands and DNA polymerase links the adjacent nucleotides
3. Two identical daughter strands are produced, each one containing one original strand.

Question 2

What is the process of replication called?

Answer 2

semi-conservative

Question 3

How did Meselson and Stahl provide evidence for the semi-conservative model?

Answer 3

They grew bacteria in a growth medium containing only 15N, this made the DNA denser.
The bacteria were then put in a growth medium containing only 14N. The DNA was extracted and centrifuged.
the result was a single band of medium density DNA

Question 4

Which model could be rejected after the first replication which produced one band of medium DNA?

Answer 4

Conservative because it would have shown one heavy and one light band as one DNA molecule would have the original parent DNA (15N) and the other would have two new strands of 14N

Question 5

What results did another round of replication on 14N produce and which model did it support?

Answer 5

One band of medium and one band of light

supported the semi conservative model

Question 6

Why was the fragmentary model rejected?

Answer 6

If it were correct it would have produced a single band containing a mix of heavy and more light DNA

Question 7

What is a mutation?

Answer 7

A change in the gene sequence of DNA

Question 8

What are the 3 types of mutation?

Answer 8

Addition, subtraction and deletion

Question 9

What effect can a mutation have?

Answer 9

It can code for a different amino acid or a stop codon so the protein produced may be faulty

Question 10

How does a mutation cause sickle cell anaemia?

Answer 10

A substitution in one of the polypeptide chains in haemoglobin results in the wrong amino acid being added to the protein, valine rather than glutamic acid
It makes the haemoglobin less soluble.
The red blood cells become distorted and cannot carry as much oxygen and may block blood vessels.

Question 11

Define gene

Answer 11

a segment of DNA that codes for a certain characteristic

Question 12

Define locus

Answer 12

the position of a gene on a chromosome

Question 13

Define homologous chromosome

Answer 13

chromosome pairs, one from each parent, that are similar in length and locus

Question 14

Define alleles

Answer 14

different versions of the same gene

Question 15

Define dominant allele

Answer 15

phenotype is expressed if there is only one present

Question 16

Define recessive allele

Answer 16

phenotype only expressed if there is no dominant allele present

Question 17

Define heterozygous

Answer 17

two different alleles

Question 18

Define homozygous

Answer 18

two identical alleles

Question 19

Define carrier

Answer 19

Have one normal allele and one mutated allele but are not affected by the gene mutation

Question 20

Define genotype

Answer 20

the genes an individual has

Question 21

Define phenotype

Answer 21

characteristics expressed by the genotype