Key area 2- Structure & Replication of DNA

Question 1

What are DNA nucleotide’s made up of?

Answer 1

.Deoxyribose sugar
.Phosphate
.A base

Question 2

What are the complementary base pairs of DNA?

Answer 2

.Adenine
.Thymine
.Guanine
.Cytosine

Question 3

Where is the base and phosphate attached to on the deoxyribose sugar?

Answer 3

.It has a base attached to Carbon 1
.It has a phosphate attached to Carbon 5 and Carbon 3

Question 4

Why does DNA have a sugar-phosphate backbone?

Answer 4

. Because of the strong chemical bonds which form between the phosphate of one nucleotide and the carbon 3 of the deoxyribose on the next nucleotide

Question 5

How are the two DNA strands held together?

Answer 5

.By hydrogen bonds
.In an anti-parallel structure

Question 6

How are base pairs held together?

Answer 6

.By weak hydrogen bonds

Question 7

What structure does the two DNA strands have?

Answer 7

. It has an anti-parallel structure, which means the nucleotide strands run in opposite directions
. The strands coil into a double helix

Question 8

What does the base sequence of DNA form?

Answer 8

.The genetic code

Question 9

Before it can divide, what replicates DNA?

Answer 9

.DNA Polymerase

Question 10

What does DNA Polymerase need to start DNA replication?

Answer 10

.It needs a primer

Question 11

What is a primer?

Answer 11

.It is a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing polymerase to add DNA nucleotides

Question 12

What are the stages in DNA replication?

Answer 12

.DNA is unwound and hydrogen bonds between bases are broken to form two template strands
. One strand of the replication fork is a template for the leading strand and the other is the template for the lagging strand
.DNA polymerase can only add DNA nucleotides in one direction, through complementary base pairing, resulting in the leading strand being replicated continuously and the lagging strand being replicated in fragments

Question 13

What are the stages in the leading strand?

Answer 13

.The DNA template strand replicates and has the 3’ end is continuous and forms the leading strand
.The DNA primer, made of a short sequence of nucleotides, must be present to create an existing chain for the enzyme DNA polymerise to work on
.DNA polymerase adds DNA nucleotides using complementary base pairing to the deoxyribose, 3’, end of the new DNA strand which is forming
.DNA polymerase brings about the formation of the sugar-phosphate bonds between the primer and the nucleotides, and individual nucleotides at the 3’ end
.This results in the leading strand being replicated continuously

Question 14

What are the stages in the lagging strand?

Answer 14

.The DNA template strand replicates and has the 5’ end is discontinuous, as it has to be replicated in fragments starting with the 3’ end of a primer
.Each fragment has to be primed to allow DNA polymerase to bind nucleotides together
.A primer is a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing DNA polymerase to add DNA nucleotides
.Once replication of a fragment is complete, ligase enzyme joins the DNA fragments together to create the lagging strand of DNA

Question 15

What are the requirements for DNA Replication?

Answer 15

.DNA (to act as a template)
.Primers (to create an existing chain for DNA polymerase to work on)
.DNA nucleotides (Adenine, Thymine, Guanine & Cytosine)
.Enzymes (DNA polymerase, ligase)
.ATP (for energy)

Question 16

What does the Polymerase Chain Reaction (PCR) amplify?

Answer 16

It amplifies DNA using complementary primers for specific target sequences

Question 17

What are the primers that are used in PCR?

Answer 17

.They were short strands of DNA nucleotides which are complementary to specific target sequences at the two ends of the region of DNA to be amplified

Question 18

What is PCR?

Answer 18

.PCR involves repeated cycles of heating, to separate the strands. and cooling, so the primer binds, therefore the target region of DNA can be amplified

Question 19

What is heat-tolerant DNA Polymerase?

Answer 19

.It replicates the target region of DNA

Question 20

What are the stages of PCR?

Answer 20

.DNA is heated to between 92 & 98C- Hydrogen bonds between chains break and they separate into two strands
.Mixture is cooled to between 50 & 65C- Allows primers to bind to the target sequence
.Heated to between 70 & 80C for heat tolerant DNA polymerase to attach nucleotides- Heat tolerant DNA polymerase then replicates the target region of DNA
.Repeated cycles of heating and cooling amplify the target region of DNA

Question 21

What is PCR used for?

Answer 21

.Help solve crime scenes
.Settle paternity cases
.Archaeology
.Testing food
.Diagnose genetic disorders (by screening a cell sample from a patient for the presence or absence of a particular sequence)