AQA A-level Biology - Topic 1B - DNA replication || 100%
VERIFIED QUESTIONS & ANSWERS!!
Why does DNA copy itself before replication takes place? correct answers So that each new
cell has the full amount of DNA
What method is used to replicate DNA? correct answers Semi-conservative replication
What is semi-conservative replication? correct answers When half of the strands in each new
DNA molecule are from the original DNA molecule
Describe the process of semi-conservative replication correct answers 1)The enzyme DNA
helicase breaks the hydrogen bonds between the bases of the two polynucleotide strands,
separating them
2)Each original strand acts as a template for the new strand. Complimentary base pairing
means that free floating DNA nucleotides are attracted to their complimentary exposed bases
on each template strand
3)Condensation reactions join the nucleotides together- catalysed by the enzyme DNA
polymerase. Hydrogen bonds form
4)Each new DNA molecule contains one strand of original and one strand of new DNA
What is different about the ends of the DNA? What are they called? correct answers Each end
of the DNA is slightly different in its structure
One end is the 'three prime' and the other 'five prime'. They are antiparallel to eachother
Why is it helpful to have antiparallel strands? correct answers The active site of DNA
polymerase is only complimentary to the 3' end, so it can only add nucleotides to that end.
This means the new strand is made in a 5' to 3' direction and DNA polymerase moves into a
3' to 5' direction.
Who provided evidence for semi-conservative replication? correct answers Meselson and
Stahl
What would have the results of the experiment by Meselson and stahl shown is it was
conservative replication? correct answers It would have shown that the original DNA strands
would have stayed together, and the new DNA molecule would contain two new strands
What did Meselson and Stahl use in the experiment? correct answers They used two isotopes
of nitrogen- heavy nitrogen and light nitrogen.
Describe the experiment that Meselson and Stahl carried out? correct answers 1)Two samples
of bacteria were grown, one in light nitrogen, and the other in heavy. The bacteria gradually
took up the isotopes to help it grow
2)A sample of DNA was taken from each , and spun in a centrifuge. The DNA from the
heavy nitrogen settled lower than the light nitrogen
3)Both the bacteria sample grown in heavy nitrogen was put in light. They were left for one
round of replication, then another sample was taken and centrifuged
VERIFIED QUESTIONS & ANSWERS!!
Why does DNA copy itself before replication takes place? correct answers So that each new
cell has the full amount of DNA
What method is used to replicate DNA? correct answers Semi-conservative replication
What is semi-conservative replication? correct answers When half of the strands in each new
DNA molecule are from the original DNA molecule
Describe the process of semi-conservative replication correct answers 1)The enzyme DNA
helicase breaks the hydrogen bonds between the bases of the two polynucleotide strands,
separating them
2)Each original strand acts as a template for the new strand. Complimentary base pairing
means that free floating DNA nucleotides are attracted to their complimentary exposed bases
on each template strand
3)Condensation reactions join the nucleotides together- catalysed by the enzyme DNA
polymerase. Hydrogen bonds form
4)Each new DNA molecule contains one strand of original and one strand of new DNA
What is different about the ends of the DNA? What are they called? correct answers Each end
of the DNA is slightly different in its structure
One end is the 'three prime' and the other 'five prime'. They are antiparallel to eachother
Why is it helpful to have antiparallel strands? correct answers The active site of DNA
polymerase is only complimentary to the 3' end, so it can only add nucleotides to that end.
This means the new strand is made in a 5' to 3' direction and DNA polymerase moves into a
3' to 5' direction.
Who provided evidence for semi-conservative replication? correct answers Meselson and
Stahl
What would have the results of the experiment by Meselson and stahl shown is it was
conservative replication? correct answers It would have shown that the original DNA strands
would have stayed together, and the new DNA molecule would contain two new strands
What did Meselson and Stahl use in the experiment? correct answers They used two isotopes
of nitrogen- heavy nitrogen and light nitrogen.
Describe the experiment that Meselson and Stahl carried out? correct answers 1)Two samples
of bacteria were grown, one in light nitrogen, and the other in heavy. The bacteria gradually
took up the isotopes to help it grow
2)A sample of DNA was taken from each , and spun in a centrifuge. The DNA from the
heavy nitrogen settled lower than the light nitrogen
3)Both the bacteria sample grown in heavy nitrogen was put in light. They were left for one
round of replication, then another sample was taken and centrifuged
