Functions of DNA

Question 1

Which organelles contain DNA?

Answer 1

Small molecules of DNA can be found in chloroplasts and mitochondria.

Question 2

What are the two main functions of DNA?

Answer 2

Replication and protein synthesis.

Question 3

How does DNA synthesise proteins?

Answer 3

The sequence of the bases represent the information carried in the DNA and determine the sequence of amino acids and proteins. Proteins determine all the characteristics of an organism.

Question 4

How does DNA replicate?

Answer 4

DNA comprises of two complimentary strands where the base sequence of one strand is determined by the other one. If the strands in a double helix were to separate into two identical double helices each parent strand would act as a template for synthesis of a new strand. Replication allows accurate copying of DNA for cell division.

Question 5

What enzyme separates the double helix?

Answer 5

DNA Helicase

Question 6

What are the stages of DNA replication?

Answer 6

Firstly the double helix is unwinded by DNA helicase which breaks the hydrogen bonds found between the complimentary base pairs. Each strand is now a template for the new strands. Free DNA nucleotides bind to the template strands where the free nucleotides form hydrogen bonds with the complimentary base pairs on the template strand. DNA polymerase is responsible for this and the DNA strands rewind to form a double helix.

Question 7

What is it meant by the term semiconservative?

Answer 7

It is the mode of DNA replication in which each strand of the parental double helix acts as a template for the formation of a new molecule, each containing an original parental strand and a newly synthesised complimentary daughter strand.

Question 8

What must also replicate in order to receive the exact copy of genetic information?

Answer 8

Chromosomes where the replication must take place in the nucleus during interphase.

Question 9

What were the three possible methods for DNA replication?

Answer 9

Conservative, semiconservative and dispersive.

Question 10

What is the Conservative method for replication?

Answer 10

It is when the parental double helix remains intact i.e it is conserved and a whole new double helix is made.

Question 11

What is the semiconservative method for replication?

Answer 11

It’s when the parental double helix separates into two individual strands where each one acts as a template for the synthesis of a new strand.

Question 12

What is the dispersive method for DNA replication?

Answer 12

The two new double helices contain fragments from both strands of the parental double helix.

Question 13

What is the experiment called which proved semiconservative replication?

Answer 13

The Meselson – stahl experiment.

Question 14

What was the bacteria originally cultured in for several generations?

Answer 14

It was in a medium containing amino acids. made from heavy isotope 15N instead of the normal light isotope and 14N.

Question 15

What happened to the DNA after being in the medium of 15N?

Answer 15

Bacteria incorporated the 15N into their nucleotides and then into the DNA so eventually it only contained 15N.

Question 16

What happened to the DNA after it was centrifuged?

Answer 16

The DNA settled at low point of the tube as the 15N isotope made it heavy.

Question 17

Why was the 15N bacteria washed before being transferred into a medium containing 14N?

Answer 17

It prevented contamination between the two mediums and so that the 15N was not incorporated in any new strands.

Question 18

Where did the DNA settle after the first generation culture?

Answer 18

It had a midpoint density so settled in the middle of the test tube.

Question 19

Why was Conservative replication ruled out after the first generation?

Answer 19

As there would’ve been a band which showed the parental molecule being entirely heavy. The intermediate position could imply both semiconservative replication of the DNA or dispersive replication.

Question 20

Where did the DNA from the second generation grown in 14N settle in the tube?

Answer 20

It settled at the midpoint and highpoint of the tube.

Question 21

What did the high point and midpoint of the DNA show?

Answer 21

It showed that the sample had a midpoint of an intermediate density and the sample found at the high points contained only 14N.

Question 22

Why was dispersive replication ruled out at the second generation?

Answer 22

Dispersive replication would always have a mixture of light and heavy in every strand so only one band would form.

Question 23

Why does this prove semiconservative replication?

Answer 23

As one parent to strand is conserved so provides conclusive evidence for this hypothesis.