DNA and RNA

Question 1

What is the role of DNA?

Answer 1

Stores genetic information

Question 2

What is the role of RNA?

Answer 2

Transfers genetic info from DNA to ribosomes

Question 3

What are ribosomes made out of?

Answer 3

RNA and proteins

Question 4

What monomer are DNA and RNA made from?

Answer 4

Nucleotides

Question 5

Give the structure of a DNA nucleotide:

Answer 5

Phosphate group, deoxyribose, nitrogen-containing bases (adenine, thymine, cytosine and guanine)

Question 6

Give the structure of an RNA molecule:

Answer 6

Phosphate group, ribose, nitrogen-containing bases (adenine, uracil, cytosine, guanine)

Question 7

What reaction between 2 nucleotides forms what bond?

Answer 7

A condensation reaction between 2 nucleotides forms a phosphodiester bond

Question 8

Describe the structure of DNA:

Answer 8

A double helix with two polynucleotide chains held by hydrogen bonds between specific complementary base pairs.

Question 9

Is RNA longer or shorter than DNA?

Answer 9

Shorter

Question 10

Why did scientists doubt that DNA held genetic code?

Answer 10

Because of it’s relatively simple composition.

Question 11

Which scientists discovered the structure of DNA?

Answer 11

Watson and Crick

Question 12

Name 4 differences between DNA and RNA:

Answer 12

1. RNA is single-stranded whereas DNA is double-stranded.
2. An RNA nucleotide contains a ribose sugar whereas a DNA nucleotide contains a deoxyribose sugar.
3. DNA contains thymine but RNA contains Uracil.
4. RNA is relatively short whereas DNA is long.

Question 13

Why does DNA replicate?

Answer 13

So that each new cell has the full amount of DNA.

Question 14

Why is it called semi-conservative replication?

Answer 14

Because half of the strands in each new DNA molecule are from the original DNA molecule.

This means there’s genetic continuity between generations of cells.

Question 15

How is DNA replicated?

Answer 15

1. DNA Helicase breaks hydrogen bonds between the complementary base pairs on the two DNA strands. Helix unwinds into 2 strands.
2. Strands act as template strands. Free-floating nucleotides are attracted to exposed complementary bases.
3. Condensation reactions join nucleotides together catalysed by DNA polymerase. Hydrogen bonds form between complementary base pairs.

Question 16

During DNA replication, which end is DNA polymerase complementary to?

Answer 16

3’ (3 prime) so can only add nucleotides to the new strand from the 3’ end.

Question 17

Which direction is the new strand made in?

Answer 17

5’ to 3’ direction

Question 18

Why does DNA polymerase on one template strand work in the opposite way to another on the opposite strand?

Answer 18

Because the strands in the double helix are antiparallel

Question 19

What evidence is there for semi-conservative replication?

Answer 19

Meselson and Stahl’s experiment:

1. 2 samples of bacteria grown - one in light nitrogen and one in heavy nitrogen.
2. Sample of DNA spun in centrifuge. Heavy nitrogen DNA settled lower because it’s heavier.
3. Bacteria from heavy put in light. Another sample in centrifuge.
4. If conservative, heavy DNA would still be together.
5. If semi-conservative, settle between.
6. Bacteria settled in middle.