Structure of RNA and DNA

Question 1

Function of DNA

Answer 1

Used to store genetic information, all the instructions needed to grow and develop from a fertilised egg to a fully grown adult.

Question 2

Function of RNA

Answer 2

One of the main functions is to transfer genetic information from the DNA to ribosomes.

Question 3

What are the 3 components of a nucleotide?

Answer 3

Pentose sugar, nitrogen-containing sugar organic base and a phosphate group.

Question 4

What is the sugar in DNA called?

Answer 4

Deoxyribose.

Question 5

What are the 4 bases of DNA?

Answer 5

Adenine (A), thymine (T), cytosine (C) and guanine (G).

Question 6

What is the sugar in RNA called?

Answer 6

Ribose.

Question 7

What are the 4 bases in RNA?

Answer 7

Adenine (A), Uracil (U), cytosine (C) and guanine (G).

Question 8

What is a polynucleotide? How are they formed? What is the bond formed by condensation reactions?

Answer 8

A polymer of nucleotides. They join up between the phosphate group of one nucleotide and the sugar of another. The bond formed is a phosphodiester bond.

Question 9

Wat is a chain of sugars and phosphates known as?

Answer 9

The sugar-phosphate backbone.

Question 10

How are two DNA strands joined together?

Answer 10

By hydrogen bonds between bases C and G or A and T due to complementary base pairings.

Question 11

How many hydrogen bonds form between the DNA bases?

Answer 11

A&T-2

C&G-3

Question 12

How are the two strands of a DNA molecule described?

Answer 12

Two antiparallel polynucleotide strands twisted to form a double-helix.

Question 13

Watson and Crick

Answer 13

They worked out the structure of DNA by looking at X-rays of the diffraction patterns of DNA.

Question 14

How does the structure of RNA differ from DNA?

Answer 14

It is made from a single strand of polynucleotide and is much shorter than most DNA strands. It contains base U instead of T.

Question 15

What is a purine and which bases are purines?

Answer 15

Composed of 2 carbon rings, A and G.

Question 16

What is a pyrimidine and which bases are pyrimidines?

Answer 16

Composed of 1 carbon ring, U, T and C.

Question 17

How and why is DNA stable?

Answer 17

The phosphodiester backbone protects the more chemically reactive bases inside. It is relatively stable as a molecule as it passes from generation to generation, only rarely with any changes.

Question 18

How is DNA adapted to its function?

Answer 18

• It’s stable so mutations happen rarely
• The 2 strands can separate allowing DNA replication
• The base pairings are protected inside the helix
• The base pairings of DNA lead to RNA being able to transfer information.

Question 19

Which carbon is which in a nucleotide?

Answer 19

3’ has a hydroxyl group and 5’ is attached to the phosphate.

Question 20

Why can nucleotides only be synthesised in the 5’-3’ direction?

Answer 20

The enzyme DNA polymerase (the enzyme that assembles nucleotides into a DNA molecule) can only attached nucleotides to the hydroxyl group of the 3’ carbon as the active site is complementary to this end.