TOPIC 1B - MORE BIOLOGICAL MOLECULES

Question 1

Draw a nucleotide.

Answer 1

(see page 16 I. the revision guide for a diagram)

Question 2

What is the sugar in DNA and RNA called?

Answer 2

DNA - deoxyribose

RNA - ribose

Question 3

What are the four bases in DNA?

Answer 3

Adenine - Thymine

Cytosine - Guanine

Question 4

What are the four bases in RNA?

Answer 4

Adenine - Uracil

Cytosine - Guanine

Question 5

How many bonds are there between Adenine and Thymine?

Answer 5

Two bonds.

Question 6

How many bonds are there between Cytosine and Guanine?

Answer 6

Three bonds.

Question 7

What reaction do nucleotides join together by?

Answer 7

Nucleotides join together by a condensation reaction.
The bond forms between the phosphate group one nucleotide and the sugar of another.
- This forms an ester bond.
(see page 17 in the revision guide for a diagram)

Question 8

What is a phosphodiester bond?

Answer 8

It consists of a phosphate group and two ester bonds.

see page 17 in the revision guide for a diagram

Question 9

What is a sugar-phosphate backbone?

Answer 9

The chains of sugars and phosphates in DNA and RNA is known as the sugar-phosphate backbone.

Question 10

Describe the structure of DNA.

Answer 10

Two antiparallel polynucleotide strands twist to form the DNA double-helix.
(see page 17 in the revision guide for a diagram)

Question 11

Describe semi-conservative replication.

Answer 11

(see page 18 in the revision guide)

Question 12

Which way along the DNA strand does DNA polymerase move?

Answer 12

3’ to 5’

see page 18 in the revision guide for more information

Question 13

How did Meselson and Stahl provide evidence for semi-conservative replication?

Answer 13

(see page 19 in the revision guide)

Question 14

What are four main functions of water in relation to its importance in life?

Answer 14

1) Water is a metabolite in lots of metabolic reactions, including condensation and hydrolysis reactions.
2) Water is a solvent. Most metabolic reactions take place in a solution, so water is essential for this.
3) Water helps with temperature control because it has a high latent heat of vaporisation and a high specific heat capacity.
4) Water molecules are very cohesive which helps water transport in plants as well as transport in other organisms.

(see page 20 and 21 in the revision guide for a more in-depth description of these four main points)

Question 15

Describe the simple structure of water.

Answer 15

(see page 20 in the revision guide)

Question 16

Describe the structure of ATP

Answer 16

• Adenosine triphosphate

see page 22 in the revision guide

Question 17

How is ATP is quickly made and used?

Answer 17

(see page 22 in the revision guide for a diagram of the cycle)

Question 18

What is a cation and an anion?

Answer 18

Cation - an ion with a positive charge.

Anion - an ion with a negative charge.

Question 19

What is an inorganic ion?

Answer 19

An inorganic ion is an ion which does not contain a carbon atom.

Question 20

What is the role of iron ions in the body?

Answer 20

Iron ions are an important part of haemoglobin.

• Haemoglobin is a large protein that carries oxygen around the body, in the red blood cells.
• It is made up of four different polypeptide chains, each with and iron ion (Fe2+) in the centre.
• It is the Fe2+ that actually binds to the oxygen, the ion then becomes Fe3+ for a short while until oxygen is then released.

Question 21

What is the role of hydrogen ions in the body?

Answer 21

Hydrogen ions (H+) determine pH.

Question 22

What is the role of sodium ions in the body?

Answer 22

Sodium ions (Na+) help transport glucose and amino acids across membranes.
- A molecule of glucose or an amino acid can be transported into a cell alongside sodium ions. This is known as co-transport.

Question 23

What is the role of phosphate ions in the body?

Answer 23

Phosphate ions are an essential component of ATP and DNA.

• When a phosphate ion (PO4 3-) is attached to another molecule it is known as a phosphate group.
• DNA, RNA and ATP all contain phosphate groups.
• It is the bond between phosphate groups that store energy in ATP.
• The phosphate groups in DNA and RNA allow nucleotides to join up to form the polynucleotides.