Nucleic Acids, Water and Ions

Question 1

Name some nucleic acids

Answer 1

Deoxyribonucleic acid - DNA

Ribonucleic acid - RNA

Question 2

Role of DNA

Answer 2

stores genetic information in all living cells

Question 3

Role of RNA

Answer 3

Transfers genetic information from DNA to ribosomes in all living cells

Question 4

What are ribosomes formed of?

Answer 4

RNA and protein

Question 5

Structure of a general nucleotide

Answer 5

pentose sugar, nitrogen-containing organic base, phosphate group

Question 6

How do bonds form between nucleotides?

+ what type of bonds

Answer 6

Phosphodiester bonds form in condensation reactions, catalysed by DNA/RNA polymerase.

Question 7

DNA nucleotide structure vs RNA nucleotide structure

Answer 7

DNA - sugar is deoxyribose, bases are adenine, cytosine, guanine and uracil.
RNA - sugar is ribose and there is uracil instead of thymine as a base.

Question 8

Why didn’t scientists used to think DNA carried the genetic code? What did they think instead?

Answer 8

As DNA has a relatively simple structure.

They thought proteins, which are much more complex and varied in structure, carried the code instead.

Question 9

Why does DNA need to be replicated? What happens to the replicated DNA?

Answer 9

When a cell divides, one of each copy goes into each daughter cell. This ensures genetic continuity between generations of cells.

Question 10

What is the method of DNA replication?

Answer 10

semi-conservative method

Question 11

Process of DNA replication

Answer 11

1) The enzyme DNA helicase breaks the hydrogen bonds between complementary base pairs in the polynucleotide strands.
This causes the DNA double helix to unwind and the strands to separate.

2) Each strand acts as a template to form a new, complementary chain. Complementary free nucleotides attach to the exposed bases on the template strands via complementary base pairing - A to T and C to G. Hydrogen bonds form between complementary bases.
3) DNA polymerase catalyses the condensation reactions which join adjacent nucleotides of the new strands together.

Question 12

Describe semi-conservative DNA replication.

Answer 12

Each new DNA molecule contains 1 strands from the original DNA and 1 new strand. Each of the existing strands acts as a template in the formation of a new strand.

Question 13

Describe complementary base pairing in DNA.

Answer 13

Hydrogen bonds form between complementary base pairs - A with T and C with G.

Question 14

Describe the conservative theory of DNA replication.

Answer 14

Original DNA strands stay together and the new DNA molecules contain 2 new strands.

Question 15

What does ATP stand for?

Answer 15

adenosine triphosphate

Question 16

What does antiparallel mean wrt DNA structure?

Answer 16

the 2 strands of DNA in a molecule run in opposite directions.

Question 17

Why can DNA polymerase only add new DNA nucleotides to the 3’ end?

Answer 17

• DNA polymerase is an enzyme and has an active site with a specific tertiary structure which is only complementary to the 3’ end of a DNA molecule.
• DNA polymerase can therefore only bind and form ES complex with so add new nucleotides to the 3’ end.

Question 18

Structure of ATP

Answer 18

formed of ribose, adenine and 3 phosphate groups.

Question 19

What is ATP?

Answer 19

a nucleotide derivative which is the immediate energy source in a cell.

Question 20

ATP hydrolysis reaction

Answer 20

ATP + H2O ⇒ ADP + Pi

Question 21

ATP hydrolysis enzyme

Answer 21

ATP hydrolase

Question 22

How is ATP reformed?

Answer 22

In a condensation reaction between ATP and Pi, catalysed by ATP synthase during respiration or photosynthesis.
ADP + Pi ⇒ ATP + H2O

Question 23

Uses of ATP

in a cell, not processes

Answer 23

• The hydrolysis of ATP can be coupled to energy-requiring reactions within cells.
• The inorganic phosphate released during ATP hydrolysis can be used to phosphorylate other compounds and make them more reactive.

Question 24

Processes that require ATP

Answer 24

active transport, muscle contraction

Question 25

How is ATP suited to its role?

Answer 25

- Energy is released quickly, in a single-step reaction. - Energy is released in small, manageable quantities. - ATP can’t pass out of cells

Question 26

Important properties of water (6)

Answer 26

- Metabolite in many metabolic reactions such as condensation and hydrolysis. - A universal solvent, in which metabolic reactions occur. - Has a relatively high heat capacity, so buffers changes in temperature - a large amount of energy is required to raise the temperature of water. - Relatively large latent heat of vaporisation (energy needed to evaporate) so provides a cooling effect with little water loss through evaporation. (sweat evaporates and transfers energy from body to surroundings). - Strong cohesion between water molecules - means columns of water in tube-like transport systems such as the xylem can form. - Cohesion also produces surface tension where water meets air.

Question 27

Importance of the structure of water

Answer 27

It is a polar molecule with a partially positive and partially negative end - so water can form hydrogen bonds (strong IMB).

Question 28

Where are inorganic ions found in living organisms?

Answer 28

In cell cytoplasm and body fluids

Question 29

Name 4 ions which are important to living organisms.

Answer 29

Fe2+, H+, Na+, PO4 3-

Question 30

Why is Fe2+ important?

Answer 30

It is a component of haemoglobin - each of the 4 polypeptide chains contains an iron ion in its centre, which binds to oxygen and allows it to be carried around the body.

Question 31

Why is H+ important?

Answer 31

H+ concentration determines pH. pH = -log10[H+]. The higher the H+ concentration, the lower the H and the more acidic the conditions. pH affects the rate of enzyme controlled reactions.

Question 32

Why are Na+ important?

Answer 32

Na+ are important in the co-transport of glucose and amino acids across cell membranes against their concentration gradients. Also important in maintaining the resting potential of a neurone and generating an action potential.

Question 33

Why are phosphate ions important?

Answer 33

Component of ATP and DNA. = phosphate group when attached to another molecule. E.g. bonds between phosphate groups store energy in ATP, and phosphate groups in DNA and RNA allow nucleotides to join and form polynucleotides.