Nucleic Acids

Question 1

what does DNA consist of

Answer 1

Deoxyribose sugar, a phosphate group and a nitrogen containing base (adenine, cytosine, guanine or thymine)

Question 2

What does RNA consist of

Answer 2

Nucleotides containing ribose sugar, a phosphate group and a nitrogen containing base- adenine, uracil, cytosine and guanine

Question 3

The purpose phosphodiester bond and how one forms

Answer 3

Forms: condensation reaction between adjacent nucleotides
Forms the sugar-phosphate backbone of the nucleic acid

Question 4

What does DNA code for

Answer 4

Codes for the primary sequence of amino acids
3 bases=triplet=one amino acid

Question 5

Describe the antiparallel nucleotide structure

Answer 5

To remain parallel the complementary base pairs pair together with the two strands of DNA running in opposite directions.
Each end of the molecule has a 5’ and 3’ end
DNA polymerase is only complementary to the 5’ end of the molecule.

Question 6

How does the structure of DNA allow it to carry out its function

Answer 6

1. Sugar phosphate backbone and double helix structure- provides strength and stability- protects bases and protects the hydrogen bonds between bases
2. Long large molecule- so stores a lot of information
   3.helical so compact
   4.base sequence allows information to be stored/codes for amino acids and therefore proteins
3. Double stranded so replication can occur semi conservatively, because each strand acts as a template
   6.complementary base pairs- allows accurate replication, identical copies are made
4. Hydrogen bonds between bases are weak, allows for easy strand separation for semi-conservative replication
5. Many weak hydrogen bonds so DNA is strong

Question 7

Describe the role of DNA polymerase

Answer 7

• catalyses the condensation reactions between DNA nucleotides to form the sugar-phosphate backbone of the new strand

Question 8

Describe the role of DNA helicase

Answer 8

Breaks the hydrogen bonds between complementary base pairs so each strand can act as a template

Question 9

Describe the process of DNA replication

Answer 9

• DNA helicase breaks weak hydrogen bonds between complementary base pairs
• both strands act as a template
• adjacent nucleotides bind to complementary base pairs, adenine, thymine, cytosine and guanine
• DNA polymerase joins adjacent nucleotides together to form phosphodiester bond
• consists of one old and one new strand

Question 10

Describe how DNA polymerase works

Answer 10

DNA polymerase has a specific active site to the 5’ end of the incoming free DNA nucleotide and the 3’ end of the developing strand.

Question 11

What would a conservative model be

Answer 11

An entirely new molecule is synthesised from a DNA template

Question 12

What would a semi-conservative model look like

Answer 12

Each new molecule consists of one newly synthesised strand and one template strand

Question 13

Explain what a dispersive model would look like

Answer 13

New molecules are made of segments of new and old DNA

Question 14

What is ATP

Answer 14

Adenosine triphosphate consists of nitrogenous organic base, ribose sugar and three phosphate groups

Question 15

2 uses of ATP

Answer 15

1. Provides energy for active transport, muscle contraction, protein synthesis
2. Phosphorylation of molecules with lower activation energy- makes substrates more reactive by altering tertiary structure

Question 16

Describe how ATP formed

Answer 16

The condensation reaction between ADP and Pi catalysed by condensation reaction, it requires energy to add phosphate group to ADP to form ATP creating a high energy bond

Question 17

How is ATP broken down

Answer 17

Breaks back down into ADP and Pi catalysed by ATP hydrolase
Pi can be used to phosphorylate other compounds and make them more reactive

Question 18

Why is ATP useful

Answer 18

1. Releases relatively small amounts of energy
2. Releases energy instantaneously
3. Phosphorylates other compounds,making them more reactive
4. Can be rapidly re-synthesised
5. It is not lost from the cells

Question 19

Contrast the structures of ATP and a nucleotide found in DNA

Answer 19

1. ATP has ribose and DNA nucleotide has deoxyribose
2. ATP has 3 phosphate and DNA nucleotide has one phosphate
3. ATP base always has adenine and in DNA nucleotide base can be different

Question 20

What are the properties of water important in Biology

Answer 20

1. Polar (molecules);
2. Dissolves charged particles/acts as a (universal) solvent;
   OR
3. A metabolite;
4. Involved in metabolic/cell reaction/condensation/hydrolysis;
   OR
5. Water molecules stick together/cohesion between water
   molecules;
6. Provides surface tension/prevents columns of water
   breaking;
   OR
7. High specific heat capacity;
8. Reduces fluctuations in temperature (of water bodies);
   OR
9. High latent heat of evaporation;
10. Evaporation of small amount of water cools organisms;

Question 21

Suggest why water becomes lighter as it expands and explain an advantage

Answer 21

1. Density=mass/volume
2. Ice has same mass of water but greater volume
   Advantage: ice is colder than water, ice floats on water, reduces freezing of water

Question 22

Explain why water is considered so important for life to occur

Answer 22

1. Life has evolved in water
2. Water provides support for bodies of organisms
3. Water is a major component of the cytoplasm
4. Water is a universal solvent so metabolic reactions occur
5. Water is a metabolite
6. Water stabilises external temperature