biological molecules, markscheme

Question 1

Describe the chemical reaction involved in the conversion of monomers to polymers and polymers to monomers.
Give two examples of polymers and their associated monomers.

Answer 1

• a condensation reaction joins monomers together and forms a chemical bond and releases water
• a hydrolysis reaction breaks a chemical bond between monomers and uses water

Two examples:
1) amino acids and polypeptides/protein/enzyme (peptide bond)
2) nucleotides and polynucleotides/DNA/RNA (ester bonds)
3) alpha glucose and starch(1,4 glycosidic bonds)/glycogen(1,4 and 1,6 glycosidic bonds
4) beta glucose and cellulose (1,4 glycosidic bonds)

• refer to a correct bond within the polymer (in brackets)

Question 2

What is a monomer (1)

Answer 2

A small repeating molecule from which larger molecules (polymers) are made

Question 3

What are two features of DNA and how is it important for semiconservative replication? (2)

Answer 3

• Easily broken hydrogen bonds between bases that allow the two strands to separate/unzip
• there are two strands so both can act as templates
• complementary base pairing allows accurate replication

Question 4

Name the process by which prokaryotic cells divide?

Answer 4

Binary fission

Question 5

What is the bond between glycerols and fatty acids within a triglyceride

Answer 5

An ester bond.

Question 6

Describe how you would test a liquid sample for the presence of a lipid and how you would recognise a positive result (2)

Answer 6

Shake sample with ethanol and then water.
Pos result- milky white emulsion

Question 7

What is a polymer

Answer 7

A molecule made from large numbers of polymers joined through a condensation reaction

Question 8

Three examples of a monomer

Answer 8

Monosaccharide, nucleotide, amino acid

Question 9

Why is the tertiary structure of proteins important for metabolic reactions

Answer 9

Enzymes a proteins that stark use biological reactions
The tertiary structure affects the shape of an enzymes active site
The shape of the active site needs to be specific to the shape of the substrate to catalyse the reaction

Question 10

Why is the tertiary structure of proteins important for metabolic reactions

Answer 10

Enzymes a proteins that stark use biological reactions
The tertiary structure affects the shape of an enzymes active site
The shape of the active site needs to be specific to the shape of the substrate to catalyse the reaction

Question 11

State and explain the property of water that can help to buffer changes in temperature

Answer 11

Water has a high specific heat capacity, it takes a lot of heat to change temperature.

Question 12

What are two products of atp hydrolysis

Answer 12

Adenosine diphosphate and inorganic phosphate

Question 13

What is the primary structure of a protein

Answer 13

Sequence of amino acids joined by peptide bonds

Question 14

What is the primary structure of a protein

Answer 14

Sequence of amino acids joined by peptide bonds

Question 15

Describe two differences between the structure of the triglyceride and a phospholipid (2)

Answer 15

For a triglyceride:
3 fatty acids instead of two
3 ester bonds rather than two
No phosphate groups

Question 16

Explain why phospholipids can form a bilayer but triglycerides cannot

Answer 16

Phospholipid is hydrophobic and hydrophilic (it is polar/charged)
Triglycerides are only hydrophobic (non polar)
Hydrophilic/phosphate groups attracts water (to each side of bilayer)

Question 17

Explain how the formation of an enzyme-substrate complex increases the rate of reaction

Answer 17

• reduces activation energy
• due to bending bonds