1-B: More Biological Molecules

Question 1

Describe the structure of DNA (5)

Answer 1

• polynucleotide
• each nucleotide formed from a deoxyribose, a phosphate group and a nitrogenous base
• phosphodiester bonds between nucleotides
• double helix held by hydrogen bonds
• between adenine, thymine and cytosine, guanine

Question 2

Name the two scientists who proposed models of DNA replication

Answer 2

Watson and Crick

Question 3

Give the (3) features of DNA that are important to semi conservative replication

Answer 3

• weak hydrogen bonds make it easy to unzip
• there are two strands, so both can act as a template
• complementary base pairing allows accurate replication

Question 4

How does DNA helicase cause DNA to unzip?

Answer 4

It causes the breaking of hydrogen bonds

Question 5

Describe the structure of ATP

Answer 5

• 3 phosphate groups in a tail
• ribose suger
• adenine

Question 6

Why do enzymes only work in one direction on an DNA strand

Answer 6

• DNA has antiparallel strands
• nucleotides align differently
• enzymes have active sites with specific shapes
• only substrates with complementary shape-to the 3’ end-can bind

Question 7

Give the ways in which ATP is a good energy source for cells (5):

Answer 7

• energy is released instantaneously
• it is rapidly resynthasised
• little energy is lost as heat (small amount released)
• phosphorylates other compounds making them more reactive
• does not leave cells

Question 8

What are the used of ATP in cellular processes?

Answer 8

• to provide energy for other reactions
• to add phosphate groups to other substances and make them more reactive

Question 9

Explain the 5 properties of water:

Answer 9

• reactive metabolite in condensation/hydrolysis reactions
• polar molecule so is a universal solvent so metabolic reactions occur faster (in solution)
• high specific heat capacity so buffers change in temperature ( can gain/lose lots of energy though changing temp)
• large latent heat of vaporisation so provides a cooling effect through evaporation (lots of energy needed/ removed through vaporisation )
• cohesion between water molecules so supports column of water in plants/ surface tension for supporting small organisms

Question 11

What is a cation?

Answer 11

A positive ion

Question 12

What is an anion

Answer 12

A negative ion

Question 13

Describe the role of iron ions in haemoglobin:

Answer 13

• 4 different polypeptide chains, each with Fe2+ in the centre
• oxygen binds to it
• temporarily becomes Fe3+

Question 14

Describe the importance of hydrogen ions:

Answer 14

• PH is based on the conc of hydrogen ions
• more H+ = lower PH
• enzyme controlled reactions are affected by PH

Question 15

Describe the role of sodium ions:

Answer 15

• co-transports glucose/amino acids across cell membranes into cells

Question 16

Describe the importance of phosphate ions:

Answer 16

• PO4^3- is attached to other molecules
• DNA/RNA/ATP all contain them
• bonds between the phosphate groups in ATP store energy
• allow nucleotides to join up to form polynucleotides in DNA/RNA

Question 17

What is an inorganic ion?

Answer 17

A molecule with an electric charge that doesn’t (usually) contain carbon