Amino acids, DNA and proteins

Question 1

What are the features of an amino acid (3)

Answer 1

• amino acids except glycerine are chiral molecules
• amphoteric = they have acidic and basic properties
• can exist as zwitterions at their isoelectric point

Question 2

What are zwitterions? Draw amino acids as zwitterions

Answer 2

a molecule with both positive and negative ions

Question 3

What is an isoelectric point?

Answer 3

the pH at which the average overall charge is zero (neutrol pH)

Question 4

Draw an amino acid in alkaline conditions

Answer 4

Question 5

Draw an amino acid in acid conditions

Answer 5

Question 6

What is the structure of an amino acid and what does R represent?

Answer 6

The R can be one of twenty different chemical groups

the NH2 must be on the carbon next to the COOH group

Question 7

Explain the chemistry behind why amino acids become overall different charges at different pH

Answer 7

At low pH there is an excess amount ofH+in solution. The excessH+is attracted to the negatively charged carboxylate ion resulting in its protonation. The COO- group will convert to COOH and NH2 to NH3+

At high pH there is an excess amount ofOH−in solution. COOH donates its H+ to the OH- to form H2O and COO- group

Question 8

What is the level of inhibition on enzymes is dependant on?

Answer 8

• The relative concentration of substrate and drugs
• .The relative binding strength of the drug and the substrate.

Question 9

What is cisplatin? Describe its structure and how it does its job

Answer 9

• anti-cancer drug.
• Cisplatin is a square planar platinum complex with two ammonia and two chloride ligands.
• Cisplatin undergoes a ligand exchange reaction in the body and binds to nitrogenous bases in DNA.
• Pt binds to N in two guanines in DNA (in place of chloride ligand) – this prevents cell replication

Question 10

What are the problems with cisplatin?

Answer 10

• A problem with this anticancer drug is its adverse side effects.
• Cisplatin is NOT selective and also stops normal cells from replicating.
  
  • So patients become unwell when taking the medication.

Question 11

What are the different types of bonding that can occur with amino acids?

Answer 11

• hydrogen bonding
• ionic bonding
• disulfide bridges

Question 12

Draw the bonds between AT and GC

Answer 12

Question 13

Draw one 2-deoxyribose unit and show how the C atoms are numbered.

Answer 13

Question 14

Scientists talk about ‘3 prime’ and ‘5 prime’ ends in DNA. What do these terms refer to?

Answer 14

The number of the C atom that the phosphate group is bonded to

Question 15

Draw trans-platin and explain why this would not stop DNA replication.

Answer 15

Question 16

Why would lysine act as a base in neutral pH?

Answer 16

It has 2 NH2 groups so overall there would be a net gain in H+ ions at neutral pH, making it a H+ acceptor