Amino Acids, Proteins & DNA

Question 1

What is a zwitterion

Answer 1

An amino acid in neutral conditions
- has a COO- group and a NH3+ group

Question 2

Why do zwitterions have a higher melting point than amino acids that are not charged

Answer 2

Because of the ionic interaction between zwitterions compared to the weaker H bonding that occurs in the no charge form

Question 3

Describe a basic vs an acidic amino acid

Answer 3

Basic - have an extra amine group
Acidic - have an extra carboxylic acid group

Question 4

What happens to amino acids structure in acidic conditions/low pH

Answer 4

All amine groups change to NH3+

Question 5

What happens to amino acids structure in alkaline conditions/high pH

Answer 5

All carboxyl groups change to COO-

Question 6

How could you determine protein structure from a diagram?

Answer 6

Does the chain show bending and folding?. If no - 1°
Does it show bonding between R groups? No- 2°, yes - 3°

Question 7

Describe how secondary protein structure forms

Answer 7

• nitrogen and oxygen are very electronegative
• Therefore C=O and N-H are polar
• Which results in the formation of a hydrogen bond between O and H
• The loan pair on the oxygen atom is strongly attracted to the Delta positive H

Question 8

Why can a stereospecific active site only bond to one enantiomeric form of a substrate or a drug

Answer 8

If the substrate is chiral then it is likely that only one enantiomer will have the correct stereochemistry to fit in the active site of the enzyme. So only one isomer will be catalysed

Question 9

How do scientists design enzyme inhibitors

Answer 9

With computers

Question 10

How would you identify the DNA base in the question

Answer 10

• if it has 2 rings and O2 then it’s guanine, if it has no O2 then it’s adenine
• if it has 1 ring and CH3 then it’s thymine. If it has no CH3 then it’s cytosine

Question 11

How do DNA bases react with sugar phosphate

Answer 11

The N-H group on the base reacts with the OH on the sugar

Question 12

Why does cisplatin prevent DNA replication and treat cancer

Answer 12

It bonds to the DNA in cancer cells and creates a distortion in the strand so it can’t unwind and be copied

Question 13

What kind of bonds are disulfide bridges

Answer 13

Covalent bonds

Question 14

Describe primary protein structure

Answer 14

• amide linkage between amine group and carboxylic groups of two amino acids

Question 15

Describe secondary protein structure

Answer 15

• Hydrogen bonding between C=O group and N-H

Question 16

Describe tertiary structure

Answer 16

• ionic interactions between side chains
• disulfide bridges between two cysteines