Biochemistry Amino Acids

Question 1

What is the isoelectric point of an amino acid?

Answer 1

The isoelectric point is the pH at which the molecule is electrically neutral. It will be dipolar having one positive charge and one negative charge.

Question 2

What is the isoelectric point of non-ionizable amino acids?

Answer 2

The ISP is around 6 due to the formula:

ISP= pKa1 + pKa2 / 2

Question 3

What is the formula to calculate the isoelctric point for acidic amino acids?

Answer 3

ISP = pka(side chain) + pkA (COOH) / 2.

This is usually an acidic value around 2-3.

Question 4

What is the relationship between pH and pKa?

Answer 4

If the pH is less than the pKa then the species is protonated.

If the pH is greater than the pKa then the species is deprotonated.

Question 5

What is the relationship between pH, pKa, and titrations?

Answer 5

When the pH is close to the pKa then the solution will act like a buffer. This area will be a flat line on a titration curve.

Question 6

What are the key amino acid pKa values?

Answer 6

Alpha Carbonyl group: 2
Alpha Amino group: 9
Side carbonyl group: 4.2
Side amino grou: 10.5

Question 7

What is the sterochemistry of amino acids?

Answer 7

All amino acids, except glycine, are chiral.

Question 8

What is the fischer projection for amino acids?

Answer 8

L amino acids have the amino group on the left to to form the S absolute confirmation EXCEPT CYSTEINE.

Question 9

How are peptide bonds formed in amino acids?

Answer 9

Peptide bonds are formed via a condensation reaction with the removal of water. A bond is formed between the carbonyl group and the amino group. This bond is partially double bond in character so there is no free rotation.

Question 10

What is the formula for isoelectric points in a basic amino acid?

Answer 10

ISP= pKa (Side chain) + pKa (amino group) / 2

Question 11

Describe the hydrolysis of proteins.

Answer 11

Water acts to break the peptide bond. A hydrogen is added to the nitrogen and OH is added to the carbonyl group.

Question 12

What is the formula for calculating pH?

Answer 12

pH = - log [ H+ ]

Question 13

In what order are amino acids formed in terms of the C and N terminal?

Answer 13

Amino acids start from the N terminus and build toward the C terminus.

Question 14

What is unique about proline’s structure?

Answer 14

The structure causes kinks in the secondary structure of proteins.

Question 15

Describe the secondary structure of proteins.

Answer 15

Comprised by hydrogen bonds between the peptides. Two forms, either alpha or beta.

Question 16

What are the types of bonds in tertiary structure?

Answer 16

Covalent disulfide bonds
Hydrogen
Electrostatic
Van der Vaals
Hydrophobic

Question 17

How do you calculate tripeptide combinations?

Answer 17

Count the number of amino acids then use factorials.

x!