Lecture 4

Question 1

List the properties of an Amino acid?

Answer 1

Amino group
Carboxyl group
Alpha carbon
Side chain (part that varies)

Question 2

Describe the chirality of amino acids?

Answer 2

Amino acids have a chiral carbon and therefore are chiral, (non superimposable mirror images enantiomers.) They come in the L or D form, of which L is the dominant form.

Question 3

How do amino acids act in solution as zwitterions?

Answer 3

Dissolving an amino acid in water will result in ionisation as it donates a proton.The H is lost from the carboxyl group and the amine becomes a base.

Question 4

How is the charge affected by amino acids in solution?

Answer 4

A protonated amine group will have a positive charge and as deprotonated carboxylic acid group will have a negative charge

Question 5

What is a zwitterion?

Answer 5

A molecule that has two separate positively and negatively charged groups

Question 6

Non polar amino acids?

Answer 6

Hydrophobic amino acids that pack together and appear where oily patches are needed (typically the oily patches are deep inside of a protein.)

Question 7

Characteristics of glycine?

Answer 7

The R group is an H which means glycine is not chiral. This makes it very flexible.
Tends to be found in loops or areas of tight contact.
Could be in a group by itself

Question 8

Characteristics of cysteine?

Answer 8

Has a self hydryl group (SH group) .

Due to this cysteine is commonly found in an enzyme called protease.

Question 9

Characteristics of henalslenine and Tryptophan?

Answer 9

Have aromatic side chains.
Hydrophobic
Bulky
tryptophan slightly polar due to NH group
Resonance, ability to flores
Used to help determine the concentration of proteins

Question 10

Characteristics of Methionine?

Answer 10

Large, bulky, hydrophobic residue

Question 11

Characteristics of Proline?

Answer 11

R group consists of methionines that do a full loop and bind back to the amino acid (makes it an imino acid). Closed ring creates rigidity Can be modified by hydroxylation.

Question 12

How many charged (acidic) polar amino acids are there?

Answer 12

5 in total. 2 negatively charged and 3 positively charged.

Question 13

Characteristics of negatively charged polar amino acids?

Answer 13

Aspartic acid and glutamic acid. Have side chains with a second carboxylic acid group. they are negatively charged despite being acid because they are the conjugate bases after the proton has been donated. They are located on the surface, interacting with water.

Question 14

Characteristics of positively charged polar amino acids?

Answer 14

Lysine, Arginine and histidine. Bases but have already been protonated therefore are in conjugate acid form.
Tend to be located at the surface also. Can be found in active sites (lysine and histidine especially). Lysine can also be hydroxylated.

Question 15

List the polar uncharged amino acids?

Answer 15

Serine
threonine 
Tyrosine
Asparagine
Glutamine