Amino Acids

Question 1

Draw the general structure of an amino acid.

Question 2

Why are amino acids considered amphoteric?

Answer 2

They can act as acids since the carboxyl group can donate a proton. They can act as bases since the amine group can accept a proton.

Question 3

Why do amino acids showcase optical isomerism?

Answer 3

The chiral carbon usually has 4 different groups attached to it.

Question 4

Draw the structure of 2-aminoethanoic acid.

Question 5

Draw the structure of 2-amino-3-methylbutanoic acid.

Question 6

What is a zwitterion?

Answer 6

An ion that has both a positive and negative charge.

Question 7

When do amino acids become zwitterions?

Answer 7

At their isoelectric point.

Question 8

What happens if you put the amino acid in acidic conditions?

Answer 8

The amine group gains a proton and the carboxyl group remains unchanged.

Question 9

What happens if you put the amino acid in alkali conditions?

Answer 9

The carboxyl group loses a proton and the amine group remains unchanged.

Question 10

What happens if the amino acid is near its isoelectric point?

Answer 10

The amine group gains a proton and the carboxyl group loses a proton. The amino acid has become a zwitterion.

Question 11

What are proteins?

Answer 11

Many amino acids are joined together by peptide links.

Question 12

Draw the two dipeptides that can form when alanine bonds with glycine.

Question 13

What are the conditions needed to hydrolise a protein into amino acid?

Answer 13

6 mol dm-3 of HCL
heat under reflux for 24 hours

Question 14

What is the primary structure of a protein?

Answer 14

The sequence of amino acids.

Question 15

What is the secondary structure of a protein?

Answer 15

Hydrogen bonds form between the peptide links and the chain folds into a 2D structure. This can either be an alpha helix or a beta-pleated sheet.

Question 16

What is the tertiary structure of a protein?

Answer 16

The formation of more hydrogen bonds, disulfide bridges and ionic bonds causes the chain to fold into its 3D shape.

Question 17

Draw how hydrogen bonds form in the polypeptide chain.

Question 18

Draw how disulfide bridges form between cysteine amino acids.

Question 19

Where do ionic bonds form in the polypeptide chains?

Answer 19

Between the positive and negative ends of the zwitterions.

Question 20

Why are enzymes considered biological catalysts?

Answer 20

They speed up chemical reactions without being used up.

Question 21

What is the lock and key model?

Answer 21

For a reaction to be catalysed, the substrate must fit into the active site of the enzyme.

Question 22

Why are the active sites of enzymes considered stereospecific?

Answer 22

Only one enantiomer of the amino acid will fit into the active site of the enzyme and the other won’t so a reaction can’t be catalysed with that enantiomer.

Question 23

What are inhibitors?

Answer 23

molecules that have the same shape as the substrate so they can bond with the active site instead of the substrate.

Question 24

What does the relative amount of inhibition depend on?

Answer 24

The concentration of the inhibitors and substrates.

Question 25

Why can you use thin-layer chromatography to separate amino acids?

Answer 25

They all have slightly different solubilities meaning some of them will be more attracted to the stationary phase compared to others.

Question 26

What can be used to stain the amino acids to make them visible?

Answer 26

1. Nihydrin solution which causes the amino acids to turn purple.
2. A plate that contains fluorescent dye.

Question 27

How does the fluorescent dye help us identify the amino acids?

Answer 27

When under UV light the amino acids will cover the dye and make certain spots look darker.