Amino Acids & Peptides

Question 1

What do all AAs (excluding Pro) have in common structurally?

Answer 1

1. An acidic carboxyl group connected to the alpha carbon
2. A basic amino group connected to alpha carbon
3. An alpha hydrogen connected to the alpha carbon

Question 2

What is unique about the R group in Glycine

Answer 2

The fourth substituent (R group) is also a hydrogen. It’s the simplest AA.

Question 3

What do neutral AAs have

Answer 3

One COOH & one NH2 group

Question 4

What do acidic AAs have

Answer 4

Two COOH and one NH2 groups

Question 5

What do basic AAs have

Answer 5

One COOH group and two NH2 groups

Question 6

Which 3 AAs are basic

Answer 6

1. Lysine (Lys)
2. Arginine (Arg)
3. Histidine (His)

Question 7

Which 2 AAs are acidic

Answer 7

1. Aspartic acid (Asp)
2. Glutamic Acid (Glu)

Question 8

What do AAs with non polar side chains not participate in

Answer 8

Hydrogen or ionic bonding

Question 9

Why is Cysteine a special AA

Answer 9

The SH group of two cysteines can be oxidised to form a covalent cross link called a disulphide bond

Question 10

Why is Glycine a special AA

Answer 10

It’s R group is a hydrogen molecule

Question 11

Why is Proline a special AA

Answer 11

Its side chainand alpha amino N form a rigid ring structure. Proline is therefore often found at bends or turns in protein structure.

Question 12

What is desmosine (elastin) formed from

Answer 12

4 Lysine residues

Question 13

Ubiquitination

Answer 13

• Ubiquitin (a protein) attaches to Lysine via an isopeptide bond
• Mediates protein degradation (tidies AAs before degradation), signalling, trafficking

Question 14

To which AAs does the process of methylation occur

Answer 14

• Attachment of a methyl group to Lys/Arg
• This regulates RNA processing, transcription, DNA damage repair

Question 15

To which AAs does phosphorylation occur

Answer 15

• Attachment of a phosphate group to Ser/Thr/Tyr residues
• Done by kinases, reversible process
• Regulates enzymatic activity

Question 16

To which AAs does Glycosylation occur

Answer 16

• Attachment of glycans (sugars?) to Asn/ Ser/ Thr/ Tyr residues
• Involved in cell-cell interaction and recognition, protein folding and chaperone recruitment

Question 17

To which AAs does Acetylation occur

Answer 17

• Attachment of an acetyl group to Lysine
• Mediates protein-protein interaction

Question 18

What form do AAs exist as at low pH

Answer 18

They exist in a positively charged form (cation) at low pH

Question 19

What form do AAs exist as at high pH

Answer 19

They exist in a negatively charged form (anion) at high pH

Question 20

When the molecule has both a positive and negative charge, what does the AA exist as

Answer 20

The AA exists in zwitterion form (- carboxyl group & + amino group)

Question 21

What is the Isoelectric Point of an AA

Answer 21

The point when the net charge of the AA is zero.

Question 22

What happens to the AA at its isoelectric point

Answer 22

1. AA is least soluble in water
2. AA doesn’t migrate in electric field

Question 23

What AA can act as a buffer in two pH ranges

Answer 23

Glycine

Question 24

What type of reaction is involved in peptide bond formation

Answer 24

Dehydration/condensation reaction (requires ATP)

Question 25

Where to start when naming peptides

Answer 25

At the N-terminal (Amino Terminal)

Question 26

4 Functions of peptides

Answer 26

1. Hormones & Pheromones: insulin, oxytocin
2. Neuropeptides: substance p (pain mediator)
3. Antibiotics: polymyxin B (for gram neg), bacitracin (for gram pos)
4. Protection: e.g: toxins

Question 27

3 things proteins could be comprised of

Answer 27

Polypeptides & possibly:
1. Cofactors
2. Coenzymes
3. Prosthetic groups

Question 28

What differences does separation of proteins rely on

Answer 28

• Charge
• Size
• Affinity for a ligand
• Solubility
• Hydrophobicity
• Thermal Stability