Topic 3 - Amino Acids & Peptides

Question 1

Draw the functional group Carboxylic Acid (COOH) and describe its properties

Answer 1

Higher oxidation state, more readily loses H

OH=hydroxyl group

Question 2

Draw the functional group Amino (H3N+) and describe its chemical properties

Answer 2

Polar & charged. H bonding & basic (base) properties (H acceptor)

Question 3

Draw the basic structure of an amino acid with labels

Answer 3

Coo- = carboxyl

H3N+ = amino

H= hydrogen

R = functional group

C = alpha carbon

Question 4

Amino acids are monomers of….?

Answer 4

proteins

Question 5

Proetins have different properties because of…?

Answer 5

Different orders and arrangements of aa’s

Question 6

Name the 5 groups of amino acids and their defining properties

Answer 6

1. Non-polar (No O, N => hydrophobic R groups
2. Aromatic (relatively hydrophobic)
3. Polar, uncharged (H bonding)
4. Positively charged (basic & hydrophilic)
5. Negatively charged (acidic)

Question 7

Draw the structures of Glycine (Gly G) and Alanine (Ala A). What amino acid group do they belong to?

Answer 7

Non-polar aa group.

Question 8

Draw the structure of Phenylalanine (Phe F). What aa group does it belong to?

Answer 8

Aromatic aa group.

Question 9

Draw the structure of Asparagine (Asn N) and the similar structure of Glutamine (Gln Q).
What aa group do they belong to?

Answer 9

Polar, uncharged aa group.

Glutamine is same structure w/ 1 extra CH2

Question 10

Draw the structure of Lysine (Lys K). What aa group does it belong to?

Answer 10

Positively charged aa group (basic & hydrophilic)

Question 11

Draw the structure of Aspartate (Asp D) and Glutamate (Glu E). What aa group do they belong to?

Answer 11

Negatively charged aa group (acidic)

Question 12

Name the aa’s and their abbreviations in the nonpolar, aliphatic group

Answer 12

Glycine (Gly G)
Alanine (Ala A)
Proline (Pro P)
Valine (Val V)
Leucine (Leu L)
Isoleucine (Ile I)
Methionine (Met M)

Question 13

Name the aa’s and their abbreviations in the aromatic group

Answer 13

Phenylalanine (Phe F)
Tyrosine (Tyr Y)
Tryptophan (Trp W)

Question 14

Name the aa’s and their abbreviations in the polar, uncharged group

Answer 14

Serine (Ser S)
Threonine (The T)
Cysteine (Cys C)
Asparagine (Asn N)
Glutamine (Gln Q)

Question 15

Name the aa’s and their abbreviations in the positively charged group

Answer 15

Lysine (Lys K)
Histidine (His H)
Arginine (Arg K)

Question 16

Name the aa’s and their abbreviations in the negatively charged group

Answer 16

Aspartate (Asp D)
Glutamate (Glu E)

Question 17

What properties of an aa allow it to act as an acid and a base (amphoteric) (buffer)?

Answer 17

have both an amine and carboxylic acid functional group.
Carboxyl group on side chain have high tendency to donate protons (acid)

Amino group on side chain have a high tendency to accept protons (base)

Question 18

What is a zwitterion?

Answer 18

A neutral molecule w/ a + & - charge, but no overall charge. Parts are seperately charged.

Question 19

What is the Isoelectric Point (pI)? State the equation to find pI.

Answer 19

pH at which aa is neutral, where there is no net electrical charge.

pI = (pK1 + pK2) / 2
=> look for neutrally charged species & average pKa’s around it.

Question 20

State the pK1, pK2 & pI value for the Glycine titration curve.

Answer 20

pK1 (pKa COOH) = 2.34

pK2 (pKa NH3+) = 9.60

pI (neutral charge) = 5.97

Question 21

Do the calculations for the pI table 3.1 for MSE

Answer 21

See slide 51.

Question 22

Briefly describe peptide bond formation

Answer 22

Carboxyl group of one aa reacts w/ amino group of another aa.
Carboxyl group of aa now becomes ketone (amine => amide) so no longer ionisable.
Only ionisable groups left will be the R groups.

Question 23

How do you do calculaions for Table 3.1?
P1 = (pK1 + pk2) / 2

But what about for…
Lysine, Histidine & Arginine?
Aspartate & Glutamate?

Tyrosine?

Cysteine?

Answer 23

L,H,A = go for 2 highest numbers

A & G = go for 2 lowest numbers

T = closest numbers to 7

C = lowest and middle number