Topic 3 - Amino Acids & Peptides Flashcards
Draw the functional group Carboxylic Acid (COOH) and describe its properties
Higher oxidation state, more readily loses H
OH=hydroxyl group
Draw the functional group Amino (H3N+) and describe its chemical properties
Polar & charged. H bonding & basic (base) properties (H acceptor)
Draw the basic structure of an amino acid with labels
Coo- = carboxyl
H3N+ = amino
H= hydrogen
R = functional group
C = alpha carbon
Amino acids are monomers of….?
proteins
Proetins have different properties because of…?
Different orders and arrangements of aa’s
Name the 5 groups of amino acids and their defining properties
- Non-polar (No O, N => hydrophobic R groups
- Aromatic (relatively hydrophobic)
- Polar, uncharged (H bonding)
- Positively charged (basic & hydrophilic)
- Negatively charged (acidic)
Draw the structures of Glycine (Gly G) and Alanine (Ala A). What amino acid group do they belong to?
Non-polar aa group.
Draw the structure of Phenylalanine (Phe F). What aa group does it belong to?
Aromatic aa group.
Draw the structure of Asparagine (Asn N) and the similar structure of Glutamine (Gln Q).
What aa group do they belong to?
Polar, uncharged aa group.
Glutamine is same structure w/ 1 extra CH2
Draw the structure of Lysine (Lys K). What aa group does it belong to?
Positively charged aa group (basic & hydrophilic)
Draw the structure of Aspartate (Asp D) and Glutamate (Glu E). What aa group do they belong to?
Negatively charged aa group (acidic)
Name the aa’s and their abbreviations in the nonpolar, aliphatic group
Glycine (Gly G)
Alanine (Ala A)
Proline (Pro P)
Valine (Val V)
Leucine (Leu L)
Isoleucine (Ile I)
Methionine (Met M)
Name the aa’s and their abbreviations in the aromatic group
Phenylalanine (Phe F)
Tyrosine (Tyr Y)
Tryptophan (Trp W)
Name the aa’s and their abbreviations in the polar, uncharged group
Serine (Ser S)
Threonine (The T)
Cysteine (Cys C)
Asparagine (Asn N)
Glutamine (Gln Q)
Name the aa’s and their abbreviations in the positively charged group
Lysine (Lys K)
Histidine (His H)
Arginine (Arg K)
Name the aa’s and their abbreviations in the negatively charged group
Aspartate (Asp D)
Glutamate (Glu E)
What properties of an aa allow it to act as an acid and a base (amphoteric) (buffer)?
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)
What is a zwitterion?
A neutral molecule w/ a + & - charge, but no overall charge. Parts are seperately charged.
What is the Isoelectric Point (pI)? State the equation to find pI.
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.
State the pK1, pK2 & pI value for the Glycine titration curve.
pK1 (pKa COOH) = 2.34
pK2 (pKa NH3+) = 9.60
pI (neutral charge) = 5.97
Do the calculations for the pI table 3.1 for MSE
See slide 51.
Briefly describe peptide bond formation
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.
How do you do calculaions for Table 3.1?
P1 = (pK1 + pk2) / 2
But what about for…
Lysine, Histidine & Arginine?
Aspartate & Glutamate?
Tyrosine?
Cysteine?
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
