1What are amino acids?
Amino acids are the structural units or monomers of proteins. Amino acid chemistry MBBS 59.pdf
2What two functional groups are present in amino acids?
An amino group and a carboxyl group.
3What is the general structure of an amino acid?
A central α-carbon attached to an amino group, a carboxyl group, a hydrogen atom, and an R group (side chain).
4What is the R group of an amino acid?
The R group is the side chain that differs between amino acids.
5What are essential amino acids?
Amino acids that the body cannot make.
6What are D and L forms of amino acids?
They are two stereoisomeric forms of amino acids with one asymmetric carbon.
7What is the relationship between D and L amino acids?
They are mirror images of each other and are not superimposable; they are enantiomers.
8How is an amino acid classified as D or L according to the lecture?
If the NH₂ group is on the right side of the α-carbon, it is D; if the NH₂ group is on the left side, it is L.
9What are enantiomers?
Mirror images that are not superimposable on each other.
10What is the R group of glycine?
A single hydrogen atom.
11What is the R group of alanine?
A methyl group.
12What is the R group of glutamic acid?
A carboxymethyl/propanoic acid chain.
13What is the R group of histidine?
An imidazole ring.
14Why is glycine achiral?
Because it has no asymmetric carbon.
15What is the significance of glycine in protein structure?
Glycine provides flexibility in protein structure.
16What is the buffering property of glycine?
Glycine acts as a buffer due to its amphoteric nature.
17What is the significance of alanine in proteins?
Alanine has hydrophobic interactions in proteins and helps stabilize protein structure.
18What is the acid-base property of alanine?
Alanine participates in acid-base buffering.
19What is the acid-base property of glutamic acid?
Glutamic acid is an acidic amino acid and is negatively charged at physiological pH.
20What is the role of glutamic acid in protein structure?
Glutamic acid forms salt bridges in protein structure.
21What is the buffering role of glutamic acid?
Glutamic acid has a strong role in buffering.
22What is the significance of histidine in enzyme active sites?
Histidine is involved in enzyme active sites as a proton donor/acceptor.
23Why is histidine an effective buffer near physiological pH?
Its imidazole group has a pKa close to physiological pH.
24What are standard amino acids?
Amino acids encoded directly by the genetic code through codons in mRNA and incorporated into proteins during ribosomal translation.
25How many standard amino acids are given in the lecture?
20 amino acids.
26What are non-standard amino acids?
Amino acids that are not directly encoded by the standard genetic code.
27Give examples of non-standard amino acids.
Ornithine, citrulline, GABA, homocysteine, taurine and homoserine.
28How can non-standard amino acids arise?
They can arise as free metabolic intermediates and are not incorporated into proteins.
29What are post-translationally modified amino acids?
Standard amino acids that are chemically modified after the protein has been synthesized by the ribosome.
30What are the three post-translationally modified amino acids or examples listed in the lecture?
4-hydroxyproline and 4-hydroxylysine, gamma-carboxyglutamate, and methyl lysine.
31How are 4-hydroxyproline and 4-hydroxylysine formed?
By hydroxylation of proline and lysine residues in polypeptide chains of collagen.
32Where are 4-hydroxyproline and 4-hydroxylysine found?
In collagen.
33What is gamma-carboxyglutamate formed by?
Gamma carboxylation of glutamic acid residues.
34Where is gamma-carboxyglutamate found?
In clotting factors II, VII, IX and X.
35How is methyl lysine formed?
By methylation of lysine.
36Where is methyl lysine found?
In histones.
37How are amino acids classified according to the lecture?
Based on the nature of their side chain and based on their metabolic fate.
38What are polar amino acids?
Amino acids that are hydrophilic in nature.
39What are examples of polar amino acids given in the lecture?
Glycine, serine, cysteine, threonine, glutamine, lysine, arginine and glutamic acid.
40What are non-polar amino acids?
Amino acids that are hydrophobic in nature.
41What are examples of non-polar amino acids given in the lecture?
Alanine, phenylalanine, tryptophan, valine, leucine, isoleucine and methionine.
42What are glucogenic amino acids?
Amino acids whose catabolism yields pyruvate or one of the intermediates of the TCA cycle.
43Why are glucogenic amino acids called glucogenic?
Their catabolic intermediates can give rise to the net synthesis of glucose in the liver and kidney.
44What are examples of glucogenic amino acids given in the lecture?
Alanine, aspartate, glycine and methionine.
45What are ketogenic amino acids?
Amino acids whose catabolism yields either acetyl-CoA or acetoacetate.
46Which amino acids are listed as ketogenic amino acids?
Leucine and lysine.
47What are amino acids that are both glucogenic and ketogenic?
Amino acids whose catabolism yields both glucogenic and ketogenic intermediates.
48Which amino acids are both glucogenic and ketogenic according to the lecture?
Isoleucine, tyrosine, phenylalanine and tryptophan.
49What are the two ionizable groups in an amino acid?
The amino group and the carboxyl group.
50What is the acid-base role of the amino group?
The amino group acts as a base.
51What is the acid-base role of the carboxyl group?
The carboxyl group acts as an acid.
52What is a zwitterion?
A molecule that carries both a positive and a negative charge simultaneously, with an overall net charge of zero.
53What is the origin of the term zwitterion?
It comes from the German word “zwitter,” meaning hybrid.
54What is the isoelectric point (pI)?
The specific pH at which an amino acid or protein carries zero net charge and therefore does not migrate in an electric field.
55What is the net charge of an amino acid at its pI?
Zero, because the positive and negative charges balance.
56What form does an amino acid exist in at its pI?
It exists as a zwitterion.
57What happens to the mobility of an amino acid in an electric field at its pI?
It does not migrate towards the anode or cathode.
58What happens to the solubility of an amino acid at its pI?
It has minimum solubility and is least soluble.
59What happens to the buffering capacity of an amino acid at its pI?
It has minimum buffering capacity.
60What happens to the electrical conductivity of an amino acid at its pI?
It has low electrical conductivity.
61Is the pH nature at the pI the same for all amino acids?
No. It is specific for each amino acid and may be acidic, neutral or basic.
62What is the effect of pI on protein stability according to the lecture?
There is an increased tendency for aggregation or precipitation.
63What structural feature of histidine allows it to act as a buffer?
Histidine contains an imidazole group in its side chain.
64What is the pKa of the imidazole group of histidine given in the lecture?
Approximately 6.5.
65Why is histidine suitable as a buffer near physiological pH?
The pKa of its imidazole group is close to physiological pH (~7.4).
66How does histidine act as a buffer when pH is below its pKa?
It acts as a base.
67How does histidine act as a buffer when pH is above its pKa?
It acts as an acid.
68What allows histidine to resist changes in pH near physiological conditions?
Its imidazole group has a pKa close to physiological pH, allowing it to act as a buffer.