BCH 203 Protein Chemistry

Question 1

Definition of proteins

Answer 1

Proteins are linear chains of amino acids that are linked together by covalent, peptide bonds.
Each protein has specific and unique sequence of amino acids that defines both its three dimensional structure and its biologic function.

Question 2

Ways of classifying amino acids

Answer 2

1. Chemical nature of the amino acid in the solution
2. Structure of the side chain of the amino acids
3. Nutritional requirement of amino acids
4. Metabolic product of amino acids
5. Nature or polarity of the side chain of the amino
   acids.

Question 3

Aliphatic side chain

Answer 3

Glycine Gly (G)
Alanine Ala (A)
Valine Val (V)
Leucine Leu (L)
Isoleucine Ile (I)

Question 4

Hydroxylic (OH) group containing side chains

Answer 4

Serine Ser (S)
Threonine Thr (T)
Tyrosine Tyr (Y)

Question 5

Sulfur containing side chains

Answer 5

Cysteine Cys (C)
Methionine Met (M)

Question 6

Side chains containing acidic groups (–COOH) and their amides

Answer 6

Aspartic acid Asp (D)
Aspargine Asn (N)
Glutamic acid Glu (E)
Glutamine Gln (Q)

Question 7

Basic groups containing side chains

Answer 7

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

Question 8

Aromatic group containing side chains

Answer 8

Histidine His (H)
Phenylalanine Phe (F)
Tyrosine Tyr (Y)
Tryptophan Trp (W)

Question 9

Imino acids

Answer 9

Proline Pro (P)

Question 10

Neutral amino acids with examples
The amino acids which are neutral in solution and are mono amino-monocarboxylic acids (i.e. having one amino group and one carboxylic group),

Answer 10

Glycine
Serine
Phenylalanine
Alanine
Threonine
Tyrosine
Valine
Cysteine
Tryptophan
Leucine
Methionine
Aspargine
Isoleucine
Proline
Glutamine

Question 11

Basic amino acid with examples
These are basic in solution and are diamino-monocarboxylic acids,

Answer 11

• Lysine
• Arginine
• Histidine.

Question 12

Acidic amino acid
These are acidic in solution and are monoamino dicarboxylic acids

Answer 12

• Aspartic acid
• Glutamic acid

Question 13

Aromatic amino acids
Amino acids containing aromatic ring in the side chain

Answer 13

• Phenylalanine
• Tyrosine
• Tryptophan.

Question 14

Dicarboxylic acid and their amides
Amino acids having carboxylic group in their side chain,

Answer 14

• Glutamic acid
• Glutamine (amide of glutamic acid)
• Aspartic acid
• Aspargine (amide of aspartic acid).

Question 15

List the 10 Essential amino acids

Answer 15

Phenylalanine * Methionine
* Valine * Histidine
* Threonine * Arginine
* Tryptophan * Lysine
* Isoleucine * Leucine

Question 16

Define an Essential amino acid

Answer 16

Essential amino acids cannot be synthesized by the body and must, therefore, be essentially supplied through the diet

Question 17

Why are histidine and arginine semi-essential amino acids?

Answer 17

among the ten essential amino acids; arginine and histidine are known as semi-essential amino acids since these amino acids are synthesized partially in human body. Arginine and histidine become essential in diet during periods of rapid growth as in childhood and pregnancy.

Question 18

List and describe the Metabolic Classification of Amino Acids

Answer 18

On the basis of their catabolic end products, the twenty standard amino acids are divided in three groups
i. Glucogenic amino acids: Those which can be
converted into glucose. Fourteen out of the twenty standard amino acids are glucogenic amino acids

ii. Ketogenic amino acids: Those which can be
converted to ketone bodies. Two amino acids
leucine and lysine are exclusively ketogenic.

iii. Both glucogenic and ketogenic: Those which can be converted to both glucose and ketone bodies.
Four amino acids isoleucine, phenylalanine,
tryptophan and tyrosine are glucogenic and
ketogenic.

Question 19

. Both glucogenic and ketogenic amino acids

Answer 19

isoleucine, phenylalanine,
tryptophan and tyrosine

Question 20

Ketogenic amino acids

Answer 20

leucine and lysine

Question 21

Importance of Amino Acids

Answer 21

• Formation of proteins: Amino acids are joined to each
  other by peptide bonds to form proteins and peptides.
• Formation of glucose: Glucogenic amino acids are
  converted to glucose in the body.
• Enzyme activity: The thiol (-SH) group of cysteine
  has an important role in certain enzyme activity.
• Transport and storage form of ammonia: Amino acid
  glutamine plays an important role in transport and
  storage of amino nitrogen in the form of ammonia.
• As a buffer: Both free amino acids and some amino acids
  present in protein can potentially act as buffer, e.g. histidine can serve as the best buffer at physiological pH.
• Detoxification reactions: Glycine, cysteine and
  methionine are involved in the detoxification of
  toxic substances.
• Formation of biologically important compounds:
  Specific amino acids can give rise to specific
  biologically important compounds in the body