BCH 203 Protein Chemistry Flashcards
Definition of proteins
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.
Ways of classifying amino acids
- Chemical nature of the amino acid in the solution
- Structure of the side chain of the amino acids
- Nutritional requirement of amino acids
- Metabolic product of amino acids
- Nature or polarity of the side chain of the amino
acids.
Aliphatic side chain
Glycine Gly (G)
Alanine Ala (A)
Valine Val (V)
Leucine Leu (L)
Isoleucine Ile (I)
Hydroxylic (OH) group containing side chains
Serine Ser (S)
Threonine Thr (T)
Tyrosine Tyr (Y)
Sulfur containing side chains
Cysteine Cys (C)
Methionine Met (M)
Side chains containing acidic groups (–COOH) and their amides
Aspartic acid Asp (D)
Aspargine Asn (N)
Glutamic acid Glu (E)
Glutamine Gln (Q)
Basic groups containing side chains
Arginine Arg (R)
Lysine Lys (K)
Histidine His (H)
Aromatic group containing side chains
Histidine His (H)
Phenylalanine Phe (F)
Tyrosine Tyr (Y)
Tryptophan Trp (W)
Imino acids
Proline Pro (P)
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),
Glycine
Serine
Phenylalanine
Alanine
Threonine
Tyrosine
Valine
Cysteine
Tryptophan
Leucine
Methionine
Aspargine
Isoleucine
Proline
Glutamine
Basic amino acid with examples
These are basic in solution and are diamino-monocarboxylic acids,
- Lysine
- Arginine
- Histidine.
Acidic amino acid
These are acidic in solution and are monoamino dicarboxylic acids
- Aspartic acid
- Glutamic acid
Aromatic amino acids
Amino acids containing aromatic ring in the side chain
- Phenylalanine
- Tyrosine
- Tryptophan.
Dicarboxylic acid and their amides
Amino acids having carboxylic group in their side chain,
- Glutamic acid
- Glutamine (amide of glutamic acid)
- Aspartic acid
- Aspargine (amide of aspartic acid).
List the 10 Essential amino acids
Phenylalanine * Methionine
* Valine * Histidine
* Threonine * Arginine
* Tryptophan * Lysine
* Isoleucine * Leucine
Define an Essential amino acid
Essential amino acids cannot be synthesized by the body and must, therefore, be essentially supplied through the diet
Why are histidine and arginine semi-essential amino acids?
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.
List and describe the Metabolic Classification of Amino Acids
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.
. Both glucogenic and ketogenic amino acids
isoleucine, phenylalanine,
tryptophan and tyrosine
Ketogenic amino acids
leucine and lysine
Importance of Amino Acids
- 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
