ITS 232: PROTEINS AND AMINO ACIDS
CONTENT
Concepts Amino Acids
Properties
Techniques of analyzing amino acids.
Protein structures
Chemical tests
Importance of proteins
1
, CONTENT
AMINO ACIDS
Amino acids are organic molecules that are the building blocks of proteins.
They combine in different sequences to create a vast array of proteins, each with unique
functions in the body, such as building tissues, catalyzing chemical reactions, and
transporting materials. The human body can make 11 of the 20 amino acids it needs, while
the other 9 (essential amino acids) must be obtained through diet.
STRUCTURE:
Each amino acid molecule consists of a central carbon atom bonded to an amino group (−NH2), a
carboxyl group (−COOH), a hydrogen atom, and a side chain (R-group) that is unique to each
amino acid. It is these two groups that give amino acids their name. The third component that is
always bonded to the carbon atom is a hydrogen atom.
Figure 2.16 (a) The general structure of an amino acid. (b) Structure of the simplest amino acid,
glycine, in which the R group is H, hydrogen.
The only way in which amino acids differ from each other is in the remaining fourth, group of
atoms bonded to the central carbon. This is called the R group. 20 different amino acids occur in
the proteins of living organisms, all with a different R group.
Naturally occurring amino acids are predominantly L-form (laevo), meaning they are the "left-
handed" version and are used almost exclusively to build proteins in living organisms. While the
vast majority of proteins are made of L-amino acids, D-amino acids (dextro or "right-handed")
also exist naturally. However, they are less common and are found in various roles, like in some
peptide antibiotics.
2
, Fig.2.5. D and L-Alanine
Note: Most naturally occurring carbohydrates are in D (+) form (dextrorotatory). But most
naturally occurring amino acids are in L-(-) form (laevorotatory).
This is important because if a D-(+)-glucose bind to a receptor molecule that has L-
configuration, the glucose won’t be effective and the cell will not receive the intended
signal even if the sugar is present. In our body system, most of the molecules where a D
(+)- glucose binds are to the right. But L(-)-amino acids bind to L-configuration
receptors. So, if an L-(-)-amino acid binds to a D(+)-receptor on a cell surface, the
receptor will be inactivated.
That is the reason the glucose container is Glucose-D. The D-represent (Dextro-Glucose).
PEPTIDE BONDS
The peptide bond Figure 2.17 shows how two amino acids can join together. One loses a
hydroxyl (–OH) group from its carboxylic acid group, while the other loses a hydrogen atom
from its amine group. This leaves a carbon atom of the first amino acid free to bond with the
nitrogen atom of the second. The link is called a peptide bond. The oxygen and two hydrogen
3
, atoms removed from the amino acids form a water molecule. This is a condensation reaction,
similar to glycosidic bonds formation in carbohydrates and in the synthesis of triglycerides in
lipids. The new molecule which has been formed, made up of two linked amino acids, is called a
dipeptide.
Any number of extra amino acids could be added to the chain in a series of condensation reactions.
A molecule made up of many amino acids linked together by peptide bonds is called a
polypeptide. A polypeptide is another example of a polymer and a macromolecule, like a
polysaccharide.
A complete protein molecule may contain just one polypeptide chain, or it may have two or more
chains which interact with each other. In living cells, ribosomes are the sites where amino acids
are joined together to form polypeptides. The reaction is controlled by enzymes.
Polypeptides can be broken down to amino acids by breaking the peptide bonds. This is a
hydrolysis reaction, involving the addition of water, and happens naturally in the stomach and
small intestine during digestion. Here, protein molecules in food are hydrolysed into amino
acids before being absorbed into the blood.
4
CONTENT
Concepts Amino Acids
Properties
Techniques of analyzing amino acids.
Protein structures
Chemical tests
Importance of proteins
1
, CONTENT
AMINO ACIDS
Amino acids are organic molecules that are the building blocks of proteins.
They combine in different sequences to create a vast array of proteins, each with unique
functions in the body, such as building tissues, catalyzing chemical reactions, and
transporting materials. The human body can make 11 of the 20 amino acids it needs, while
the other 9 (essential amino acids) must be obtained through diet.
STRUCTURE:
Each amino acid molecule consists of a central carbon atom bonded to an amino group (−NH2), a
carboxyl group (−COOH), a hydrogen atom, and a side chain (R-group) that is unique to each
amino acid. It is these two groups that give amino acids their name. The third component that is
always bonded to the carbon atom is a hydrogen atom.
Figure 2.16 (a) The general structure of an amino acid. (b) Structure of the simplest amino acid,
glycine, in which the R group is H, hydrogen.
The only way in which amino acids differ from each other is in the remaining fourth, group of
atoms bonded to the central carbon. This is called the R group. 20 different amino acids occur in
the proteins of living organisms, all with a different R group.
Naturally occurring amino acids are predominantly L-form (laevo), meaning they are the "left-
handed" version and are used almost exclusively to build proteins in living organisms. While the
vast majority of proteins are made of L-amino acids, D-amino acids (dextro or "right-handed")
also exist naturally. However, they are less common and are found in various roles, like in some
peptide antibiotics.
2
, Fig.2.5. D and L-Alanine
Note: Most naturally occurring carbohydrates are in D (+) form (dextrorotatory). But most
naturally occurring amino acids are in L-(-) form (laevorotatory).
This is important because if a D-(+)-glucose bind to a receptor molecule that has L-
configuration, the glucose won’t be effective and the cell will not receive the intended
signal even if the sugar is present. In our body system, most of the molecules where a D
(+)- glucose binds are to the right. But L(-)-amino acids bind to L-configuration
receptors. So, if an L-(-)-amino acid binds to a D(+)-receptor on a cell surface, the
receptor will be inactivated.
That is the reason the glucose container is Glucose-D. The D-represent (Dextro-Glucose).
PEPTIDE BONDS
The peptide bond Figure 2.17 shows how two amino acids can join together. One loses a
hydroxyl (–OH) group from its carboxylic acid group, while the other loses a hydrogen atom
from its amine group. This leaves a carbon atom of the first amino acid free to bond with the
nitrogen atom of the second. The link is called a peptide bond. The oxygen and two hydrogen
3
, atoms removed from the amino acids form a water molecule. This is a condensation reaction,
similar to glycosidic bonds formation in carbohydrates and in the synthesis of triglycerides in
lipids. The new molecule which has been formed, made up of two linked amino acids, is called a
dipeptide.
Any number of extra amino acids could be added to the chain in a series of condensation reactions.
A molecule made up of many amino acids linked together by peptide bonds is called a
polypeptide. A polypeptide is another example of a polymer and a macromolecule, like a
polysaccharide.
A complete protein molecule may contain just one polypeptide chain, or it may have two or more
chains which interact with each other. In living cells, ribosomes are the sites where amino acids
are joined together to form polypeptides. The reaction is controlled by enzymes.
Polypeptides can be broken down to amino acids by breaking the peptide bonds. This is a
hydrolysis reaction, involving the addition of water, and happens naturally in the stomach and
small intestine during digestion. Here, protein molecules in food are hydrolysed into amino
acids before being absorbed into the blood.
4
