SPPT2040- Biochemistry Modulhfue 4- -.pdf

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1. School of Physiotherapy
Dr. Ramasamy Rajesh Kumar
BSc (Microbio), MSc (BioTech), PGDBI, MPhil (BioTech), PhD (Env BioTech), Post Doc (CBNU, South Korea), MBA (HRM),
Post Doc (NKU, China), Post Doc (ZJU, China), LLB (General), MSc ( Counselling and Psychotherapy)
LMISTE, FAELSc, FSOE, SMAPCEEBS, MISALS, FSMBB, MWASET

SPPT2040: Biochemistry
Module: 02

2. Proteins are the most abundant organic molecules of the living system.
They occur in every part of the cell and constitute about 50% of the cellular dry
weight.
Proteins are the polymers of amino acids.
Proteins form the fundamental basis of structure and function of life.
The term protein is derived from a Greek word proteios, meaning holding the
first place.
Mulder (Dutch chemist) in 1838 used the term proteins for the high molecular
weight nitrogen-rich and most abundant substances present in animals and
plants.
These include metabolism, movement, defense, cellular communication, and
molecular recognition.


PROTEINS

3. The term protein is generally used for a polypeptide containing more than 50
amino acids.
Proteins composition- C -50 – 55% ,H- 6 – 7.3% ,O- 19 – 24% ,N -13 – 19%, S- 0 – 4%.
For the determination of secondary and tertiary protein structures, X-ray
crystallography is most commonly used.
Nuclear magnetic resonance (NMR) spectra of proteins provides structural and
functional information on the atoms and groups present in the proteins.
Protein separation is achieved by utilizing electrophoresis, isoelectric focussing,
immuno-electrophoresis, ion-exchange chromatography, gel-filtration, high
performance liquid chromatography (HPLC) etc.
PROTEINS COMMON INFORMATIONS

4. STRUCTURE OF PROTEINS
1.Primary structure : The linear sequence of amino acids forming the
backbone of proteins (polypeptides).
2.Secondary structure : The spatial arrangement of protein by twisting of the
polypeptide chain.
3. Tertiary structure : The three dimensional structure of a functional protein.
4. Quaternary structure : Some of the proteins are composed of two or more
polypeptide chains referred to as subunits. The spatial arrangement of these
subunits is known as quaternary structure

6. Proteins perform a great variety of specialized and essential functions in the living
cells. These functions may be broadly grouped as static
(structural) and dynamic.
Structural functions : Certain proteins perform brick and mortar roles and are
primarily responsible for structure and strength of body.
These include collagen and elastin found in bone matrix, vascular system and other
organs and ??????- keratin present in epidermal tissues.
Dynamic functions : The dynamic functions of proteins are more diversified in
nature.
These include proteins acting as enzymes, hormones, blood clotting factors,
immunoglobulins, membrane receptors, storage proteins, besides their function in
genetic control, muscle contraction, respiration etc.

FUNCTIONS OF PROTEINS

7. 1.Covalent bonds -Peptide and Disulfide bonds
2. Non-covalent bonds - Hydrogen bonds, Van der Waals forces, Electrostatic bonds,
& Hydrophobic bonds
Peptide bond
The amino acids are held together in a protein by covalent peptide bonds or linkages.
The amino group of an amino acid combines with the carboxyl group of another
amino acid, a peptide bond is formed .
BONDS RESPONSIBLE FOR PROTEIN STRUCTURE

8. Three major types of classifying proteins based on their function, chemical
nature and solubility properties and nutritional importance
A.Functional classification of proteins
1. Structural proteins : Keratin of hair and nails, collagen of bone.
2. Enzymes or catalytic proteins : Hexokinase, pepsin.
3. Transport proteins : Hemoglobin, serum albumin.
4. Hormonal proteins : Insulin, growth hormone.
5. Contractile proteins : Actin, myosin.
6. Storage proteins : Ovalbumin, glutelin.
7. Genetic proteins : Nucleoproteins.
8. Defense proteins : Snake venoms, Immunoglobulins.
9. Receptor proteins for hormones, viruses.

CLASSIFICATION OF PROTEINS

9. B. Protein classification based on chemical nature and solubility

10. C. Nutritional classification of proteins
1. Complete proteins : These proteins have all the ten essential amino acids in the
required proportion by the human body to promote good growth. e.g. egg albumin,
milk casein.
2. Partially incomplete proteins : These proteins partially lack one or more
essential amino acids, and can promote moderate growth. e.g. wheat and rice
proteins (limiting Lys, Thr).
3. Incomplete proteins : These proteins completely lack one or more essential
amino acids. Hence they do not promote growth at all e.g. gelatin (lacks Trp), zein
(lacks Trp, Lys)

11. AMINO ACIDS
Amino acids are a group of organic compounds containing two functional groups—
amino and carboxyl.
The amino group (—NH2) is basic while the carboxyl group (—COOH) is acidic in
nature.
The D-carbon atom binds to a side chain represented by R which is different for each
of the 20 amino acids found in proteins.
In recent years, a 21st amino acid namely selenocysteine has been added.
The 20 amino acids found in proteins are divided into seven distinct groups.
Structure of amino acids

12. 20 MAIN AMINO ACIDS AND THEIR STRACTURES