1. CLASSIFICATION OF
PROTEINS

2. Functions / importance of Proteins
Type Examples
Structural tendons, cartilage, hair, nails
Contractile muscles
Transport hemoglobin, albumin
Storage ferritin
Hormonal eg. insulin, growth hormone
Enzyme eg. hydroxylases
Protection immunoglobulins
Energy k.cal/gm

3. 1. Classification of proteins based on physical properties
2. Classification of proteins based on function
3. Classification of proteins based on complexity
Simple
Conjugated
Derived

4. Classification of proteins based on physical properties
II GLOBULAR PROTEINS
Albumins
2. Globulins
3. Histones
4. Protamines
I. FIBROUS PROTEINS
1. Collagens
2. Elastin
3. Keratins

5. CLASSIFICATION OF PROTEINS BASED ON PHYSICAL PROPERTIES
Examples
I. FIBROUS PROTEINS
Insoluble in aqueous solutions elongated molecules often consisting of several coiled polypeptide chains
1. Collagens
Can be converted into soluble gelatins by boiling contain large amounts of hydroxy-proline and hydroxylysine but no cysteine or tryptophan
The major proteins of connective tissues
2. Elastin
Similar to collagens but cannot be converted to gelatins by boiling
Proteins of tendons and arteries
3. Keratins
Contain large amounts of cysteine
Hair, wool, nails (Hair is about 14% cysteine)

6. CLASSIFICATION OF PROTEINS BASED ON PHYSICAL PROPERTIES
Examples
II GLOBULAR PROTEINS
Soluble in aqueous solutions spherical or ellipsoidal in shape
Albumins
Readily soluble in pure water coagulated by heat function as carriers for hydrophobic molecules
Serum albumin, egg albumin
2. Globulins
Insoluble or only slightly soluble in pure water very soluble in aqueous salt solutions can be coagulated by heat
Enzymes and antibodies
3. Histones
Basic proteins contain large amounts of arginine and lysine soluble in pure water
Histones in chromatin
4. Protamines
Very basic proteins contain large amounts of arginine but no tryptophan or tyrosine
Found in sperm cell chromosomes

7. Classification of proteins based on function
II. NONCATALYTIC PROTEINS
1. Carrier proteins
2. Receptor proteins
3. Membrane transport proteins
4. Structural proteins
5. Contractile
6. Protein hormones
7. Antibodies
CATALYTIC PROTEINS
Enzymes

8. Classification of proteins based on function
Properties
Examples
CATALYTIC PROTEINS
Enzymes
Catalyze chemical reactions
Lactate dehydrogenase (LDH) amylase pyruvate dehydrogenase
II. NONCATALYTIC PROTEINS
1. Carrier proteins
Carry molecules or ions through the bloodstream
Hemoglobin, albumin
2. Receptor proteins
Bind hormones and neurotrans mitters to cell membranes
The insulin receptor
3. Membrane transport proteins
Carry molecules across cell membranes
Na+ K+ Atpase, which transports K+ ions into cells and pumps Na+ ions out of cells
4. Structural proteins
Form extracellular structures such as hair and nails
Collagen keratin
5. Contractile proteins
Extend or contract to produce movement of muscles cells or subcellular parts
Myosin, tubulin

9. Classification of proteins based on function……. cont
Properties
Examples
6. Proteins hormones
Messenger molecules that direct the activities of various cells and organs
Insulin, adreno corticotropic hormone (ACTH), growth hormones
7. Antibodies
Bind to foreign substances and activate their elimination from the body
Anti-Rh, Anti –A (antibodies in Rh factor and to blood group A)

10. Classification of proteins based on complexity
Simple
Conjugated
Derived

11. I SIMPLE PROTEINS
Water soluble , coagulated by heat eg. albumin, lactalbumin, ovalbumin
Insoluble in water, soluble in dilute salt solutions. Heat coagulable to variable extent eg lact globulins, immune globulins, myosine
Rich in histidine. Unite with heme to form hemoglobin
Soluble in 70-80% ethanol and insoluble in water eg. gliadin of wheat and zein of maize
Soluble in water but not in ammonium hydroxide. Present in nucleus
Like histones but present in sperm cells. Soluble in ammonium hydroxide.
Also called scleroproteins eg. collagen , elastin and keratin
Albumin
Globulin
Globin
Prolamines
Histones
Protamines
Albuminoids

12. II CONGUGATED PROTEINS
Types
Prosthetic Group
Properties
Example
Nucleoproteins
Nucletic acid (DNA,RNA)
Large, compact complexes
Chromatin, ribosomes
Mucoproteins*
Carbohydrate
More than 4% carbohydrate by weight
Human chorionic gonadotrophin, a hormone used to test for pregnancy
Glycoproteins * Lipoproteins
Lipid
Less than 4% carbohydrate Water soluble
Antibodies
Serum lipoproteins
Proteolipids
Not very water soluble, soluble in nonpolar solvents
Cell membranes
Hemoproteins
Heme group
Characteristic color
Hemoglobin, cytochrome c
Metalloproteins
Metal ion (Fe3+, Zn2+ Mg2+, Mn2+ )
Require a metal ion to function
Carbonic anhydrase
*The distinction between mucoproteins and glycoproteins is somewhat arbitrary

13. III Derived Proteins Primary Derived Secondary Derived
Eg. Denatured proteins
Polypeptides, oligopeptides, proteosis, peptones

14. Peptides Amino acids can be polymerized to form chains:
Two amino acids  dipeptide  one peptide bond.
Three amino acids  tripeptide  two peptide bonds.
Four amino acids  tetrapeptide  three peptide bonds.
Few (2-20 amino acids)  oligopeptide.
More (>20 amino acids)  polypeptide.
Some make 100 AA as the dividing line

15. PEPTIDES AND PROTEINS Amino terminal- N-terminal- Carboxyl terminal-
C-terminal

16. Peptide bond
In proteins, amino acids are joined covalently by peptide bonds, which are amide linkages between the á-carboxyl group of one amino acid and the á-amino group of another. For example, valine and alanine can form the dipeptide valylalanine through the formation of a peptide bond. Peptide bonds are not broken by conditions that denature proteins, such as heating or high concentrations of urea

17. Peptide Bond (amide bond)

18. Characteristics of the peptide bond: The peptide bond has a partial double-bond character, that is, it is shorter than a single bond, and is rigid and planar . This prevents free rotation around the bond between the carbonyl carbon and the nitrogen of the peptide bond. However, the bonds between the á-carbons and the á-amino or á-carboxyl groups can be freely rotated (although they are limited by the size and character of the R-groups). This allows the polypeptide chain to assume a variety of possible configurations..

19. Peptide Bond Key features: 1. Planar
2. Fairly rigid, due to partial double bond character.
3. Almost always in trans configuration.
4. Polar. Can form at least two hydrogen bonds.
5. Places restrictions on the conformation of the polypeptide chain.

21. Each amino acid in a chain makes two peptide bonds.
The amino acids at the two ends of a chain make only one peptide bond.
The amino acid with a free amino group is called amino terminus or NH2-terminus.
The amino acid with a free carboxylic group is called carboxyl terminus or COOH-terminus.