Proteins are multifunctional biomolecules that are involved in nearly all cellular processes. They have complex structures ranging from primary to quaternary that determine their diverse functions. Proteins can be classified based on their structure, biological function, shape/solubility, composition, and nutritional properties. They perform critical roles such as metabolism, support, transport, defense, regulation, and motion. Common properties include denaturation through heat, acids, bases, and other chemical and physical changes.

1. Proteins
2006-2007
Multipurpos
e
molecules

2. Proteins
⚫ Most structurally & functionally diverse
group of biomolecules
⚫ Function:
⚫involved in almost everything
⚫Metabolism
⚫Support
⚫Transport
⚫Regulation
⚫Motion

3. PROTEIN CAN BE CLASSIFIED BY:
❖Structure
❖Biological function
❖Shape and solubility
❖Composition
❖Nutritional basis

4. CLASSIFICATIO
N BY
STRUCTURE

5. PRIMARY STRUCTURE
� The primary structure of proteins is defined as a linear sequence of amino
acids joined together by peptide bonds.
� Peptide bonds and disulfide bonds are responsible for maintaining the
primary structure.

7. SECONDARY STRUCTURE
� The secondary structure of a protein is defined as a local spatial
structure of a certain peptide segment, that is, the relative positions of
backbone atoms of this peptide segment.
� H-bonds are responsible for stabilizing the secondary structure.
� Repeating units of Ca-C(=O)-N(-H)-Ca constitute the backbone of
peptide chain.
� Six atoms, Ca-C(=O)-N(-H)-Ca, constitute a planer peptide unit.

9. TERTIARY STRUCTURE
� The tertiary structure is defined as the three- dimensional arrangement
of all atoms of a protein.

11. QUATERNARY
STRUCTURE
� The quaternary structure is defined as the spatial arrangement of
multiple subunits of a protein.
� These subunits are associated through H-bonds, ionic interactions, and
hydrophobic interactions

13. CLASSIFICATIO
N BY
BIOLOGICAL FUNCTION

14. ENZYMES
� Those proteins which
specialized in their function
are highly
with
catalytic activity.
� These proteins regulate almost all biological reactions going
on inside all living cells.
� There are about 2000 different enzymes has been recognized;
each capable of catalyzing a different kind of biochemical
reaction.

15. TRANSPORT PROTEINS
� are those proteins which help in transportation
of life sustaining chemicals vital gases and nutrients.
� Carry essential substances throughout the body.
� Example:
- Haemoglobin is a globular protein present in RBC of blood can binds with
oxygen when blood passes though longs and distributes oxygen through out
the body cells to affect cellular respiration.
- Blood plasma contains lipoprotein which carries lipids from the liver to other
organs.

16. STORAGE PROTEINS
� are those stored inside the cells or tissue as reserved food and can be
mobilized at the time of nutrient requirement to provide energy.
� Store nutrients.
� Example:
- Casein stores protein in milk.
- Ferritin stores iron in the spleen and liver.

17. CONTRACTILE/MOTILE PROTEINS
� Move muscles.
� the ability to contract to change the shape or to
move about.
� These proteins includes. Actin and myosin; which are present in form of
filamentous protein in muscle cells for functioning in the contractile systems.

18. STRUCTURAL PROTEINS
� This type of protein form major component of tendons, cartilages and bones.
� These are fibrous proteins named collagen. Ligaments are contains special
structural protein capable of stretching in two dimensions called as elastin.
� Hairs finger nails, feathers of birds consists of tough insoluble protein named
keratin.
� Major component of silk fibers, threads of spider web contain structural
protein named fibroin.

19. DEFENSE PROTEINS
� Many proteins in body of organisms posses defending action against the
invasion and attack of foreign entities or protect the body from injury.
� Among these proteins special globular protein named
immunoglobulin's or antibodies in
vertebrate’s body is the most indispensible protein.
� It synthesized by lymphocytes and they can neutralize the foreign protein
produced by bacteria, virus and other harmful microbes called antigens
through precipitation or glutination.

20. REGULATORY PROTEIN
� Some proteins help to regulate cellular or physiological activity. Among them
are many hormones, such as insulin; which is a regulatory protein formed in
pancreatic tissue help to regulate the blood sugar level.
� Growth hormones of pituitary and parathyroid hormones regulate Ca++ and
phosphate transport in body. Other proteins called repressors regulate
biosynthesis of enzymes.

21. OTHER FUNCTIONAL PROTEINS
� There are number of proteins whose functions are not yet specified and are
rather exotic. These includes –
� Monelin: - A protein of an African plant has an intensely sweet taste and
used as non toxic food sweetener for human use.
� Antifreeeze: A protein present in blood plasma of Antarctic fisher which
protect their blood freezing in ice cold water.
� Resillin: A type of protein present in wing hinges of some insects with elastic
properties.

22. CLASSIFICATIO
N
BY
SHAPE & SOLUBILITY

23. FIBROUS PROTEINS
� these proteins have a rod like structure. They
are not soluble in water.
(a)These are made up of polypeptide chain that are parallel to the axis & are
held together by strong hydrogen and disulphidebonds.
(b)They can be stretched & contracted like thread.
� Examples:
-Collagen
-Keratin
-Fibrinogen
-Muscle protein

24. GLOBULAR PROTEINS
� these proteins more or less spherical in
nature. Due to their distribution of
amino acids (hydrophobic
hydrophillic
are very
aqueous
inside, outside)
they soluble
in
solution.
� Examples
Myoglobin, albumin, globu lin, casein,
haemoglobin, all of the enzymes, and
protein hormones.

25. MEMBRANE PROTEINS
� These are protein which are in association with lipid membranes.
� Those membrane proteins that are embedded in the lipid bilayer have
extensive hydrophobic amino acids that interact with the non-polar
environment of the bilayer interior.
� Membrane proteins are not soluble in aqueous solution.

26. CLASSIFICATIO
N BY
COMPOSITION

27. SIMPLE PROTEINS
� are those which on hydrolysisyield only
amino acids and no other
major organic or inorganic
hydrolysis products. They usually contain
23%
oxygen,
about
16%
50% carbon,7% hydrogen,
nitrogen and 0–3% sulphur.
� Example:
-Egg (albumin)
-Serum (globulins)
-Wheat (Glutelin)
-Rice (Coryzenin)

28. CONJUGATED PROTEINS
� are those which on hydrolysis yield not only amino acids but also organic or
inorganic components. The non-amino acid part of a conjugated protein is
called prosthetic group.
� Conjugated proteins are classified on the basis of the chemical nature of their
prosthetic groups.

30. NUTRITIONAL BASIS

31. COMPLETE PROTEINS
� A complete protein contains an adequate amount of all of the essential amino
acids that should be incorporated into a diet.
� Some protein contains all the amino acids needed to build new proteins,
which generally come from animal and fish products. A complete protein
must not lack even one essential amino acid in order to be considered
complete.
� Sources: The following foods are examples of complete proteins, which need
not be combined with any other food to provide adequate protein: Meat,
Fish, Poultry, Cheese, Eggs, Yogurt, Milk

32. INCOMPLETE PROTEINS
� An incomplete protein is any protein that lacks one or more essential amino
acids in correct proportions. These can also be referred to as partial
proteins.
� Even if the protein contains all the essential amino acids, they must be in
equal proportions in order to be considered complete. If not, the protein is
considered incomplete.
� Sources of Incomplete Proteins: Grains, Nuts, Beans, Seeds, Peas, Corn

33. COMBINING INCOMPLETE PROTEINS TO
CREATE COMPLETE PROTEINS
� By combining foods from two or more incomplete proteins, a complete
protein can be created. The amino acids that may be missing from one type
of food can be compensated by adding a protein that contains that missing
amino acid.
� When eaten in combination at the same meal, you are providing your
body with all the essential amino acids it requires. These are considered
complementary proteins when they are combined to compensate for each
other's lack of amino acids.

34. � create a complete protein in one meal include:
� Grains with Legumes - sample meal: lentils and rice
⚫ with yellow peppers.
� Nuts with Legumes - sample meal: black bean and
peanut salad.
� Grains with Dairy - sample meal: white cheddar and
⚫ whole wheat pasta.
� Dairy with Seeds - sample meal: yogurt mixed with
sesame and flax seeds.
� Legumes with Seeds - sample meal: spinach salad
⚫ with sesame seed and almond salad dressing.

35. SAMPLES OF COMPLEMENTARY
PROTEINS

36. PROPERTIES
OF
PROTEINS
•Physical Properties
•Chemical Properties

37. PHYSICAL PROPERTIES
� contains carbon, hydrogen, oxygen, nitrogen and small amount of
sulphur.
� composed of amino acids that are linked together by peptide bonds
� act as catalysts, enzymes that speed up the rate of chemical reactions
� provides structural support for cells
� transports substances across cell membrane
� provides a defense mechanism against pathogens (antibodies)
� responds to chemical stimuli
� secretes hormones.

38. TO DETERMINE MOLECULAR NATURE
•In order to determine the nature of the molecular and ionic species that are
present in aqueous solutions at different pH's, we make use of the Henderson -
Hasselbalch Equation.

39. ISOELECTRIC POINT
� the negatively and positively charged molecular species are present in equal
concentration. This behavior is general for simple (difunctional) amino acids.

41. ELECTROPHORESIS
� The distribution of charged species in a sample can be shown experimentally
by observing the movement of solute molecules in an electric field, using the
technique of electrophoresis.

43. CHEMICAL PROPERTIES
� Denaturation of Proteins
Denaturation is a process in
⚫which proteins or nucleic acids lose the
quaternary structure, tertiary structure and
secondary structure which is present in their
native state, by application of some external
stress or compound such as a strong acid or
base, a concentrated inorganic salt, an
organic solvent (e.g., alcohol or chloroform),
radiation or heat.

45. � Denaturation occurs because the bonding interactions responsible for the
secondary structure (hydrogen bonds to amides) and tertiary structure are
disrupted.
� In tertiary structure there are four types of bonding interactions between "side
chains" including: hydrogen bonding, salt bridges, disulfide bonds, and non-polar
hydrophobic interactions. which may be disrupted.
� Therefore, a variety of reagents and conditions can cause denaturation. The most
common observation in the denaturation process is the precipitation or
coagulation of the protein.

46. HEA
T
Heat can be used to disrupt hydrogen bonds and non-polar hydrophobic
interactions. This occurs because heat increases the kinetic energy and
causes the molecules to vibrate so rapidly and violently that the bonds are
disrupted. The proteins in eggs denature and coagulate during cooking.
Other foods are cooked to denature the proteins to make it easier for
enzymes to digest them. Medical supplies and instruments are sterilized by
heating to denature proteins in bacteria and thus destroy the bacteria.

47. ALCOHOL DISRUPTS HYDROGEN BONDING:
� Hydrogen bonding occurs between amide groups in the secondary protein structure.
Hydrogen bonding between "side chains" occurs in tertiary protein structure in a variety of
amino acid combinations. All of these are disrupted by the addition of another alcohol.
� A 70% alcohol solution is used as a disinfectant on the skin. This concentration of alcohol is
able to penetrate the bacterial cell wall and denature the proteins and enzymes inside of the
cell. A 95% alcohol solution merely coagulates the protein on the outside of the cell wall and
prevents any alcohol from entering the cell. Alcohol denatures proteins by disrupting the side
chain intramolecular hydrogen bonding. New hydrogen bonds are formed instead between
the new alcohol molecule and the protein side chains.

48. ACIDS AND BASES DISRUPT SALT BRIDGES:
� Salt bridges result from the neutralization of an acid and amine on side
chains. The final interaction is ionic between the positive ammonium group
and the negative acid group. Any combination of the various acidic or amine
amino acid side chains will have this effect.
� The denaturation reaction on the salt bridge by the addition of an acid
results in a further straightening effect on the protein chain as shown in the
graphic on the left.

49. HEAVY METAL
SALTS
� Heavy metal salts act to denature proteins in much the same manner as acids and bases.
Heavy metal salts usually contain Hg
+2
, Pb
+2
, Ag
+1
Tl
+1
, Cd
+2
and other metals with high
atomic weights. Since salts are ionic they disrupt salt bridges in proteins. The reaction of a
heavy metal salt with a protein usually leads to an insoluble metal protein salt.
� This reaction is used for its disinfectant properties in external applications. For example
AgNO3 is used to prevent gonorrhea infections in the eyes of new born infants. Silver nitrate is
also used in the treatment of nose and throat infections, as well as to cauterize wounds.
� Mercury salts administered as Mercurochrome or Merthiolate have similar properties in
preventing infections in wounds.

50. Acids
� Acidic protein denaturants
include:
� Acetic acid
[8]
� Trichloroacetic acid 12% in water
� Sulfosalicylic acid
Solvents
� Most organic solvents are denaturing,
including:
� Ethanol
� Methanol
Cross-linking reagents
� Cross-linking agents for proteins
include:[citation needed]
� Formaldehyde
� Glutaraldehyde
� Chaotropic agents
� Chaotropic agents include:
� Urea 6 – 8 mol/l
� Guanidinium chloride 6 mol/l
� Lithium perchlorate 4.5 mol/l
Disulfide bond reducers[edit]
� Agents that break disulfide
bonds by reduction include:
[citation
needed]
� 2-Mercaptoethanol
� Dithiothreitol
� TCEP (tris(2-
carboxyethyl)phosphine)
Other
� Picric acid
� Radiation
� Temperature

51. Example of denaturation that occurs in
our living:
1. Denaturation of human hair
� The extent to which fatty acid oxygenases
are activated in the normal epidermis is not known
2. In cooking eggs
� cooking eggs turns them from runny to solid
� cooking food makes it more digestible.
3. Milk forms a solid curd on standing
� ·
� ·
� ·
� ·
� ·
bacteria in milk grows forms
lactic acid
protonates carboxylate groups
becomes isoelectric coagulates into a
solid curd

52. Metabolism
⚫Enzymes
⚫Biological catalysts – speed up chemical
reactions
⚫ Digestive enzymes aid in hydrolysis
o Lipase
o Amylase
o Lactase
o Protease
⚫ Molecular Biology
o Polymerase
o Ligase
⚫ Industry
o Dairy, baby food, rubber, beer, photography,
contact lense cleaner

53. Support
⚫Structural proteins
⚫Keratin – hair and nails
⚫Collagen – supports ligaments, tendons, and
skin
⚫Silk – cocoons and spider webs

54. Transport
⚫Channel and carrier proteins in the cell
membrane
⚫Allows substances to enter and exit the cell
⚫Transport molecules in blood
⚫Hemoglobin – transports oxygen in the
blood

55. Defense
⚫Antibodies
⚫Combat bacteria and viruses

56. Regulation
⚫Hormones
⚫Intercellular messengers that influence
metabolism
⚫Insulin – regulates the amount of glucose in
the
blood and in cells
⚫Human growth hormone – its presence
determines
the height of an individual
⚫Receptor Proteins
⚫Built into the membranes of nerve cells
⚫Detect chemical signals (neurotransmitters)
released by other nerve cells

57. Motion
⚫Muscle contraction
⚫Actin and myosin – make up muscle fibers
⚫Motor proteins within the cell
⚫Allow cell components to move from place
to place
⚫Flagella- move the cell
⚫Cilia- move contents around the cell

58. Proteins
⚫ Structure:
⚫monomer = amino acids
⚫20 different amino acids
⚫12 made by body
⚫8 essential amino acids (must get from
food)
⚫polymer = polypeptide
⚫protein can be one or more polypeptide
chains folded & bonded together
⚫large & complex molecules
⚫complex 3-D shape
Rubisc
o
hemoglobi
n
growth
hormone

59. Amino acids
▪ Structure:
◆ central carbon (α carbon)
◆ amino group
◆ carboxyl group (acid)
◆ R group (side chain)
▪ variable group
▪ confers unique
chemical properties
of the amino acid —N—
H
H
C—OH
||
O
R
|
—C—
|
H

60. Nonpolar amino acids
▪ nonpolar & hydrophobic

61. Polar amino acids
▪ polar or charged & hydrophilic

62. Sulfur containing amino acids
⚫ Form disulfide bridges
⚫ cross links betweens sulfurs in amino acids
You wondered
why perms
smelled like
rotten eggs?
H-S – S-H

63. Building proteins
⚫ Peptide bonds
⚫ linking NH2 of one amino acid to
COOH of another
⚫ C–N bond
⚫ N terminus – C terminus
peptide
bond
dehydration
synthesis