Proteins- Definition, Clasification and functions; Amino Acids Properties and Functions; Enzymes definition, classification and enzyme action; Lipids Definition, classification and Functions

1. PROTEINS CLASSIFICATION
ASHOK KUMAR BOLLAPALLI
LECTURER IN ZOOLOGY
KRK GOVT DEGREE COLLEGE
ADDANKI-523201

2. INTRODUCTION
Polymers of Amino Acids
Polymers formed by condensation of Amino acids
bonded by Amide/Peptide bonds
Swedish chemist Jöns Jacob Berzelius, who in 1838
coined the term protein,
a word derived from the Greek prōteios, meaning
“holding first place.”
two German chemists, Emil Fischer and Franz
Hofmeister, independently stated in 1902 that
proteins are essentially polypeptides consisting of
many amino acids

4. I. CLASSIFICATION OF PROTEIN ON THE BASIS OF
STRUCTURE AND COMPOSITION

This Classification of protein is based on shape or
structure and composition.
 They are classified into three types;
 fibrous,
 globular and
 derived protein.

5. 1. FIBROUS PROTEIN
 They are elongated or fiber like protein.
 Axial ratio (length: breadth ratio) is more than 10
 They are static in nature with simple structure.
 They have less biological functions
 They are mostly present in animals
 Examples;
 Fibrous proteins are further classified as- simple and
conjugated

6.  i. Simple fibrous protein:
 Examples; Scleroprotein (Keratine, elastin, collagen, fibroin
etc)
 Scleroprotein or Albuminoids: they make animal skeleton
and they are water insoluble.
 ii. Conjugated fibrous proteins:
 Examples; pigments present in chicken feather.

7. 2. GLOBULAR PROTEIN
 They are spherical or globular in shape.
 Axial ratio is always less than 10
 They are dynamic in nature (can flow or move) with
higher degree of complexity in structure.
 They have variety of biological functions
 Examples; enzymes, hormones etc
 Globular protein is further classified on the basis of
composition or solubility.

8. I. SIMPLE OR HOMO GLOBULAR PROTEIN
 They are composed of amino acids only.
 Some examples are;
 a. Protamine:
 They are positively charged (basic) proteins mostly present in
animals and fishes (sperm)
 Protamines binds with DNA in embryonic stage and later
replaced by histone
 It is soluble in water and ammonium hydroxide solution
 It is not coagulated by heat
 It precipitate out in aqueous solution of alcohol
 Protamine are rich in arginine and lysine whereas devoid of
sulfur containing and aromatic amino acids.
 Eg: Salmin of Salman sperm

9. B. HISTONES
 They are basic protein but weak base in
comparison to protamine.
 Histone is low molecular weight protein and are
water soluble, dilute acid/base soluble. Insoluble in
Ammonia
 It is not coagulated by heat.
 Yield lysine and arginine on hydrolysis
 Histone is present in nucleic acids as nucleohistone
binding with DNA.

10. C. ALBUMIN
 It is the most abundant protein in nature
 It is most commonly found in seeds in plants and in
blood and muscles in animals.
 Molecular weight of albumin is 65000 KD
 It is water soluble and can be coagulated by heat
 Plant albumins; Leucosine, Legumelins etc
 Animal albumins; serum albumin, lactalbumin, ova-
albumin etc

11. D. GLOBULIN
 Insoluble in water but soluble in dilute salt solutions
 Coagulated by heat
 Pseudoglobulin (water soluble) and Euglobulin (water
insoluble)
 Eg: ovoglobulin, serum globulin, myosin, legumin of peas

12.  e. Glutelins:
 Water insoluble
 Soluble in dilute acids and alkalies. Eg. Glutenin (wheat),
glutelin (corn), oryzenin (rice)
 f. Prolamine:
 They are storage protein found in seeds.
 They are water insoluble. But soluble in dilute acid or
detergents and 60-80% alcohol.
 They are coagulated by heat
 Prolamine is rich in proline and glutamine
 Deficient in lysine
 Examples; Gliadin (wheat), zein (corn), Hordein (barley),
Avenin (oats)

13. G.SCLEROPROTEINS/ALBUMINOIDS
 Insoluble in any solutions
 Animal proteins of hair, hooves, horns, nails etc.

14. II. COMPLEX OR CONJUGATE OR HETERO
GLOBULAR PROTEIN
 These proteins in which protein are always linked
by non-protein moiety to become functional.
 So, they are composed of both protein and non-
protein components.
 The non-protein component is known as prosthetic
group.
 On the basis of prosthetic group, they are classified
as follows;

15. A. METALLOPROTEIN
 They have metal prosthetic group.
 Metal storage forms- ferretin stores iron
 Some metals such as Hg, Ag, CU, Zn etc, strongly binds
with proteins such as collagen, albumin, casein by –SH
group of side chain of amino acids.
 Eg. Ceruloplasmin; contains copper as prosthetic group
 Some other metals such as Calcium weakly binds with
protein. Eg. Calsequestrin, calmodulin
 Some metals such as Na, K etc do not binds with protein
but associate with nucleic acids protein.
 Zinc in alcohol dehydrogenase and carbonic anhydrase

16. B. CHROMOPROTEIN
 They have colored prosthetic group.
 Some examples are;
 Haemoprotein: Haemoglobin, myoglobin, chlorophyll,
cytochrome, peroxidase, haemocyanin
 Flavoprotein: Riboflavin (Vit B2) give yellow/orange color
to FAD requiring enzymes
 Rhodopsin which bind Retinal

17. C. GLYCOPROTEIN/ MUCOPROTEIN
 They have carbohydrate as prosthetic group
 Eg. Antibody, complement proteins, Heparin,
Hyaluronic acid, fibronectin- cells to extracellular
matrix

18. D. PHOSPHOPROTEIN
 They have phosphate group as prosthetic group.
 Eg. Caesein (milk protein binds with calcium ion to
form calcium salt of caseinate)
 Ovovitellin; present in egg yolk
 Calcineurin

19. E. LIPOPROTEIN
 They have lipid as prosthetic group.
 Eg. Lipovitelline, chylomicrons

20. NUCLEOPROTEINS
 Prosthetic groups are nucleic acids
 Nucleoprotein conjugates have many roles in
storage and transmission of genetic information
 Ribosomes are the sites of protein synthesis
 Ribosomes and Chromosomes, virus particles

21. FLAVOPROTEINS
 Flavin, a derivative of riboflavin is an essential
component for the activity of a number of
oxidoreductases
 Eg: FMN is the prosthetic group for NADH
dehydrogenase of cytochrome system and
 FAD is the prosthetic group of succinic dehydrogenase

22. 3. DERIVED PROTEIN
 These protein are the derivatives of either simple or
complex protein resulting from the action of heat,
enzymes and chemicals.
 Some artificially produced protein are included in this
group.
 They are classified as primary derived protein and
secondary derived protein.

23. I. PRIMARY DERIVED PROTEIN
 The derived protein in which the size of protein molecules
are not altered materially but only the arrangement is
changed.
 Some examples are;
 a. Proteans:
 Obtained as a first product after the action of acid or
enzymes or water on protein.
 They are insoluble in water.
 Eg. Edestan, myosin

24. B. METAPROTEIN
 They are produced by further action of acid or alkali on
protein at 30-60°C.
 They are water insoluble but soluble in dil acid or alkali.
 Also known as Infraprotein.
 Eg. Curd

25. C. COAGULATED PROTEIN
 They are produced by the action of heat or alcohol on
protein.
 They are insoluble in water.
 Eg. Coagulated egg

26. II. SECONDARY DERIVED PROTEIN
 The derived protein in which size of original protein are
altered.
 Hydrolysis has occurred due to which size of protein
molecule are smaller than original one.
 Examples; a) Proteoses:
 They are produced by the action of dilute acid or digestive
enzymes when the hydrolysis proceeds beyond the level
of metaprotein.
 They are soluble in water
 They are not coagulated by heat. • Eg. Albumose,
Globulose etc.

27. II. CLASSIFICATION OF PROTEIN ON THE BASIS OF
BIOLOGICAL FUNCTIONS:
 Catalytic protein:
 They catalyze biochemical reaction in cells. Eg. Enzymes and
co-enzymes
 2. Structural protein;
 They make various structural component of living beings.
 Eg. Collagen make bone, Elastin make ligamnets and keratin
make hair and nails
 3. Nutrient protein:
 They have nutritional value and provide nutrition when
consumed.
 Eg. Casein in milk
 4. Regulatory protein:
 They regulate metabolic and cellular activities in cell and tissue.
 Eg. Hormones

28.  5. Defense protein:
 They provide defensive mechanism against pathogens.
 Eg. Antibodies, complement proteins
 6. Transport protein:
 They transport nutrients and other molecules from one organ to
other.
 Eg. Haemoglobin
 7. Storage protein:
 They stores various molecules and ions in cells.
 Eg. Ferritin store Iron
 8. Contractile or mobile protein:
 They help in movement and locomotion of various body parts.
 Eg. Actin, myosin, tubulin etc
 9. Toxic protein:
 They are toxic and can damage tissues.
 Eg. Snake venom, bacterial exotoxins etc

29. REFERENCES
 https://www.onlinebiologynotes.com/classification-of-
protein-on-the-basis-of-structure-composition-and-
function/#:~:text=They%20are%20classified%20into%20t
hree,fibrous%2C%20globular%20and%20derived%20prot
ein.
 Telugu Academy B.Sc third year Zoology
 https://www.britannica.com/science/protein/Plant-proteins

30. AMINOACIDS
 Amino Acids are the organic compounds that combine to form
proteins,
 The building components of proteins.
 These biomolecules are involved in several biological and chemical
functions in the human body
 The necessary ingredients for the growth and development of
human beings.
 There are about 300 amino acids that occur in nature.
 Amino acids are organic compounds containing the basic amino groups
(-NH2) and carboxyl groups (-COOH).
 The ingredients present in proteins are amino acids.
 Both peptides and proteins are long chains of amino acids.
 Altogether, there are twenty amino acids, which are involved in the
construction of proteins.
 Methionine and cysteine are sulphur-containing amino acids.
 Amino acids have both acidic and basic properties. This is why they are
amphoteric. The predominant form of the amino acid is based on the pH
of the solution.

31. 20 AMINO ACIDS WITH THE CHEMICAL FORMULA
Alanine C3H7NO2 Leucine C6H13NO2
Aspartic Acid C4H7NO4 Lysine C6H14N2O2
Asparagine C4H8N2O3 Methionine C5H11NO2S
Arginine C6H14N4O2 Proline C5H9NO2
Cytosine C4H5N3O Phenylalanine C9H11NO2
Cysteine C3H7NO2S Serine C3H7NO3
Glycine C2H5NO2 Tyrosine C9H11NO3
Glutamine C5H10N2O3 Threonine C4H9NO3
Histidine C6H9N3O2 Tryptophan C11H12N2O2
Isoleucine C6H13NO2 Valine C5H11NO2

32. ESSENTIAL AND NON-ESSENTIAL AMINO ACIDS
 Out of 20 amino acids, our body can easily synthesize a
few on its own, which are called non-essential amino acids.
 These include alanine, asparagine, arginine, aspartic acid,
glutamic acid, cysteine, glutamine, proline, glycine, serine,
and tyrosine.
 Apart from these, there are other nine amino acids, which
are very much essential as they cannot be synthesized by
our body.
 They are called essential amino acids, and they include
isoleucine, histidine, lysine, leucine, phenylalanine,
tryptophan, methionine, threonine, and valine.

34. GENERAL PROPERTIES OF AMINO ACIDS
PHYSICAL PROPERTIES
 Amino acids are colorless, crystalline solid.
 All amino acids have a high melting point greater than 200o
 In taste, few Amino acids are sweet, tasteless, and bitter.
 Solubility: They are soluble in water, slightly soluble in alcohol,
and dissolve with difficulty in methanol, ethanol, and propanol.
R-group of amino acids and pH of the solvent play important role
in solubility.
 On heating to high temperatures, they decompose.
 All amino acids (except glycine) are optically active.
 Peptide bond formation: Amino acids can connect with a peptide
bond involving their amino and carboxylate groups. A covalent
bond formed between the alpha-amino group of one amino acid
and an alpha-carboxyl group of other forming -CO-NH-linkage.
Peptide bonds are planar and partially ionic.

35. CHEMICAL PROPERTIES
 Zwitterionic property
 A zwitterion is a molecule with functional groups, of which at least
one has a positive and one has a negative electrical charge.
 The net charge of the entire molecule is zero.
 Amino acids are the best-known examples of zwitterions.
 They contain an amine group (basic) and a carboxylic group
(acidic).
 The -NH2 group is the stronger base, and so it picks up H+ from
the -COOH group to leave a zwitterion.
 The (neutral) zwitterion is the usual form of amino acids that exist in
the solution.
 Amphoteric property
 Amino acids are amphoteric in nature that is they act as both acids
and base due to the two amine and carboxylic groups present.
 Ninhydrin test
 When 1 ml of Ninhydrin solution is added to a 1 ml protein solution
and heated, the formation of a violet color indicates the presence of
α-amino acids.

36.  Xanthoproteic test
 The xanthoproteic test is performed for the detection of
aromatic amino acids (tyrosine, tryptophan, and
phenylalanine) in a protein solution. The nitration of benzoid
radicals present in the amino acid chain occurs due to a
reaction with nitric acid, giving the solution yellow coloration.
 Reaction with Sanger’s reagent
 Sanger’s reagent (1-fluoro-2, 4-dinitrobenzene) reacts with
a free amino group in the peptide chain in a mild alkaline
medium under cold conditions.
 Reaction with nitrous acid
 Nitrous acid reacts with the amino group to liberate nitrogen
and form the corresponding hydroxyl.

37. CLASSIFICATION OF AMINOACIDS
 Nonpolar, Aliphatic amino acids: The R groups in this class of
amino acids are nonpolar and hydrophobic. Glycine, Alanine,
Valine, leucine, Isoleucine, Methionine, Proline.
 Aromatic amino acids: Phenylalanine, tyrosine, and tryptophan,
with their aromatic side chains, are relatively nonpolar
(hydrophobic). All can participate in hydrophobic interactions.
 Polar, Uncharged amino acids: The R groups of these amino
acids are more soluble in water, or more hydrophilic, than those of
the nonpolar amino acids, because they contain functional groups
that form hydrogen bonds with water. This class of amino acids
includes serine, threonine, cysteine, asparagine, and glutamine.
 Acidic amino acids: Amino acids in which R-group is acidic or
negatively charged. Glutamic acid and Aspartic acid
 Basic amino acids: Amino acids in which R-group is basic or
positively charged. Lysine, Arginine, Histidine

38. CLASSIFICATION OF AMINO ACIDS ON THE BASIS OF
THE METABOLIC FATE
 Glucogenic amino acids: These amino acids serve as
precursors of gluconeogenesis for glucose formation.
Glycine, alanine, serine, aspartic acid, asparagine, glutamic
acid, glutamine, proline, valine, methionine, cysteine,
histidine, and arginine.
 Ketogenic amino acids: These amino acids break down to
form ketone bodies. Leucine and Lysine.
 Both glucogenic and ketogenic amino acids: These
amino acids break down to form precursors for both ketone
bodies and glucose. Isoleucine, Phenylalanine, Tryptophan,
and tyrosine.

39. FUNCTIONS OF AMINOACIDS
 In particular, 20 very important amino acids are crucial for
life as they contain peptides and proteins and are known to
be the building blocks for all living things.
 The linear sequence of amino acid residues in a
polypeptide chain determines the three-dimensional
configuration of a protein, and the structure of a protein
determines its function.
 Amino acids are imperative for sustaining the health of the
human body. They largely promote the:
Production of hormones
• Structure of muscles
• Human nervous system’s healthy functioning
• The health of vital organs
• Normal cellular structure

40.  The amino acids are used by various tissues to synthesize
proteins and to produce nitrogen-containing compounds
(e.g., purines, heme, creatine, epinephrine), or they are
oxidized to produce energy.
 The breakdown of both dietary and tissue proteins yields
nitrogen-containing substrates and carbon skeletons.
 The nitrogen-containing substrates are used in the
biosynthesis of purines, pyrimidines, neurotransmitters,
hormones, porphyrins, and nonessential amino acids.
 The carbon skeletons are used as a fuel source in the citric
acid cycle, used for gluconeogenesis, or used in fatty acid
synthesis.

41. REFERENCES
 https://byjus.com/biology/amino-acids/

42. ENZYMES, DEFINITION ,CLASSIFICATION AND MODE OF
ACTION
 Enzymes are proteins or biological molecules acting as
catalysts facilitating complex reactions.
 They are typically active in mild conditions hence are
extremely beneficial to be utilized in food technology,
wherein raw materials are treated without interfering with
the nutritional value.
 Enzymes work by binding to the substrates of the reaction,
their reactants on a temporary basis, hence lowering the
amount of activation energy required to accelerate the
reaction.
 They are distinguished by a remarkably high rate of
specificity and efficiency.

43. NAMING AND CLASSIFICATION OF ENZYMES
 The International Union of Biochemistry and Molecular
Biology is entrusted with designating names to enzymes in
addition to assigning a number in order to identify them.
 Apart from a few originally studied enzymes such as rennin,
pepsin and trypsin, almost all the enzyme names end in “ase”.
As per the standards, focal points of nomenclature of
enzymes are both the type of reaction catalyzed and the
substrate acted upon.
 Most commonly, enzymes are named to provide data on the
function as opposed to the structure of the enzyme.
 However, there are 3 significant features of the nomenclature
process of enzymes, which are:

44.  Suffix -ase recognizes a substance as that of an enzyme
 Suffix -in is observed in the name of first enzymes learnt as
pepsin, chymotrypsin, trypsin
 Prefix is identified by the type of reaction the enzyme
catalyzes
 Enzyme hydrolase : catalyzes a hydrolysis reaction
 Enzyme oxidase : catalyzes an oxidation reaction
 In addition to the type of reaction, the identity of the
substrate is taken into consideration
 Glucose oxidase – catalysis of glucose oxidation
 Lactate dehydrogenase – catalysis of eliminating hydrogen from
lactate ion
 Lactase – hydrolysis of lactose is catalyzed
 Urease – hydrolysis of urea is catalyzed

45. CONVENTIONS OF NAMING – EC NUMBERS
 The nomenclature developed by the International Union of
Biochemistry and Molecular Biology has something called EC
numbers where each enzyme is preceded by EC.
 The first number in this series classifies this enzyme on the basis
of its mechanism.
 EC numbers
 There are six groups of enzymes as per the reaction that is being
catalyzed. Therefore, all enzymes are designated as “EC
numbers”.
 This classification does not consider protein structure, amino
acid sequence or even the chemical mechanism.
 EC number is a 4 digit number for instance – a.b.c.d. Here “a” is
class, “b” is subclass, “c” is sub-subclass and “d” is the sub-sub-
subclass.
 The “b” and “c” part of the EC number describes the reaction, “d”
differentiates between different enzymes with similar function on
the basis of the actual substrate in the reaction.
 Example – EC number of Alcohol: NAD+ oxidoreductase is
1.1.1.1

46.  Six Classes of Enzymes – Enzyme Classification
 EC 1. Oxidoreductases
 EC 2. Transferases
 EC 3. Hydrolases
 EC 4. Lyases
 EC 5. Isomerases
 EC 6. Ligases

47. ENZYMES CLASSIFICATION
 “Enzymes can be defined as biological polymers that
catalyze biochemical reactions.”
 The majority of enzymes are proteins with catalytic
capabilities crucial to perform different processes.
Metabolic processes and other chemical reactions in the
cell are carried out by a set of enzymes that are necessary
to sustain life.
 According to the International Union of Biochemists (I U B),
enzymes are divided into six functional classes and
are classified based on the type of reaction in which they
are used to catalyze.
 The six kinds of enzymes are hydrolases, oxidoreductases,
lyases, transferases, ligases and isomerases.

48. OXIDOREDUCTASES
 These catalyze oxidation and reduction reactions, e.g.
pyruvate dehydrogenase, catalysing the oxidation of
pyruvate to acetyl coenzyme A.
 a) Dehydrogenase (Alcohol Dehydrogenase)
 b) Oxidase (Cytochrome Oxidase)
 c) Peroxidase (Glutathione Peroxidase)
 Alcohol dehydrogenase (EC 1.1.1.1) :
 This enzyme oxidizes ethanol into acetaldehyde. It
requires the coenzyme NAD+ (Niacinamide Adenine
Dinucleotide) which gets reduced to NADH.

49. TRANSFERASES
 These catalyze transferring of the chemical group from one
to another compound.
 An example is a transaminase, which transfers an amino
group from one molecule to another.
 Transaminase (Transfers an amino group
 Example Aspartate amino transferase)
 Transacylase (Transfers an acyle group
 Example Malonyl transacylase)
 Phosphorylase (Transfers a phosphate group
 Example Glycogen phosphorylase)

50. TRANSAMINASE
They catalyse the transfer of amino group from amino acid to
keto acid.
Example: Glutamate oxaloacetate transaminase (GOT) or
Aspartate transaminase (AST; EC 2.6.1.1).
This enzyme catalyses the transfer of amino group from
glutamic acid to oxaloacetic acid.
It requires pyridoxal phosphate (PLP) as coenzyme for its
activity.

51. HYDROLASES
 They catalyze the breakdown of a bond by addition of water
molecules. (hydrolysis)
 For example, Lipase ,Urease , Glycosidase.
 the enzyme pepsin hydrolyzes peptide bonds in proteins.
 Amylase hydrolyses glycosidic bonds in a polysaccharides
 Lipase hydrolyses phospho diester bonds in triglycerides

52. LIPASE (EC 3.1.1.3):
 These are enzymes which hydrolyze the ester linkage.
 For example triacyl glycerol lipase (EC 3.1.1.3) splits the
ester linkage between glycerol and fatty acid.

53. LYASES
 These catalyze the breakage of bonds without catalysis,
 These enzymes catalyze the addition or elimination of
groups like H2O, CO2, and NH3 etc.
 e.g. Aldolase (an enzyme in glycolysis) catalyzes the
splitting of fructose-1, 6-bisphosphate to glyceraldehyde-3-
phosphate and dihydroxyacetone phosphate,
decarboxylase

54. FRUCTOSE BISPHOSPHATE ALDOLASE (EC
4.1.2.13)
 It catalyzes the reversible conversion of fructose-1,6-
bisphosphate to glyceraldehyde-3-phosphate and
dihydroxyacetone phosphate by aldol cleavage of the C3–
C4 bond.

55. ISOMERASES
 They catalyze the formation of an isomer of a compound.
 These enzymes catalyze the inter-conversion of isomers
such as optical, geometrical or positional isomers.
 Example: phosphoglucomutase catalyzes the conversion of
glucose-1-phosphate to glucose-6-phosphate
 (phosphate group is transferred from one to another
position in the same compound) in glycogenolysis
 (glycogen is converted to glucose for energy to be released
quickly).
 Example : Alanine racemase (EC 5.1.1.1)

56. B) TRIOSEPHOSPHATE ISOMERASE
(EC 5.3.1.1)
 This enzyme catalyzes the isomerization of
glyceraldehyde-3-phosphate into dihydroxy acetone
phosphate.

57. LIGASES
 Ligases catalyze the association of two molecules.
 These enzymes catalyze the synthetic reactions. They link
two substrates together with the utilization of ATP or GTP.
 For example,
 DNA ligase catalyzes the joining of two fragments of DNA
by forming a phosphodiester bond.
 Example : Glutamine synthetase.
 Glutamine synthetase (EC 6.3.1.2):
 This is a ligase which catalyzes the synthesis of glutamine
from glutamate and NH3.

59. COFACTORS
 Cofactors are non-proteinous substances that associate with
enzymes.
 A cofactor is essential for the functioning of an enzyme.
 An enzyme without a cofactor is called an apoenzyme.
 An enzyme and its cofactor together constitute the holoenzyme.
 There are three kinds of cofactors present in enzymes:
 Prosthetic groups: These are cofactors tightly bound to an
enzyme at all times. FAD (flavin adenine dinucleotide) is a
prosthetic group present in many enzymes.
 Coenzyme: A coenzyme binds to an enzyme only during
catalysis. At all other times, it is detached from the enzyme.
NAD+ is a common coenzyme.
 Metal ions: For the catalysis of certain enzymes, a metal ion is
required at the active site to form coordinate bonds. Zn2+ is a
metal ion cofactor used by a number of enzymes.

60. MECHANISM OF ENZYME REACTION
 Any two molecules have to collide for the reaction to occur
along with the right orientation and a sufficient amount of
energy.
 The energy between these molecules needs to overcome
the barrier in the reaction.
 This energy is called activation energy.
 Enzymes are said to possess an active site.
 The active site is a part of the molecule that has a definite
shape and the functional group for the binding of reactant
molecules.
 The molecule that binds to the enzyme is referred to as the
substrate group.
 The substrate and the enzyme form an intermediate
reaction with low activation energy without any catalysts.

62.  The enzyme action basically happens in two steps:
 Step1: Combining of enzyme and the reactant/substrate.
 E+S → [ES]
 Step 2: Disintegration of the complex molecule to give
the product.
 [ES]→E+P
 Thus, the whole catalyst action of enzymes is
summarized as:
 E + S → [ES] → [EP] → E + P

63.  Once substrate (S) binds to this active site, they form a
complex (intermediate-ES) which then produces the
product (P) and the enzyme (E).
 The substrate which gets attached to the enzyme has a
specific structure and that can only fit in a particular
enzyme.
 Hence, by providing a surface for the substrate, an enzyme
slows down the activation energy of the reaction.
 The intermediate state where the substrate binds to the
enzyme is called the transition state.
 By breaking and making the bonds, the substrate binds to
the enzyme (remains unchanged), which converts into the
product and later splits into product and enzyme.
 The free enzymes then bind to other substrates and the
catalytic cycle continues until the reaction completes.

65. ENZYME ACTION- THEORIES
 There are two processes for this mode of action:
 Lock and key concept:
 Emil fisher proposed
 According to the "lock and key" hypothesis, the substrate
fits precisely into the enzyme's lock.
 Induced fit:
 Koshland proposed
 In the induced fit hypothesis, the active site is not a rigid
structure, but a flexible one, which can change shape to fit
precisely with the substrate molecule.

66. FISCHER'S LOCK AND KEY THEORY
 proposed by Fisher.
 According to this theory, first a physical contact is made between the
enzyme and the substrate.
 As only a specific key fits in a particular lock to open it, a specific
substrate combines with the active site of specific enzyme.
 This combination leads to the production of enzyme - substrate
complex.
 Then the enzyme acts on the substrate and changes it into products.
 After the reaction is over, enzyme is released from the enzyme -
substrate complex and is ready to bind with another molecule of the
substrate for further action.
 The cyclic reaction is summarized by the equation
E + S -><-[ES]-><-PS
 ( where, E - enzyme, S - substrate and P - product)
 When a dissimilar substrate approaches the enzyme, it cannot
combine with the active site of the enzyme, as a wrong key cannot
open the lock. Thus, the enzyme action is inhibited.

67. KOSHLAND'S INDUCED FIT THEORY
 Induced fit theory was proposed by Koshland.
 Proteins are not rigid.
 The substrate induces the enzyme to adjust its shape
leading to the formation of enzyme sub-strate complex.
 Then, the enzyme acts on substrate and forms products.
Many enzymes function in this way.

69. REFERENCES
 https://byjus.com/biology/enzymes/
 https://byjus.com/neet/enzyme-names/

70. LIPIDS- CLASSIFICATION
 Esters of alcohols and fatty acids
 Biomolecules that are soluble in organic solvents like
chloroform and methanol but are insoluble in water
 They constitute a broad group of naturally occuring
molecules which include oils,fats waxes phospholipids
sterols fat soluble vitamins, eicosanoids and others
 Types of Lipids
 Within these two major classes of lipids, there are numerous
specific types of lipids, which are important to life, including
fatty acids, triglycerides,glycerophospholipids, sphingolipids
and steroids.
 These are broadly classified as simple lipids and complex
lipids.

71.  Lipids are made of the elements Carbon, Hydrogen and Oxygen,
but have a much lower proportion of water than other molecules
such as carbohydrates.
 Unlike polysaccharides and proteins, lipids are not polymers—
they lack a repeating monomeric unit.
 They are made from two molecules: Glycerol and Fatty Acids.
 A glycerol molecule is made up of three carbon atoms with a
hydroxyl group attached to it and hydrogen atoms occupying the
remaining positions.
 Fatty acids consist of an acid group at one end of the molecule
and a hydrocarbon chain, which is usually denoted by the letter
‘R’.
 They may be saturated or unsaturated.
 A fatty acid is saturated if every possible bond is made with a
Hydrogen atom, such that there exist no C=C bonds.
 Unsaturated fatty acids, on the other hand, do contain C=C
bonds. Monounsaturated fatty acids have one C=C bond, and
polyunsaturated have more than one C=C bond.

72. STRUCTURE OF TRIGLYCERIDES
 Triglycerides are lipids consisting of one glycerol molecule
bonded with three fatty acid molecules.
 The bonds between the molecules are covalent and are
called Ester bonds.
 They are formed during a condensation reaction.
 The charges are evenly distributed around the molecule so
hydrogen bonds to not form with water molecules making
them insoluble in water.

73. CLASSIFICATION OF LIPIDS
 Lipids can be classified according to their hydrolysis
products and according to similarities in their molecular
structures. Three major subclasses are recognized:
 1. Simple lipids
 2. Compound lipids
 3. Derived lipids

74. SIMPLE LIPIDS
 Esters of fatty acids with various alcohols.
 Fats: Esters of fatty acids with glycerol. Oils are fats in the
liquid state, which yield fatty acids and glycerol upon
hydrolysis.
 Waxes: Esters of fatty acids with higher molecular weight
monohydric alcohols, which yield fatty acids and long-chain
alcohols upon hydrolysis.

75. FATS AND OILS
 Both types of compounds are called triacylglycerols
because they are esters composed of three fatty acids
joined to glycerol, trihydroxy alcohol.
 The difference is on the basis of their physical states at
room temperature. It is customary to call a lipid a fat if it is
solid at 25°C, and oil if it is a liquid at the same
temperature.
 These differences in melting points reflect differences in the
degree of unsaturation of the constituent fatty acids.

76. WAXES
 Wax is an ester of long-chain alcohol (usually mono-
hydroxy) and a fatty acid.
 The acids and alcohols normally found in waxes have
chains of the order of 12-34 carbon atoms in length.

77.  Complex Lipids
 Esters of fatty acids containing groups in addition to alcohol
and fatty acid.
 Phospholipids: which yield fatty acids, glycerol, amino alcohol
sphingosine, phosphoric acid and nitrogen-containing alcohol
upon hydrolysis.
 Theymaybe glycerophospholipids or sphingophospholipid
depending upon the alcohol group present (glycerol or
sphingosine).
 Glycolipids (glycosphingolipids): Glycolipids, which yield
fatty acids, sphingosine or glycerol, and a carbohydrate upon
hydrolysis.
 They may also
be glyceroglycolipids or sphingoglycolipid depending
upon the alcohol group present (glycerol or sphingosine).
 Other complex lipids: Lipids such as sulfolipids and amino
lipids. Lipoproteins may also be placed in this category.

78. DERIVED LIPIDS
 Hydrolysis product of simple and compound lipids is called
derived lipids. They include fatty acid, glycerol,
sphingosine and steroid derivatives.
 Steroid derivatives are phenanthrene structures that are
quite different from lipids made up of fatty acids.

79. STEROIDS
 Our bodies possess chemical messengers known
as hormones, which are basically organic compounds
synthesized in glands and transported by the bloodstream
to various tissues in order to trigger or hinder the desired
process.
 Steroids are a kind of hormone that is typically recognized
by their tetracyclic skeleton, composed of three fused six-
membered and one five-membered ring, as seen above.
The four rings are assigned as A, B, C & D as observed in
the shade blue, while the numbers in red indicate the
carbons.

80. CHOLESTEROL
 Cholesterol is a wax-like substance, found only in animal source
foods. Triglycerides, LDL, HDL, VLDL are different types of
cholesterol found in the blood cells.
 Cholesterol is an important lipid found in the cell membrane. It is
a sterol, which means that cholesterol is a combination of steroid
and alcohol. In the human body, cholesterol is synthesized in the
liver.
 These compounds are biosynthesized by all living cells and
are essential for the structural component of the cell membrane.
 In the cell membrane, the steroid ring structure of cholesterol
provides a rigid hydrophobic structure that helps boost the rigidity
of the cell membrane. Without cholesterol, the cell membrane
would be too fluid.
 It is an important component of cell membranes and is also the
basis for the synthesis of other steroids, including the sex
hormones estradiol and testosterone, as well as other steroids
such as cortisone and vitamin D.

81. FUNCTIONS
 It is established that lipids play extremely important roles in the normal
functions of a cell. Not only do lipids serve as highly reduced storage forms of
energy, but they also play an intimate role in the structure of cell membrane
and organellar membranes. Lipids perform many functions, such as:
 Energy Storage
 Making Biological Membranes
 Insulation
 Protection – e.g. protecting plant leaves from drying up
 Buoyancy
 Acting as hormones
 Act as the structural component of the body and provide the hydrophobic
barrier that permits partitioning of the aqueous contents of the cell and
subcellular structures.
 Lipids are major sources of energy in animals and high lipid-containing seeds.
 Activators of enzymes eg. glucose-6-phosphatase, stearyl CoA desaturase and
ω-monooxygenase, and β-hydroxybutyric dehydrogenase (a mitochondrial
enzyme) require phosphatidylcholine micelles for activation.


82. REFERENCES
 https://microbenotes.com/lipids-properties-structure-
classification-and-functions/#classification-types-of-lipids
 https://www.notesonzoology.com/lipids/lipids-definition-
classification-an-functions-biochemistry/3510