Chapter-5
VARIETY OF LIFE
BASIS OF CLASSIFICATION OF LIVING ORGANISMS
The living organisms are classified on the basis of Homology, comparative Biochemistry cytology and Genetics.
(a) Homology
(b) Cytology.
(c) Bio-chemistry.
(d) Genetics
(A) HOMOLOGY
The organisms placed in a particular group, all have many fundamental similarities in their structure. EXAMPLE
The flipper, wing and arm are, all build on the same pattern but during the course of evolution, each has been modified from its basic pattern to serve a particular and usually highly specialized function, due to its adaptation different to environment or habitate. (Structures that are similar because of their common origin but may differ functionally is known as Homologus)
(B) BIOCHEMISTRY
It is particularly useful, when we classify organism like bacteria, which may all look alike and have an identical cellular structure with the help of chromatography and electrophoresis we can compare the amino acid sequence in the protein of different organisms or the order of bases in their DNA.
(C) CYTOLOGY
Microscopic observations of cell structure are also used to make a fundamental split in the classification of living things. They can be useful at the level of generic and species level. This sort of technique can show delicate difference between species or sub-species, which are identical in many other respects. Specie ? Genus ? Family ? Order ? Class ? Division ? Kingdom
(D) GENETICS
All the morphological, Bio-chemical properties and cytological aspects of an individual, or of a species depend on its genetic constitution. Hence the final tool helping in classifying an organism is Genetics.
TAXONOMIC HIERARCHY
The basic unit of the biological classification is specie. Closely related species are grouped-together into Genera. Genera are grouped into Families, families into order, orders into classes, classes into phyla and phyla or divisions into kingdoms. Each grouping of organisms with in the hierarchy is called taxon and each taxon has a rank and a name. For example class “mammalia” or Genus “Homo”. This ascending series of successively larger, more inclusive groups make up the “Taxonomic Hierarchy”.
CHANGES PROPOSED BY MARGUILES AND SCHWARTZ IN THE FIVE-KINGDOM SYSTEM
Marguiles and schwartz were American Biologist, put forward a modification of Robert Whittaker’s scheme. According to this modification.
• The multicellular alga should be removed from the plant kingdom and placed along with all unicellular organisms, in a new kingdom called “PROTOCTIST” which would replace Whittaker’s Protista kingdom.
• This modification made the plant kingdom a more natural group.
• Due to this modification the kingdom Protoctista became a kingdom that contains all those organisms, which cannot be fitted into any of the other kingdom.
VIRUS
Virus are very minute non cellular bodies considered between living and non-living organisms.
DISCOVERY OF VIRUS
The word virus is derived from a Latin word meaning “Poison”. A Russian Biologist Iwanosky in 1892 discovered Virus.
CHARACTERISTICS OF VIRUS
1. Viruses are non-cellular parasitic entities (obligate parasite)
2. Viruses cannot live and reproduce outside the living cells because they lack the machinery to do so by themselves.
3. The size of the viruses in range 20nm-250nm.
4. Viruses are either virulent destroying the cell in which they occur. While temperate Viruses become integrated into their host genome and remain stable for long period of time.
STRUCTURE OF VIRUS
1. The viruses may be small sphere like or golf balls, like rod shape tadpole and polyhedral.
2. They mainly consist of viral genome, capsids, envelopes and tail Fibers.
(A)GENOME
Viral genomes may consist of a single or several molecules of DNA or RNA.
(B)PROTEIN CAPSID (PROTEIN CORE)
The protein coat that encloses the viral genome is called Protein capsid. It may be of different shapes and mainly made up of proteins sub units called “capsomeres”
(C)VIRAL ENVELOPES
In some viruses accessory structure called Viral Envelopes are present that help them in infecting their host. They are membranes that enclose the protein core.
TAILS AND TAIL FIBRES
Many viruses possesses thread like long tail and tail fibers. These structures help in infecting the host. FIGURE / 5.5 (THE STRUCTURE OF BACTERIOPHAGE)
CLASSIFICATION OF VIRUSES
(A) ON THE BASIS OF MORPHOLOGY
Viruses are generally classified on the basis of Morphology and nucleic acids they contain. e.g. On the basis of morphology, Viruses are classified into rod shape (TMV), spherical (Polio Virus) and Tadpole (Bacteriophage Virus).
(B) ON THE BASIS OF MODES OF ORIGIN
Viruses can be classified on the basis of their mode of origin, which provide a systematic idea of some of their diversity. Following are the main characteristics of these groups:
1. Unenveloped plus strand viruses.
2. Enveloped plus strand RNAViruses.
3. Minus strand RNA Viruses.
4. Viroids
5. Double strand RNA Viruses.
6. Small genome DNA Viruses.
7. Medium genome and large genome DNA Viruses.
8. Bacteriophage.
LIFE CYCLE OF THE BACTERIOPHAGE
The virus that infects the bacteria (mostly E.coli) is known as “Bacteriophage”
Bacteriophage can reproduce by two alternative mechanisms.
1. The lytic cycle
2. The Lysogenic cycle.
(1)THE LYTIC CYCLE
The life cycle of the bacteriophage that eventually ends in death of the host cell is known as “A LYTIC CYCLE”
The following are the stages of lytic cycle.
1. Initially the bacteriophage uses his tail fibers to stick to specific receptor present on the outer surface of E-coli bacteria.
2. The sheath of the viral tail contracts, thrusting a hollow core through the bacterial wall and membrane of the bacterial cell and then phage injects its DNA into the cell.
3. The empty capsid of the phage is left outside the cell.
4. The bacterial cell’s DNA is destroyed (hydrolyzed).
5. The phage DNA takes control over the bacterial metabolic machinery and uses it to produce phage proteins and viral nucleotide.
6. Copies of the phage genome are developed and different parts of the phage come together forming daughter phages.
7. In the last stage of lytic cycle the daughter phages released, hydrolytic enzymes “lysozymes”, which digest the bacterial cell wall.
8. Due to osmosis, bacterial cell swells and finally burst releasing 100-200 daughter phage particles.
2. THE LYSOGENIC CYCLE
The life cycle of the Bacteriophage in which the viral genome replicates without destroying the host cell is known as lysogenic cycle.
Viruses that are capable of using both modes of reproduction with in a bacterium are called “Temperate Viruses”.
The following are the stages of lysogenic cycle.
(1) In this cycle infection of the E-coli cell begins when the phage binds to the surface of cell and injects its DNA.
(2) With in the host cell, the phage DNA molecule forms a circle.
(3) The DNA molecules of Viruses incorporated by genetic recombination into a specific site on the host cell’s chromosome. Now it is known as “Prophage cycle”
(4) The phage genome is mostly silent with in the bacterium.
(5) When E-coli cell prepares to divide, it replicates the phage DNA also, and passes the viral copies to the daughter cells.
(6) This mechanism enables the virus to propagate with out killing the host cell upon which it depends.
At some point, prophage give rise to the active phages that lyses their host cells. It is usually an environmental trigger such as radiations, or the presence of certain chemicals that convert the virus from the lysogenic to the lytic mode.
VIRAL DISEASES
1. ANIMAL DISEASES
(1) Poliomyelitis.
(2) Colds
(3) Encephalitis.
(4) Dengue fever.
(5) Yellow fever.
(6) AIDS
(7) Rabies.
(8) Measles.
(9) Mumps.
(10) Hepatitis.
2. PLANT DISEASES
(1) Tobacco Mosaic Virus (TMV) (Tobacco leaves disease) or (Tobacco Mosaic Disease)
AIDS
CAUSITIVE AGENT
AIDS is stand for Acquired Immuno-Deficiency Syndrome, caused by Human Immune Deficiency Virus (HIDV)
SYMPTOMS
(1) Short flu like illness.
(2) Pneumonia like conditions.
(3) Disfiguring form of Skin Cancer (Kaposi’s Sarcoma)
(4) Weight loss and fever.
(5) Dementia (loss of thoughts)
(6) Diarrhea (loose motion with increasing frequency)
(7) Septicemia (Blood Poisoning)
Severity of the Immuno-Deficiency varies and bouts of illness may persist for years.
HIV mostly infects lymphocytes and causes brain cell damage, in more than 50% of cases. Irreversible dementia and eventual death occurs.
TRANSMISSION
(1) The HIV virus can only survive in the body fluids and transmitted by blood or semen.
(2) In 90% of cases the transmission occurs by ***ual contact. Some other modes of transmission are as follow:
• Unsterilized syringes and needles mostly in intravenous drug abusers.
• By giving blood or blood products already infected with HIV.
• Close contact between infected and non-infected people.
• From an infected pregnant women to her baby through placenta or through breast milk.
CONTROL AND TREATMENT
No particular drug is available for treatment of AIDS but there are some drugs, which are effective against this disease like Azidothymadine, Zidovudine and sumarin.
PREVENTION
• Use of the clean needles and sterilize syringes.
• Education and public awareness about the disease and restricted ***-ual contacts with preventive measures.
• Tranfusion of screened blood and blood products.
HEPATITIS
Hepatitis is an inflammation of the liver cells caused by viral infections, toxic agents or drugs.
SIGNS AND SYMPTOMS
• Jaundice.
• Abdominal pain.
• Liver enlargement.
• Fatigue and fever.
TYPES OF HEPATITIS
There are various types of Hepatitis few of them are as follow:
(1)HEPATITIS “A”
• Cause by non-enveloped RNA virus.
• Transmitted by contact with faeces from infected individual.
• Most common form of Hepatitis world wide.
(2)HEPATITIS “B” (SERUM HEPATITIS)
• Caused by DNA viruses.
• More common in Asians, Africans and male homo***uals.
• Often persist in carrier form without causing any symptoms.
• Transmission mostly occurs through skin contacts, blood transfusion and other medical procedures. (Surgery, NG tube, Catheters)
• The virus of this disease can cause liver cancer mostly in carriers.
TREATMENT AND PREVENTION
• New vaccines against the virus have been produced which are of great importance especially for person who required frequent blood transfusion.
(3)HEPATITIS “C”
• Transmission occurs through mother to child during pregnancy.
• By ***-ual contacts.
• Most common transfusion associated Hepatitis.
• It causes liver cancers more often than HBV.
Chapter-4
THE CELL
CELL
It is the basic structural and functional unit of life, which is able to carry out all the life processes.
CELL THEORY
The cell theory was collectively proposed by “Schleiden(1838), Schawnn(1839) and Virchow (1858).
IMPORTANT POSTULATES
The fundamental points of the cell theory are:
(a) The cell is the structural and functional unit of all living organism.
(b) All organisms are composed of one or more cells.
(c) New cells can arise only by division of pre-existing cells.
Thus cell theory established the concept that the function of an organism is the result of activities and interaction of the cell units.
MICROSCOPE
DEFINITION
An instrument with the help of which we see small, tiny and minute objects which can’t be observe by naked human eye.
TYPES OF MICROSCOPE
There are three main types of microscope.
1. LIGHT MICRO SCOPE
In this microscope visible light is used as source of illumination.
2. X-RAY MICROSCOPE
X-Rays are used as source of illumination.
3. ELECTRON MICROSCOPE
Electron beam is used as source of illumination.
There are further two sub-types of electron microscope which are:
(A)TRANSMISSION ELECTRON MICROSCOPE
In this type resultant image is obtained on a fluorescent screen or photographic film.
(B)SCANNING ELECTRON MICROSCOPE
In this type resultant image is obtained on a television screen.
MAGNIFICATION OF MICROSCOPE
Ability of microscope to increase the shape and size of the objects image. It can be calculated by multiplying the power of its eye pieces with its magnifying power of its objective.
RESOLUTION OF MICROSCOPE
The capacity of microscope to separate adjacent forms or object. Also known as “Minimum Resolved Distance”.
CONTRAST
It is important to distinguishing one part of cell from another.
• Difference between light and electron microscope
• Prokaryotes and eukaryotes
CELL MEMBRANE
Each cell is covered by an asymmetrical, porous, thin, semi permeable sheet called cell membrane or plasmalemma.
CHARACTERISTICS OF CELL MEMBRANE
Living part of the cell, consist of lipid + protein.
• 1.5 micron in thickness.
• Consist of two layers of lipid.
• Lipid of plasma membrane are,
1. Phospho-lipids
2. Glycolipids
3. Sterol
4. Cholesterol.
STRUCTURE OF CELL MEMBRANE
Cell membrane made up of phospho-lipids bilayer and each layer consists of ,
1. Head (hydrophilic end)
2. Tail (hydrophobic end)
HEAD (HYDROPHILIC/POLAR END)
Present towards the surface and formed of phosphates.
TAIL (HYDROPHOBIC/NON-POLAR END)
Present towards the center and formed of fatty acids.
The non-polar ends of phospho lipids face each other, whereas their polar ends are in association with protein or carbohydrates between every two phospo lipids molecule lies a molecule of “Cholesterol”.
FLUID MOSAIC MODEL
INTRODUCTION
The fluid mosaic, bilayer model was proposed by “Singer and Nicolson (1972).
POSTULATES OF FLUID MOSAIC MODEL
Important postulates of this model are,
(a) The cell membrane consists of lipid bilayer, in which a variety of proteins are present.
(b) These proteins float in the fluid matrix of lipid (as ice bergs in the sea)
ARRANGEMENT OF PROTEINS
According to the fluid mosaic model proteins are:
1. INTRINSIC/INTEGRAL PROTEINS
These proteins peneterate the membrane surface and enter the lipid layers (partially or wholly)
2. EXTRINSIC/PERIPHERAL PROTEINS
These are located adjacent to outer and inner surface of membrane and float like ice-berg in the sea.
ARRANGEMENT OF LIPIDS
The non-polar end face each other while their polar ends are towards the surface.
SIGNIFICANCE OF MODEL
• Cell membrane is flexible.
• Can change shape (because the protein and lipid of the membrane can move).
FUNCTION OF MEMBRANE PROTEIN
• Certain proteins themselves act as enzymes.
• Some protein act as carrier for active transport.
• Provide elasticity to membrane.
• Pores are lined by the proteins.
FUNCTION OF LIPIDS PRESENT IN MEMBRANE
• The lipids give rigidity to cell membrane.
• They lower the surface tension.
FUNCTIONS OF CELL MEMBRANE
• It performs the two main function.
• Protection of Protoplasm.
• Regulation of material (In and Out of cell) through its permeabality.
PERMEABILITY OF MEMBRANE
The permeability of membrane is regulated by two processes.
(1) Passive Transport (Osmosis and Diffusion)
(2) Active Transport (Endocytosis, Exocytosis)
1. PASSIVE TRANSPORT
Such type of molecules transport which does not require energy. It is further divided into,
DIFFUSION
Spreading and free movement of molecules (or ions) from the region of higher concentration to the region of lower concentration (till equilibrium state)
SIGNIFICANCE
• Movement of oxygen and digested food (glucose, amino acids, fatty acids) into the cell.
• Movement of excretory waste out of cell.
OSMOSIS
Diffusion of water by semipermeable membrane or the movement of solvent molecules from higher to lower concentration across semi permeable membrane.
SIGNIFICANCE
• Liquids, primarily water molecules enter and leave the cell by Osmosis.
• It helps to maintain a balance (osmotic pressure) in and out of cell.
2. ACTIVE TRANSPORT
Such type of molecule transport which require energy. Or Movement of molecules against the concentration by the expenditure of energy through a carrier (i.e. movement of molecules from the region of lower concentration to higher concentration by protein using ATP as energy.
SIGNIFICANCE
Absorption of excess food (glucose), ions (K+ and Na+) takes place by Active transport.
CONDITIONS
• It is unidirectional.
• ATP provides energy.
• Protein act as carrier.
Active transport is further subdivided into,
(1) Phagocytosis and Pinocytosis (Endocytosis).
(2) Exocytosis.
PHAGOCYTOSIS
Process of picking and ingestion of large solid particle by plasma membrane (which can not enter by diffusion, osmosis or active transport).
SIGNIFICANCE
• Ingestion of solid food particles.
• WBCs pick foreign particles (certain bacteria)
PINOCYTOSIS
Process of fluid intake, for absorbing fluid by forming pinocytic vesicle (the fluid which cannot be absorbed by osmosis, enters through it)
SIGNIFICANCE
Helps in absorption of harmones, lipids etc.
CELL WALL
The cell wall is the outer most covering of a plant cell. It is composed of cellulose (a carbohydrate) and some other chemical substances.
This hard covering gives form, firmness and strength to the plant cell.
In a young cell it is thin and delicate but in a mature cell it becomes thick due to the deposition of various chemical substances on its inner surface.
There are three layer of cell wall.
1. MIDDLE (LAMELLA)
• First formed cell plate.
• Cementing layer between two daughter cells.
• Composed of Ca++ and Mg++ pectate.
• ells are separated when this layer is dissolved.
2. PRIMARY WALL
• First product of cell synthesized by protoplast.
• In young cells it is thin and elastic while it becomes thick and rigid on maturity.
• Made up of Hemicellulose (50%), cellulose (25%) and pectate substances.
3. SECONDARY WALL
• Composed of cellulose.
• Present inside the primary wall.
• Can be modified through the deposition of lignin and other substances.
NUCLEUS
It control all the activities of the cell and was discovered by Robert Brown in 1831.
It consist of the following parts,
(1) Nuclear Membrane.
(2) Nucleoplasm or Karyoplasm.
(3) Nucleolus.
(4) Chromatin Network.
1. NUCLEAR MEMBRANE
The nucleus is bounded by a double layered membrane which bears pores and is known as “Nuclear Membrane”
2. NUCLEOPLASM
Inside the nuclear membrane is a structure less fluid called “Nucleoplasm” and highly rich with proteins.
3. NUCLEOLUS
It is a patch work of granules rich in R.N.A formed in the nucleus. They may be more than one in a single nucleus. It contains mRNA formed from DNA, later mRNA comes out of nucleus to control protein formation.
4. CHROMATIN NETWORK
There is a network of threads dispersed in the karyoplasm called (Chromatin network)
Each individual thread is called (Chromosomes).
These are made up of DNA and are carrier of genes.
MEMBRANE BOUND ORGANELLES
(1) ENDOPLASMIC RETUCULUM
It is a complex series of tubules in the cytoplasm. Endoplasmic reticulum are of two types,
(1) Agranular or Smooth EPR.
(2) Granular or Rough EPR.
SMOOTH EPR
• It has no attached ribosome’s.
• Function is to synthesis lipid.
ROUGH EPR
• It has ribosome’s attached to its outer surface.
• Synthesize protein and also transport material within the cell.
(2) MITOCHONDRIA
An oval body bounded by a double membrane. The inner membrane is folded to form shelves/incomplete partitions. Which are known as “Crista”, here oxidative enzyme are present. They are sites for aerobic cellular respiration and the energy is produced. Therefore also known as “Power house of cell”
(3) GOLGI APPARATUS(DICTYOSOMES)
These are thin, plate like structures and are usually located near the nucleus. These are the site of formation of lysosomes and also conjugate protein, modify structure of substances, synthesized by EPR to form lysosomes and secretary vesides. Golgi bodies of plants and lower animals (mostly invertebrates) are known as “Dictyosomes”.
(4) LYSOSOMES
They are large, some what irregular structure formed in the cytoplasm formed by golgi-bodies. They contain hydrolytic enzymes which destroys foreign particles. They are also known as “Suicide Sacs” because after secreting the enzymes they digese their own proteins (Autophagy).
NOTE: (Lysosomal Storage Diseases )
(5) PLASTIDS
They are specialized organelles of plant cell that contain pigment or they synthesize reserve substances.
They are of three kinds,
(A) LEUKOPLAST
leuco = white
Leukoplast are colourless and store nutrient material.
(B)CHLOROPLAST
Chloroplast are green having chlorophyll that performs photosynthesis.
(C) CHROMOPLAST
Chromo = Colour
Chromoplast contain different coloured (red, yellow, orange or other than green) pigments. They are found in the cells of different coloured flowers and fruits.
(6) MICRO BODIES
It includes peroxisome and glyoxysome.
(A) PEROXISOME
These are the single membrane bounded microbodies contain enzymes for transferring hydrogen atom to oxygen i.e. forming hydrogen peroxide.
• Hydrogen peroxide is very toxic to the cell therefore it is immediately break down to water by enzyme catalyst.
• These microbodies help in detoxyfication of alcohal and mostly present in liver cells.
(B) GLYOXYSOME
• It is a single layered membrane bound structure containing enzymes which metabolize some molecules in photosynthesis and respiration.
• They also cause oxidation of fatty acids.
CYTOSKELETON
Cytoskeleton means skeleton of the cell, which is mostly composed of microtubules, microfilaments and intermediate filaments.
(A) MICRO TUBULES
• Microtubules are hollow cylinders with an outerdiameter of 25nm.
• They are made up of a special type of globular protein tubulin.
• In single microtubule consist of hundredth of thousands of tubulin sub units, which are usually arranged in 13 columns called Protofilaments.
• Microtubules are arranged in assemble and disassemble manner.
• In animal cells and lower plants they also form centriole, cilia and flagella.
(B) MICROFILAMENTS
• Microfilaments are solid structures, thread like with a diameter of 7nm.
• They are also composed of globular proteins.
• Each microfilament consist of two actin (Protein) chains that inter wing in a helical fashion.
(C) INTERMEDIATE FILAMENTS
• They are intermediate in size having a diameter of 8nm to 11nm.
• They are rope like polymers of Fibrous protein.
• In skin and hair these filaments are made up of protein keratin.
• They provide mechanical strength to the cell and support the nuclear envelope.
NON MEMBRANE BOUND CYTOPLASMIC ORGENELLE
(1)RIBOSOMES
• These are small structures concerned with protein synthesis in all type of the cells i.e. Prokaryotic as well as Eukaryote.
• They are freely dispersed in cytoplasm of Prokaryotic cell but in Eukaryotic cells they may be free or attached with endoplasmic reticulum.
• More than 50 type of proteins are present in ribosome structure and they contain high quantity of RNA.
• Under the direction of Nucleus ribosome produce the protein made it by the cell.
• Each Ribosome consist of two unequal parts.
• These are the smallest and most vital cellular components, manufactured in the nucleolus.
(2) CENTRIOLE
• They are only present in animal cells and certain lower plants.
• Mostly near the nucleus.
• Each centriole consist of two cylinders lying perpendicular to one another.
• Each cylinder consist of nine parallel triplets of hollow cylindrical microtubules.
• During the cell division they replicate and move towards opposite poles of the cell.
• In mitosis and meiosis they form thread like fibers which rediate from each centriole are known as mitotic apparatus.
(3)VACUOLES
• These are non-protoplasmic fluid filled cavities in the cytoplasm.
• Their membrane is known as Tonoplast.
• They are more prominent in mature cells.
• In plant cells vacuoles are filled with cell sap and act as store, house.
• They also play an important role in plant defence.
• In animal cells vacuole contain hydrolytic enzymes (i.e. lysosomes)
Chapter-3
ENZYMES
ENZYMES(BIO-CATALYSTS)
Enzymes are bio-catalyst which speed up the chemical reactions by lowering “Energy of activation”.
ENERGY OF ACTIVATION
Amount of energy which is required to start a chemical reaction. OR Energy required to break a (particular covalent) bond present in reactant.
NOMENCLATURE OF ENZYMES
Enzyme is a Greek word means-En(in) and Zyme(yeast).
DISCOVERY OF ENZYME
Term “Enzyme” was coined by F.W Kuhne in 1978.
NATURE OF ENZYME
Almost all enzymes are protein in nature except few which are nitrogenous acids like RNA-DNA(Ribozymes). Ribozymes catalyze reactions in genetic informations.
CHARACTERISTICS OF ENZYMES
• Protein in nature and are formed by living cells.
• May be intracellular or extra cellular.
• Remains unchanged during and after the reaction.
• Speed up the rate of reaction by decreasing energy of action.
• Specific in their nature.
• Heat sensitive and act on particular (optimum) temp.
• Each has specific substrate pH for its activity.
• Action can be alter by activators and inhibitors.
CLASSIFICATION OF ENZYME (ON THE BASIS OF STRUCTURE)
Pure or Simple Enzyme consist of only protein (e.g.Amylase and Pepsin) Conjugated or Holoenzymes: May contain a non-protein part “Prosthetic group” as well (e.g. Phosphatase and Peptidase)
Holoenzyme = Apoenzyme + Prosthetic group
................(Protein part)....(Non-protein part)
CLASSIFICATION OF ENZYME (ON THE BASIS OF FUNCTIONS)
(1) OXIDOREDUCTASE
Catalyze reactions in which one substrate is oxidized while other is reduced. Sub classes are:
• Dehydrogenases(convert single bond to double bond)
• Oxidases (use oxygen as oxidant)
• Peroxidases (use H202 as oxidant)
• Hydroxylases (introduce hydroxyl group)
• Oxygenases (introduce mol. Oxygen in place of double bond).
(2) TRANSFERASES
Transfer one carbon group (e.g. methyl) from one substrate to another substrate.
(3) HYDROLASES
Catalyze hydrolytic cleavage of C-O, C-N, C-C and P-O bonds and other single bonds (e.g. Peptidases, Esterases, Glycosidases and Phosphatidases).
(4) LYASES
Catalyze Elimination reactions to form double bond and reversible reaction by adding groups across double bond (e.g. Decarboxlases, Aldolases and Dehydratases).
(5) ISOMERASES
They alter the structure but not the atomic composition by moving a group from one position to another in one molecule (e.g. Epimerases, Mutases).
(6) LIGASES
Catalyze reaction in which two molecules are joined. They are also known as synthtases.
ROLE OF ENZYME
The enzyme react with (energy rich or energy poor) molecules and forms an intermediate complex that breaks into,
(a) Product
(b) Enzyme
(i) Substrate + Enzyme = Complex
(ii) Complex = Product + Enzyme
The equilibrium is achieved if the ratio of conc of reactants (substrate) and product remains same.
Rate of reaction 1/ยต Energy of activation
MODE OF ACTION OF ENZYMES
1- The action of enzyme depends on its chemical structure. A typical enzyme molecule, has “3D” structure.
2- Has depression or pit for substrate (to fit in) known as “Active site”.
3- Any other site other than active site is called “Allosteric site”
There are two theories in respect of enzyme action, which are as follows.
LOCK AND KEY MODEL
Proposed by Fischer (1898) and modified by Paul Filder and D.D Woods according to this model,
• The active site of enzyme has distinct shape.
• It allows few substrate to fit in (like a particular lock allows particular key to fit in)
• Enzyme breaks substrate to product
FIGURE From Text Book 3.3 page #46 (The cycle of Enzyme - substrate Interaction)
INDUCE FIT MODEL
Proposed by koshland (1959), it states that
• Enzyme binds with a substrate
• This binding induce changes in enzyme structure
• Due to this change enzyme acts and forms product
FACTORS AFFECTING ENZYME ACTIVITY
The activity of enzymes depend on following factors,
1. SUBSTRATE CONCENTRATION
• Increases with increase in substrate concentration (up to a limit)
• At very high concentration, activity again decreases due to saturation of enzyme with substrate and saturation of product i.e. higher concentration of product.
2. TEMPERATURE
• Increases with in temperature(up to limits)
• Maximum activity at optimum temperature.
• Highly active at 37°C and destroyed at 100°C
• At 0°C minimum activity.
3. PH
Enzymes are pH specific i.e. work in specific pH(because of protein can act both in acidic and basic medium.
4. WATER
Enzyme activity is usually maximum (up to limits) but decrease after limits (dilution of enzyme)
5. RADIATIONS
Enzymes become inactive due to radiations (including Alpha, Beta, Gamma rays).
6. CO-ENZYME AND ACTIVATORS
Induce the enzyme activity.
THINGS TO BE REMEMBER
INHIBITORS
Substances which decreases the activity of enzymes.
COMPETITIVE INHIBITORS
Inhibitor molecules which resemble the normal substrate molecule and compete for admission into the active site. They block the substrate from entering active site.
NON-COMPETITIVE INHIBITORS
Inhibitors bind to a part of the enzymes away from the active site (Allosteric site). This binding cause change in the enzyme molecule shape and decrease in enzyme activity.
FEED BACK INHIBITION
Common biological control mechanism of brain in order to regulate enzyme activity.
PROSTHETIC GROUP
Non-protein part of enzyme (Co-enzyme or Co-factor)
CO-ENZYME
When prosthetic group consist of organic molecules (like FAD/NAD)
CO-FACTORS/ACTIVATORS
When prosthetic group consist of inorganic molecules (like Ca++, Na+ etc).
APOENZYME
Protein part of enzyme.
