BIOLOGY TUTORIALS

ENZYMES               ENZYMES are  true catalyst,  greatly enhance the rate of specific reaction that would otherwise occurs only very slowly.They cannot change the equilibrium point of reaction they promote nor they used up or permanently changed by these reactions.                             HOW ENZYMES WORKS ?- This phenomenon is also called as CATALYSIS . DNA in each cell has message for production of enzymes. Cell uses this information. ENZYMES retain their ability even after extraction from cell. They are synthesised by the living cell. Enzyme contain a non- protein part called PROSTHETIC GROUP . It is tightly bound to enzyme, some are metal compounds ex- iron-porphyrin complex of cytochrome .  For enzyme activity some organic compounds and inorganic ions are required. They are loosely bound to enzyme called CO-FACTORS . NAD  [NICOTINAMIDE ADENINE DINUCLEOTIDE] precursor of nicotinic acid, FAD [FLAVIN ADENINE DINUCLEOTIDE], the active form of vitamin B2

CELL DIVISION  CELL CYCLE- When cell divides.It synthesise its components including genetic material in duplicate. After division This passes to DAUGHTER CELLS. Sequence of events by which cell duplicate its contents & divides into two called CELL CYCLE. IMPORTANCE IN EUKARYOTES- From single cell trillions of cells develop.Rate & no. officer division vary.In adult tissues like bone marrow division is continuous.In fully formed organism less division occurs. CELL CYCLE  It Has two periods: 1- INTERPHASE : - Period of rest or RESTING STAGE .Preparatory phase for cell division. 2- MITOSIS : -  Three processes occurs during this phase: REPLICATION OF DNA & SYNTHESIS OF PROTEINS AS HISTONES. IN ANIMALS-DUPLICATION OF CENTRIOLE -Two daughter centrioles formed at right angle to each other. SYNTHESIS OF ENERGY RICH COMPOUNDS -Provides energy for mitosis & synthesis of proteins MITOSIS  ITS DIFFERENT PHASES & SIGNIFICA

 NUCLEIC ACIDS  [DNA &RNA] There are chromosomes in the nucleus of cell,which are thread like.They are visible only during cell division.Chromosomes are uncoiled in loose network called chromatin contains DNA,RNA,& PROTEINS.                                  DNA means DEOXYRIBONUCLEIC ACID  RNA means RIBONUCLEIC ACID. DNA & RNA both are information storage devices of cell.These are two kinds of nucleic acids. DNA: It has special coded genetic programme with detailed & specific instructions for each organism heredity.[one gene one character passed to offspring]. Its model was proposed by WATSON & CRICK In 1953. It consists of linear polymers of repeating monomer subunits called nucleotides. Each nucleotide contains A PENTOSE SUGAR,A PHOSPHATE GROUP,NITROGENOUS BASE[PURINE or PYRIMIDINE] A ,G ,C,T SUGAR RIBOSE in RNA DEOXYRIBOSE In DNA[One oxygen lacking] DNA is double helicle, two polynucleotide chains he

It develops from ovule inside ovary [female reproductive part of flower]after fertilisation with pollen. SEED has four parts  1 OUTER SEED COAT 2 COTYLEDONS 3 PLUMULE 4 RADICLE                                            DICOT  Means if two cotyledons are present.Two chambers which stores food .They have seed coat Ex PEA ,GRAM.[ALL PULSES]  Embryo is embedded inside endosperm has two thin cotyledons joined to an axis called  TIGELLUM  It shows  RADICLE & PLUMULE  hidden between cotyledons.Ex GRAM PEA. HILUM  Point of attachment of seed with stalk.    MONOCOT  Means if one cotyledon stores food as in RICE, WHEAT ,MAIZE. Monocot have no seed coat. Single cotyledon,endospermic, NO SEED COAT .Outer covering is membranous fused with fruit wall. ENDOSPERM  is separated from embryo by  ALEURONE LAYER .Embryo is small in a groove at one end.It consists of one cotyledon called  SCUTELLUM ,a short axis with plumule & radicle