On the basis of functions microbodies are of following types�--

(1) Sphaerosomes :-

`->` Sphaerosomes occur only in plant cells. They are major site of lipid storane and synthesis in plants.

`->` Sphaerosomes also have lysosome like activity so they also termed as plant lysosomes.

(2) Peroxisomes or Uricosomes :-

`->` In animal cells peroxisomes concerned with peroxide (H_(2)O_(2))rnetabolisrn. Catalase degrade the `H_(2)O_(2)` water and
oxygen.

`->` In plants, peroxisomes occurs in cells of green tissues andconcerned with photorespiration (glycolate pathway}.

`->` Peroxisornes involved in !3-oxidation of fatty acids.

(3) Glyoxysomes :- Occurs in oil conti:lining seeds, yeast cells.

`->` Glyoxysornes occurs only in plants especially in fatty seeds (castor seed. ground nut seed etc.).

`->` Glyoxysornes are considered as a highly specialised peroxisomes. Clyoxylate acid cycle takes place in glyoxysornes. This cycle convert fats in!o carbohydrats.

INTRODUCTION:

`->` Nucleus as a cell organelle was first described by Robert Brown as early as `1831`. Later the material of the nucleus stained by the basic dyes (Acetocarmine) was given the name chromatin by Flemming.

`->` "Nucleus is double membrane bound dense protoplasmic body, which controls all cellular metabolism and encloses the genetic information of cell".

`->` Nucleus is consider as controller or director of cell. Importance of nucleus in control of heredity, growth and metabolism was experimentally proved by Hammerling. (Experiment was on Acetabularia a single cell largest alga).

`->` If the nucleus of a cell is, experimentally removed, then unicellular organism will die after some time. Thus nucleus is very important.

`->` Strasburger stated that :- "Nucleus arises from divison of pre-existing nucleus only. The study of nucleus is known as Karyology.

`->` Generally eukaryotic cell contain at least one nucleus but nucleus is absents in mature phloem sieve tube elements and mature RBCs of mammals. (exceptionaly nucleus is present in RBCs of camel & lamma).

`->` Dikaryotic (Paramecium) and multikaryotic cells are also known.

Interphase nucleus : Nucleus of cell when it is not dividing.

(i) Nuclear membrane or karyotheca.

(ii) Nuclear matrix I Nucleoplasm/Karyolymph/Karyoplasm.

(iii) Chromatin net

(iv) Nucleolus/little nucleus/Ribosome factory

Electron microscopy has revealed that the nuclear envelope, which consists of
two parallel membranes with a space between (10 to 50 nm) called the perinuclear space.

`->` These membrane forms a barrier between the materials present inside the nucleus and that of the cytoplasm.

`->` The outer membrane usually remains continuous with the endoplasmic reticulum and also bears ribosomes on it. At a number of places the nuclear envelope is interrupted by minute pores, which are formed by the fusion of its two membranes.

`->` These nuclear pores are the passages through which movement of RNA and protein molecules takes place in both directions between the nucleus and the cytoplasm.

`->` The size of nuclear pores is, 300 to 1 oooA diameter. Each nuclear pore is guarded by a octagonal discoid structure of nucleoplasmin protein this structure is called as annulus or Bleb. (Annulus+ Pore = Nuclear Pore complex).

`->` The inner side of inner nuclear membrane is lined by nuclear lamina. This structure is formed by filaments of lamin protein.

`->` Pore complex provides the main channel, between nucleoplsm and cytoplam. while nucleoplasmin regulates nucleocytoplasmic traffic.

Nucleoplasm or Nuclear sap is a ground substance of nucleus which is a complex colloidal formed of a number of chemicals like nucleotides, nucleosides, ATPs, proteins & enzymes of RNA & DNA polymerases, endonucleases, minerals, (`Ca^(++)`, `Mg^(++)`) etc. Nucleoplasm contain high concentration of Nucleotides in the form of triphosphate. (ATP, GTP, TTP, CTP, UTP)

`->` Chromatin net and nucleolus are embeded in nucleoplasm. Nucleoplasm provides site for process of
transcription.

`->` Interphase nudes has a loose and indistingt network of nucleoprotein fibers called chromatin, which embeded in nucleoplasm. Chromatin net is mainly formed of DNA and histone protein complexes. Chromatin fibres contain genetic information and condensed to form constant number of chromosomes during cell division.

`->` During different stages of cell division cells show structured chromosomes in place of nucleus.

`->` Chemically chromatin consists of DNA, RNA, Histone protein (basic proteins) and non histone proteins

(Acidic proteins). 20 to 30% part of histone is made up of arginine and lysine amino acids.

On the basis of relative amount of arginine and lysin there are five type of Histone protein.


`(H_(2)A, H_(2)B, H_(3), H_(4), H_(1))`

Amino acid Type of histone

Lysin rich - `H_1`
Slightly lysin rich - `H_(2)A, H_(2)B`
Arginine rich - `H_(3), H_(4)`


`->` Chromatin net has two type of chroma tins.


(a) Euchromatin :- This is lightly stained and diffused part of chromatin. Which is transcriptionally or
genetically more active. Generally euchromatin lies at central part of nucleus.

(b) Heterochromatin :- This is dark stained, thick and condensed pati of chromatin this part has more histone and less acidic protein. Heterochromatin is genetically less active chromatin. Heterochroma!ln occurs near nuclear membrane.

(i) Constitutive heterochromatin:- Occurs in all cells in all stages e.g. centromeric region.

(ii) Facultative heterochromatin:- Occurs in some cells in some stages e.g. barr body.

`->` Barr body in female cells is a facultative heterochromatic structure. (By M.Barr)

`->` Number of Barr body in nucleus of an individual is number of X-chromosome minus one.

`->` The nucleoplasm also contain nucleous.

`->` The nucleoli are spherical and membraneless structure so that the content of nucleous is continous with the rest of the nucleoplasm.

`->` It is a site for active ribosomal RNA synthesis.

`->` Nucleolus usually attached to chromatin {or chromosomes) at specific site called Nucleolar organiser renion/NOR.

`->` Number of nucleolus in a nucleus is one. Onion cell has 4. and in oocytes of amphibian has `2000` nucleoli. Human cell has 5 pair of nucleoli.

`->` Nucleolus disappears durin~J prophase and reappears in telophase.

(Ultrastructure of nucleolus):

(i) Fibrillar region :-This is central fibrous part of nucleolus, which is consist of mainly DNA and proteins.

(Nucleonema)

(ii) Granular region :-This is peripheral granular part of nucleolus which is consist of rRNA and protiens

(iii) Amorphous matrix or pars amorpha :-This is proteirwceous nround matrix, which contains both fibres and nranules.

Ribosome formation is the chief role of nucleolus, thus its called as Ribosme factory of celt the protiens of ribosomes are synthesised in cytoplasm but it diffused in to nucleus and reach at nucleolus. Here r-RNA and ribosomal proteins are assembled to form ribosomes which move to cytoplasm through nuclear pores.

`->` Larger and more numerus nucleoli are present in cells actively carrying out protein synthesis.

(i) Genetic information :- Nucleus contains genetic information in its chromatin. (store house of genetic material)

(ii) Transmission of genetic information:- Nucleus takes part in transmission of genetical information from parent cell to daughter cell or the one generation to next.

(iii) In cell-division :-Division of nucleus is pre-requisite to cell division.

(iv) Control of metabolism :-Nucleus controls metabolism of cell by sending m-RNA in cytosol (Basically biornolecule DNA controls cellular activities through directing synthesis of enzyme).

(v) Variations :-Variation develops due to change in genetic material of nucleus. (Evolutionary role).