Chapter 4 Cell- The Unit of Life Part 4 by Teaching Care online coaching classes

Chapter 4 Cell- The Unit of Life Part 4 by Teaching Care online coaching classes,

File name : Chapter-4-Cell-The-Unit-of-Life-Part-4_watermark.pdf

Flagella:

  • Flagella are 1 – 4 per cell where as cilia are infinity in
  • Cilia are smaller and flagella are longer in size, 5 – 10 m m and 150 m m
  • Structure : Both cilia flagella are structurally similar and possess similar parts-basal body, rootlets, basal plate and shaft

 

  • Basal body : These are also termed as blepharoplast (kinetosome) or basal granule. It is present below the plasma membrane in cytoplasm. The structure is similar to centriole made of 9 triplets of microtubules. Out of the 3 fibrils of a triplet first is A which is round and other two B and C are semi-circular. 9 triplets are connected to the centre by ‘C’ fibrils disappears as it enters into shaft.
  • Rootlets : Made of microfilament and providing support to the basal These are striated fibrillar outgrowths.

 

Central microtubule

Outer

microtubules Inner arm Outer arm

Spoke Head Interdoublet

link Subtubule A

Subtubule B

Radial spoke

Membrane Link

Central

sheath

 

Bridge

 

  • Basal plate : Central fibril develop in this area. It is highly dense and lie above plasma-membrane.

Fig : A diagram of T.S. Cilium or flagellum

 

  • Shaft : It is the hair like projecting part of cilia and flagella which remains outside the cytoplasm. It has 9 duplets of microtubules in radial symmetry. These are called axonema. Each axonema has 11 fibrils, 9 in the periphery and 2 in the centre. The arrangement is called 9 + 2 pattern. Central fibrils are singlet fibrils and covered by a central sheath. 9 pheripheral fibrils are duplet and are present at 10o difference from each other. Inner fibril of duplet is known as subfibre A with two bent arms and the outer one is subfibre-B. Peripheral fibrils are linked with each other by peripheral linkage and with the central fibril by radial
  • Chemical composition : Chemically, the central tubules are formed of dynein protein while the peripheral microtubules are formed of tubulin protein. Dynein is the ATPase enzyme which hydrolyses the ATP to provide free energy for ciliary /flagellar beating. The interdoublet linkers are formed of nexin protein. Quantitatively, it is formed of

Proteins = 74 – 84%              Lipids = 13 – 23%

Carbohydrates = 1 – 6%            Nucleotides = 0.2 – 0.4%

  • Type of flagella : There are two types of
    • Tinsel – type : In this, flagellum has lateral hair-like processes, called flimmers or
    • Whiplash – type : In this, flagellum has no
  • Motion : Cilia beat in coordinated rhythm either simultaneously (synchronus) or one after the other (metachronic rhythm). The cilia produce a

 

sweeping or pendular stroke. The flagella beat independently, hence produce undulatory motion.

Whiplash                     Tinsel

Fig : Types of flagella

 

(10)  Function

  • They help in locomotion, respiration, cleaning, circulation, feeding,
  • Being protoplasmic structure they can function as sensory
  • They show sensitivity to changes in light, temperature and
  • Ciliated larvae take part in dispersal of the species.
  • The cilia of respiratory tract remove solid particles from Long term smoking damages the ciliated epithelium, allowing dust and smoke particles to enter the long alveoli.
  • The cilia of urinary and genital tracts drive out urine and

Difference between cilia and flagella

CharactersCiliaFlagella
NumberMore in number (may be upto 14,000 per cell).Less in number (1-8).
SizeSmall sized (5-10 m m ).Large sized (upto 100-200 m m ).
DistributionGenerally distributed on whole body.Generally located at anterior end of body.
BeatingBeat in either metachronous or synchronous

coordination.

Beat independently.
Type of motionSweeping or rowing motion.Undulatory motion.
FunctionLocomotion, feeding, circulation, etc.Only locomotion.

 

Important Tips

  • Kinocilia : True or motile cilia e.g. of epithelial cells of respiratory
  • Stereo cilia : Immobile cilia g. of epididymis.
  • Bacterial flagellum consists of a single fibril composed of flagellin

 

  Cytoskeleton.

In eukaryotic cell, a framework of fibrous protein elements became necessary to support the extensive system of membranes. These elements collectively form cytoskeleton of the cell. There are of three types.

(1)  Microtubules :

  • Discovery : These were first discovered by De Robertis and Franchi (1953) in the axons of medullated nerve fibres and were named
  • Position : The microtubules are electron-microscopic structures found only in the eukaryotic cellular structures like cilia, flagella, centriole, basal-body, astral fibres, spindle fibres, sperms tail, neuraxis of nerve fibres These are absent from amoebae, slime-moulds and prokaryotes.
  • Structure : A microtubule is a hollow cylindrical structure of about 250 Å in diameter with about 150 Å Its wall is about 50Å thick. Its walls is formed of 13 parallel, proto-tubules, each being formed of a liner series of globular dimeric protein molecules.
  • Chemical composition : These are mainly formed of tubulin A tubulin protein is formed of 2

sub-units : a – tubulin molecule and b – tubulin molecule which are alternatively in a helical manner.

 

(v)  Function

  • These form a part of cytoskeleton and help in cell-shape and mechanical
  • The microtubules of cilia and flagella help in locomotion and
  • The microtubules of asters and spindle fibres of the mitotic apparatus help in the movement of chromosomes towards the opposite poles in cell-division.
  • These help in distribution of pigment in the chromatophores, so help in skin
  • These also form micro-circulatory system of the cell which helps in intracellular
  • These control the orientation of cellulose microfibrils of the cell wall of

(2)  Microfilament

  • Position : These are electron-microscopic, long, narrow, cylindrical, non-contractile and proteins structures found only in the eukaryotic cytoplasm. These are present in the microvilli, muscle fibres (called myofilaments) etc. But these are absent from the These are also associated with the pseudopodia, plasma membrane of fibroblats, etc. These are either scattered or organized into network or parallel arrays in the cytoplasmic matrix.
  • Discovery : These were discovered by Paleviz al. (1974).
  • Structure : Each microfilament is a solid filament of 50-60 Å diameter and is formed of a helical series of globular protein These are generally grouped to form bundles.
  • Chemical composition : These are mainly formed of actin-protein.

(v)  Functions

  • The microfilaments forms a part of cytoskeleton to support the relatively fluid
  • The microfilaments bring about directed movements of particles and organelles along them in the
  • The microfilaments also produce streaming movements of
  • The microfilaments also cause cleavage of animal cells which is brought about by contraction of a ring of
  • The microfilaments also participate in gliding amoeboid motion shown by amoebae, leucocytes and
  • The microfilaments are also resoponsible for the change in cell shape curing development, motility and
  • Myofilaments bring about muscle
  • The microfilaments cause movements of villi to quicken absorption of
  • The microfilaments are responsible for the movement of cell membrane during endocytosis and
  • The microfilaments cause plasma membrane undulations that enable the firoblasts to

(3)  Intermediate filaments

  • Location : They are supportive elements in the cytoplasm of the eukaryotic cells, except the plant They are missing in mammalian RBCes and in the prokaryotes.
  • Structure : The IFs are somewhat larger than the microfilaments and are about 10 nm They are solid, unbranched and composed of nonmotile structural proteins, such as keratin, desmine, vimentin.

 

(iii) Functions

  • They form a part of cytoskeleton that supports the fuild cytosol and maintains the shape of the cell.
  • They stabilize the epithelia by binding to the spot
  • They form major structural proteins of skin and
  • They integrate the muscle cell components into a functional
  • They provided strength to the
  • They keep nucleus and other organelles in

Differences between microtubules and microfilaments

 

MicrotubulesMicrofilaments
Are hollow cylinders.Are solid rods.
About 200 to 270 Å thick.About 50 to 60 Å thick.
Composed of 13 longitudinal protofilaments each.Not composed of protofilaments.
Formed of protein tubulin.Formed of proteins actin and myosin.
Subunits are dimers that have bound GTP and GDP.Subunits are monomers that have bound ATP and ADP.
Are noncontractile.Are contractile.
Have no role in cytoplasmic streaming, endocytosis and exocytosis.Play a role in cytoplasmic streaming, endocytosis and exocytosis.

 

Important Tips

  • Microtubule term was given by
  • Tubulin proteins is dimeric protein formed of two globular polypeptides called atubulin and b
  • Microtubules associated proteins like Tau- protein and kinase control polymerization of tubulin dimer’s.
  • Hyman (1917) proposed sol-gel-theory for amoeboid locomotion and was supported by

 

 

 Metabolically inactive cell inclusions/Deutoplasmic substances/Ergastic material .

Within the cytoplasm of a cell there occur many different kinds of non-living structures which are called inclusions or ergastic substances. They are formed as a result of metabolic activities. They are of following types:

  • Vacuoles : It is a non-living reservoir, bounded by a differentially or selectively permeable membrane, the tonoplast. The structure of tonoplast is similar to that of single unit membrane i.e. tripartite structure. The vacuole is filled with cell sap or tonoplasm. The thin layer of protoplasm, pushed towards the wall of the cell is called as primordial They contain water and minerals.

The vacuole in plants was discovered by Spallanzani. The vacuole is not air filled cavity, rather it is filled with a highly concentrated solution the vacuolar sap. It is generally neutral, but at maturity it becomes acidic. The cell sap contains following.

 

  • Gases : CO2, O2

and

N2 .

 

  • Inorganic salts : Nitrates, chlorides, sulphates, phosphates of

K, Na, Ca

and Mg.

 

  • Organic acids : Malic acid, formic acid, acetic acid, oxalic acid or their

 

  • Sugars : Cane sugar, glucose and
  • Soluble proteins :
  • Glycosides : Like anthocyanins (water soluble pigment)

Some protozoans have contractile vacuoles which enlarge by accumulation of fluid or collapse by expelling them from the cell. The vacuoles may be sap vacuoles, contractile vacuoles or gas vacuoles (pseudo vacuoles).

  • Function of vacuoles : Vacuole maintains osmotic relation of cell which is helpful in absorption of They also act as reservoir of cells. Turgidity and flaccid stages of a cell are due to the concentrations of sap in the vacuole. In animal cell, it is phagocytic, food vacuole, autophagic or contractile in nature.

(2)  Reserve food material

The reserve food material may be classified as follows :–

Food

 

Nitrogenous                                Non-nitrogenous

Proteins

 

Carbohydrates                                         Fats and oils

 

Starch

Cellulose

 

Sugar

Glycogen

Inulin

 

  • Carbohydrates : Non-nitrogenous, soluble or non- soluble important reserve food material. Starch cellulose and glycogen are all
  • Starch : Found in plants in the form of minute solid Starch grains are of two types:

Assimilation starch : It is formed as a result of photosynthesis of chloroplasts. Diastase enzyme converts it into soluble sugar at night time. The conversion of sugar into reserve or storage starch is brought about by leucoplast as amyloplast.

Reserve starch : Thick layers are deposited around an organic centre called hilum. When hilum is situated just at the centre of starch grain, it is said to be concentric e.g. pea, bean, wheat etc. While it is situated not at the centre, but nearer the margin it is said to eccentric e.g. potato.

  • Glycogen : Glycogen or animal starch occurs only in colourless plants like fungi. It occurs in the cytoplasm as an amorphous
  • Inulin : It is a complex type of polysaccharide, soluble found dissolved in cell sap of roots of Dahlia, Jaruslem, Artichoke, Dandelion and members of compositae. When these roots are preserved in alcohol it precipitates in the form of “ Sphaerites” or fan shaped
  • Sugars : A number of sugars are found in solution of cell These include glucose, fructose, sucrose, etc. Glucose and fructose are monosaccharides while can sugar is disaccharide and occurs in beet root and sugar- cane.
  • Cellulose : Chemical formula is (C6 H10 O5 )n . The cell wall is made up of It is insoluble in water.

 

  • Fats and Oils : These are important reserve food material. These are always decomposed into glycerol and fatty acids by enzymatic action. Fat is usually abundant in cotyledons than in the endosperm. g. flax seed produce linseed oil, castor produce castor oil, cotton seeds produce cottonseed oil, etc.
  • Proteins and Amides (Aleurone grains) : Storage organ usually contain protein in the form of crystalline bodies known as crystalloids (potato). Proteins may be in the form of aleurone grains as in pea, maize, castor, wheat, etc. Each aleurone grain consists of a large crystalline grain of protein known as crystalloid associated with it there is a smaller body It is not a protein but double phosphate of calcium and magnesium.
  • Excretory Products : The organic waste products of plants are by-product of metabolism. They are stored as Depending upon chemical composition they are classified as:
  • Resins : They are believed to be aromatic compounds consisting of carbon, hydrogen and oxygen and are acidic in nature. Sometimes they are found in combination with gums and are called gum resin. g. Asafoetida (heeng). These are used in making varnishes and gums.
  • Tannins : They are complex nitrogenous compounds of acid nature having an astringent They are used in conversion of hide into leather. With ferric salt they are largely used manufacture of ink. Presence of tannin in plants makes its wood hard durable and germ proof.
  • Alkaloids : These are organic, basic, nitrogenous substance. They occur in combination with organic acids and most of them are poisonous. From plants, cocaine, hyoscine, morphine, nicotine, quinine, atropine, strychnine and daturine are extracted.
  • Glucosides : Some glucosides or glycosides function as storage substance g. amygdaline of the bitter almond. Erythrocyanins and Anthocyanins are responsible red and blue colour and flavines for cream colour. Carotene is an unsaturated fatty acid and not a glycoside, gives red and orange colour to roots.
  • Etherial and Essential oils : These consist mixture of various hydrocarbons known as tarpenes and their oxygen They are responsible for flavor of many fruits and scent of many flowers etc. They are volatile and are soluble in water, ether, petroleum etc. e.g. lavender, mint, clove oil, eucalyptus oil, theme oil etc.
  • Mineral matter : Many minerals are waste products in
  • Calcium oxalate : It occurs in the form of crystals of various

Raphides : Needle shaped crystals are known as raphides. They are found single or in bundles. e.g. in plants like jamikand, Colocasia, water hyacinth (Jal kumbhi), amorphophallus and aroids.

Rosette or Sphaeraphides : Star shaped crystals. They occur in special mucilaginous parenchyma cells of the petiole of arum, water hyacinth, etc. Crystals in the form of cubes are found in tunic of onion bulb. In the leaf of belladona, these crystals are in the form of sand and also called as sand crystals.

Calcium oxalate crystals : In members of family solanaceae. They are found as cubics, rods and prisms.

  • Calcium carbonate : It is deposited in the form of crystalline masses hanging from a cellulose stalk in enlarged epidermal cells of leaves of Ficus elastica (Indian rubber plant) and is called as cystolith.
  • Latex : It is an emulsion in water having many substances either in suspension or in true solution. It may contain sugars, alkaloids and It is watery in banana, milky white in Euphorbia, yellow or orange red in opium (poppy) is dried latex.

 

  • Organic acids : Tartaric acid in tamarind, and grapes, citric acid in lemon, orange etc. malic acid in apple and Bryophyllum. Oxalic acid in the form of
  • Gums : It is formed by decomposition of cellulose cell Gum arabic of commerce is obtained from

Acacia senegal.

  • Secretory products : The chief secretion of plants are enzymes nectar, colouring matter, water etc. These secretion are helpful to

 Nucleus

  • Definition : (Karyon = Nucleus) The nucleus also called director of the It is the most important part of the cell which directs and controls all the cellular function.
  • Discovery : The nucleus was first observed by Robert Brown (1831). Nucleus plays determinative (in heredity) role in cell and organism, that was experimentally demonstrated by Hammerling (1934) by conducting surgical experiments with green marine unicelled algae Acetabularia.
  • Occurence : A true nucleus with definite nuclear membrane and linear chromosome, is present in all the eukaryotes except mature mammalian RBCs, sieve tube cell of phloem, tracheids and vessels of xylem. The prokaryotes have an incipient nucleus, called nucleoid or prokaryon or genophore or false nucleus or bacterial
  • Number : Usually there is a single nucleus per cell e. mononucleate condition, e.g. Acetabularia.
    • Anucleate (without nucleus) : RBCs of mammals, phloem sieve tube, trachids and vessels of
    • Binucleate : g. Ciliate, Protozoans like Paramoecium.
    • Polynucleate : g. fungal hyphae of Rhizopus, Vaucheria. Polynucleate condition may be because of fusion of a number of cells. i.e. syncytium, coconut endosperm or by free nuclear divisions without cytokinesis i.e. coenocyte.
  • Shape : It varies widely, generally spherical g. cuboidal germ cells, oval e.g. columnar cells of intestine, bean shaped in paramoecium, horse-shoe shaped in vorticella, bilobed, e.g. WBCs (acidophils), 3 lobed e.g. basophil, multilobed e.g. neutrophils, long and beaded form (moniliform) e.g. stentor and branched in silk spinning cells of platy phalyx insect larva.
  • Size : The size of nucleus is variable e. 5 – 30m. In metabolically active cells size of the nucleus is larger than metabolically inactive cells. The size depends upon metabolic activity of the cells. It is directly proportional to number of chromosomes.

(7)  Chemical composition of nucleus

Proteins = 80% (65% acidic, neutral and enzymatic proteins; 15% basic proteins-histones) DNA            = 12%

RNA       = 5%

Lipids     = 3%

Enzymes like polymerases are abundantly present and help in synthesis of DNA and RNA. Minerals like

Ca 2+ , Mg 2+ , Na + , and K + are present in traces.

 

  • Ultrastructure : The nucleus is composed of following structure
    • The nuclear membrane
    • The
    • The nuclear sap or
    • The chromatin

The nuclear membrane or karyotheca

  • Definition : It is defined as a regulatory envelope which controls the nucleo-cytoplasmic interacitons and

 

exchange of materials.

  • Discovery : Nuclear membrane, also called nuclear envelope or nucleolemma or karyotheca, was first discovered by Erclab (1845).
  • Structure : It is a bilayered envelope. Each membrane is about 90 Å thick lipoproteinous and Outer membrane, called ectokaryotheca, is

studded with ribosomes on its cytoplasmic surface and

 

Ribosomes

Euchromatin                                  Nuclear pore Parinuclear space

 

Heterochromatin Perinucleolar

chromatin Intranucleolar chromatin

Nuclear envelope Inner membrane

 

is continuos with RER at some points. Inner membrane, called endokaryotheca, is without ribosomes and is internally lined by electron-dense material of protein

Endoplasmic

reticulum         Nucleolus

Fig : Electron microscopic structure of nucleus

Outer membrane

fibres called fibrous or nuclear lamina nuclear cortex or hoeny comb layer (about 300 Å thick). Two membranes are separated by a fluid-filled intermembranous perinuclear space (about 100-300Å). Nuclear membrane contains following structure.

  • Nuclear pore : Nuclear membrane is porous and has 1,000-10,000 octagonal nuclear pores. Each nuclear pore is about 400-1,000 Å in diameter (average size is 800 Å). The number and size of the nuclear pores depend upon the needs of the

Nuclear pores are interspaced at about 1000-1500 Å. Each nuclear pore is fitted with a cylindrical structure, called annulus (with a lumen of 500 Å) and both collectively form the pore complex or pore basket. Annulus has 8 micro- cylinders (each about 200 Å in diameter and with a lumen of 50 Å) in its wall. It also encloses a channel having nucleoplasmin for the movement of

Outer nuclear membrane                Pore complex          Ribosomes   Perinuclear space

 

I

Fig : V.S. of nuclear envelope showing nuclear pore, Ribosomes and fibrous lamina

 

substances. Annulus acts as a diphragm and regulates the size of the nuclear pore.

  • Nuclear blebbing : The nuclear envelope shows evagination. As a result, blebs are formed which are pinched off. This phenomenon is called blebbing. The nuclear vesicles so formed are thought to give rise to mitochondria, plastids, Blebbing may also occur from the outer unit membrane only. A row of these blebs move

 

 

towards the periphery. As a result of deposition of matrix material in between these blebs, and annulate lamella is formed. The annulate lamellae is thought to give rise to ER cisternae.

  • Origin : It is formed by the fusion of ER elements during the telophase of cell

(v)  Functions

  • It regulates the nucleo-cytoplasmic interactions.
  • It allows the passage of inorganic ions and small organic
  • It helps in pinocytosis and phagocytosis of large sized molecules .
  • It allows passage of ribosomal subunits, RNAs and proteins through nuclear
  • It maintains the shape of the
  • Fibrous lamina strengthens the nuclear It also helps in dissolution and reformation of nuclear membrane during cell division.

The nucleolus (Little nucleus)

  • Discovery : Nucleolus was first observed by Fontana (1781) in the skin cells of an eel. Term ‘nucleous’ was coined by Bowman (1840). Its light microscopic structure was given by Wagner (1840).
  • Position : It is generally associated with nucleolar organizer region (NOR) of the nucleolar It is absent in muscle fibres, RBC, yeast, sperm and prokaryotes.
  • Number : Generally, a diploid cell is with two nucleoli but there are five nucleoli in somatic cell of man and about 1000 nucleoli in the oocytes of

 

  • Structure : (De Robertis al 1971). A nucleolus is distinguishable into following regions :-
  • Chromatin : The nucleolus is surrounded by perinucleolar Heterochromatic intrunsions are also seen in the nucleolus which constitutes the intranucleolar chromatin.
  • Pars fibrosa : Fibrils of 80 – 100 Å size form a part of the
  • Pars granulosa : Granules of 150 – 200 Å diameter constitute the granular part of the They appear like vesicle with a light central core. The granules may be joined by filament forming a beaded primary nucleolonema. The fibrils may also be associated to it. The primary nucleolonema may further coil to form the secondary nucleolonema.

Perinucleolar chromatin

Intranucleolar chromatin

Matrix Fibrils

Granules

 

Fig : Ultrastructure of a Nucleolus

 

  • Pars amorpha : The granules and the fibrils lie dispered in an amorphous proteinaceous matrix. Nucleolus contains large amount of proteins mainly phosphoproteins. There are no histones proteins. RNA methylase, an enzyme that transfers methyl groups to the RNA bases has been localized in Nucleolus is stained by “pyronine”. It is not bounded by any limiting membrane. Fibrillar region of nucleolus is called secondary constriction or nucleolar organising region (NOR) and this region directs the synthesis of rRNA. Ribosomes are assembled here as such it is also called ribosome producing machine or factory. Ribosomal units so formed are joined together by thin filament (rRNA) forming a structure like string of beads and it is called “nucleonema”.

 

  • Chemical composition : Nucleolus is mainly formed of RNA and non histone acidic It is a

storehouse of RNA.

  • Origin : A nucleolus is formed at specific sites, called the nucleolar organizers, present on certain chromosomes region (NOR).

(vii)  Functions

  • It is seat of biogenesis of rRNA and also stores
  • It plays important role in spindle formation during cell
  • It receives the ribosomal proteins from the cytoplasm, combines the rRNAs and ribosomal proteins to form ribosomal

Nucleoplasm : It is also called karyolymph. It is transparent, homogenous, semifluid, colloidal, ground substance present inside the nuclear membrane in which nuclear chromatin and nucleoli are embedded. Chemically it contains. Nucleoplasm is also known as protoplasm of nucleus.

  • Nucleic acid : Monomer nucleotides of DNA and RNA
  • Proteins : Basic proteins (nuclear protamines and nucleohistones and acidic proteins (non-histone)
  • Enzymes : DNA polymerase, RNA polymerase, NAD synthetase, nucleoside triphosphatase, and pyruvic acid kinase,
  • Minerals : Phosphorus, potassium, sodium, calcium, magnesium,
  • Ribonucleoproteins : Contain perichromatin granules and interchromatin Histone proteins are basic because they contain arginine in much amount e.g. H1 , H 2 A, H 2 B, H3and H 4 .

The nucleoplasm helps in maintaining the shape of nucleus formation of spindle protein of NAD, ATP, DNA, RNAs and ribosomal subunits. Plasmosome and karyosome combindly called “amphinucleoli”.

Chromatin  fibres  /Nuclear  chromatin  :  The nucleoplasm contains many thread like, coiled and much elongated structures which take readily the basic stains such as “basic fuschin”. These thread like structures are known as chromatin fibre. They are uniformly distributed in the nucleoplasm. They are observed only in the “interphase stage”. Chromatin fibres are made of chromosomes. In resting nondividing eukaryotic cells the genome is nucleoprotein complex and it is called chromatin.

 Chromosome .

  • Definition : During interphase, chromatin threads are present in the form of a network called chromatin At the time of cell division, these thread like structures of chromatin become visible as independent structures, called chromosomes.
  • Structure of chromosome : Each chromosome consists of two coiled filaments throughout its length called chromonemata by Vejdovsky. These have bead like structures called chromomeres which bear genes. Chromatid is a half chromosome or daughter chromosome. The two chromatids are connected at the centromere or primary constriction. Primary constriction (centromere) and secondary constriction gives rise to satellite. The secondary constriction consists of genes which code for ribosomal RNA and nucleolus hence it is called as “nucleolar organizer region”. Chromosomes having satellite are called SAT

 

The ends of chromosomes are called “telomeres” (which do not unite with any other structure). A tertiary constriction is also present in chromosomes, which perhaps helps in recognition of chromosomes.

In 1928 Emile Heitz developed a technique for stainning of chromosomes. Chromosomes can be stainned with acetocarmine or fuelgen (basic fuschin) there are two types of regions are seen :–

  • Heterochromatin : It is formed of thick regions which are more darkly stained than others It is with condensed DNA which is transcriptionally inactive and late replicating. It

 

A                                                                                                                                             E

Fig : Chromosomes A. Diagrammatic B, C, D, E-Different parts of chromosome

 

generally lies near the nuclear lamina. Heterochromatin are of two types : –

  • Facultative heterochromatin : Temporarily inactivated chromatin and forms 5% of the genome.
  • Constitutive hetrochromatin : Permanently inactivated chromatin and generally ground near
  • Euchromatin : It is true chromatin and is formed of thin, less darkly stained It is with loose DNA which is transcriptionally active and early replicating.
    • Chemical chomposition : DNA – 40%. Histone – 50%. Other (acid) Proteins – 8.5%. RNA – 1.5%. Traces of lipids, Ca, Mg and Histone are low molecular weight basic proteins which occur alongwith DNA in 1 : 1 ratio. Nonhistone chromosomal or NHC proteins are of three types– structural, enzymatic and regulatory. Structural NHC proteins form the core or axis of the chromosome. They are also called scaffold proteins. Enzymatic proteins form enzymes for chemical transformation, e.g., phosphates, RNA polymerase, DNA polymerase. Regulatory proteins control gene expression. HMG (high mobility group) proteins get linked to histones for releasing DNA to express itself.
    • Ultrastructure and Models of chromosomes : (See in genetics).

Important Tips

  • Syncytium is multinucleate condition formed by the fusion of cells g. in plasmodium of slime moulds.
  • Coenocytic is multinucleate condition by repeated Karyokinesis but not followed by cytokinesis g. in vaucheria, rhizopus.
  • Callan and Tamlin (1950) first to observe nuclear pore in nuclear
  • Staining property of chromosomes is called as
  • Satellite is also called trabant.
  • Centromere or kinetochore is responsible for chromosomal movement during cell
  • Idiogram : Karyotype of a species is represented with the help of a diagram called
  • Genome : It is defined as the haploid set of
  • Plasmon : Genes present in cytoplasm are called “plasmons”
  • Non histone proteins (acidic proteins) are rich in nucleus and less

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