cell and its organelles

Principles of Genetics &

Population Genetics

AGB 121

2012-13

Dept. Of Animal Genetics and Breeding

Veterinary College

Hebbal, Bangalore -24

Cell and its Organelles

Cell is the basic unit of organization of living matter.

It is the unit of biological activity delimited by a semi permeable membrane and capable of self reproduction in medium free of other living systems.

Cellular organisms have either prokaryotic or eukaryotic cells.

2/1/2013 2Dr. R. Jayashree, Asst. prof(AGB)

Prokaryotic cells

Composed of primitively organized

cytoplasm and nucleus.

Nuclear substance is not separated

by nuclear membrane from

cytoplasm.

Cytoplasm does not have

endoplasmic reticulum, Golgi

complex.

e.g: Blue green algae & Bacteria


Eukaryotic cell

Have true nucleus with nuclear

membrane.

Nucleus has chromosomes,

nucleolus and nucleoplasm.

The cytoplasm is enclosed in

plasma membrane and has

cell organelles

Other organelles

Mitochondria, Endoplasmic reticulum, Vacuoles,

Lysosomes, Chloroplasts,Centrioles & Ribosomes.


Features Animal Cell Plant cell

Size

Cell wall

Plastids

Vacuoles

Golgi

apparatus

Centrosomes

and

centrioles

Small

Absent

Absent except

in Euglena

Large numbers

are present

Single highly

complex

Present.

Large

Rigid cell wall cellulose

Present

Large single in the

centre.

Simpler unit called

dictyosomes.

Absent

2/1/20137

PLASMA MEMBRANE


Consists of Lipids 20-40 %, Proteins-55-75% and Carbohydrates-1-5%

Plasma Membrane

• Protection of cells from injury.

• Passage of substances in and out of cell by

selective permeability.

• Absorption, Secretory, Excretory and waste

product removal.

• Determine antigen specificity

• Helps in movement of unicellular organisms

like Amoeba.


Functions:

Cytoplasm

Is a Jelly like semi fluid mass of protoplasm

excluding nucleus but includes all other

components-cytoplasmic matrix, cell

organelles & cell inclusions.

Contains water in liquid state and other

particles like minerals, sugars, amino acids,

tRNA, nucleotides, vitamins, proteins and

enzymes in colloidal state.2/1/2013 10Dr. R. Jayashree, Asst. prof(AGB)

Functions of cytoplasm

• Provides raw materials to cell organelles

• Exchange of materials between cell organelles

• Biosynthesis of fat, nucleotides, proteins,

co-enzymes etc

• Catabolic activities.

• Uniform distribution of various materials

• Cytoplasmic streaming or cyclosis


Mitochondria

Power house of the cell (production of ATP)

Cylindrical, length -5-10 micron,

Diameter- 0.5-1.0 micron


Mitochondria

• Two membranes-Outer membrane is smooth

and permeable & Inner membrane is folded

to from involutions called cristae

• Two Chambers- Outer chamber contains

enzymes and inner chamber contains

proteins, ribosomes, RNA, mitochondrial

DNA, enzymes of Kreb’s cycle, amino acid

synthesis and fatty acid metabolism


Functions of Mitochondria

• Oxidation of food materials

• Matrix has enzymes for synthesis of

fatty acids.

• Synthesis of amino acids


Endoplasmic Reticulum

Provides surface for

attachment of Ribosome's

Helps in packaging of

polypeptides to produce

proteins & enzymes.

Does not have Ribosome's.

Helps in synthesis of fat

inside cells and adipose

tissue.

Rough Smooth


Endoplasmic Reticulum

Inter connection of membrane linked channels that run

through the cytoplasm.

Channels contain fluid called endoplasmic matrix.

Exists in three forms

Cisternae- Sac like formed bundles and lie parallel to

one another actively involved in synthetic activity.

Vesicles- Oval rounded sacs also called as

microsomes.

Tubules- Tube like structures connecting cisternae and

Vesicles2/1/2013 16Dr. R. Jayashree, Asst. prof(AGB)

Function of EPR

Synthesis of glycogen and glygenolysis in liver, sterols and hormones in testes and ovary, formation of Visual pigment from Vitamin A in retinal cells.


GOLGI APPARUTUS

Golgi complex

Camillo Golgi in 1898


GOLGI APPARATUS

Complex protoplasmic structure made up of

smooth membrane saccules or cisternae, a

network of tubules with vesicles and

vacuoles.

Shape is not fixed depending on the

physiological state the shape varies.


Structure of Golgi

Complex

Cisternae: 4-8 membrane bound saccules or

cisternae. They have two side -convex side

called forming face & concave side called

maturing face.

Tubules: In the form of network towards the

periphery and maturing face of golgi apparatus.

They inter connect different cisternae.


Vesicles: Small sacs of Smooth

(containing secretary substance called

secretion vesicles) & coated vesicles

have rough surface and elaborate

membrane proteins)

Vacuoles-modified form of cisternae.

Some function as lysosomes.2/1/2013 21

Function of Golgi complexSecretion vesicles contain zymogen granules,

are sent out of the cells through exocytosis or reverse pinocytosis.

Transformation of membrane: Convert one type of membrane to another and recycling of plasma membrane.

Form glycoprotein from protein of EPR

Synthesis of complex carbohydrates such as pectin, mucoploysaccharaids, hemicellulose,cellulose etc.

2/1/2013 22

Function of Golgi complex

Hormones: Production of hormones by endocrine glands, formation of matrix of connective tissue, synthesis of retinal pigments in chick embryo.

Formation of acrosome.

Vitelogenesis- formation of oocytes and development of yolk.

Formation of lysosomes

Store house of digestive enzymes.

Membrane vesicles join the region of cytokinesis and produce new plasmalemma


LYSOSOMES- Suicidal bags

•Small vesicles bounded by a single membrane.

•Contain hydrolytic enzymes in the form of

minute crystalline or semi crystalline granules.

•Important enzymes- Phosphatases, sulphatases,

proteases, nucleases, liposases and glycosidases.


Types of Lysosomes

Primary –Newly pinched of vesicles from golgi apparatus.

Secondary- Fusion of primary lysosomes with phagosomes and also known as digestive vacuoles.

Residual bodies or tertiary lysosome- throw out the residues and undigested food materials into the external environment by exocytosisAutophagic vaculoes- formed by fusion of primary lysosomes and worn out organelles


Functions of Lysosmes

• Intracellular digestion of food

• Lysosomes of leucocytes eliminate foreign proteins, toxic substances, bacteria and other microorganisms.

• Provide nutrition during starvation by hydrolyzing organic food.

• Removal of old ,aged and useless organelles.

• Provide enzymes for sperm penetration


Functions of Lysosmes- contd

Essential for cell division by overcoming

agents that cause repression of mitotic

cycles.

Lysosome related nucleases might result in

mutation, breakage of chromosomes and

blood cancer.

Lysosomes remove carcinogens by

engulfing and separating them.


ENDOSOMES & ENDOCYTOSIS

Membrane-bound vesicles,

formed via a complex family

of processes collectively

known as endocytosis.

The basic mechanism involves

the invagination (folding

inward) of a cell's plasma

membrane to surround

macromolecules or other

matter diffusing through the

extracellular fluid.


Sphaerosomes

Small cell organelles bounded by single

membrane take part in storage and

synthesis of fat.

They arise from endoplasmic reticulum

and have some lysosome activity.


Peroxisomes or Microbodies

Small cell organelles with single membrane

which absorbs molecules of oxygen and take

part in oxidation other than those involved in

respiration.


Types of Microbodies

Peroxisomes- contain enzymes for

peroxidase synthesis.

Glycoxysomes-contains enzymes for

beta oxidation of glyoxylate.


RIBOSOMES

• Tiny organelles composed of approximately

60 percent RNA and 40 percent protein.

• In eukaryotes, ribosomes are made of four

strands of RNA.

• In prokaryotes, they consist of three strands

of RNA.

• Protein and RNA complex responsible for

protein synthesis. 2/1/2013 32Dr. R. Jayashree, Asst. prof(AGB)

Ribosomes

Organelle ribosome- found in

mitochondria

Cytoplasmic ribosome - remain

attached to Endoplasmic reticulum.

Size of ribosome is measured in

Svedberg Unit.


Ribosomes

May occur in linear or helical groups called

as polyribosome and connected with thick

strand of mRNA.

Polyribosomes are found during active

protein synthesis.


Functions of Ribosome

Protein synthesis

Storage of rRNA

Temporary storage of

protein and finally

transfer it to the

cytoplasmic reticulum.


Microfilaments

2/1/2013 36

http://micro.magnet.fsu.edu/primer/techniques/fluorescence/gallery/cells/index.html

Microfilaments

Ultra microscopic rods

or protein filaments made

of actin like lobule

protein molecule.

Microfilaments associate

to form hexagonal bundle

are contractile.


http://micro.magnet.fsu.edu/primer/techniques/fluorescence/gallery/cells/index.html

Microfilaments-Functions• Cytoplasmic streaming

• Microvilli are maintained through support provided by microfilaments.

• Spindle apparatus formation.

• Movement of fibroblast to undulation of microfilaments.

• Associated with cleavage furrow at the time of cytokinesis.

2/1/2013 38

MICRO TUBULES

• Straight, hollow cylindrical

organelles.

• Functions, ranging from

transport to structural support

(Cytoskeleton)

• Help in movement of cilia and

flagella

• Movement of nuclei during cell

division2/1/2013 39Dr. R. Jayashree, Asst. prof(AGB)

CILIA AND FLAGELLAAre essential for the locomotion of

individual organisms in

unicellular organisms.

In multicellular organisms, cilia

function to move fluid or

materials past an immobile cell as

well as moving a cell or group of

cells..

Passage of eggs in oviduct

Conjugation and fusion of gametes

2/1/2013 40

CENTRIOLES

• Self-replicating organelles

made up of nine bundles of

microtubules and are found

only in animal cells.

•They appear to help in organizing cell

division, but aren't essential to the process.

•Complex formed of centrioles and

cytoplasm is called centrosome or central

apparatus. 2/1/2013 41Dr. R. Jayashree, Asst. prof(AGB)

Centrioles

Prior to nuclear division the two centrioles

present in a centrosome move to opposite

poles.

Centrioles possess a whorl of nine

peripheral fibrils and each fibril is made

up of three sub fibrils called triplet fibril.


Functions-Centriole

• The distal centrioles give

rise to axial filament or tail

in spermatozoa

• Basal bodies formed from

centrioles give rise to cilia

and flagella.

Formation of nucleating centres.

Forming poles of the spindle


CHLOROPLAST[PLASTIDS]


CHLOROPLAST

Surrounded by a double membrane, containing stacked membranes.

Responsible for photosynthesis, the trapping of light energy for the synthesis of sugars.

Contains DNA, and like mitochondria is believed to have originated as a captured bacterium.


VACUOLES

Membrane surrounded "bags" that contain water

and storage materials in plants.


NUCLEUS


Nucleus

(Robert brown in 1831)

It is a specialized double membrane

bound protoplasmic body, which

contains all the genetic information for

controlling cellular metabolism and

transmission of posterity.

Cells have single nucleus.


Nuclear envelope or Karyotheca

• Made of two lipoproteins and trilaminar membrane. Contains large number pores or perforations.

• Inner membrane is smooth

•Outer membrane may be smooth or may be rough on the cytoplasmic surface.

•Two membranes are separated by a electron transparent perinuclear space.


Nucleoplasm or Nuclear sap or

Karyolymph

• Transparent semifluid colloidal substance which

fills nucleus.

• Contains nucleosides and number of enzymes

(DNA polymerase, RNA polymerase and

nucleoside phosphorylase)

• For synthesis and function of DNA, RNA,

nucleoproteins etc.

• Some proteins are essential for spindle formation.


ChromatinHereditary DNA-protein fibrillar complex

Chromatin is in the form of overlapping and coiled fibres

which appear to produce a network of chromatin

reticulum.

Chromatin fibres are disrtibuted through out the

nucleoplasm.


Euchromatin and Heterochromatin

Euchromatin contains

functional genes.

Heterochromatin is a

condensed region believed

to be genetically inert.

During prophase the

chromatin fibres

condenses to form

chromosomes


Nucleolus (Fontana in 1781)

Is a naked round structure which is attached

to the chromatin at specific region called

Nucleolar organizer region.

NOR regions of chromosome associated

with nucleolus and containing genes for

rRNA.

Commonly 1-4 nucleoli are found in a

nucleus.2/1/2013 53Dr. R. Jayashree, Asst. prof(AGB)

Nucleolus

Has four components

Amorphus matrix –

homogenous ground substance-

protein

Granular part- Granules of

Protein, RNAFibrillar portion- made of protein-RNA to be

precursor of granules.

Chromatin portion- that part of chromatin

associated with nucleolus2/1/2013

54

Nucleolus- Function

Principle site of

development of

ribosomal RNA

Centre of formation of

ribosomes

Forms nucleo proteins

Essential for formation of spindle fibres

during nuclear division.2/1/2013

55

• Possess genetic information

• Controls all cellular activities.

• Variations are caused due to changes in genetic material

• Helps in cell growth and membrane development.

• For cell differentiation by allowing certain sets of genes.

• Cell replication

Functions of Nucleus


Thank you


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