CELL STRUCTURE

Presented by Sneha Adhikari

Discovery of

cell

He invented microscope•With he could examine the specimens at magnification 1000-2000 times their original size

He studied cork slice under the microscope

He established that plant composed of cell

He established that animal composed of cell

Structures in a general plant cell

Structures in a general animal cell

Three imp cell regions

Cell membrane:- Outer most boundary of cell

Nucleus:- Control centre of the cell that contains DNA

Cytoplasm:- Part between the nucleus & cell membrane.

It contains a liquid called as cytosol which may contains cell organelles.

Cell wall STRUCTURE PLANT

Only plant cells andbacterial cells possesa protective structureas the cell wall outside the plasma membrane.In bacteria It is basically made up of long

polymers of glucosamine (NAG) and muramic acids (NAM)

In higher plants cell walls mainly made up of cellulose fibres. Addition to these, pectins, hemicelluloses and lignin are also deposited on primary cellulose layer.

Cell wall made up of three layers1.Middle lamella: it is composed of pectates of Ca &Mg.2.Primary cell wall: It is the first true cell wall to be deposited & made up of Cellulose, hemicellulose & some polysaccharides. 3.Secondary cell wall: it is made up of cellulose,hemicellulose and other polysaccharides impregnated with lignin, suberin,Si,Ca,Mg.

Cell wall functions

It a rigid, dead & protective covering.

Cell membrane structure

Cell membrane It is also known as plasma membrane.It is composed of two layer of phospholipids.A phospholipid is a type of fat composed of1. A hydrophilic phosphate head that faces aqueous environment. 2.Two hydrophobic fatty acid tails that faces

other fatty acid tail.

Cell membranes may also contain protein, sterols & sugarFor the structural organization of various compounds with in the membrane various theories were given:1. Trilamellar model or Sandwich model: By

Denielli Davson2. Unit membrane model : By Robertson3. Fluid mosaic model : By Singer & Nicolson proteins & lipids are oriented towards each

other in such a way, they exhibit semi fluid properties & the arrangement of lipids and proteins is of mosaic pattern

Cell membrane function

1.Responsible for protecting and separating the protoplasm from the external environment

2.Helps in selective uptake and transport Of ions

3.Provides surface area for many biochemical signal transduction reaction.

4. Plasma membrane is also the site for pinocytosis and phagocytosis.

Nucleus structure

It also known as master organelle.In some cases like sieve tubes, in plants

and red blood cells in animals nucleus disappears at the later stages of development.

Nucleus FUNCTIONS

Nucleolus is very important structure for; it acts as the site of synthesis and assembly of cytoplasmic ribosome's.

Karyolyph contains all the required components for the DNA replication and repair, transcription, assembly of ribosome's.

It play imp role in inheritance & gene expression

Mitochondria structure

Mitochondria are considered as ‘power plants’ of the cells.  Whenever or wherever, there is a need for higher amount

of energy output, mitochondria are found in large number.Mitochondria absent in RBC of mammals.Mitochondria are bounded by two single unit membranes. 

Mitochondria Functions

Also known as power house of the cell.Krebs cycle accur in matrix of

mitochondria.Enzymes responsible for ETS located in

inner membrane.

Endoplasmic reticulum structureIt is in contact with the outer plasma lemma and

the outer nuclear membrane.Absent in mature erythrocytes and cells of bacteria.ER is made up of two single unit membranes.Ultra structures: 1.Cisternae 2.Tubules

Endoplasmic reticulum functions

Mechanical support for the fluid protoplasm

Synthesis and storage of lipidsSynthesis and storage and transport

of proteins to different destination through golgi membranes.

Detoxification, transport of various cellular components, formation of micro bodies, formation of secretory vesicles

Golgi body StructureGolgi complex is surrounded by Endoplasmic reticulumThey are present in all cells except bacterial and blue-

green algal cells. In secretory tissues like thyroid and liver they are present

in large numbers than in other type of cells.The stacked Golgi membranes have two faces, i.e.

formation face is called cis face and maturation face as trans face.

Golgi body functions

Glocolysation of proteins Synthesis of cell wall

polysaccharidesMaturation of zymogen granules Formation of primary lysosomesSecretion of lipid bodiesPacking, maturation and

secretion of specific substances are the most important events of Golgi functions

Plastid Structure Plastids are very important cell organelles found mostly in

plant cells. They are mainly responsible for photosynthesis. plastids have been broadly classified into colorless plastids

(Leucoplasts) and color plastids (Chromoplasts). CHLOROPLAST: Basically most of the chloroplasts are bounded by two single

unit membranes and the space between them is called periplastid space

Plastids Functions

 Chloroplasts perform light reactions where light energy captured, converted into chemical energy and stored in energy rich bonds of ATP and reducing power NADPH+H. 

Ribosome Structure Ribosomes are ultramicroscopic particles, first observed by Palade They have been broadly classified into two types, i.e. 80 S and 70 S

types. Ribosomes found in the cytoplasm exist either in membrane bound

state or free state. It is made up of 2 sub units 1. larger (Dome) 2.smaller(cup

shaped) These two units united with the help of Mg+2

Ribosome's functionsRibosome act as dynamic

machinery for the synthesis of proteins.  This is achieved by the association of ribosome's with messenger RNA (m.RNA) and amino acid loaded transfer RNA

Lysosomes StructuresAlso known as suicidal bags.Lysosomes are bounded by a single

unit membrane and enclose a group of hydrolytic enzymes.

Lysosomes are divided in 4 parts 1. primary lysosomes 2. secondary lysosomes/ digestive

vacuoles 3.Residual bodies 4.Autophagic vacuoles

Lysosomes Functions It helps in 1.Phagocytosis 2.AutophagyPlay a very important role in metamorphosis of amphibians

and insects. For example, during the transformation of tadpole into adult frog; the long tail of the tadpole gets digested by the lysosomal activity, the process called resorption

Micro bodies StructureThey are bounded by a single unit

membrane.  Such structures are found in both animal and plant cells

There are three types of micro bodies and they are characterized by their functions:

1.Sphaerosomes 2.Peroxisomes 3.Glyoxysomes

Vacuoles Structure

Vacuoles are the spaces in the cells surrounded by single unit membranes.

It is separated from the rest of the cytoplasm by a single unit membrane called tonoplast.

It is filled with cell sap.

Vacuoles FunctionsThe content of the cell vacuole is

important in maintaining the turgidity of the cells.

 These vacuoles have been found to show lysosomal activities.

Cytoskeleton Structure1. Micro tubules: fine tubuler proteins Functions: 1.provides structural support to various cell. 2.Help in spindle & astral ray formation

2. Micro filaments: thin protein fibreFunction:1.Amaeboid movement of protozoans

Centrioles StructureCentrioles are the characteristic organelles of animal cells

they are almost absent in plant cells with the exception of some lower unicellular algae.

They are found in the cytoplasm at one pole of the nucleus.The wall of the open barrel shaped structure is made up of

nine groups of microtubules arranged in a circle.

Centrioles FunctionsCilia and flagella in lower

organisms and other cells take their origin from centrioles

During cell division, centrioles help in the organization of mitotic apparatus in a particular plane.

Polymerise cell microtubules for formation of spindle fibres and astral rays during cell division

Chromosome StructureDarkly stained rod shaped bodies visible under light

microscope in cell during metaphase stage of mitosis.Chromosome morphology 1. Centromere 2. Cromatid 3. Secondary constriction

4. Telomere 5. Chromomere 6. Chromonema 7. Matrix

Chromosome Function

It carry DNA so it play role in inheritance.

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