Cell+ +Cell+Membrane

8/9/2019 Cell+ +Cell+Membrane

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Cell & Cell

MembraneDr. Muhammad RafiqueAssistant Professor

Anatomy

03/11/2008


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Objective

Definition of cell and type of cell

Definition of cell membrane and differencebetween cell membranes and cell wall

Anatomical Structures of cell membrane

Different constituents of cell membrane

Fluid Mosaic Model of cell membrane

Electron microscopic features of cellmembrane


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Types of CellsCell is the basic structural & Functional unit of

lifeAll living things are divided into two major

groups depending on how their cells are

appear and presence or absence of NucleusProkaryotes (without Proper Nucleus)

Eukaryote (with Nucleus)

All living things are made up of one or morecells.

Unicellular (one cell)multicellular (More than one cell)


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Types of Cells

A prokaryote is a kind ofsimple cell, Unicellularbecause it doesn't havea membrane boundnucleus, or many of theother membrane-boundorganelles.Prokaryotes are usuallyunicellular - unlike

eukaryotes, which aresometimes unicellular,but usuallymulticellular.


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Types of Cells

Eu-karyote means 'true-nucleus', to the extent

that, unlike

prokaryotes,

eukaryotic cellscontain a nucleus.

They also contain

many other organelles

most of them aremembrane bound.

Multicellular


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Components of CellA cells consists of:

1. Cell Membrane2. Cytoplasm

a. Rough endoplasmic reticulum

b. Smooth endoplasmic reticulum

c. Golgi apparatus

d. Mitochondria

e. Lysosome

f. Vacuole

g. Peroxisome

h. Centriolei. Ribosome

3. Nucleusa. Nuclear Membrane

b. Nucleoplasm

c. NucleolusNon membrane Bound organelles

Membrane

Bound

organelles

Non membrane

Bound organelles


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Cell Membrane / Plasma Membrane

A cell is a containercontaining cytoplasm

which on outer aspect

bound surrounded by a

membrane. A cell

membrane is very

flexible and the cell can

change shape quiteeasily.


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Cell Wall

Some cells have given up thisflexibility for greater

strength and protection in

the form of a 'cell wall'.

A cell wall is not flexible socells that have cell wall

have a constant shape.

Most bacteria have cell

walls, and all plants and allfungi also have a cell wall

around every cell.


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CELL COVERINGS

Animal cells howevernever have a cell wall. The cell wall is built

outside of the cell

membrane so it canprotect the cell.

So things that need to getinto or out of the cell have

to go through two sets of

doors, one in the cell wall

and one in the cell

membrane


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Cell MembraneAll Cells are surrounded by

an external limitingmembrane: cell membraneor plasmalemma

This membrane is 7-11 nm inthickness, can not be

visible by light microscopeServes as the dynamic

interference betweeninternal and externalenvironments

The cell interacts with twotypes of externalenvironmentAdjacent cell

Intercellular space


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Cell Membrane Cont

The functions of cellmembrane:Transfers of nutrients &

Metabolites

Attachments of cell toadjacent cells and otherstructures

Cell to cellcommunications

These functions dependsto some extents onspecialized nature ofcell


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Structure of Cell Membrane

On biochemical analysisof plasmalemma consists

of 35% lipid, including

phospholipids and

cholesterols, 60% proteins

and a small amount of

carbohydrates

Cell membrane consistsof bilayer of

phospholipids


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Structure of Cell Membrane Cont

Phospholipids consistsof two poles Hydrophilic (water loving)Head

Hydrophobic (waterhating) Tail

Polar Heads are derivedfrom Glycerol and nitrogenouscompound like choilne,

ethanolamine or serineThese nitrogenous compoundattached to glycerol by meansof phosphate bridge


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Structure of Phospholipid

Head consists ofNitrogenous compoundwhich attached toGlycerol with the

phosphate bridge. Twochains of Fatty Acid areattached to glycerol bythe covalent bonds. Thenitrogenous compoundare positively charged &Hydrophilic while thePhosphate group isnegatively charged.

+

-


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Structure of Cell Membrane ContThe phosphate group isnegatively charged whilethe nitrogenouscompounds are positivelychargedNon-Polar Tails of

phospholipids moleculeconsists of two long chainsof fatty acidsOne of fatty acid chain isstraight saturated while the

another fatty acid chain isunsaturated chain havingkink or band this providesflexibility to membrane


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Each chain covalently linked

to glycerol components of the

polar head

Because ofamphipathic in

nature having bothhydrophilic & Hydrophobic

Phospholipids in aqueous

solution form a bilayer with

Hydrophobic (P

olar) Headstowards directed towards the

Surfaces and hydrophobic

Heads directed inwards


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Cholesterol molecules arealso present in bilayerin ratio of 1:1 withphospholipids.

Cholesterol molecules areamphipatic and havekinked configuration.

Cholesterol molecules

thus stabilize andregulates the fluidity ofphospholipids bilayer

Cholesterol molecules are

interspersed among phospholipid

tails in the bilayer.


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On the external surfaceof plasma membraneof animals cellsmany of themembrane proteins

and some ofmembrane lipids areconjugated withpolysaccharides on

the outer surface ofcell membrane calledas Glycocalyx (cellcoat). This layerprotects the cellmembrane.


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The fluid mosaic model of membrane structure. The membrane consists of a

phospholipid double layer with proteins inserted in it (integral proteins) or bound

to the cytoplasmic surface (peripheral proteins). Some of these proteins

completely span the bilayer and are called transmembrane proteins, whereas

others are embedded in either the outer or inner leaflet of the lipid bilayer.


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Electron Microscopic Appearance of Cell

Membrane

Singer and Nicholson, in early 1970sproposed the Fluid Mosaic Model

of membrane structure.

On electron microscope examination

of cell membrane, exhibits a

trilaminar structure; there are

two electron dense lines and

separated by an electron lucent

zone

These arrangement is found notonly in cell membrane but also all

the organelles present inside the

cell. This trilaminar structure is

also called as Unit Membrane.

Outer

Radio-opaque Appearance

of Hydrophilic heads

Radiolucent Appearance

of Proteins

Radio-opaque Appearance of

Hydrophilic heads

Inner


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Electron Microscopic Appearance of Cell Membrane

Outer Radio-opaque Layer

Central Radio-lucent Layer

Inner Radio-opaque Layer


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CytosolSum total of the contents of the cell, the protoplasm) were

commonly classified into the contents of the nucleus (theNucleoplasm and the remainder of the cell contents, the

cytoplasm. The cytoplasm was further classified into solid

structures, such as organelles and the cytoskeleton, and a

liquid component that was variously called the cell sap,ground substance Cytosol.

The fluid portion of a cell's cytoplasm, which lies outside the

organelles (A differentiated structure within a cell, such as

a mitochondrion, vacuole, or chloroplast, that performs a

specific function and other insoluble components of the

cytoplasm. Cytosol contains water, free proteins, and a

variety of other substances


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Termed as Cytosol

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