cell basic unit of life biology chapter no 4

By Sajjad Hussain Mirani

Sindh University Jamshoro

What Is Cell? Cell is the smallest entity in which life

can exist.

How Cell Was Discovered? Cells are microscopic in nature so

their discovery was dependent upon the invention of microscope.

Microscope was invented by David Jensen in 1590 A. D. But 1st useful microscope was invented by Galileo (a great astronomer) in 1610 A.D.

Galileo

In 1665 A.D. Robert Hooke discovered cell by his own made microscope in a slice of cork.

What Hooke Had Seen?

Robert Hooke seen many small empty spaces which he named as cell (empty room)

Who Discovered The Nucleus? In 1831 A.D. Robert Brown discovered

the nucleus in the cells of orchid.

Who Discovered Cytoplasm?

In 1839 A.D. Schwann observed that nucleus was surrounded by a fluid in cell. Now named as cytoplasm.

Introduction To Cell Theory Put forward by Schleiden (a botanist)

and Schwann (a zoologist) in 1839 A.D.

Cell theory was later corrected by Rudolf Virchow in 1855 A.D.

Schwann.

Schleiden.

Virchow.

Points Of Cell Theory1. Cell is a basic unit of life.

2. All living organisms are made up of cells.

3. New cells are produced from preexisting cells.

Definition Of CellNow cell is defined as “Structural and functional unit of life made up of protoplasm containing nucleus surrounded by cytoplasm and bounded by cell membrane.

What Is Microscope? Microscope is an optical instrument through

which we can visualize small objects which we are unable to see with naked eye.

In 1590 A.D. David Jansen invented 1st microscope.

Later Galileo, Robert Hooke and other scientists made useful developments in microscope.

Types Of Microscope On the basis of source of illumination microscope is

divided into following three types.

1. Light Microscope Type of microscope in which light is used as a

source of illumination.

2. X – Ray MicroscopeType of microscope in which x – rays are used as a

source of illumination.

3. Electron Microscope Most powerful microscope.

Can magnify objects up to 10,000 times.

Built in 1930’s.

Electron beam is used as source of illumination.

Qualities Of Microscope

A science student should three qualities of a microscope.

1. MagnificationMagnification is measurement of ability of microscope to enlarge images.Magnification can be calculated by multiplying power of eyepiece with the power of objective lenses.

2. ResolutionIt is measurement of clarity of image.

Qualities Of Microscope

3. ContrastAbility of microscope to distinguish b/w two closely related points or features in a microscopic field.

Isolation Of Cellular ComponentsCell fractionation is a technique to isolate various parts of cell to determine their composition.

In cell fractionation 1st number of cells are open in an ice cold environment.

Then cells are placed in homogenizer or motor to break various parts of cell.

In last cells centrifuged by the spinning action of centrifugation machine.

Large particles e.g. nucleus, etc are settle on slow while small particles e.g. ribosome are settled on fast motion.

Types Of CellsCells are basically of two types

Prokayotic Cell It is a type of cell which lack all membrane

bounded cellular structures.

Eukaryotic Cell It is a type of cell which contain all

membrane bounded structures.

Prokayotic Cell & Eukaryotic Cell

Do not contain membrane bounded nucleus.

Nuclear material is concentrated in a region called “Nucleoid”.

Do not contain other membrane bounded structures.

Only contain mesosomes which are infoldings of cell membrane for the respiration purpose.

Prokaryotes are unicellular living organism like bacteria, etc.

Contain a membrane bounded nucleus in their cells.

Nucleus is very well defined and usually spherical in shape.

Contains all membrane bounded cell organelles.

Contain mitochondria, Golgi bodies, endoplasmic reticulum, lysosome, peroxisome, etc.

Eukaryotes are both multi cellular and unicellular in nature.

Parts Of Eukaryotic Cell A eukaryotic cell usually contain following

four parts.

1. Plasma Membrane.

2. Cell Wall.

3. Cytoplasm.

4. Nucleus.

Plasma Membrane Also called cell membrane, plasma lemma.

Outer boundary of animal cell and second outer most boundary of plant, bacterial and fungal cells.

Protects cytoplasm.

Helps in transport of different materials across it.

It is semi permeable in nature

Composition Cell membrane is made up of following

substances.

1. Lipids (phospholipids and cholesterol).

2. Proteins (intrinsic and extrinsic).

3. Carbohydrates.

Lipids They are arranges in 2 parallel layers called lipid bi

layer.

Have two ends i.e. polar and non polar ends.

The non-polar ends faces each other.

Polar heads are linked with Carbohydrates and Proteins

Phospholipids most important lipid molecule.

Cholesterol is also present.

Lipid Bi Layer Of Cell Membrane

Structure

Fluid Mosaic Model Most popular model which explains the structure of

cell membrane.

Given by Singer & Nicolson (1972).

According to this model lipids are forming bi layer.

Proteins are either completely inside or outside.

Protein molecules act like channels which transport different substances from place to place.

ProteinsIntegral or Intrinsic ProteinsThey are located inside phospholipid bi

layer of cell membrane.

Peripheral or Extrinsic ProteinThey are located outside the

phospholipid bi layer of cell membrane.

Proteins Of Cell Membrane

FunctionsCell membrane performs various functions few important are as follows,

Diffusion (both passive and facilitated).

Osmosis.

Active transport.

Endocytosis.

Exocytosis.

Cell Wall Outer most boundary of plant, bacterial and algal

cells.

Made up of cellulose which are non living carbohydrate molecules.

Made from Cellulose and pectin.

Some times lignin may be present.

Cell wall may have three parts (Middle lamella, Primary cell wall and Secondary cell wall)

Middle Lamella It is a layer between 2 daughter cells is

called middle lamella.

When it dissolves, the daughter cells separate.

Composed of calcium and magnesium pactate.

Primary Wall Formed inside the middle lamella.

1st layer which is synthesized by cell.

It is thin in young cells.

In mature cells it becomes thick.

It is made of 50% hemi cellulose, 25% cellulose and some pectin

Secondary Wall It is formed inside the primary wall.

It is made from cellulose

Some times Lignin is also added in it

What is Plasmodesmata?

These are the places of cell wall where deposition of wall material does not take place.

Plasmodesmata are pores in cell wall.

Functions Of Cell Wall Provide mechanical support to the cell.

Give specific shape to the cell.

Provide cell with the property of rigidity.

Hydrophilic so helps in imbibition of water.

Facts About Nucleus Discovered by Robert Brown in 1831.

Nucleus all activities of cell.

Usually spherical in shape.

Bounded by perforated nuclear membrane.

There may be one, two or more nuclei per cell.

Components Of Nucleus Nucleus contain following parts.

Nuclear membrane.

Nucleoplasm or Karyolymph.

Chromatin network.

Chromosomes.

Nucleic Acids.

Diagram Of Nucueus

Nuclear membrane Out boundary of nucleus It has pores called nucleo-pores Nuclear pores allows different

substances to pass from nucleus to cytoplasm.

Nucleoplasm It is a fluid which is filled inside the

nucleus. It is also known as karyolymph.

Chromatin Network It is a term which refer to the uncoil chromosomes which are present inside the nucleus.

These sort of chromosomes are seen during interphase

Chromosomes Chromatin network coils upon itself to form a thread like structure called chromosomes.

Chromosomes are species specific i.e. every species have an specific number of chromosomes like 46 in man.

What Is Cytoplasm Cytoplasm is a part of protoplasm which lies b/w cell membrane and nuclear membrane.

Cytoplasm is collection of many small sub units called cytoplasmic organalles.

Cytoplasmic organalle are of following types.

Endoplasmic Reticulum (ER)

Important Facts About ER Intracellular network of tubules which act like pathway for transporting materials.

ER extend from cell membrane to nuclear membrane.

Of Two types, i.e.

Rough ER Smooth ER Highly coated with

ribosome.

Occur in protein synthesizing cells.

Found in pancreas, slivery glands, etc.

Surface is not coated with ribosome.

Occur chiefly in steroid producing cells.

Found in adipose tissue, etc.

Functions Of ER In skin it converts cholesterol into vitamin

D.

Rough ER gives platform to ribosomes.

ER provides pathway for import/export.

Help in protein synthesis.

Help in detoxification.

Smooth ER involves in lipid synthesis.

Mitochondria

Key Facts Of Mitochondria Present in all eukaryotic cells so it is a universal structure.

Also known as chondriosomes.

Rod shape, cigar shaped, capsule shape, etc.

Remain in constant motion.

They are center of respiration of cell.

0.2-1.0u in diameter and 10u in length.

Internal Structure Double membrane bounded structure.

Outer membrane is smooth.

Inner membrane is folded and folds are known as Cristae.

Folds are filled with matrix.

Cristae has enzymes and co-enzymes required for oxidation of pyruvate.

Here, glucose, amino acids and fatty acids are digested and ATP are made.

They are called Power Houses of cell.

Unique Characters Of Mitochondria

They have their own DNA.

They are semi-autonomous.

Can produce new mitochondria independent of cell division.

Transfer only by mother to her offspring.

Golgi Complex

Important Points About Golgi Discovered by Camilo Golgi (1898).

Also called Dictyosomes in plants and invertebrates.

They have Cisternae.

One in animal cell.

Many in plant cells.

Located near to the nucleus.

Functions Of Golgi Bodies Act as packaging centre in cell where different

proteins are packed and transported to various parts of cell.

They store proteins.

Make enzymes & Co-enzymes.

In plants, they make cell wall.

In animals they make lysosomes

Lysosomes

Important Points About Lysosomes

Lysosomes are formed by Golgi bodies.

They contain various types of digestive enzymes so help in intra cellular digestion.

Lysosomes are found in animal cells.

They can lead to digestion of their own cell if their membrane got ruptured so also known as suicidal sacs.

The process in which lysosomes digest their own cell is called autophagy of cell.

Lysosomal Storage Diseases Lysosomes have alpha – glycosidase

enzyme.

Absence of alpha glucosidase leads to glycogen storage in lysosomes.

Due to extra glycogen, lysosomes are ruptured.

Ruptured lysosomes releases enzymes which digest cells.

Lysosomal Storage Diseases Tay – Sachs.

Gaucher’s Disease.

Krabbe’s Disease.

Plastids

Key Points Of PlastidsDouble membrane bounded organelles.

Occur in greatest number in plant cells.

Plastids are absent in animal cells.

Immature and colorless plastids are found in newly formed cells of meristem and are known as proplastids.

Plastids are of three types i.e.

1. Chloroplast Contain chlorophyll.

Give green color to plant.

Manufacture food by photosynthesis.

Contain its own DNA and

2. Chromoplast Contain pigments like xanthophylls, carotenes, etc.

Give various color combination in plants except green.

3. Leucoplast Colorless plastids.

Developed in absence of sunlight.

Commonly found in all under ground parts of plant.

Peroxisomes

Key Facts About Peroxisomes Single membrane bounded structures.

Contain enzymes for transferring hydrogen atom to oxygen.

Forms hydrogen peroxide (H2O2).

Hydrogen peroxide is broken down by catalase.

Thought to metabolize alcohol so abundant in alcohol metabolizing cells.

Glyoxisomes Single membrane bounded structures.

Found in plants only.

Present in fat storing tissues.

Contain fine granular stroma.

Having enzymes that convert fats into carbohydrates i.e. gluconeogenesis.

Cytoskeleton

Facts About Cytoskeleton These are straight fibers made up of proteins.

They are located in cytoplasm and support the structure of cell.

Help in cell division.

Help in locomotion in form of cilia, flagella, etc.

Maintain shape of cell.

There are 2 types microtubules and microfilament

MicrotubulesMicrofilament Hollow

25nm diameter

Made of tubulin protein

Solid

7nm diameter

Made of Actin protein

Intermediate Filament 8-11nm in size.

Rope like.

They are made of keratin protein.

They make skin and hairs.

They give support only.

Ribosomes

Key Facts About RibosomesNamed because contain high concentration of RNA.

One of the most vital cell organelles.

Ribosome are chief site for protein synthesis so also known as protein factories of cell.

Manufactured in nucleolus.

Found free as well as attached to surface of rough endoplasmic reticulum.

Contain about 50 types of different proteins.

There is millions of ribosome present per cell.

Each ribosome consist of two unequal parts (i.e. large dome shaped part and small cap like part which is attached on surface of dome shaped part).

Centrioles

Key Facts About Centrosomes

Cell organelles found in animal cell and lower plant cells.

Absent in higher plant cells.

Each Centrosome consists of two cylinders like portions called centrioles.

Each centriole consists of nine parallel triplets of cylindrical microtubules.

Centrioles replicate during cell division and form mitotic apparatus and helps in cell division.

Vacuole

Key facts About Vacuole Vacuoles are non protoplasmic liquid filled cavities

in cytoplasm.

Surrounded by a membrane called tonoplast.

Tonoplast is not a true membrane and selectively permeable in nature.

Plant cells contain a large vacuole which contain cell sap and act as store house of cell.

In plant cells vacuoles also contributed in defence of plant cell.

After death of plant cell enzymes of vacuoles released and cause lysis of plant cell.

In animal cells vacuoles are formed at time of their need.

Vacuoles of animal cells are rich in hydrolytic enzymes and participated in digesting foreign material.