Cellstructure

• Presented by• Lahange Anil Trimbak• Borse Shaila Bhausaheb

GuideProf. Desale S. Y.

Introduction to cell

It was Robert hook who In 1665 first discovered these building blocks when he observed a thin slice of cork under his self designed microscope.

These compartments of cork were empty. He found they resembled the structure of honey comb and

labeled them, as ‘cell’ which in Latin means ‘small rooms’. Every living things , however different, is made up of these

separate tiny units called ‘cells’ .

Morphology of cells Size of cells varies greatly [0.1µm to 18cm] in diameter. The unit used to measure size of a cell is micrometer[µm] 1 micrometer = 1/1000 millimeter. Small size of cell ensures greater surface area . Greater

surface area ensures greater diffusion of nutrients into the cell ,greater extent of exchange of materials in &out of the cell ,also easy repair of the damaged cell.

Smallest cell – cells of Mycoplasma galliseptium (0.1µm) Largest cell – egg of an ostrich (18cm) in diameter .

Cell structure

Parts of a Cell 1.Plasma membrane2 .Cell wall [in plant cell].3.Cytoplasm4.Cell organelles

Plasma membrane As a cell is a distinct unit of life ,every cell is bound by a thin

covering which separates the contents of the cell from its external environment & gives separate identity to the cell this covering is called plasma membrane.

It is a living, extremely delicate elastic membrane of about 70A0 thickness (1A0=10µm =107 mm).

It made up of a lipid bilayer having integrated protein molecule .

The organization of the plasma membrane is not fixed & hence it is flexible.

Cell wall In addition to plasma membrane ,plant cell have another

rigid outer covering called the cell wall . The cell wall is non living &freely permeable . It is made up of cellulose. It gives protection to the cell & also determines its shape .

Cytoplasm The fluid which lies in between the plasma membrane &

nucleus is called cytoplasm. Living cytoplasm is constantly moving . It is jelly- like substance. Many cell organelles lie in the cytoplasm . Cellular chemical reactions take place in the cytoplasm The part of cytoplasm other than organelles is called

cytosol. It stores vital substance like amino acids ,glucose ,vitamins

etc.

Cell organelles Nucleus Endoplasmic reticulum Golgi Apparatus Lysosomes Mitochondria Plastids Vacuoles

Nucleus Nucleus is a large spherical body generally lying at the Centre

of a cell . It is the most important part of the cell . Nucleus covered by a double layered nuclear membrane . The nuclear membrane has pores

• Functionsi. It controls all metabolic activities of the cell . If it is

removed ,the cell ultimately dies.ii. It play an important role in cell divisioniii. It is involved in transmission of hereditary characters from

Parents to offspring.

Endoplasmic reticulum Endoplasmic reticulum is a large network of membrane

bound ,fluid filled inter connecting tubules & sheets. ER spreads from the nuclear membrane to the plasma

membrane. Endoplasmic reticulum is of two type -Rough endoplasmic reticulum (RER) - Smooth endoplasmic reticulum (SER)

Functions of ER:i. Along with intracellular transport it also acts as a supportive

framework for a cellii. It synthesize proteins &lipids and transports them. Some lipids

synthesized by it are used in building plasma membrane while some other lipids and proteins are used as hormones and enzymes

iii. It transports proteins synthesized by ribosomes.iv. SER of certain cells of liver play a crucial role in detoxification many poisons and drugs which enter our body through food ,air or water.

Golgi Apparatus Golgi apparatus was first described by a German scientist

“Camillo Golgi ’’. It comprises of five to eight (sometime more ) sacs which

resemble deflated balloons placed approximately parallel to each other .

These sacs are called cisternae and filled with different enzymes.

• Functionsi. Golgi complex is the secretory organ of the cell .ii. It modifies , sorts and packs materials synthesized in the cell

( enzymes mucous secretion , proteins ,lipids ,pigments etc.) .&dispatches them to various targets inside the cell or outside the cell.

iii. It produce vacuoles & secretory vesicles.iv. It plays the role in formation of the cell wall , plasma membrane

& lysosome.

Lysosomes Lysosomes are simple one membrane bound sacs ,filled with

digestive enzymes. These powerful enzymes are made by RER and are capable of

digesting and breaking down all organic matter . It is the cell’s waste disposal system .

• Functions-i. As it is the digestive system of the cell ,it protect the cell by

destroying any foreign material like bacteria &viruses that invade the cell.

ii. They remove worn out cellular organelles and remove all the organic debris . This process is called autolysis .So they are called as ‘Demolition Squads’.

iii. When a cell gets old or it damaged ,lysosome burst and the enzyme digest their own cells .therefore lysosomes are also called as ‘Suicide Bags’ .

Mitochondria

It is also known as power house of the cell because it produce energy for the cell.

It is double membrane structure . The outer membrane is porous while the inner membrane

is deeply folded . These folds are called cristae . The interior cavity is filled with proteinaceous gel like

matrix which contains ribosomes ,phosphate, granules &DNA.

Mitochondria oxidize carbohydrates &fats present in the cells with the help of enzymes .

• Functionsi. Mitochondria produce the energy rich compound ATP

which is the energy currency of the cell.ii. The body uses the energy stored in ATP to synthesize

chemical compounds and to do mechanical work.

Plastids Plastids are double membrane structures present only in

plant cells . They are of two types :- Chromoplasts Leucoplast Chloroplast are a type of chromoplasts which are green in

color due to the presence of green colored pigment called chlorophyll.

Functions i. Chloroplasts helps to harness solar energy and convert it

into chemical energy in the form of foodii. Chromoplasts give color to flowers and fruits.iii. Leucoplasts are involved in the synthesis and storage of

various kinds of food like starch ,oil &proteins.

Vacuoles Vacuole are storage sacs for solid or liquid contents . They do not have any shape or size. The structure of the vacuole changes according to the need of

the cell. Vacuole is bound by a single membrane.

• Functions i. Vacuole help to maintain osmotic pressure of the cell .ii. They store metabolic byproducts and end products e.g.

Glycogen, protein &water iii. They stores waste products and food in animal cell .iv. In plant cells vacuoles are full of cell sap and provide

turgidity and rigidity to them.

Difference between Plant cell &animal cell

Plant cell

i. It contains chloroplastii. Plant cell larger than animal celliii. Centrioles absentsiv. Large vacuoles are present

Animal cell

i. It does not contains chloroplast ii. Animal cells are smaller than plant celliii Centrioles presetiv Few small sized and temporary vacuoles are present

Difference between prokaryotic & eukaryotic cell

Prokaryotic cells

i. In Greek ; Pro = before Karyone= nut , kernel ii. Their nucleus lacks nuclear membrane

iii. Prokaryotic cells are smaller in size ranging from 1-10 µmIv. They contain a single chromosome.

Eukaryotic cellsi. In Greek ; Eue =true Karyone =nut ,kernelii. They have well defined nucleus i.e. with nuclear membrane , nucleus & nucleoplasm.iii. Size of eukaryotic cells ranges from 5-100 µm.Iv. They have more than one chromosome.

Eukaryotic cells

V. Mitochondria are absent.Vi. E.g. Blue green algae

Prokaryotic cells

V. Mitochondria are present.Vi. E.g. higher advanced unicellular and multicellular plants & animals