CELL : THE UNIT OF LIFE PART 3

BY AISHA…GULF ASIAN ENGLISH SCHOOL..

TOPICS COVERED:- CELL WALL ENDOMEMBRANE SYSTEM ENDOPLASMIC RETICULUM GOLGI APPARATUS LYSOSOMES VACUOLES MITOCHONDRIA PLASTIDS CHLOROPLASTS.

CELL WALLPresent only in plants and fungi. Consist of primary wall, secondary wall, middle lamella with calcium pectate.FUNCTIONS:- gives shape and protects the cell from mechanical damage.- cell to cell interaction-barrier to undesirable macromolecules. Cell wall of algae consist of cellulose, galactants, mannans, minerals like calcium carbonate. Cell wall of other plants consist of cellulose, hemicellulose, pectins and protiens. PRIMARY CELL WALL: -Capable of growth.- diminishes as the cell matures.

ENDOMEMBRANE SYSTEMEndomembrane system contains only those organelles whose functions are coordinated.It consists of: Endoplasmic reticulum(ER) Golgi complex lysosomes Vacuoles

ENDOPLASMIC RETICULUMDiscovered by porter and thompson. ER are a network of tiny tubular structures scattered in the cytoplasm. consists of 30-40% of endomembrane system ER divides into 2 compartments. 1. luminal(inside ER) 2. extra luminal(cytoplasm)FUNCTIONS:

1. Mechanical support 2. Conduction of information 3. Intercellular transport 4. Localization of enzyme 5. Large surface area.

ER are of two types: *Rough ER *Smooth ER

bear ribosomes they are extensive and continuous performs protein synthesis and secretion attached to nuclear membrane.

does not bear ribosomes performs synthesis of lipid In animal cells lipid like steroidal hormones are synthesized in SER. storage

GOLGI APPARATUS… discovered by Camillo Golgi in 1898. found in eukaryotic cells (except mammalian erythrocytes). they are reticular structures near the nucleus. consist of cisternae which are flat, disc-shaped sacs parallel to each other. 2 faces:- 1. convex cis or the forming face. 2. concave trans or the maturing face. FUNCTIONS:-1. Packaging materials to be

delivered to the intercellular targets or secreted outside.

2. Protein synthesized by ribosomes are modified in the cisternae.

3. important site for formation of glycoproteins and glycolipids.

... Lysosomes...

Lysosomes.

These are membrane bound vesicular structures. Formed by packaging of golgi apparatus rich in hydrolytic enzymes Active at acidic pH these enzymes are capable of digesting carbohydrates, proteins, lipids and nucleic acids. Popularly called “sucide bags “.

…VACUOLES…They are membrane bound

space found in cytoplasmContains water, sap, excretory product and other materials not useful for plants.The vacuole is bounded by a single membrane called tonoplast.In Amoeba, contractile vacuole and in protista food vacuole.

…MITOCHONDRIA…

They are double membrane-bound structures with the outer and inner membrane. Outer membrane forms continuous limiting boundary of the organelle. Inner membrane forms infoldings called cristae to increase surface area. They are the sites for aerobic respiration. Produce cellular energy in the form of ATP molecules.

Sausage- shaped or cylindrical having diameter of 0.2- 1.o μm and length 1.0 – 4.1 μm.

Known as powerhouses of the cell.Divide by fission.The membranes divide the lumen into 2 aqueous compartments, namely: 1.outer compartment 2.inner compartment called matrix.

…Plastids…Found in plants and euglenoids.They are largeThey contain pigments, imparting colors and storage products.Plastids can be classified into: *CHLOROPLAST *CHROMOPLAST *LEUCOPLAST•Contains chlorophyll and carotenoid pigments.•Found mainly in mesophyll of leaves .•These are lens shaped, oval shaped, spherical, discoid or even ribbon-like organelles.

•Contains fat soluble carotenoid pigments like carotene, xanthrophylls and others are present.•Found in yellow, orange, red.

•Colorless plastids•Various shapes and sizes with stored nutrients•LEUCOPLAST can be divided into 3:- 1.Amyloplasts – store carbohydrates 2.Elaioplasts – store oils and fats 3. Aleuroplasts – store proteins.

CHLOROPLASTDouble membrane boundInner membrane is less permeableThe space limited by inner membrane is called stromaFlattened membranous sacs called thylakoids are present in the stromaThylakoids are arranged in stacks like piles of coins called grana or intergranal thylakoidsFlat membranous tubules called the stroma lamellaeThe membrane of thylakoids enclose a space called lumen.Stroma contains enzymes required for the synthesis of carbohydrates and proteins.It also contains DNA molecules and smaller ribosomes.Chlorophyll pigments are present in thylakoids