Biology

BIOLOGY (FORM 6)FIRST TERMSPresentation about :- chapter 2 :- structure cell and organelles( endoplasmic reticulum & ribosome )

{Is the system of tightly packed and flattened membrane-bound sacs forming tubes and sheets within cytoplasm.The sacs is known as cristae, are full of fluid.Found in all nucleated cells (eukaryotic cells) and is especially well developed in growing cells.The ER membrane ,is single units membrane ,separates the internal compartment of the ER from cytoplasm.The membrane is continuous with the nuclear envelope while the perinuclear space of the nucleus is continuous with the internal space of the ER.ENDOPLASMIC RETICULUM

This is example picture of endoplasmic reticulumSTRUCTURE OF THIS ORGANELLES :-Membrane system consisting of flattened sacs called cristernae. It has ribosome attached on its surfaces .Cotinuous with nuclear membrane

FUNCTION :- AS THE SITE OF SYNTHESIS PROTEIN.The growing protein ( polipeptide molecules ) which consist of a chain of amino acids , is bound to the ribosome at the surface of rough ER until the synthesis protein. The receptor in the ER membrane provides a channel through which the protein can pass through into the ER .In the cristernae , the protein may be modified by addtion of carbohyrates or lipids ( ex. Glycoprotein or Glycolipids ).

Rough Endoplasmic Reticulum ( Rough ER )ACT AS PACKAGING AND TRANSPORT PROTEINThe modified protein are transport and transferred to the Golgi apparatus by small transport vesicles that bud off the ER membrane and fuse with the membrane of Golgi apparatus to be processed.From the Golgi apparatus , the transport vesicles containing the modified protein move to the plasma membrane and are secreted from the cell or these molecules may be passed on to other organelles in the cells.The cristernal space of rough ER functions as an intracellular transport system that facilitates the movement of substances from one part of the cell to another.Rough ER also manifactures more membranes for the cells.

Polipeptide chain formed is passes into the cristernae ( lumen rough ER)

The syntesis , packaging and transport of secretory protein by Rough ERSTRUCTURE OF THIS ORGANELLES :-Is tubular rather than flatDoes not have attached of ribosomes May extend separately from outer membrane of the nucleus or extend from rough ER.

FUNCTION :-SYNTHESIS AND TRANSPORT OF LIPIDS INCLUDING OILS AND PHOSPOLIPIDS.- For instance , in the intestines, smooth ER synthesis lipids from fatty acids and glycerol absorbed from the small intestines and passes them on to the Golgi apparatus for export.

SMOOTH ENDOPLASMIC RETICULUM ( SER )SYNTHESIS OF STEROID ( HORMONES) Corticosteroid made in the adrenal cortex , and sex hormones testosterone and oestrogen made in testis and ovaries.

METABOLISM OF CARBOHYDRATES.Smooth ER in the liver cells produce enzymes to helps regulate the amount of sugar released from liver cells into bloodstream . For ex. Glucagon and Insulin

SERVES AS A MAJOR DETOXIFICATION SITE.- The enzymes located along smooth ER in the liver cells helps to break down toxic chemical and covert that chemical into water-soluble product that can be excreted.ORGANELLESFOUND FUNCTIONSROUGH ENDOPLASMIC RETICULUM (RER )THE CELLS OF SALIVARY GLAND AND PANCREAS.SYNTHESIS AND EXCRETE PROTEINS (EX. ENZYME )SMOOTH ENDOPLASMIC RETICULUM (SER )TESTIS,OVARIES,IN THE ADRENAL CORTEX ,MUSCLE CELLS (SACROPLASMIC RETICULUM),LIVER CELLS , IN THE SMALL INTESTINE SITE OF SYNTHESIS LIPID , HORMONES (TESTOSTERONE , CARTICOSTEROID ,TESTOSTERONE ,OESTROGEN , INSULIN AND GLUCAGON ) AND ALSO MAJOR SITE OF DETOXIFICATION.THE DENSITY AND FUNCTION OF SPECIFIC CELLS RIBOSOMESTiny , spherical organelles ,about 20 nm in diameter.Consist two subunits ; the large subunit and the small subunit.Made up by ribosomal ( rRNA ) and protein. Ribosomal subunits are synthesised in the nucleolus and move through nuclear pores into cytoplasm.Consist of three RNA strands and 75 different proteins and together these molecules to form a complex three-dimensional structure.Two types of ribosomes :-Bound ribosomes ( attached on membrane s rough ER and nuclear envelope )Free ribosomes suspended in the cytosol.

STRUCTURE OF THE ORGANELLESSITE OF SYNTHESIS PROTEIN.During protein synthesis , ribosomes move along the messenger RNA ( mRNA ) molecules which carries the genetic instructions form the nucleus . The transfer RNA ( tRNA ) molecules brings the required amino acids to the ribosomes and the growing polipeptide chains.Acts as binding sites of polipeptide chains through precisely positioned relative to each other.The protein synthesised by a free ribosomes are released into the cytoplasm where act as enzymes or structural proteins for growth within the cells.The protein synthesised by ribosomes attached to the rough ER move into cristernae of the reticulum and transferred to the Golgi apparatus.Finally, the proteins are synthesis from the cell in form of enzymes or hormones.Some of these proteins remain in the cells as lysosomes.FUNCTION OF THIS ORGANELLES

Two basic types of ribosomes :-70S ribosomes ( prokaryotic cell, mitochondria & chloroplast )80S ribosomes ( in cytoplasm of eukaryotic cells ) structure of ribosome

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