Ribosomes & Endoplastic Reticulum

Ribosomes Organelles that make protein Found in cytoplasm or bound to E.R. Made of two subunits: Nucleic acids and

proteins

Ribosomes Translate information (mRNA) and link together amino acids from

cytoplasm tRNA Found in eukaryotic and prokaryotic cells

Mitochondria, chloroplasts Can be broken down and recycled

Endoplastic Reticulum(ER):

network of membranous sacs and tubes (called cisternae), active in membrane

synthesis and other synthetic and metabolic processes

Endoplastic Reticulum -accounts for half the total membrane in eukaryotic cells-there are two distinct regions of the ER that differ in structure and function: smooth ER and rough ER

Smooth ER -its outer surface lacks ribosomes-functions in metabolic processes including synthesis of lipids, metabolism of carbohydrates, and detoxification of drugs and poisons-The smooth ER helps in the production of steroids in the animal cells such as sex hormones secreted by the adrenal glands- In liver cells the smooth ER and its associated detoxification enzymes make alcohol and drug molecules more soluble and easier to flush from the body, thus increasing the rate of detoxification.

Rough ER -has ribosomes on the outer surface of membrane therefore appears “rough”-the ribosomes attached to the rough ER secrete proteins. -For example pancreatic cells synthesize the protein insulin on the ER and secrete this hormone into the bloodstream.-The secretory proteins depart from the ER wrapped in transport vesicles which transit from one part of the cell to the other. -The rough ER is a membrane factory for the cell, it grows in place by adding membrane protein and phospholipids to its own membrane.