Structures and functions of organelles: ER and Golgi apparatus and Lysosomes

Endoplasmic reticulum and ribosomes

Rough ER is so called because it is covered with many organelles called ribosomes. They are the sites of protein synthesis. They are made of RNA and protein. They form a system of sacs.

Proteins made by the ribosomes on the rough ER enter the sacs and move through them. Small sacs called vesicles can break off from the ER and these can join together to form the Golgi apparatus. Smooth ER makes lipids and steroids. 

Golgi apparatus

The Golgi apparatus is a stack of flattened sacs. The stack is constantly being formed at one end from vesicles which bud off from the ER, and broken down again to form Golgi vesicles. It collects, processes and stores molecules (proteins), ready for transport to other parts of the cell. 

Lysosomes

Are spherical sacs, surrounded by a single membrane and having no internal structure. Contain digestive juices. Breaks down unwanted structures. 

Mitochondria

Carry out aerobic respiration. As a result, they make ATP, the energy carrier in cells. Also involved in synthesis of lipids. 

Microvilli 

Finger-like extensions of the cell surface membrane. Greatly increase surface area. 

Centrioles

Formed from a ring of microtubules, made of a protein. Starting point for growing spindle microtubules for nuclear division. 


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  • Created by: AdibaR
  • Created on: 08-10-13 11:58

Comparison of prokaryotic and eukaryotic cells

Prokaryotes

  • average diameter of cell is 0.5-5 micrometers
  • DNA is circular and lies free in the cytoplasm
  • DNA is naked
  • slightly smaller (70S) ribosomes than those of eukaryotes
  • no ER 
  • few organelles
  • cell wall present

Eukaryotes

  • cells commonly 40 micrometers in diameter and 1000-10000 times volume of prokaryotic cells
  • DNA is not circular and is inside a nucleus surrounded by two membranes
  • DNA is associated with protein, forming structures called chromosomes
  • slightly larger (80S) ribosomes 
  • ER Present
  • many types of organelle present
  • cell walls present in plants and fungi 
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