Saturday, December 7, 2013

Cytomembrane System

The cytomembrane system is a series of interacting organelles between the nucleus and the plasma
membrane. Its main function is to make lipids, enzymes, and proteins for secretion, or for insertion into cell membranes. It also destroys toxins, recycles wastes, and has other specialized functions. The
system’s components vary among different types of cells, but here we present the most common ones:
Components of Cytomembrane System
– Endoplasmic reticulum
– Golgi bodies
Vesicles

Endoplasmic Reticulum

Part of the cytomembrane system is an extension of the nuclear envelope called endoplasmic reticulum, or ER. ER forms a continuous compartment that folds into flattened sacs and tubes. The space inside the compartment is the site where many new polypeptide chains are modified. Two kinds of ER, rough and smooth, are named for their appearance in electron micrographs. Thousands of ribosomes are attached to the outer surface of rough ER.
Rough ER
  •  Arranged into flattened sacs
  •  Ribosomes on surface give it a rough appearance
  •  Some polypeptide chains enter rough ER and are modified
  •  Cells that specialize in secreting proteins have lots of rough ER
Smooth ER
  •  A series of interconnected tubules
  •  No ribosomes on surface
  •  Lipids assembled inside tubules
  •  Smooth ER of liver inactivates wastes, drugs
  •  Sarcoplasmic reticulum of muscle is a specialized form that stores calcium

Functions of Smooth & Rough ER

• The smooth ER
1. Synthesizes lipids
2. Metabolizes carbohydrates
3. Detoxifies drugs and poisons
4. Stores calcium ions

• The rough ER
1. Has bound ribosomes
2. Distributes transport vesicles,
proteins surrounded by membranes
3. Is a membrane factory for the cell

Golgi Bodies

Golgi : The Golgi is a series of flattened membrane compartments, whose purpose is to process and
package proteins produced in-the rough endoplasmic reticulum. The processed molecules are packaged into membrane vesicles, then targeted and transported to-their final destinations.
Functions of the Golgi apparatus
• Modifies products of the ER
• Manufactures certain macromolecules
• Sorts and packages materials into transport vesicles

Vesicles

Small, membrane-enclosed, saclike vesicles form in great numbers, in a variety of types, either on their own or by budding. There are many types but two main are:
 Lysosomes: Digestion & recycling centers






Lysosomes that bud from Golgi bodies take part in intracellular digestion. They contain powerful enzymes that can break down carbohydrates, proteins, nucleic acids, and lipids. Vesicles inside white blood cells or amoebas deliver ingested bacteria, cell parts, and other debris to lysosomes for destruction. The enzymes work best in the acidic environment inside the lysosome. Lysosomes break down worn out cell parts or molecules so they can be used to build new cellular structures. Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole. A lysosome fuses with the food vacuole and digests the molecules Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy

Peroxisomes: In plants and animals, vesicles called peroxisomes form and divide on their own, so they are not part of the endomembrane system. Peroxisomes contain enzymes that digest fatty acids and amino acids. They also break down hydrogen peroxide, a toxic byproduct of fatty acid metabolism. Peroxisome enzymes convert hydrogen peroxide to water and oxygen, or use it in reactions that break down alcohol and other toxins.