Cell Organelles

Cell Organelles

Nucleus

• Its function is to control the cell's activities and retain the chromosomes. 
• The nucleus is bound by a double membrane, the nuclear envelope. The nuclear envelope has pores in it to allow the transport of mRNA.
•  The cytoplasm like material is called nucleoplasm which contains chromatin (coils of DNA and histone proteins), it is chromatin that condenses to form chromosomes during cell division.

•  Within the nucleus is a small spherical body called the nucleolus which manufactures RNA to from ribosomes.

Ribosomes

• Are very small organelles but are present in large numbers. 
• They are made up of two subunits, the large subunit and the small subunit. 
• 70s ribosomes are found in prokaryotes whilst 80s ribosomes are found in eukaryotes.
•  They are involved in protein synthesis.
• They can either be found free in the cytoplasm or on the outer surface of the rough endoplasmic reticulum. 

Mitochondria

• Aerobic respiration occurs here producing ATP (the energy currency of the cell).
•  They have a highly folded inner membrane which provides a large surface area for the respiration reactions. 
• Some reactions also take place in the matrix (Kreb's cycle) as well as the cytosol of the cytoplasm. 
• The number of mitochondria varies from cell to cell. More are found in cells with greater ATP requirements these are; cells that move a lot (sperm, muscle), cells with a high metabolic rate (liver) and cells that carry out active transport (small intestine). 

Endoplasmic reticulum

Is an elaborate system of membrane bound sacs (cisternae) that are often continuous with the Golgi body and the nuclear envelope. There are two types of endoplasmic reticulum (ER)

• Rough ER (rER) - has ribosomes lining it and is involved in protein synthesis as a transport system

• Smooth ER (sER) - lacks ribosomes and is involved in the synthesis and transport of lipids

Golgi Apparatus

Is a collection of flattened membrane bound sacs that are constantly forming on one side and budding off as vesicles on the other.

Its functions are:

• to package proteins for secretion
• to secrete carbohydrates
• to produce glycoproteins
• to transport and store lipids
• to form lysosomes

Lysosomes

They are membrane bound vesicles which contain digestive enzymes. They are especially abundant in secretory cells and phagocytic blood cells.

Its functions are to:

• digest material from the environment. Useful chemicals are absorbed into cytoplasm and waste is egested by exocytosis e.g white blood cells and…