Biology 1- Cell structure

Eukaryote cells contain membranous organelles which are enclosed areas within the cytoplasm. This has the advantage that any potentially harmful chemicals and/or enzymes can be isolated. Membranes also provide a large surface area for the attachment of enzymes involved in metabolic processes, as well as providing a transport system within the cell.

Nucleus

This is the most prominent feature in the cell. Its function is to control the cell's activities and to retain the chromosomes. The nucleus is made up of a number of components:

• It is bound by a double membrane called the nucleur membrane or envelope. Its outer membrane is continuous with the endoplasmic reticulum. The membrane also has pores in it to allow the passage of large molecules such as mRNA out of the nucleus.
• The granular jelly-like material within the nucleus is called the nucleoplasm. It contains chromatin, which is made up of coils of DNA bound to protein. During cell division the chromatin condenses to form the chromosomes.
• Within the nucleus is a small spherical body called a nucleolus. Its function is to manufacture RNA, which is needed to make ribosomes.

Mitochondria

Mitochondria are rod shaped. They are made up of:

• A double membrane separated by a narrow fluid-filled inter-membrane space. The inner membrane is folded inwards to form extensions called cristae.
• An organic matrix containing numerous chemical compounds including protein, lipids and traces of DNA that allows the mitochondria to control the production of their own protein.

Mitochondria are the sites of aerobic respiration in the cell. Some of the reactions take place in the in the matrix while others occur on the inner membrane. The cristae provide a large surface area for the attachment of enzymes involved in respiration.

The function of mitochondri is to produce the energy-carrier molecule, ATP. Metabolically active cells such as muscle cells need a plentiful suppy of ATP. They are found to contain large number of mitochondria, reflecting the high metabolic activity taking place. 

Endoplasmic Reticulum

This consists of an elaboate system of parallel double membranes forming flattened sacs. The fluid-filled spaces between the membranes are called cisternae. The ER is connected with the nuclear membrane and may link to the Golgi body. The cavities are internconnected and this system allows the transport of materials throughout the cell. 

There are two types of ER:

• Rough ER has ribosomes on the outer surface. Functions of the rough ER are transporting proteins made by the ribosomes. Rough ER is present in large amounts in cells that make enzymes that may be secreted out of the cell. 
• Smooth ER has membranes that lack ribosomes. These are concerned with the synthesis and transport of lipids.

Cells that need to store large quantities of carbohydrates, proteins and fats have extensive ER. Such cells include liver and secretory cells.

Ribosomes

Ribosomes are found in both prokaryote and eukaryote…