Structure of Epithelial Cells

The nucleus is 10-20 micrometres and controls the cells activities and stores the cells herditary infomation.

• The nuclear envelope is a double membrane with ribosomes on the outer layer. It controls the movement of substances in/out of the nucleus and contains reactions inside of the nucleus.
• Nuclear pores occur on the surface of the nucleus and vary between 40-100 nanometres. They act as a passage for large molecules eg: (messenger RNA).
• Chromatin is a semi liquid substance that makes up most of the mass of the nucleus. It contains lipids, proteins and traces of DNA.
• The nucleolus is an extra spherical body within the nucleus. It's function is to produce RNA and assemble the ribosomes.

The mitochondria is 1-10 micrometres in length and is usually at sites of respiration where it's function is the production of ATP. Therefore, mitochondria are numerous and bigger in cells that require a lot of energy.

• The cristaeare folds in the inner membrane of the mitochondrian. It's function is to create a large surface area for enzymes to attach onto.
• The matrix is a semi-liquid substance that makes up the bulk of the mitochondria containing proteins, lipids and traces of DNA. 

The endoplasmic reticulum (ER) is a complicated 3D maze-like structure that has many folds that weave in and out of each other. The two types of ER are rough (RER) and smooth (SER) endoplasmic reticulum.

• RER has ribosomes on the surface to provide a large surface area for protein + glycoprotein synthesis. RER also is used as a passage for proteins.
• Unlike RER, SER lacks ribosomes on it's surface. The function of SER is to synthesize store and transport lipids + carbohydrates.

The golgi is similar in structure to the SER but the tubes are more narrow and compact. The proteins and lipids produced by the ER are passed through the golgi to be modified by adding components to their molecules, packaged by labelling where their destination is and secreted via a vesicle which are regularly pinched off the golgi.

Lytosomes are up to 1 micrometre in diameter and are responsible for the removal of useless and potentially dangerous material out of the cell.

• Lytosomes are formed when the vesicles pinched off the golgi contain hydrolytic enzymes.
• The vesicle is formed around the useless organelle.
• The enzymes break down the organelle.
• Soluble products are absorbed into the cytoplasm.
• Insoluble products fuse with the cell membrane and are egested.

Ribsomes are small granular shaped organelles in the cytoplasm.

There are two types:

80S Type

70S Type

Ribosomes are important for protein synthesis.