eukaryotic and prokaryotik cells Essay

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Eukaryotic cells

Cell membrane (or plasma membrane). This is a thin, flexible layer round the outside of all cells made of phospholipids and proteins. Its separates the contents of the cell from the outside environment, and controls the entry and exit of materials. The membrane is examined in detail later.

Cytoplasm (or cytosol). This is the solution within the cell membrane. It contains enzymes for glycolysis (the first stage of respiration) and other metabolic reactions together with sugars, salts, amino acids, nucleotides and everything else needed for the cell to function. This is where the first stage of respiration takes place.

Nucleus. This is the largest organelle surrounded by a nuclear envelope. Which is a double membrane with nuclear pores – large holes containing proteins that control the exit of substances such as Mrna AND ribosomes from the nucleus. The interior is called genes. During cell division the chromatin becomes condensed into discrete observable chromosomes. The nucleolus is a dark region of the nucleus, involved in making ribosomes and processing m-RNA (i.e. removing introns)

80S Ribosomes. These are the smallest and most numerous of the cell organelles, and are the sights of protein synthesis. They are composed of protein and RNA and are manufactured in the nucleolus of the nucleus. Ribosomes can be free in the cytoplasm, or (more commonly) are attached to the rough endoplasmic reticulum. They are often found in groups called polysomes. NB all eukaryotic ribosomes are the larger, 80s, type.

Endoplasmic reticulum. This collection of membrane channels forms an important transport ‘highway’ within the cell, allowing molecules to move from one place to another. It is attached to, and formed from, the outer membrane of the nucleus, and plays an important part in protein synthesis. It comes in two distinct forms:
Rough endoplasmic reticulum. This is studded with numerous 80S Ribosomes which give it, its rough appearance. The ribosomes synthesise proteins which are processed in the SER before being exported from the cell via the Golgi body.
Smooth endoplasmic reticulum. Similar to the rer, but without the ribosomes. Series of membrane channels involved in the synthesis and transport of materials, mainly lipids and glycoproteins, needed by the