The Digestive system

Eukaryotic Cells

Eukaryotic Cells

One type of eukaryotic cell is the epithelial cell which is located in the small intestine. As you can see, they contain a number of different organelles.

Plasma membrane or the Cell membrane – A thin layer surrounding the outside of a cell composed of proteins and phospholipids. This separates the inside of the cell from its outer environment and controls what enters and leaves the cell.

Cytoplasm – The solution within the membrane. It contains all the parts required for the cell to function including the enzymes required for respiration and other metabolic reactions.

Nucleus – This is the largest of the cell’s organelles. It’s enclosed within a double membrane called the nuclear envelope which contains small holes called nuclear pores which control what enters and leaves the cell. The inside of the nucleus is known as the nucleoplasm which contains chromatin. It also contains the nucleolus. This is where cell division takes place. The chromatin condenses into chromosomes during the process. The nucleolus produces ribosome’s.

Mitochondria – Sausage shaped organelle which is about 8?m in length and consists of a double membrane. The outer membrane is quite permeable and simple in shape. The inner membrane is folded into cristae which increase its surface area. It’s studded with stalk particles which are in fact enzymes whose function is to produce ATP for respiration. The centre space is called the matrix in which small circular pieces are DNA are contained. This is where aerobic respiration takes place. They release energy in the form of ATP which they make using energy-rich molecules like carbohydrates and lipids.

Ribosomes – These are the smallest organelle in the cell and the most numerous. They’re found either floating free in the cytoplasm or attached to rough endoplasmic reticulum. Eukaryotic cells only contain the 80S type of ribosome. This is where protein synthesis takes place. Free ribosomes produce protein for the cell while attached ribosomes produce proteins for other cells.

Endoplasmic Reticulum (ER) – This is composed of numerous membrane channels. There are two types of ER: rough endoplasmic reticulum (RER) is studded with ribosomes while the smooth endoplasmic reticulum (SER) contains no ribosomes. The RER transports protein produced by its ribosomes out of the cell via the Golgi Body. The SER processes different materials for the cell, like lipids.

Golgi apparatus – This is composed of flattened membrane vesicles and created by the ER. It carries the proteins made from the ribosomes on the RER to the cell membrane. The RER fuses parts of itself containing protein to the Golgi Body on one side. On the other side vesicle then bud off from the Golgi Body containing the protein and fuse with the cell membrane. Their contents are released by exocytosis.

Lysosomes – Little membrane-bound vesicles which are produced by the RER. These vesicles contain digestive enzymes capable of degrading unwanted substances (like toxins or chemicals), breaking down whole cells to be recycles, and digesting the contents of vacuoles by fusing with them.

Microvilli – Small, finger-like extensions which increase the surface area of the cell. A number of them together create a brush border. By increasing the surface area in the kidney and intestine then increase the rate of absorption of different materials.