The appearance, ultrastructure and function of the nucleus.

Nucleus:

• Nuclear envelope
• Double membrane
• Controls the movement of substances in and out of the nucleus
• Can have ribosomes on the surface
• Can be continuous with (joined/next to) endoplasmic reticulum
• Contains chromatin
• DNA for the cell
• Form chromosomes take when the cell is not dividing
• Nucleolus
• Makes rRNA (coding for ribosomes)
• Assembles ribosomes
• Makes mRNA (coding for proteins) and controls protein synthesis
• Nucleoplasam
• Viscous liquid
• Molecules and organelles of the nucleus suspended in it
• Holds the structure of the nucleus

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The appearance, ultrastructure and function of microvilli.

Microvilli are tiny protrusions that help to increase surface area. Epithelial cells in the small intestine need have these in order to increase the rate of diffusion: there is a bigger surface area so more things can diffuse at the same time.

They are also thin walled to decrease the diffusion distance and so increase the rate of diffusion. This is key in the small intestine so that all the useful molecules from food eaten can be absorbed by the cells before the food moves on.

Under a light microscope the microvilli in the intestines are so tightly packed they look like a bush and are referred to as a 'bush border'.

course1.winoa.edu

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The appearance, ultrastructure and function of Golgi apparatus.

The Golgi apparatus receives proteins in vesicles (packages) from the endoplasmic reticulum: it modifies them (like adding carbohydrate) and packages them in a new vesicle which is labelled (so it can travel to the right place). The Golgi apparatus can also transport, modify and store lipids.

Mostly the vesicles are going to the cell surface membrane to release their content outside the cell: an example of this in practice is enzymes being secrete in the pancreas to digest food.

The Golgi apparatus is made up of flattened sacs called cisternae. To make a vesicle a bit of the cisternae breaks off into a circular shaped package- this will contain either proteins, carbohydrates or lipids.

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The appearance, ultrastructure and function of endoplasmic reticulum.

Endoplasmic reticulum (ER) provides a surface for the synthesis of different molecules needed in a cell. It can also store and transport these materials.

The molecules involved depend on the type of ER:

• Rough endoplasmic reticulum (RER) makes and transport proteins and glycoproteins; it has ribosomes on its surface because they are involved in protein synthesis.
• Smooth endoplasmic reticulum (SER) stores, transports and synthesises lipids and carbohydrates.

ER is sometimes continuous with (attached to) the nucleus of a cell.

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ER is made up of 'flattened sacs' called cisternae surrounded by a membrane. Both types are complex structures but SER looks more tubular compared to the 'liney' RER.

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The appearance, ultrastructure and function of ribosomes.

Riosomes play a role in protein synthesis. mRNA (coding for proteins) is read by them and used to assemble amino acids.

They can be found in the cytoplasm or on the surface of rough endoplasmic reticulum.

They consist of two sub-units (a large and a small) that are not bound by a membrane.

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The appearance, ultrastructure and function of lysosomes.

Lysosomes are sacs containing digestive enzymes. They are created by the golgi apparatus.

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The enzymes in the lysosomes have many important functions

• Digest material that phagocytic cells engulf: commonly this would mean digesting a pathogen that had been engulfed by a white blood cell.
• Digest old organelles (if left to build up they can be toxic)
• Digest old cells (autolysis)
• Release enzymes outside the cell so they can digest things externally (exocytosis)
• Digesting food that is delivered to the cell into useful components

When a lysosome has digested something, including waste products like old organelles, and useful chemicals are absorbed into the cytoplasm to be used again by the cell.

The appearance, ultrastructure and function of mitochondria.

Mitochondrion are the organelles where aerobic respiration takes place.

The stages of respiration that take place there require enzymes, so there is DNA that allows the cell to manufacture its own proteins (enzymes.) This DNA is held in the matrix; a material that also contains proteins and lipids.

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A mitochondria has a double membrane: the two both control the movement of substances in and out of the cell. The inner membrane provides the surface area for the reactions in respiration: it is folded many times into cristae to create a large surface area. This area is covered in the enzymes needed for respiration.

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The appearance, ultrastructure and function of the cell surface membrane.

The cell surface membrane is an example of a plasma membrane (click for more detail on plasma membranes) and has several jobs to perform:

• Separates the cell content from the surrounding environment
• Controls the movement of substances into and out of the cell
• Allows for the conditions inside the cell to differ from those outside

  

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