* The largest cell organelle
* The nucleus houses nearly all the cell’s genetic material * It has the instructions for making proteins
Part of the nucleus
| * The chromatin consists of DNA and proteins. * Some of these proteins controls the activities of the cell * When cells divide, chromatin condenses into visible chromosomes * The chromatin shows up as dark patches when it is stained.
| * The nucleolus makes RNA and ribosomes-these pass into the cytoplasm and proteins are assembled on them (protein synthesis) * The nucleus is a dense, spherical structure inside the nucleus * In some cells there may be two nucleus’s
| Nuclear envelope
| * This is a structure made of two membranes, the inner nuclear envelope and the outer nuclear envelope. * There is a fluid between the two membranes
| Nuclear pore
| * A lot of hole pass right through the nuclear envelope these are known as the nuclear pores * These holes are large enough for relatively large molecules to pass through such as hormones, ribosomes and mRNA
| * The cytoplasm-like material within the nucleus * It is enveloped by the nuclear envelope * Substances like enzymes are dissolved in it
| Endoplasmic reticulum
* The cytoplasm is a highly organised material consisting of a soluble ground substance called the cytosol * It contains an elaborate system of parallel flattened cavities lined with a thin membrane these are called cisternae * The cavities are interconnected and the membrane is continuous with the nuclear membrane Smooth endoplasmic reticulum
| Rough endoplasmic reticulum
| * An extensive system of membranes running through the cytoplasm.
| * Same basic structure as SER with extensive layers of membrane stacks (cisternae)
| * Does not contain any ribosomes and so appears smooth
| * Has ribosomes studding the surface and thus appears rough in EM...
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