Recapping Control of Gene Expression. ^-^

So, I have a mock test on all the genetics stuff this afternoon. Just going over stuff now. How are all of you guys going? Comment me and tell me how your unit four, or ones went in january. If you're retaking, or you're a first year flapping about Unit 2, take my email from the top of this page, or just comment by using the link at the bottom, where it says the number of comments, and drop me a line. If you're in the Leicester area, I can help you out. If not, email'll do. xD I'm happy to try. (:

So yeah. Gene Expression.

Totipotent Cells are undifferentiated cells, such as embryonic stem cells, that are not yet defined in their function. In animals, stem cells are totipotent. Plants have far more types of totipotent cells (Think of how you can make cuttings of plants, and grow an entirely new plant, given the right conditions?)

Cells loose totipotency, as, with age, different genes are swtiched on/off. When certain genes are switched of, they are not translated to produce polypeptides, meaning cells only have specific genes, the proteins produced serving only to aid their function.

Totipotent cells can be used to treat human disorders such as Parkinson's Disease, Alzheimers, Osteoarthritis, MS... all my growing new tissues from stem cells, and growing a culture of the needed type of cell after speciailisation. (That is TOTALLY spelt wrong.)

Oestrogen:

1. The DNA binding site on a Transcription Factor (the thing that stimulates transcription), can sometimes be inhibited
2. Oestrogen is lipid soluble and passes through the cell surface membrane easily
3. It binds with the receptor of the transcription factor.
4. This changes the same of the whole molecule, including the DNA binding site.
5. The Inhibitor is subsequently, removed.
6. The Transcription factor can now join to the DNA, initiating transcription (production of mRNA from DNA)

SiRNA:

1. An enzymes cuts up a piece of double stranded mRNA.
2. This makes little double stranded fragements, called SiRNA.
3. One strand of the SiRNA binds with a enzyme.
4. The enzyme is brought to the mRNA, due to the free bases of the SiRNA binding to a complimentary region on the mRNA.
5. The enzyme cuts of the mRNA into smaller fragments, seperating the sequence of triplet codons, meaning not all of the amino acids needed for the proteins are coded for, meaning the correct protein cannot be translated, as the amino acid sequence determines the strucutre, and it is not present in full.