Biology Unit 5 Notes

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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. Quick recap of oestrogen first - transcription stimulated by transcription factor, which has to bind to a specific region on the DNA. Can be inhibited. Oestrogen dissolves through phospholipid bilayer, as it is lipid soluble. Combines with receptor of transcription factor (complimentary). Changes the shape of DNA binding site, releasing inhibitor. Transcription factor can now join with DNA and stimulate transcription.

SO. The transcription factors can be inhibited. Oestrogen bind to the transcription factor on the receptor. Changes molecule shape, including DNA binding site. Releases inhibitor, and can now bind to DNA.

Righto. :P

So, now on to how SiRNA effects gene expression.

Small interferring RNA are little sections of RNA, double stranded. It prevents gene expression my breaking down mRNA. 1. Enzyme breaks down double stranded chains of mRNA into smaller sections, called SiRNA. 2. One strand of the SiRNA combines with an enzyme.

3. This one strand then pairs with the complimentary section of bases on a single stranded chain of mRNA. 4. The enzyme then cuts the mRNA down into smaller sections. The effect this has? With a broken chain of the mRNA, there is not the correct sequence of triplet codons, meaning incorrect amino acids are produced/not all of the amino acids necessary are produced - meaning the protein outcome will not have the same teritary structure, and therefore, shape, and possibly will not function in the same way. The gene is not expressed.

How this can be used? Use of SiRNA to block the genes that cause some diseases, or to identifiy the role of particular genes by eliminating them, and study the effects/missing chracteristics. Regulation of transcription and translation. OESTROGEN

1. Oestrogen is lipid soluble, so it can diffuse through the phospholipid bilayer easily. 2. Oestrogen binds to the receptor molecule on a transcription site.The are complimentary. 3. This...
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