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.

Small Interferring RNA. (SiRNA)

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 binding changes the shape of the transcription factor, causing the inhibitor (of where the DNA goes) to detatch. 
4. DNA can join with transcription factor, and transcription is stimulated. 

Totipotency and cell specialisation.

What are Totipotent Cells?
Totipotent cells are undifferentiated, non specialised cells. Initially, cells can become any type of cell (muscle, epithelial, etc.). Totipotent cells do not yet have a function.

Which cells in plants and animals are totipotent?
Fertilized egg cells.Embryonic Stem cells. Meristematic Cells in plants.

How do cells loose totipotency and become speicialised?
Cells become specialised because some genes become switched off/left on. This means that not all of the cells code for the same proteins, and therefore, have different constitutions, and have different functions due the the varying frequencies of the avaliable proteins.

How can stem cells treat human disorders?
Stem Cells can treat human disorders as they are undifferentiated. A factor can be used to force the cells to differentiate into particular cells - giving the avaliability to re-grow tissues that have been damaged, either by accidents, or via degenrative disease. For example, nerve cells being produced can combat the prgressions of diseases such as Parkinson's, Alzheimers, MS, and strokes.