Control of gene expression
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How can a zygote be said to be totipotent?
It contains all of the genes needed to produce any of the tissues in the entire organism
By which method does the zygote divide?
What are the effects of zygote division?
All of the cells in the embryo are genetically identical
Why are some genes present in embryonic cells not expressed?
- The cells become specialised as the embryo matures to form different tissues
- This means some genes are not transcribed or translated into proteins
- An example of this is the epithelial cell in the small intestine that possesses the gene for producing insulin but cannot do so
What is the name given to cells that retain their totipotency?
How do plant cells differ from human cells with regards to totipotency?
Given the right conditions and chemical stimuli, most plant cells can return to a totipotent state and produce any plant tissue
How can plant totipotency be utilised?
Through tissue culture where small groups of cells from an adult plant are used to grow clones of the original
How are stem cells suitable for human treatment?
- They are totipotent meaning they can constantly divide and differentiate into any tissue
- This means they can be used to treat human disorders without the risk of rejection if tissue from another individual was used
Which are the best cells to use for stem cell treatment?
Embryonic stem cells taken from early embryos before the cells have specialised
What is the main ethical objection to stem cell treatment?
Embryos that have the capability of providing human life are used in research
What is a transcriptional factor?
A molecule that binds to the promoter of a gene and starts transcription
How do hormones such as oestrogen affect cell transcription?
- The molecule binds to the transcriptional factor called the oestrogen receptor at a complementary shaped binding site
- This changes the shape of the receptor molecule which releases an inhibitor from the transcriptional factor allowing it to bind to the promotor of the gene, stimulating transcription
How is oestrogen suited to cell movement?
It is lipid soluble allowing it to diffuse straight through the cell membrane
Describe stage 1 of translation regulation by small interfering RNA
Double stranded RNA is produced using an enzyme that uses excess mRNA as a template to produce a complementary strand
Describe stage 2 of translation regulation by small interfering RNA
- The double stranded piece of RNA is cut by an enzyme into smaller sections
- These sections are known as small interfering RNAs (siRNA)
Describe stage 3 of translation regulation by small interfering RNA
A protein complex takes up the siRNA and removes one strand leaving only the complementary strand
Describe stage 4 of translation regulation by small interfering RNA
- The siRNA strand binds to a messenger RNA with complementary bases
- An enzyme in the protein complex cuts the messenger RNA into pieces preventing it from being translated
How can siRNA be used to prevent disease
It is manufactured and implanted into cells to block the expression of genes
How can siRNA be used for research purposes?
- They can be used to block genes to find out their uses
- If gene expression is blocked, the cell will be unable to carry out the function that the gene was responsible for
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