OCR GCSE Biology B3 Processes

Nuclear Transfer (B3)

1. An egg cell is extracted from Animal A, the nucleus is removed from this egg cell.
2. A nucleus is removed from a diploid, somatic skin cell is taken from Animal B
3. The nucleus from the skin cell is inserted into the enucleated egg cell from Animal A and an electric shock is applied to make the newly combined cell divide into an embryo.
4. The embryo is then placed into a surrogate Animal C where it then gestates before being born as a clone of the animal from which the nucleus was obtained.

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1. The cell is resting.
2. The chromosomes in the nucleus duplicate and then shorten and fatten.
3. The nuclear membrane disintegrates.
4. The centrioles duplicate and move to opposite ends of the cell.
5. The chromosomes line up along the cell equator.
6. Spindle fibres extend from the centrioles and attach to the centromeres of the chromosomes.
7. The chromosomes are pulled apart at the centromeres by the spindle fibres to opposite ends of the cell.
8. The cell divides into two and the nuclear membrane reforms around each cluster of chromosomes.
9. Two new genetically identical diploid daughter cells form.

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1. The DNA double helix unwinds.
2. The enzyme DNA helicase ‘unzips’ the two strands of DNA.
3. New bases found in the nucleus attach to their complementary bases on the single DNA strands.
4. The DNA re-zips and re-winds back into two double helix structures.

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1. Each enzyme has a unique sequence of amino acids, this results in each enzyme having a different shape and active site
2. Only one type of substrate is complementary to the active site of one enzyme. This makes enzymes specific to reactions.
3. If the substrate is complementary to the active site, it will fit into the enzyme to form the enzyme-substrate complex.
4. The enzyme acts on the substrate and turns it into a product.

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1. The desired characteristics of both species are identified.
2. The species are cross-bred by mating a male member with one characteristic with a female member with another characteristic.
3. The offspring that best express the desired characteristics are selected.
4. The selection and the breeding process is repeated for a number of generations.

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