New cells- parent and daughter cells.

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Parent and Daughters.

-New daughter cells form from parent cells in a series of events called the CELL CYCLE.

-The daughter cells produced must be able to CARRY OUT the SAME FUNCTION as the parent cell.

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Chromosomes- The instructions.

-Chromosomes are in the NUCLEUS of EUKARYOTIC cells.

-Each chromosomes witholds one molecule of DNA which includes specific lengths of DNA called GENES.

-Therefore, the chromosomes contain vital INSTRUCTIONS for making new cells.

-The daughter cell must contain an EXACT COPY of all these instructions (a full set of chromosomes).

-Human's have 46 chromosomes. 

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Copying and Separating.

-In EUKARYOTES the DNA that make up the chromosomes are WRAPPED around PROTEINS called HISTONES.

-The DNA + HISTONES= CHROMATIN.

-Before a cell can divide to produce two new daughter cells the DNA of each chromosome needs to be REPLICATED...TWO REPLICATES are produced.

-These replicates are the exact same as the original and are held together at a point called the CENTROMERE. = INTERPHASE 

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Copying and Separating part 2.

-At this stage you are UNABLE to see the chromosomes under a LIGHT MICROSCOPE.

-Now each chromosome consists of TWO DNA REPLICA STRANDS= SISTER CHROMATIDS.

-Next the sister chromatids must be SUPERCOILED to form VISIBLE chromosomes.

-Now they can take up stains and be seen under a light microscope.

-Before being supercoiled they are around 30nm thick and after they are around 500nm thick.

-They can't perform their normal functions in this state so the length of time they are in a supercoiled state needs to be as short as possible. 

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Checks and Balances.

-As the DNA is being replicated PROOF-READING ENZYMES move along the new DNA strands and check the copying has been done properly. 

-If there is a fault in the copying= a mutation= the new cell may fail to function.

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Cell Cycle- Length of time.

-The length of time taken for a parent cell to divide into two daughter cells, and for each to grow to full size, varies between species and cell type.

-It also is affected by the availability of nutrients for the cells.

-Mitosis occupies only a small proportion of the cell cycle and the remaining larger potion includes COPYING, CHECKING GENETIC INFORMATION of the DNA and PROCESSES ASSOCIATED with GROWTH. 

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