Cell Divison

Describe the process of DNA replication and the evidence for thisExplain the phases of the cell cycle

and their importance.

DNA Replication

• DNA is read 5’ to 3’• DNA polymerase adds nucleotides

together• DNA helicase unwinds the DNA by

breaking hydrogen bonds.• Nucleotides are joined by condensation• Complimentary strand is made to the other

strand causing semi conservative replication

Every dividing tissue cell in the body is always at a stage of the cell cycle. Whether it is at :-

STAGES OF MITOSISSTAGES OF MITOSIS

CytokinesisThus enabling the body

to continuously make

new body tissue for

growth and repair.

Prophase

MetaphaseAnaphase

Telophase

Interphase

} Mitosis

Prophase

Metaphase

Anaphase

Telophase

The The stages of stages of mitosismitosis

Interphase

PROPHASEPROPHASE• The chromatin (unravelled DNA)

in the nucleus, condenses to form visible chromosomes.

• The centrioles that form spindle fibres move to opposite ends of the nucleus.

• Nuclear membrane begins to break down

The structure of a highly condensed, replicated chromosome.

METAPHASEMETAPHASE

• The spindle becomes fully developed

• The chromosomes (chromatid pairs) place themselves onto individual fibres and are aligned along the centre of the spindle

• The nuclear membrane has now completely disintegrated

The SpindleThe Spindle

A spindle is a web type structure made up of microtubule fibres. It is essential for mitosis because it arranges the chromosomes into their correct positions in preparation for cell division.

Mitotic centre

MicrotubuleA cell at metaphase a spindle

ANAPHASEANAPHASE

• The chromosomes are split into their two chromatids.

(This is done by movement of the spindle fibres)

• The chromatid pairs then travel to opposite ends of the spindle

• The separated chromatids are now called chromosomes

TELOPHASETELOPHASETwo new nuclei are formed when the chromosomes reach the opposite poles of the cell

The nuclear membrane is formed.

The chromosomes uncoil and disperse in the nucleus, effectively becoming invisible again.

REMEMBER!REMEMBER!

IInterphase

PProphase

MMetaphase

AAnaphase

TTelophase

IPMAIPMATT

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• http://nobelprize.org/educational_games/medicine/2001/cellcycle.html