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What are the two main stages of cell division?

Nuclear division- The process by which the nucleus divides.

Two types- mitosis and meiosis.


Cell division- follows nuclear division and is process by which whole cell divides.


Before a nucleus divides its DNA it must be... to ensure...

REPLICATED to ensure that all the daughter cells have the genetic info to produce the enzymes and other proteins that they need.


What are the four requirements for semi-conservative replication to take place?

-The four types of nucleotide, each with their bases of adenine, guanine, cytosine and thymine, must be present

-Both strands of the DNA molecule must act as a template for the attachment of these nucleotides

-The enzyme DNA polymerase is needed to catalyse the reaction

-A source of chemical energy is required to drive the process.


Describe the process of semi-conservative replication.

-The enzyme DNA helicase breaks the hydrogen bonds linking the base pairs of DNA.

-As a result the double helix separates into its two strands and unwinds.

-Each exposed polynucleotide strand then acts as a template to which complementary nucleotides are attracted.

-Energy is used to activate these (free) nucleotides.

-The activated nucleotides are joined together by the enzyme DNA polymerase to form the 'missing' polynucleotide strand on each of the two original polynucleotide strands of DNA.

-Each of the new DNA molecules contains one of the original DNA strands i.e. half the original DNA has been saved and built into each new DNA molecule. SEMI CONSERVATIVE REPLICATION.


What does mitosis produce?

Two daughter cells that have the same number of chromosomes as the parent cell and each other.


What does meiosis produce?

4 daughter nuclei, each with half the number of chromosomes of the parent cell.


What is mitosis?

The division of the nucleus of a cell that results in each of the daughter cells having an exact copy of the DNA of the parent cell.

Except in the rare event of a mutation, the genetic make-up of the two daughter nuclei is also identical to that of the parent nucleus.



a sudden change in the amount or arrangement of genetic material in the cell.



Mitosis is preceded by a phase where the cell is not dividing- interphase.

Period of considerable cellular activity that includes a very important event- replication of DNA.


What are the four stage of mitosis?







In which the chromosomes become visible and the nuclear envelope disappears.

Nucleolus disappears.



Spindle fibres form.

In which the chromosomes arrange themselves at the centre of the cell.



Spindle fibres attached to chromatids contract.

Each of the two threads of a chromosome (chromatid) migrates to an opposite pole.



Chromatid reaches poles and becomes indistinct.

In which the nuclear envelope reforms.

Nucleolus reforms.

Spindle disintegrates.


Why is mitosis important for growth?

When two haploid cells (e.g. sperm and ovum) fuse together to form a diploid cell, this diploid cell has all the genetic info needed to form the new organism.

If the new organism is to resemble its parents, all the cells that grow from this original cell must posses this same set of genetic info.

Mitosis ensures this happens.

The cell firstly divides to give a group of identical cells.


Why is mitosis important for differentiation?

Group of identical cells (originating from single diploid cell fused from sperm and egg) change, or differentiate, to give groups of specialised cells.

These different cell types each divide by mitosis to give tissues made up of identical cells which perform a particular function.

This is essential as the tissue can only function efficiently if all its cells have the same structure and perform the same function.


Why is mitosis important in repair?

If cells are damaged or die it is important that the new cells produced have an identical structure and function to the ones that have been lost.

If they were not exact copies the tissue would not function as effectively as before. Mitosis is therefore the means by which new cells replace damaged dead ones.


Describe simply the process of the cell cycle

Cells do not divide continuously, but undergo a regular cycle of division separated by periods of cell growth.


What are the 3 stages of the cell cycle?





What are the 3 parts of interphase?

Occupies most of the cell cycle, sometimes known as resting phase because no division takes place.

1.First growth (G1) phase, when the proteins from which cell organelles are synthesised are produced.

2.Synthesis (S) phase, when DNA is replicated.

3. Second growth (G2) phase, when organelles grow and divide and energy stores are increased.


What happens during nuclear division?

When the nucleus divides either in two (mitosis) or four (meiosis)


What happens in cell division?

Follows nuclear division an is the process by which the whole cell divides into two(mitosis) or four (meiosis).


What is cancer?

A group of diseases


What causes cancer?

Growth disorder in cells.

Result of damage to genes that regulate mitosis and cell cycle.

Leads to uncontrollable growth of cells.

As a consequence, a group of abnormal cells, called a tumour, develops and constantly expands in size.


How do drugs to treat cancer disrupt the cell cycle?

-prevent DNA from replicating.

-inhibiting the metaphase stage of mitosis by interfering with spindle formation.