Cell division, diversity and cellular organisation

The cell cycle is the events that take place as one parent cell divides to produce two new daughter cells which then grow to full size

Dna and histones are called chromatin

Interphase

• Before cell division to produce 2 new daughter cells dna of each chromosome must be replicated
• Two replicas produced Exact copy of the original held together by an centromere
• Replica's called sister Chromatids
• Chromatins must be supercolied to be visible chromosomes
• There is another stage with is growth and preparation for mitosis

Cell cycles is divided into 3 stages; 1. Interphase 2. mitosis 3. Cytokineses

Mitosis is Asexual reproduction and is importaint as it provides growth, repair and replacement.

• Prophase - replicated chrmosomes are visible have been super coiled, Nuclear envelope dissappeared centriole divides into two which move to the opposite ends of the cell to form the spindle
• Metaphase - replicated chromosomes are lined at the equator
• Anaphase - the replica's of each chromosome are pulled apart by the spindles to the opposite poles of the cell.
• Telophase - two new nuclei's, daughter cells are formed new nuclear envelope. Spindle dissappears and chromosomes uncoil.

Two new cell can be made now

• Splitting in two of the cell is called cytokinesis.

There are some important differences between when and how plant and animal cells can go through the cell cycle.

• Most animal cells can go through mitosis and cytokinesis whereas plants in plants only special cells such as meristem cell can divide this way
• Plant cells do not have centrioles - tublin protein threads are made in the cytoplasm
• Cytokinesis in animal cells is started from the splitting of the membrane
• Cytokinesis in plant cells start with the formation of a cell plate where the spindle equator was, new cell membrane and new cell wall material is laid down along this cell plate.

• Gentically identical cells are clones
• bacteria single colony have been produced by one cell divided (Binary fission) also clones
• Many plants undergo Asexual reproduction e.g potato or strawberry runners - clones made - asexual reroduction known as vegatitive propagation

Artifical clones

• cuttings taken from a plant which can be made to grow into adult plants
• Genetically identical to the parent plant from which cuttings where taken. Clones to the parent

Cloning in animals

• Nucleus from a sheeps udder cell went into a sheeps egg cell which nucleus was removed
• The cell was placed into the uterus of another female sheep and the sheep was called dolly! She was a clone of another animal.

Stem cells

• mitosis produces genetically identical daughter cells that can carry a full set of genetic information.
• Stem cells can be described as omnipotent or totipotent
• Stem cells occur in small numbers in a adult animal
• Bone marrow contains stem cells that can divide to produce all the blood and bone cell types required by an adult human
• Advantages are it can use individuals own cells to repair damaged or diseased tissue organ would have a great benefit

Important differences when and how the cells of different organisms go through the cell cycle

When and where cells divide

• Animals - mitosis and cytokenisis- organisms can repair damaged cells by producing new cells to replace them
• Plants - only in specail growing regions known ad meristem can divide this way

Fusion of two cell nuclei from 2 different individuals to produce an offspring

• Each cell gives half og the total genetic information (gamete). This means special cells containing half the number of chromosomes must be produced which is called a gamete (sex cell).
• Fusion of two gametes female and male is called a zygote which can divide by mitosis to grow into a new indvidual organism
• Cell division which produces gametes is called meiosis
• normal adult cells contain 2 sets of chromosomes. DIPLOID homologous pair same genes but not neccesarily same versions of each gene
• Resulting daughter cell is Diploid only one set of chromosomes not genetically identical to each other ad each pair of the homologous chromosomes seperate into haploid cells
• Haploid daughter cells will differ as they contain particular alleles of each gene found on the members of the homologous pairs ther receive.

Meiosis is different from mitosis in two ways

• Produces cells containing half the number of chromosomes

• Produces cells that are genetically different from each other and from the parent cell