Chapter 6- Cell Division

Long periods of growth and normal working separate divisions. These periods are called interphase and a cell spends the majority of its time in this phase DNA is replicated Protein synthesis occurs in cytoplasm Mitochondria grow and divide, increasing in number in the cytoplasm Chloroplasts grow and divide The normal metabolic processes occur

G1- the first growth phase: proteins from which organelles are synthesised are produced and organelles replicate. The cell increases in size G2- the second growth phase: the cell continues to increase in size, stores are increased and duplicated DNA is checked for errors

Mitosis-the nucleus divides Cytokinesis-the cytoplasm divides

The phase in which the cell leaves the cycle temporality or permanently

Differentiation-A cell that becomes specialised to carry out a particular function. It will carry out this function indefinitely The DNA of a cell may be damaged, in which case it is no longer viable. A damaged cell can no longer divide and enters a period of permanent cell arrest. As you get older the number of these cells in your body increases

G1-if satisfies these requirements it is triggered to begin DNA replication. If not it enters G0 G2- this checkpoint is at the end of G2 phase, before the start of the mitotic phase , DNA has to of been replicated without error Spindle assembly checkpoint- at point where all spindles should be attached and aligned

For growth,tissue repair and asexual reproduction

Coil and condense to form chromosomes, the nucleoulus disappears, and nuclear envelope is broken down. Micrtubles form spindle shaped structures linking the poles of the cell. Necessary to move the chromosomes into position. Centrioles migrate to poles of the cell. By end of prophase nuclear envelope has also disappeared

The chromosomes are moved by the spindle fibres to form a plane in the centre of the cell, and then held into position

The centromeres holding together the pairs of chromatids are separated and are pulled to opposite poles of the cells and form v shaped chromatids.

Chromatids have reached the poles and are now capped chromosomes, the two new sets of chromosomes and nuclear envelope reforms around them. Chromosomes start to uncoil smd nucleolus is formed

Nucleus divides twice to produce four daughter cells

Each organisms cell contains two full sets of genes one from each parent

Chromosomes condense, the nuclear envelope disintegrates, the nucleoulus disappears and spindle formation begins.

Chromosomes lie across the metaphase plate , but not as individual chromosomes

Pulled to opposite poles of the cells but chromatids are held together. Can form recombinant chromatids. Genetic variation arises

Chromosomes assemble at each pole and nuclear membrane reforms. Chrmomsomss uncoil. Cells undergo cytokinesis

Still consist of two chromatids, condense and become visible, nuclear membrane breaks down

More independent assortment more genetic variation as they lie across the middle

V shaped chromosomes are formed same as in anaphase of mitosis

Chromatids assemble at the poles, form chromatin again nuclear envelope reforms and the nucleus becomes visible. Cytokinesis occurs forming four daughter cells in total.

Have a flattened bioconcave shape No nuclei Flexible so can squeeze through gaps

Multi lobed nucleus makes it easier for them to squeeze through gaps Cytoplasm contains many lysosomes

Have a tail so are capable of moving and contain many mitochondria to help create energy to swim Head contains enzymes which help penetrate the ovum