2.5 Cell Division

Assessment Statements Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue State that interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase) Explain how mitosis produces two genetically identical nuclei State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis

Starter: Why do cells divide? Limit to cell size (SA:VOL ratio) Growth Repair Reproduction Replace old/damaged cells Embryonic development State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis

All complex organisms originated from a single fertilised egg. Every cell in your body started here, through cell division the numbers are increased Cells then specialise and change into their various roles

2.5.1 Outline the stages in the cell cycle

2.5.3 State that interphase is an active period in the life of a cell Standard, normal condition of a cell Cell grows and DNA replicates during this stage

DNA ‘Blueprint of life’ Codes for all the proteins needed for life Describes that characteristics of every living thing Every cell with a nucleus contains ALL the instructions to make the organism

Chromosomes DNA is organised into chromosomes All sexually reproducing animals have pairs of chromosomes. One set of each pair comes from each parent Humans have 23 pairs Lions have 19 pairs African wild dogs have 39 pairs Mosquitoes have 3 pairs Some ferns have 500 pairs How many pairs? 3, 19, 23, 39, 500

Human chromatin and chromosomes Each strand may be 1.5 x 10 8 nucleotides with a length of up to 4 cm

In Eukaryotes, long threads of DNA are wrapped around proteins called histones to produces the characteristic X shape.

Imagine an organism with only two pairs of chromosomes Red = Maternal Blue = Paternal

During Interphase, each chromosome replicates and produces an exact copy of itself: Each copy of the chromosome is now called a chromatid and the pair of chromatids is called a chromosome

2.5.4 Describe the events that occur in the four phases of mitosis Prophase Metaphase Anaphase Telophase Remember though that this is a continuous process, and in the parts of an organism where cell division is occurring cells can be found in all stages. PREPARATION MIDDLE APART TWO

Standard condition of cell DNA replicates Cell enters reproductive cycle with four copies of each chromosome Chromosomes not visible Interphase centrioles

Prophase DNA supercoils and chromosomes become visible Nuclear membrane breaks down Centrioles migrate to poles

Metaphase Chromosomes line up with centromeres on equator of cell Centrioles form spindles

Anaphase Spindles fibres contract, pulling on centromeres Chromosomes migrate to poles

Telophase Nuclear membranes reform Chromosomes disperse Cytokinesis begins

Interphase Both daughter cells are exact copies of the parent cell. Genetically identical.

Which Stage?

2.5.2 State that tumours (cancers) are the result of uncontrolled cell division

Describe the events that occur during mitosis (9) sequence of stages is prophase → metaphase → anaphase → telophase; chromosomes condense/supercoil/become shorter and fatter in prophase; spindle microtubules grow (from poles to equator) in prophase/metaphase; nuclear membrane breaks down in prophase/metaphase; spindle microtubules attach to the centromeres/chromosomes in metaphase; chromosomes line up at equator in metaphase; centromeres divide / (paired) chromatids separate / chromosomes separate into two chromatids in metaphase/anaphase; (sister) chromatids/chromosomes pulled to opposite poles in anaphase; spindle microtubules disappear in telophase; nuclear membrane reforms around chromosomes/chromatids in telophase; chromosomes/chromatids decondense in telophase;