Cell Division Study Sheet

Why do cells divide? – – –

If cells grow too much their supply of DNA won’t be able to support the cell Maintain high surface area to volume ratio Volume amount of stuff that needs to pass, surface area size of membrane

Cell Division – – – – – – – – – – – – –

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Chromosomes carry DNA because they are made up of DNA Until cell division chromosomes can’t be seen because of nuclear envelope Each chromosome has 2 chromatids Interphase is made up of G1, S, and G2 M phase is mitosis G1 is growing S is DNA replication G2 creates new organelles M divides Pro, meta, ana, telo In prophase the nuclear envelope breaks down, the spindle forms, and chromosomes become visible In metaphase the chromosomes line up across the center of the cell and attach to fibers In anaphase the centromeres split apart and chromatids become individual chromosomes, they move towards the centrioles Nuclear envelopes reform, spindle breaks apart and nucleolus forms In cytokinesis cell membrane can be drawn inwards to the middle or in an plant cell the cell plate forms so that there are cell walls for each new cell

Regulation –

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Cell division rate goes up when you are cut Cells will stop dividing when they come into contact with others Cyclins regulate the timing of the cell cycle in eukaryotes Things that determine stuff inside the cell are internal regulators ex. Make sure chromosomes are finished attaching to spindle before going to anaphase External regulators speed up or slow down the cell cycle, they stimulate growth rates and stuff Uncontrolled cell growth is caused when cancer cell don’t respond to regulators This means cells can’t function right because they might not divide right

Meiosis – – –

Homologous chromosomes are pairs that have a corresponding chromosome from each parent A cell with both sets of homologous chromosomes is diploid Sexually reproducing organisms have haploid amounts

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Diploid to haploid is meiosis The number of chromosomes are split in half through the separation of homologous chromosomes through division Before meiosis 1 replication takes place and the cell divides like in mitosis In prophase of mitosis tetrads form from homologous chromosomes (4 chromatids each), exchange some parts through crossing over (between the chromosomes in a tetrad) and then it goes on like in mitosis *the new cell has one chromosome from each tetrad Two not identical cells are produced and since neither of them have two complete sets and the cell is a haploid cell Meiosis two starts without any replication or anything Each chromosome has two chromatids right now In metaphase II the chromosomes line up in the center of the cell In anaphase two the chromatids separate (paired ones) In anaphase II the chromatids separate The cells separate and each cell(4) now contains 2 chromatids which then count as chromosomes In female cells the end of meiosis I and II are different so there is only one egg produced *********************************************************************** * MITOSIS CREATES 2 IDENTICAL DIPLOID CELLS WHILE MEIOSIS PRODUCES FOUR DIFFERENT HAPLOID CELLS