CELL DIVISION Cell DivisionReproduction Why Cells divide for

CELL DIVISION Cell Division/Reproduction

Why? Cells divide for many reasons: � In order to stay small Diffusion occurs at a faster, more efficient rate in smaller cells. Why would diffusion rate matter in cells? Remember what materials need to enter and exit the cell. � DNA limits their size DNA can only control cells up to a certain size. � Repair/replace old or damaged cells. � Growth and Development We start out as one cell, mitosis allows that 1 cell to turn into billions of cells.

Cell Cycles Prokaryotic Cells No nucleus No membrane bound organelles (ex. mitochondria, vacuole, chloroplast) � A. ) Cell division takes place in 2 steps: 1. ) DNA is copied 2. ) Cell splits by binary fission

Cell Cycles Eukaryotic Cells Contain a nucleus and organelles. Repeating sequence of growth and division Occurs in two cycles for two purposes Mitosis � Occurs in somatic (ordinary body cells) for growth and repair � Creates 2 identical cells Meiosis � Occurs in germ cells (ovaries and testes) to make gametes (sex cells). � Creates 4 similar cells.

Eukaryotic Cell Cycle 3 Stages � Interphase G 1: First growth phase S: Synthesis phase G 2: Second growth phase � Mitosis nuclear division Prophase Metaphase Anaphase Telophase � Cytokinesis Division of cytoplasm

Centromere

Interphase G 1 – first growth phase: � The cell doubles in size and the organelles double S – synthesis phase: � the DNA that makes up the chromatin is copied (DNA replication) this is the longest phase of interphase. G 2 – second growth phase: � Growth and preparation for mitosis, second check-point. This is when the cell is preparing to divide. � The LONGEST phase of the cell cycle � 90% of the cell’s life is spent in Interphase. �

Interphase (G 1, S, G 2)

Terms to know: (Start a VOCAB page) DNA related terms Chromosome � Single piece of coiled DNA Diploid � A cell that contains a set of chromosomes from mom and dad. (46 in Humans) Replicated Chromosome � A single piece of DNA that has been copied through DNA replication Sister Chromatids � 2 identical strands of DNA Non-Replicated Chromosome � Single strand of DNA before it is copied Structural Terms Spindle Fibers � Fibers that are attached to centrioles to help pull apart chromosomes Centrioles � Organelles that aid in pulling apart chromosomes Centromere � Structure that holds the replicated chromosomes together

Mitosis (PMAT) Mitosis � The nucleus of a cell is divided into two nuclei with the same number of chromosomes. � Cell Stays diploid � Consists of 4 phases Prophase Metaphase Anaphase Telophase

Mitosis Step 1: Prophase Longest phase of MITOSIS � Chromatin coils and forms chromosomes � Nuclear envelope breaks down � Spindle fibers form and stretch from one end of the cell to the other They attach to the centrioles They help to pull the cell apart

Mitosis Step 2: Metaphase Chromosomes line up in the middle of the cell

Mitosis Step 3: Anaphase Centromere of each chromosome splits Two sister chromatids separate and move to opposite poles Each chromatid becomes separate (non-replicated) chromosome in each daughter cell.

Mitosis Step 4: Telophase Last stage of Mitosis Chromosomes at each pole uncoil and become chromatin Nuclear envelope reforms Spindle fibers break down

Cytokinesis NOT part of mitosis The cytoplasm divides into two cells Cell membrane reforms In plant cells the cell wall reforms