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Why does a cell need to divide? Agenda for Thursday March 3rd 1. Go over homework 2. Mitosis All late work is due TOMORROW!! Quiz – words 56-60 Cellular Growth Cell Size limitations • Ratio of surface area to volume – Difficulty providing nutrients and expel waste – Lower ratio = easier to maintain Cellular Growth Cell size limitations • Transport of Substances – Diffusion over a large area is slower & less efficient • Cellular communication – Too large means too hard to communicate The Cell Cycle • Cell reaches max size it stops growing or divides – Cells reproduce by growing and dividing = cell cycle • 3 main stages of cell cycle – Interphase – cell grows, replicates DNA – Mitosis – cell nucleus and nuclear material divide – Cytokinesis – cell’s cytoplasm divides 3 Stages of Interphase Gap 1 (G1) • Right after cell divides, cell carries out normal functions, prepares to replicate DNA Synthesis (S) • Cell copies DNA – Chromosomes are structure that contain genetic material that is passed on – Chromatin is the relaxed form of DNA Gap 2 (G2) • Cell prepares for mitosis Mitosis • Cell’s DNA separates – Creates 2 identical daughter cells – Same DNA – Same Number of Chromosomes in each cell • Increases number of cells as organisms grow • Replace damaged cells • 4 Stages – Prophase, Metaphase, Anaphase, Telophase 1. Prophase • Longest phase • Chromatin condenses into chromosomes (X – shaped) – Chromosomes consist of two chromatids – identical copies of DNA – Chromatids are connected at a centromere 1. Prophase • Spindle fibers appear between poles • Centrioles appear at the ends of each cell • Aster fibers come out of the centrioles • Spindle fibers, centrioles, and aster fibers are called spindle apparatus – Helps move chromosomes 2. Metaphase • Chromatids are pulled by motor proteins along spindle apparatus • Line up at center of cell 3. Anaphase • Chromatids pull apart • Spindle fibers start to shorten – causes chromosomes to move to end of cells 4. Telophase • • • • Chromosomes arrive at the poles Chromosomes start to unwind Two nuclear membranes begin to form Spindle apparatus disappears Cytokinesis • Divides cytoplasm • Animal Cells – Microfilaments constrict/pinch the cytoplasm • Plant Cells – Cell plate forms between two daughter nuclei – Cell walls then form on either side of cell plate Cell Cycle Regulation • Proteins called cyclins bind to enzymes called cyclin dependent kinases (CDK) to start different cell activities List the stages of the Cell Cycle Agenda for Friday March 4th 1. Quiz 2. Mitosis stuff Describe the stages of Mitosis. Agenda for Monday March 7th 1. Mitosis review 2. Review FINAL ON WEDNESDAY!! Homework • Page 253 – 257 • Questions 1 – 7 on page 257
