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 (G 1 ) 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 (G 2 ) Cell prepares for mitosis

Mitosis Cell’s DNA separates –C–Creates 2 identical daughter cells –S–Same DNA –S–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 4 th 1.Quiz 2.Mitosis stuff

Describe the stages of Mitosis. Agenda for Monday March 7 th 1.Mitosis review 2.Review FINAL ON WEDNESDAY!!

Homework Page 253 – 257 Questions 1 – 7 on page 257