Cell Growth Cell Cycle Mitosis & Cytokinesis Chapter 10

Limits to Cell Growth The larger a cell becomes, the more demands the cell places on its DNA. In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane.

Ratio of Surface Area to Volume  As the size of a cell increases, its volume increases faster than the surface area. The decrease in the cell’s ratio of surface area to volume makes it more difficult for the cell to move needed materials in and waste products out quickly enough for the cell to survive.

Ratio of Surface Area to Volume

Cell Cycle Micrograph

Events of the Cell Cycle During the cell cycle, the cell grows, replicates its DNA, and divides into two daughter cells. DNA synthesis takes place during the S phase. Cell division takes place during the M phase. G1 and G2 are gap phases.

Cell Cycle The cell cycle is the series of events that cells go through as they grow and divide. Interphase is the period of growth that occurs between cell divisions. 90% of the cell’s time is spent here.

The Phases of the Cell Cycle G1, S, G2= INTERPHASE The cell cycle consists of four phases: G1 (First Gap Phase) S Phase (Synthesis Phase) G2 (Second Gap Phase) M Phase (cell division) Mitosis (Prophase, Metaphase, Anaphase, Telophase) Cytokinesis (division on cytoplasm)

Events of the Cell Cycle During G1 (First Gap phase) the cell increases in size synthesizes new proteins and organelles During the S (Synthesis phase), chromosomes are replicated or copied DNA synthesis takes place Once a cell enters the S phase, it usually completes the rest of the cell cycle. During G2 Phase (Second Gap Phase) Copying of certain organelles and molecules required for cell division occurs Once G2 is complete, the cell is ready to start the M phase—Mitosis

Interphase “Intermission” Normal metabolic activities Major state cell spends 90% of time here DNA= chromatin NOT a stage of mitosis

Late Interphase (S and G2) Prepares for mitosis DNA doubles= Sister chromatids Centrioles double in animals X X X X X X

Cell Division In eukaryotes, cell division occurs in two major stages. The first stage, division of the cell nucleus, is called mitosis. The second stage, division of the cell cytoplasm, is called cytokinesis. FYI Some books will put cytokinesis as the last step of mitosis

Why do cells divide by Mitosis? Growth &Repair Reproduction of single celled organisms under conditions Amobea Reproducing

Cells dividing by Mitosis……. Skin Identical to original cell Same chromosome # Identical chromosome makeup

Duplicated Chromosome (After S phase of Interphase): X Sister Chromatids Centromere

A Duplicated Chromosome centromere one chromatid its sister chromatid One chromosome in the duplicated state

Diploid vs. Haploid Diploid= 2 sets of chromosomes One set from mom and one set from dad Chromosomes come in pairs Humans have 23 pairs of chromosomes Somatic Cells all cells except sperm and egg

Diploid vs. Haploid Haploid = 1 set of chromosomes Sperm or egg (sex cells) have 23 single chromosomes

Stages of Mitotic Cell Division “1st” or “before” “middle” “apart” “far” or separate Prophase Metaphase Anaphase Telophase

Stages of the cell cycle

Prophase Nuclear membrane disappears Doubled DNA = condensed “chromosomes” form Spindle fibers start to form Prophase

Metaphase Mitotic spindle now formed By centrioles in animals Spindle apparatus in plants Chromosomes line up mid- cell or center of cell

Anaphase Chromosomes move to opposite pole pulled by spindle fibers Separate chromosomes

Spindle & spindle fibers: Pull apart the sister chromatids

Telophase Cell divides Cell plate (plants) or membranes (animals) form Nucleus reappears (now 2 of them) Chromosomes gather at opposite ends of the cell and lose their distinct shape. Nuclear envelope reappears (now 2 of them) Telophase

Cytokinesis:cell’s cytoplasm divides & splits apart

Plant versus Animal Mitosis No cell wall membrane cytokinesis = cleavage furrow Centrioles Plant: Cell wall form from cell plate Spindle apparatus

Cytokinesis in Plants Cell wall Cell plate In plants, a structure known as the cell plate forms midway between the divided nuclei. This will become the spot where the cell walls will form Cell wall Cell plate

Cytokinesis in Animals Cleavage furrow forms

Cancerous cells……... 1.Divide too many times 2.Divide into more than two cells! Masses of cells = “tumors” benign malignant

Onion Root Tip Micrographs of the Interphase and mitosis

Interphase

Prophase

Metaphase

Anaphase

Telophase

Identify the following

Identify the following

Identify the following

Identify the following

Identify the following

Identify the numbered cells 5. 3 4 1. 2.

Identify the numbered cells 6 7 8