Section 2: The Cell Cycle Chapter 6 Chromosomes and Cell Reproduction Section 1: Chromosomes Section 2: The Cell Cycle Section 3: Mitosis and Cytokinesis 1

Chromosomes Objectives: Section 1 Chromosomes Objectives: Identify four examples of cell division in eukaryotes and one example in prokaryotes. Differentiate between a gene, a DNA molecule, a chromosome, and a chromatid. Differentiate between homologous chromosomes, autosomes, and sex chromosomes. Compare haploid and diploid cells. Predict how changes in chromosome number or structure can affect development. 2

Chromosomes Formation of New Cells by Cell Division Section 1 Chromosomes Formation of New Cells by Cell Division Function of Cell Division Cell division allows organisms to reproduce asexually, grow, replace worn-out or damaged tissue, and form gametes. Prokaryotic Cell Reproduction Bacteria reproduce asexually by binary fission, a process that produces identical offspring. Eukaryotic Cell Reproduction Before eukaryotic cell division, DNA coils tightly around proteins and forms chromosomes. At cell division, each chromosome consists of two chromatids attached at the centromere. 3

Chromosomes How Chromosome Number and Structure Affect Development Section 1 Chromosomes How Chromosome Number and Structure Affect Development Sets of Chromosomes Each organism has a characteristic number of chromosomes. Human somatic cells are diploid, with 23 pairs (46 in total) of homologous chromosomes. Human gametes are haploid, with 23 chromosomes. Sex Chromosomes Sex chromosomes carry information that determines an organism’s sex. 4

Section 1 Chromosomes How Chromosome Number and Structure Affect Development continued Change in Chromosome Number Changes in chromosome number can cause abnormal development. Karyotypes are used to examine an individual’s chromosomes and identify possible abnormalities in chromosome number. Change in Chromosome Structure Changes in chromosome structure, called mutations, can also cause abnormal development. 5

The Cell Cycle Objectives: Section 2 The Cell Cycle Objectives: Identify the major events that characterize each of the five phases of the cell cycle. Describe how the cell cycle is controlled in eukaryotic cells. Relate the role of the cell cycle to the onset of cancer. 6

The Cell Cycle The Life of a Eukaryotic Cell Section 2 The Cell Cycle The Life of a Eukaryotic Cell The Cell Cycle The life of a eukaryotic cell—the cell cycle—includes interphase, mitosis, and cytokinesis. Interphase Interphase consists of 3 phases: growth, DNA synthesis (replication) , and preparation for cell division. A cell spends 90 percent of its time in interphase. Mitosis and Cytokinesis A cell about to divide enters the mitosis (nuclear division) and cytokinesis (cytoplasm division) phases of the cell cycle. 7

The Cell Cycle Control of the Cell Cycle Section 2 The Cell Cycle Control of the Cell Cycle Cell Checkpoints The cell cycle is carefully controlled through three main checkpoints.: cell growth (G1) checkpoint, DNA synthesis (G2) checkpoint, and mitosis checkpoint. When Control is Lost: Cancer Failure of control of cellular growth and division can result in cancer. 8

Mitosis and Cytokinesis Section 3 Mitosis and Cytokinesis Objectives: Describe the structure and function of the spindle during mitosis. Summarize the events of the four stages of mitosis. Differentiate cytokinesis in animal and plant cells. 9

Mitosis and Cytokinesis Section 3 Mitosis and Cytokinesis Chromatid Separation in Mitosis Forming the Spindle The spindle is made up of centrioles and microtubule fibers. Separation of Chromatids by Attaching Spindle Fibers During mitosis, spindle fibers drag the chromatids to opposite poles of the cell. This leads to two nuclei that each contain a set of the original cell’s chromosomes. 10

Mitosis and Cytokinesis Section 3 Mitosis and Cytokinesis Mitosis and Cytokinesis Function of Mitosis and Cytokinesis The end result of mitosis and cytokinesis is two genetically identical cells. Mitosis Mitosis consists of four stages: prophase, metaphase, anaphase, and telophase. Cytokinesis Cytokinesis in animal cells occurs when a belt of protein threads pinches the cell membrane in half. Cytokinesis in plant cells occurs when vesicles from the Golgi apparatus fuse to form a cell plate. 11