5 2 Mitosis and Cytokinesis KEY CONCEPT Cells

5. 2 Mitosis and Cytokinesis KEY CONCEPT Cells divide during mitosis and cytokinesis.

5. 2 Mitosis and Cytokinesis Objectives • Describe the structure of a chromosome. • Follow chromosomes through the process of mitosis and cytokinesis.

5. 2 Mitosis and Cytokinesis Vocabulary • Chromosome – Long, continuous thread of DNA that consists of numerous genes and regulatory information. • Histone – Protein that organizes chromosomes and around which DNA wraps. • Chromatin – Loose combination of DNA and proteins that is present during interphase. • Chromatid – One half of a duplicated chromosome.

5. 2 Mitosis and Cytokinesis Vocabulary • Centromere – Region of condensed chromosome that looks pinched; where spindle fibers attach during meiosis and mitosis. • Telomere – Repeating nucleotide at the ends of DNA molecules that do not form genes and help prevent the loss of genes. • Prophase – First phase of mitosis when chromatin condenses, the nuclear envelope breaks down, the nucleolus disappears, and the centrosomes and centrioles migrate to opposite sides of the cell.

5. 2 Mitosis and Cytokinesis Vocabulary • Metaphase – Second phase of mitosis when spindle fibers align the chromosomes along the cell equator. • Anaphase – Third phase of mitosis during which chromatids separate and are pulled to opposite sides of the cell. • Telophase – Last phase of mitosis when a complete set of identical chromosomes is positioned at each pole of the cell, the nuclear membranes start to form, the chromosomes begin to uncoil, and the spindle fibers disassemble.

5. 2 Mitosis and Cytokinesis Chromosomes condense at the start of mitosis. • DNA wraps around proteins (histones) that condense it. DNA double helix DNA and histones Chromatin Supercoiled DNA

5. 2 Mitosis and Cytokinesis • DNA plus proteins is called chromatin. chromatid • One half of a duplicated chromosome is a chromatid. • Sister chromatids are held together at the centromere. • Telomeres protect DNA and do not include genes. telomere centromere telomere Condensed, duplicated chromosome

5. 2 Mitosis and Cytokinesis Mitosis and cytokinesis produce two genetically identical daughter cells. Parent cell • Interphase prepares the cell to divide. • During interphase, the DNA is duplicated. centrioles spindle fibers centrosome nucleus with DNA

5. 2 Mitosis and Cytokinesis • Mitosis divides the cell’s nucleus in four phases. – During prophase, chromosomes condense and spindle fibers form.

5. 2 Mitosis and Cytokinesis • Mitosis divides the cell’s nucleus in four phases. – During metaphase, chromosomes line up in the middle of the cell.

5. 2 Mitosis and Cytokinesis • Mitosis divides the cell’s nucleus in four phases. – During anaphase, sister chromatids separate to opposite sides of the cell.

5. 2 Mitosis and Cytokinesis • Mitosis divides the cell’s nucleus in four phases. – During telophase, the new nuclei form and chromosomes begin to uncoil.

5. 2 Mitosis and Cytokinesis • Cytokinesis differs in animal and plant cells. – In animal cells, the membrane pinches closed. – In plant cells, a cell plate forms.

5. 2 Mitosis and Cytokinesis Question/Answer • What is the relationship between a molecule of DNA and a chromosome? – A chromosome is made of one continuous DNA molecule • How many chromosomes does the cell have at the start of mitosis? How many does it have after cytokinesis? – Four (duplicated) chromosomes ; four (unduplicated) chromosomes. • How does cytokinesis differ in animals and plant cells? – In animal cells, the membrane pinches together to separate the cytoplasm. In plant cells, a cell plate forms and divides the cell, along which the cell membrane and cell wall re-form.