KEY CONCEPT Cells divide during mitosis and cytokinesis.

1. KEY CONCEPT Cells divide during mitosis and cytokinesis.

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

3. 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.

4. 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. 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.

6. DNA andhistones SupercoiledDNA DNA doublehelix Chromatin Chromosomes condense at the start of mitosis. • DNA wraps around proteins (histones) that condense it.

7. chromatid telomere centromere telomere Condensed, duplicated chromosome • DNA plus proteins is called chromatin. • 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.

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

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

10. During metaphase, chromosomes line up in the middle of the cell. • Mitosis divides the cell’s nucleus in four phases.

11. During anaphase, sister chromatids separate to opposite sides of the cell. • Mitosis divides the cell’s nucleus in four phases.

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

13. In animal cells, the membrane pinches closed. • In plant cells, a cell plate forms. • Cytokinesis differs in animal and plant cells.

14. 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.