CELL CYCLE MULTIPLIES CELLS Chapter 9. 2
OBJECTIVES Describe the structure of a chromosome. Name the stages of the cell cycle and explain what happens during each stage.
VOCABULARY chromatin chromosome sister chromatid centromere cell cycle interphase mitotic phase mitosis cytokinesis
CHROMOSOMES AND CELL DIVISION
Almost all of your genes of eukaryotic cells are in the nucleus. Usually found as chromatin, long thin fibers (combination of DNA and protein molecules). During replication, chromatin condenses into chromosomes.
Before cell division happens the chromosome doubles (copies) itself. This makes 2 sister chromatids that are the same DNA and are connected at the centromere. The sisters separate during division.
Some cells divide often (daily), some very rarely. Specialized cells never divide (ex. mature muscles). There are phases or steps in the cell cycle interphase mitotic phase
INTERPHASE 90% of the cell cycle is here. It is the stage where normal cell functions happen. In interphase, DNA is doubled before division starts. This is the S phase of interphase (DNA synthesis). Two gap phases (G 1 and G 2) are before and after DNA doubling.
MITOTIC PHASE Actual division is called the mitotic phase (M phase). Includes mitosis and cytokinesis. Mitosis is when the chromosomes are separated and cytokinesis is when the cytoplasm divides and cells separate.
Mitosis makes 2 identical cells. Errors are rare. In yeast, 1 in every 100, 000 divisions has a mistake. Only eukaryotic cells perform mitosis, but prokaryotes do something very similar. Eukaryotes not. have nuclear membranes, prokaryotes do