CHAPTER 12 – THE CELL CYCLE

SCIENCE STARTER Describe both the structure and function of chromosomes. What are sister chromatids? What are centromeres? 1. Chromosomes are a single long, double-stranded molecule of DNA wrapped around proteins. They function in the replication, division, and distribution of DNA from one generation to the next. The are two identical copies of a chromosome’s DNA. The are where the chromatids of a chromosome are attached.

THINK-PAIR-SHARE Brainstorm various ways to equally divide a pile of several-sized rubber bands amongst themselves. (Apply what you know about how a cell divides its genetic information to help them come up with the most efficient, even method for distributing the rubber bands.) Share your method with your elbow partner and discuss how your method compares to the method of mitosis. Be prepared to share with the class.

THE MITOTIC CELL CYCLE The mitotic phase alternates with interphase in the cell cycle The cell cycle is a well-ordered sequence of events in which a cell duplicates its contents and then divides in two. Some cells go through repeated cycles while others do not (e.g. nerve cells) Mitosis is just one portion of the cell cycle

THE MITOTIC CELL CYCLE The mitotic phase alternates with interphase in the cell cycle The mitotic (M) phase includes both mitosis and cytokinesis. Mitosis – Nuclear Division Cytokinesis – Division of Cytoplasm

THE MITOTIC CELL CYCLE The mitotic phase alternates with interphase in the cell cycle Interphase – the non-dividing phase 90% of the cell cycle Consists of 3 periods: G1 phase S phase G2 phase

THE MITOTIC CELL CYCLE The mitotic phase alternates with interphase in the cell cycle Interphase – the non-dividing phase 90% of the cell cycle Consists of 3 periods: G1 phase – First growth phase S phase G2 phase

THE MITOTIC CELL CYCLE The mitotic phase alternates with interphase in the cell cycle Interphase – the non-dividing phase 90% of the cell cycle Consists of 3 periods: G1 phase – First growth phase S phase – DNA replication G2 phase

THE MITOTIC CELL CYCLE The mitotic phase alternates with interphase in the cell cycle Interphase – the non-dividing phase 90% of the cell cycle Consists of 3 periods: G1 phase – First growth phase S phase – DNA replication G2 phase – Second growth phase

THE MITOTIC CELL CYCLE The mitotic phase alternates with interphase in the cell cycle At the end of interphase a G2 cell is characterized by: A well-defined nucleus bounded by a nuclear envelope Microtubules extend from the centrosomes in radial arrays called asters Centrosomes consist of a pair of centrioles Duplicated chromosomes cannot be distinguished individually due to loosely packed chromatin fibers

PROJECT With a partner create a 3D model of two different chromosomes. You may construct the chromosome out of any materials that you find in the classroom. (You may also use your own materials.) The model must include sister chromatids, chromatin, and a centromere for each chromosome. The chromosome model will also need to be capable of demonstrating mitosis at a future time point.