Chromosomes & Cell Division Objectives: D2 – Identify the parts of a chromosome D3 - Describe the stages of the cell cycle including DNA replication, mitosis, and the importance of the cell cycle to the growth & repair of organisms D4 - Recognize that disruptions of the cell cycle can lead to cancer

Chromosome - Super-coiled DNA

Chromosome Parts Chromatid - one half of a replicated chromosome Centromere – protein disk that plays a role in chromosome movement; where the spindle fibers attach

Cell Division - the process by which a cell divides There are 2 types of cell division: Mitosis – for growth & repair [now] Meiosis – for making sex cells (gametes) [later] Mitosis

Cell Cycle - the series of events that cells go through as they grow and divide Grows more in preparation for mitosis Mitosis (PMAT) & Cytokinesis DNA Replication Resting Growth

Cell Growth (G1 & G2 phases) “G” stands for growth The larger a cell becomes, the more demands the cell places on its DNA. The cell also has trouble moving nutrients and wastes across the cell membrane. Small cells function more efficiently than large cells. Notice that the size of the nucleus doesn’t change.

DNA Replication (S phase) “S” stands for synthesis - Copying process by which a cell duplicates its DNA DNA – Genetic Information DNA – Deoxyribonucleic acid

Mitosis (during M phase) - consists of 4 phases Prophase Metaphase Anaphase Telophase

Cytokinesis (during M phase) - Animal cells The cell membrane is drawn inward forming a cleavage furrow until the cytoplasm is pinched into 2 nearly equal parts - Plant cells A cell plate gradually develops into a separating membrane.

Cell Cycle Regulators Cyclin a protein that regulates the timing of the cell cycle - Cancer Uncontrolled cell division of abnormal cells Cells do not enter the Go (resting) phase

Mitosis for growth & repair Chromosome Mitosis for growth & repair Centrioles Spindle fibers

What cells actually look like during cell division This is part of an onion plant magnified about 40 times so you can see individual cells.

Etymology Mitosis: mitos- (Gk. warp thread) + -osis (L. act, process). So called because chromatin of the cell nucleus appears as long threads in the first stages.

Practice Chromatid Centromere 1 – 2 – Name the parts of the chromosome: 1 – 2 – Chromatid 3 – short arm 4 – long arm Centromere