Cell Division and Mitosis -Chapter 9- Honors Biology Program Mountain Pointe High School

Development Of A Human Hand future arm and hand of embryo, five weeks old

Overview: Key Roles of Cell Division Reproduction distinguishes living from non-living Multicellular organisms develop from a zygote. Cell division aids in repair & renewing of cells

Overview: Key Roles of Cell Division Cell division results in genetically identical daughter cells. Exact copy in each daughter cell. A cells genetic information, package in DNA, is called its genome. In prokaryotes DNA a long single strand Eukaryotes several DNA molecules.

Overview: Key Roles of Cell Division In meiosis gametes are produced (egg & sperm cells). Meiosis yields 4 non-identical daughter cells with ½ the number of chromosomes.

The Cell Cycle Eukaryotic cells divide in a series of steps known as the Cell Cycle. Three main parts: Interphase (b) Mitosis (c) Cytokinesis End result: two genetically identical “daughter cells”.

Interphase is divided into three stages: It’s important to understand that during Interphase, no division is taking place! Interphase is divided into three stages: G1 S G2

Interphase G1 phase, the cell grows and protein production is high. S phase, DNA is replicated. Chromosomes aren’t visible, since the DNA is in the form of chromatin. The number of cytoplasmic components is doubled. nucleus cytoplasm cytoplasm

one chromosome (unduplicated) DNA Replication “S” stage of Interphase, DNA must copy itself so that each new daughter cell will have its own copy of the genetic code. The two sister chromatids are held together by a centromere. one chromosome (unduplicated) one chromatid sister chromatid one chromosome (duplicated) CENTROMERE

These function as attachment points for the spindle microtubules. Chromosome Structure Kinetochore Attached to both sides of a centromere are connecting points known as kinetochores. These function as attachment points for the spindle microtubules. One nucleosome DNA This diagram shows how DNA wraps around protein spools known as histones. A histone & its DNA together are known as a nucleosome.

Mitosis The process of the nucleus dividing is known as “mitosis”. Mitosis has four stages: Prophase, Metaphase, Anaphase and Telophase.

Prophase The first stage of mitosis is prophase. Chromatin condenses and coils into visible chromosomes. Nucleolus & nuclear envelope disintegrate. Spindle apparatus starts to form between centrioles. Centrioles (found only in animal cells) begin moving to opposite ends of the cell. EARLY PROPHASE LATE PROPHASE LATE PROPHASE

Metaphase The shortest stage of mitosis is metaphase. During this phase, the sister chromatids are arranged at the equator of the cell. The spindle microtubules attach to the kinetochores of each chromatid.

Once separated, they are referred to as chromosomes, not chromatids. Anaphase During anaphase, the two sister chromatids are separated from each other by the spindle microtubules and moved to opposite poles. Once separated, they are referred to as chromosomes, not chromatids.

Telophase The final stage of mitosis is telophase. Chromosomes uncoil into chromatin. Nucleoli & nuclear envelopes reappear. Spindle microtubules disintegrate.

Cytokinesis The division of the cytoplasm is known as cytokinesis. Cytokinesis is the final step in the Cell Cycle. In animal cells, a cleavage furrow forms, microfilaments contract and cut the cell in two.

Cytokinesis In plant cells, the cell wall prevents the cell from being pinched in two. Instead, a “cell plate” forms between the two nuclei. Cellulose deposits begin to form at the cell plate, forming a crosswall that divides the parent cell into two daughter cells.