CHAPTER 10

Cell Growth and Division:Mitosis

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Background

Living things grow by producing more cells.This occurs through a process called mitosis, which is

(aesexual) cell division.Cell division (stage 1. mitosis & stage 2. cytokinesis)

results in “two identical daughter cells.”Before division occurs, the cell replicates/copies all of

its DNA.Then each new cell has its own complete copy of the

DNA for each new cell.Mitosis is needed for growth and repair of tissues,

and replaces lost cells (skin, digestion).

Chromosomes

Chromosomes carry the genetic info that is passed from one generation of cells to the next.

Made of DNAThe cells of every organism have a specific number of

chromosomes; humans have 46 (diploid = 2n).23 (haploid) come from mom, 23 (haploid = n) from

dad.Before the actual division occurs, the DNA doubles

itself, so there are 2 identical “sister” chromatids; one sister chromatid goes to each of the two new cells.

Each pair of chromatids are attached at the centromere.

ChromosomesPlay Video

The Cell Cycle

During the cell cycle, a cell grows, prepares for division, and divides to form 2 daughter cells, each of which begins the cycle again.

The cell cycle (the cell’s whole life) consists of 4 phases:1. M-phase (mitosis & cytokinesis)2. G1- cell growth and activity3. S-phase (chromosome replication)4. G2- cell growth and activity, prep for mitosis

* G = gap

Interphase

Mitosis

There are 4 phases of mitosis:1. Prophase2. Metaphase3. Anaphase4. Telophase

Depending on the type of cell, mitosis can last a few minutes to several days.

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DNA replication Mitosis

Two diploid cells

Prophase

•Chromatin condenses into chromosomes•Centrioles separate•Spindles begin to form•Nuclear envelope breaks down•Chromosomal material most visible

Metaphase

•Chromosomes line up across the center of the cell (equitorial plate)•Each chromosome is connected to a spindle fiber at its centromere

Anaphase

The sister chromatids separate into individual chromosomes and are moved apart.

Telophase

•Chromosomes gather up at opposite ends of the cell and lose their distinct shapes.•Two new nuclear envelopes form.

Cytokinesis

•The cytoplasm pinches in half (animal cells)

OR•A cell plate forms halfway between the two nuclei- new cell wall (plant cells)

•Either way, each daughter cell has an identical set of duplicate chromosomes

telophaseCell plate

Regulating Cell Growth

Cells grow and divide depending on the cell type.

Cyclin regulates the timing of the cell cycle in eukaryotic cells.

Other internal and external regulators control timing, etc.

Cancer: cells that do not respond to the signals that regulate the growth of most cells.

Cancer cells grow uncontrollably and create masses called tumors.

Mitosis Lab

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High power

•Also called alium root tip.•The tip of the root is a place where a lot of mitosis takes place; as the root grows through the soil, mitosis replaces lost cells and adds cells to lengthen the root.