Cell division How one cell becomes two

Mitosis + Cytokinesis = Cell division Most cells in all eukaryotic organisms will divide many times throughout the life of the organism –Mitosis is the process by which a cell duplicates its genetic materials (chromosomes and prepares for cell division –Cytokinesis is the division of the rest of the cell into two different daughter cells –Prokaryotes also divide through binary fission, but this is NOT mitosis/cytokinesis In animals, cell division occurs during embryonic development, growth, and wound healing Errors during cell division can cause cell death or cancer

Mitosis reorganizes DNA in the cell Prior to mitosis, the cell creates an exact duplicate of its DNA material During mitosis, the two copies are reorganized, repackaged into two sets of chromosomes, and divided to opposite ends of the cell In most organisms, mitosis is immediately followed by cytokinesis (the cell body dividing in two) The original cell (mother cell) is identical to the two resulting cells (daughter cells)

Mitosis vocabulary Nucleus – location of DNA inside the cell Nuclear envelope – the membrane that separates the nucleus from the cytoplasm DNA – an incredibly long molecule that contains genetic blue prints for cell behavior Chromatin – a loosely bundled coil of DNA. Most of the time, DNA is organized in this form, “ a loose rope” Histones – proteins which hold a DNA strand together in the form of chromatin Chromosome – a highly organized form of chromatin, “a tightly wrapped and carefully knotted rope ” –Each chromosome is composed of two identical parts called chromatids –Chromatids: two halves of a chromosome which contain the same genetic information –DNA exists in the form of chromosomes only during mitosis –Each chromosome looks like an X Centromere – a bundle of proteins which connects the two chromatids of a chromosome, the “knot at the center of the X“ Microtubules – part of a cell’s cytoskeleton. These are tubes of protein which use to pull chromosomes apart and to opposite ends of a cell during mitosis. They are powered by ATP! Mitotic spindle – How microtubules are organized during mitosis. This is a collection of microtubule fibers which is formed to coordinate the pulling of apart of chromosomes. Metaphase plate – the line along which chromosomes are lined up during mitosis. This arrangement is coordinated by the mitotic spindle.

Chromosome Structure

5 Phases of Mitosis Mitosis is composed of five phases –Prophase –Prometaphase –Metaphase –Anaphase –Telophase During each phase, different proteins in the cell perform specific roles to divide the two copies of genetic material Cytokinesis occurs after mitosis to create two cells

Prophase Chromatin is being organized into chromosomes inside the nucleus Microtubules are organized into mitotic spindles in the cytoplasm Nuclear envelope is dissolving By the end of prophase –Chromosomes and mitotic spindle are fully organized –Nuclear envelope has disappeared

Prometaphase Chromosomes move towards each other and into the center of the cell Microtubules move into the nuclear region and begin to connect to chromosomes at the centromere Microtubules organize into two mitotic spindles, one at each end of the cell

Metaphase The mitotic spindle is fully organized, and has pulling the chromosomes to the center of the cell The spindle aligns chromosomes so that each centromere is lined up along the metaphase plate (the center of the cell)

Anaphase Each chromosome is pulled apart into two chromatids (halves) at the centromere Microtubule fibers contract (using ATP!), pulling chromatids to opposite ends of the cell towards the two spindles

Telophase Chromatids arrive at opposite ends of the cell and begin to unfold into loose coils of chromatin New nuclear envelopes begin to form around the chromatin to create two nuclei Spindle fibers disperse into the cytoplasm The cell membrane begins to cleave in preparation for cytokinesis

Cytokinesis The cell membrane is being pinched off to form two separate compartments Cytoplasm and organelles are being divided between the two forming cells At the end of cytokinesis, the membrane fuses to create two daughter cells which contain identical copies of DNA, and equal amounts of cytoplasm and organelles Cell division is complete!

Cell division movies 9QB0http:// 9QB0 YiGyZ8&feature=relatedhttp:// YiGyZ8&feature=related Embryonic division in the worm c.elegans: PESI&NR=1 PESI&NR=1