The Cell Cycle: Cell Division and Mitosis How and Why Cells Divide

Cell Division Why do Cells Divide? Surface area to volume ratio decreases as cell grows. SA can no longer accommodate nutrients and wastes from increased volume that must cross the CM. Cells divide to maintain high SA to volume ratio. DNA can no longer accommodate cell functions

Controls on Cell Division Growth and Development Tissue Repair Contact with other cells Internal & External Regulators cyclins (proteins) respond to events inside & outside of cell What do you call uncontrolled cell growth? CANCER (does not respond to cyclins) *drugs cut off blood supply to cancer cells  die

The Details: –Chromosomes contain an organism’s genetic information. –Each new cell gets the same number of chromosomes and the exact same genes as the original cell.

How Are Chromosomes Replicated ? Each Chromosome is a gigantic molecule of DNA Starting at one end, DNA molecule UNZIPS Each Nitrogen base attracts its Complementary Nucleotide (A with T and G with C) Chromosomes are duplicated so the parent cell contains two full identical sets of chromosomes. Cell then divides resulting in each daughter cell ending up with one full set of chromosomes.

Chromosomes Chromosomes: DNA coiled around proteins called histones. DNA & histones form beadlike structure  nucleosomes. After DNA replication, chromosome structure: 2 identical sister chromatids attached by centromere.

The Cell Cycle Interphase G1 cell growth & development S DNA synthesis G2 Organelle synthesis Cell Division Mitosis & Cytokinesis

Interphase Interphase is all the time BETWEEN cell divisions Cells grow in size Cells synthesize proteins by joining Amino Acids together in specific sequences DNA (of each chromosome) unzips and Replicates This doubles the total number of chromosomes. Condensing & coiling of chromatin (DNA & proteins) mesh. Centrioles replicate

Mitosis Overview

The Steps (phases) of Mitosis Prophase Metaphase Anaphase Telophase –Cytokinesis

Prophase (longest phase of Mitosis) Chromosomes condense & coil, becoming visible under microscope Nuclear membrane disintegrates Centrioles begin to migrate to opposite poles Microtubules form a structure called a Spindle

Metaphase Paired chromatids lineup in the middle of the cell, sometimes called the equator Attach to spindle via centromere

Anaphase Centromeres split Sister Chromatids separate, moving away from the equator towards opposite Poles Microtubules of the Spindle pull them to opposite ends of the cell

Telophase Chromosomes uncoil, becoming invisible chromatin mesh Spindle disappears Nuclear membrane reappears Cytokinesis (division of cytoplasm usually follows) –Cytoplasm is divided evenly into two cells

The Importance of Mitosis Mitosis is Nature’s percent guarantee that when ANY Eukaryotic cell divides, it produces two Genetically Identical Cells. What kind of cells divide by Mitosis? Somatic (body) cells

Somatic Cells/Body Cells Heart, Muscle, and Nerve cells rarely divide if at all. Skin, digestive, and connective tissue cells divide rapidly, replacing worn out, broken down, dead cells. Following injury, rapid cell division of these cells slows as healing progresses, due to cyclins.

Different Organisms and Their Chromosome Numbers Cat38 Cow60 Fruit fly8 Goldfish94 Human46 Onion16 What do all these chromosome numbers have in common?

How Chromosomes Appear Chromosomes are found in homologous pairs. (one from each parent) –Each chromosome has a homolog that carries traits for the same genes. Diploid number (2n) –The total number of chromosomes that exist in a cell.

Mitosis in Humans ProMAT DNA Replication 46

92 ProMAT DNA Replication 46 2n 4n ProMAT DNA Replication 2n Mitosis In HumansIn ANY Species