* Cells

* Pre-existing cells (cell theory) * Mitosis

* Cell size * Damage/injury/repair * Growth

* Gene expression… next unit!

* Biology is the only subject in which multiplication is the same thing as division…

Most cell division results in genetically identical daughter cells

* Chromosomes are the genes, DNA, code for proteins * Found in the form of: * Chromatin * “invisible” DNA * Decondensed, unduplicated chromosomes in nucleus * Most of cell’s life * Chromatids * Duplicated chromosome * Sister chromatids (one to each new cell) * Visible only during mitosis due to condensed nature of DNA * Centromere – center of chromosomes

The mitotic phase alternates with interphase in the cell cycle

* Interphase – growth, functioning, preparing for division * G1 * G0 * S * G2 * Mitosis (M) - nuclear division * Prophase * Metaphase * Anaphase * Telophase * Cytokinesis – cytoplasmic/organelle division

The eukaryotic cell cycle is regulated by a molecular control system

* A multicellular organism needs to coordinate cell division across different tissues & organs * critical for normal growth, development & maintenance * coordinate timing of cell division * coordinate rates of cell division * not all cells can have the same cell cycle

G2G2 S G1G1 M metaphase prophase anaphase telophase interphase (G 1, S, G 2 phases) mitosis (M) cytokinesis (C) C * Frequency of cell division varies by cell type * embryo * cell cycle < 20 minute * skin cells * divide frequently throughout life * hours cycle * liver cells * retain ability to divide, but keep it in reserve * divide once every year or two * mature nerve cells & muscle cells * do not divide at all after maturity * permanently in G 0

* Two irreversible points in cell cycle * replication of genetic material * separation of sister chromatids * Checkpoints * process is assessed & possibly halted centromere sister chromatids single-stranded chromosomes double-stranded chromosomes There ’ s no turning back, now!

* G 1 / checkpoint is most critical * primary decision point * “restriction point” * if cell receives “GO” signal, it divides * internal signals: cell growth (size), cell nutrition * external signals: “growth factors” * if cell does not receive signal, it exits cycle & switches to G 0 phase * non-dividing, working state

* Regulatory Proteins * Cyclin * Concentration fluctuates in cycles * Builds G 1 -M, drops after M checkpoint * Cyclin-dependent kinase (CDK) * Protein that binds and adds phosphate to cyclin * Concentration stable through cycle * MPF * Cyclin-CDK complex * When reaches peak levels, cell passes M checkpoint

* Growth factors * coordination between cells * protein signals released by body cells that stimulate other cells to divide * density-dependent inhibition * crowded cells stop dividing * each cell binds a bit of growth factor * not enough activator left to trigger division in any one cell * anchorage dependence * to divide cells must be attached to a substrate * “touch sensor” receptors

* Cancer is essentially a failure of cell division control * unrestrained, uncontrolled cell growth * What control is lost? * Mutations in genes that control checkpoints * Lose checkpoint stops Normal control  Abnormal control