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

AP Biology Uses of Mitosis  Growth  Organisms grow by increasing number of cells, not cell size.  Think surface-area to volume ratio.  Tissue Repair: w ounds close by creating cells identical to those that were lost or injured.  Embryonic Growth: increasing cell number  Asexual Reproduction (Binary Fission)

AP Biology Stages of the Cell Cycle  Mitotic Phase  Refers to the process of nuclear division  Cytokinesis  The actual physical division of the cell  Not included in the mitotic phase  Division of the cytoplasm and its contents  Interphase

AP Biology Life Cycle of Cell cell is formed from a mitotic division cell grows & matures to divide again cell grows & matures to never divide again G 1, S, G 2, M G1G0G1G0 epithelial cells, blood cells, stem cells brain / nerve cells muscle cells liver cells

AP Biology Interphase (longest stage of cell’s life) Divided into 3 phases:  G 1 = 1 st Gap  Cell doing its “everyday job.”  Cell grows.  S = DNA Synthesis  Copies chromosomes.  G 2 = 2 nd Gap  Prepares for division.  Cell grows (more).  Produces organelles, proteins, membranes. G0G0 signal to divide

AP Biology S-Phase of Interphase Dividing cell replicates DNA  Must separate DNA copies correctly to 2 daughter cells.  Human cell duplicates ~3 meters DNA.  Each daughter cell gets complete identical copy.  Error rate = ~1 per 100 million bases  3 billion base pairs in mammalian genome.  ~30 errors per cell cycle  Mutations (to somatic cells).

AP Biology Organizing DNA  DNA is organized in chromosomes  Double helix DNA molecule  Wrapped around histone proteins  DNA-protein complex = chromatin  Organized into long thin fiber.  Condensed further during mitosis (prophase). ACTGGTCAGGCAATGTC After DNA duplication, chromatin condenses.

AP Biology Mitotic Chromosome Duplicated chromosome  2 sister chromatids.  Narrow at centromeres.  Contain identical copies of original DNA.

AP Biology G1, S, and G2 of interphase used to be called the “resting phase.” Why is resting phase not a good name?

AP Biology Prophase  Nucleoli disappear.  Nuclear membrane breaks down.  Each duplicated chromosome appears as two identical sister chromatids joined at centromere.  Visible in light microscope.  Mitotic spindle forms.  Centrosome  Radiating microtubules  Centrosomes move away from each other.

AP Biology Prometaphase: Transition to Metaphase  Chromosomes attach to microtubules.  At kinetochore.  Each chromosome is oriented such that the kinetochores of sister chromatids are attached to microtubules at opposite poles.  Chromosomes begin moving to the middle.

AP Biology Metaphase  All chromosomes are aligned at equator of the cell, called the metaphase plate.  Chromosomes are attached to opposite poles and are under tension.  Helps to ensure chromosomes separate properly.  Ensures each new nucleus receives only ONE copy of each chromosome.

AP Biology Anaphase  Cohesion proteins (hold sister chromatids together) cleaved by separase.  Kinetochore microtubules shorten.  Motor proteins assist.  Sister chromatids pulled to opposite sides of the cell.  Non-kinetochore microtubules lengthen and elongate cell.

AP Biology Telophase  Sister chromatids arrive at opposite poles.  Spindle disappears.  Centrioles replicate (in animal cells.  Nuclear membrane reappears.  Nucleolus becomes visible.  Chromosomes become chromatin (uncoiling).

AP Biology Cytokinesis  Animals  Cleavage furrow forms.  Splits cell in two.  A belt of actin pinches off daughter cells.  Plants  Cell plate forms.  Vesicles line up at equator and fuse.