Cell Division

What do you think??? Do we have the same skin as we were born with? What happens when we cut ourselves? What happens when we burn our skin? Why does our hair grow when we cut it?

Recall: The Cell Theory Cells are the basic fundamental units of life. All living things are composed of one or more cells. All cells come from pre-existing cells.

FUNCTIONS OF CELL DIVISION Healing & Tissue Repair Growth & Development Reproduction NOTE: In humans, 1 & 2 divide through mitosis & 3 divides through meiosis

1. Healing & Tissue Repair Millions of cells in our bodies die or are damaged every second and they need to be replaced, otherwise we would disappear!!! E.g. Scraping your knee, burning skin Video Leopard Gecko

2. Growth & Development Cells divide so that we can grow Single cells get bigger and eventually divide Materials such as nutrients and water are more easily controlled in smaller cells Eg. Getting taller

3. Reproduction Enables organisms to survive, otherwise species would die out Applies to unicellular (body cells) & multicellular organisms (sex cells)through different processes of cell division Eg. An amoeba will divide into two identical cells Video Seahorse

Sexual vs Asexual Reproduction Occurs in complex organisms Two parents Each parent donates ½ the genetic information required Cell is different from either parent Greater variety of offspring Slower process Asexual One parent Results in two cells Cells identical to parent Simple Organisms (Bacteria) Fast Process No genetic variation – susceptible to disease Produces body cells in humans Sexual vs Asexual Reproduction Produces New Cells

Cell Division & the Nucleus The nucleus is the “control centre” of the cell. It contains chromosomes, which are made of DNA and proteins. When a cell divides the genetic material must replicate and divide as well. Q: Why does the genetic material have to replicate?

Chromosome number is species dependent humans dog chimps ferns 46 78 48 1440

Terms to describe DNA Each chromosome is a long DNA molecule, typically containing 1000’s of genes Chromatin – 95% of the time the genetic material appear like this “Spaghetti like”, uncoiled, long, thin & stringy Found during interphase Chromosomes – 5% will appear like this in an actively growing cell Coiled, short & thick, can be seen under the microscope Found during Mitosis (cell division)

Variation in Genetic Material Depending on the stage of the Cell Cycle, chromosomes will have different appearances, and have different names. Unreplicated chromosome centromere Replicated/ double stranded chromosome

THE CELL CYCLE: Interphase + Cell Division A) Interphase: is a stage of growth & development B) Cell Division: Includes both Mitosis (nuclear division) & Cytokinesis (division of organelles and cytoplasm) There are four phases of Mitosis Prophase Metaphase Anaphase Telophase To Remember all the Stages: I-PMAT!!!

THE CELL CYCLE: Interphase + Cell Division

Interphase Cell grows & prepares itself for mitosis by building proteins Duplicates genetic material called CHROMATIN, now double stranded Centrioles are also replicated, more organelles form Parent Cell

Prophase Genetic material now called CHROMOSOMES chromosomes shorten & thicken, now visible in light microscope Nuclear membrane & nucleolus breakdown, freeing the chromosomes centrioles move away from each other & form spindle fibres Prophase Cytoplasm Cell Membrane

Metaphase Nuclear membrane has disappeared Centrioles have reached opposite poles Chromosomes line up in the middle of the cell or EQUATOR They are attached to the spindle fibres by their CENTROMERES. Cytoplasm Cell membrane

Anaphase Spindle fibres shorten to pull and separate duplicated chromosomes to opposite poles of the daughter cells The chromosomes are now referred to as DAUGHTER CHROMOSOMES. Cytoplasm Cell Membrane Daughter Chromosome

Telophase Daughter chromosomes have reached opposite poles & begin to uncoil Nuclear membrane & nucleolus reform Spindle fibres disappear DAUGHTER CELLS are genetically identical Cytokinesis begins Daughter Cells

Cytokinesis (animal vs. plant) Clevage Furrow Cell Plate

And…..It All Begins Again!!! Two new ‘daughter’ cells in interphase

Mitosis Overview