Mitosis and Meiosis Mitosis and Cytokinesis Biology Fall 2012

Objectives  Summarize the events of the four stages of mitosis  Differentiate cytokinesis in animal and plant cells

Bell Ringer 1. What do you think the following prefixes mean? A. Pro- B. Meta- C. Ana- D. Telo- 2. How does a cells ATP use change during mitosis?

Bell Ringer 1. What do you think the following prefixes mean? A. Pro- “earlier than” B. Meta- “later than, or after” C. Ana- “up or back” D. Telo- “end” 2. How does a cells ATP use change during mitosis? 1. The events of mitosis require a lot of additional energy, which is supplied by ATP

Chromatid separation in Mitosis  Last two phases of the cell cycle:  Mitosis and cytokinesis

Chromatid separation in Mitosis  Mitosis: nucleus divides to form two nuclei each containing a complete set of the cells chromosomes  Cytokinesis: cytoplasm is divided between the two resulting cells

Chromatid separation in Mitosis  During mitosis chromatids are physically moved to opposite sides of dividing cell with help of spindle  Spindle: cell structures made up of both centrioles and individual microtubule fibers that are involved in moving chromosomes during cell division

Forming the Spindle  Centrosome: organelle that organizes the assembly of the spindle  At each of cells poles  In animal cells a pair of centrioles are found in each centrosome

Forming the Spindle  Centrioles and spindle fibers are made of hollow tubes of protein  Called microtubules  Spindle fibers made of individual microtubules  Centrioles made of 9 triplets of microtubules arranged in a circle

Forming the Spindle  Plant cells DO NOT have centrioles  Form a spindle that is almost identical to that of an animal cell

Separation of Chomatids by Attaching Spindle Fibers  Two sets of microtubules extend out toward opposite poles  Once microtubules attach to the centromeres and poles, the two chromatids in each chromosome can be separated

Separation of Chomatids by Attaching Spindle Fibers  Paired chromosomes separate  One of the pair of chromatids will move to one of the poles of the cell  The second member will move to the other pole  Chromatids draw closer to the poles of the cell as these microtubules are broken down bit by bit and become shorter

Mitosis  Step #1: Prophase  Chromosomes coil up and become visible  Nuclear envelope dissolves and a spindle forms

Mitosis  Step #2: Metaphase  Chromosomes move to the center of the cell  Line up along equator  Spindle fibers link chromatids of each chromosome to opposite poles  Meta = middle

Mitosis  Step #3: Anaphase  Centromeres divide  Two chromatids (now called chromosomes) move toward opposite poles as the spindle fibers attached to them shorten

Mitosis  Step #4: Telophase  Nuclear envelope forms around the chromosomes at each pole  Chromosomes now at opposite poles uncoil and spindle dissolves  Mitosis complete!

Cytokinesis  Cytoplasm of cell is divided in half  Cell membrane grows to enclose each cell, forming two separate cells

Cytokinesis  In animal cells:  Lack cell walls  Cell is pinched in half

Cytokinesis  In plant cells:  Have cell walls  Form a cell plate  Cell plate: membrane bound cell wall that forms across the middle of the plant cell  New cell wall then forms on both sides of cell plate, separates the plant cell into two new cells

Cytokinesis

 Animal Cell  Plant Cell

Review  White boards:  Draw prophase  Draw metaphase  Draw anaphase  Draw telophase  Draw cytokinesis in plant cells  Draw cytokinesis in animal cells