Biology
Class Notes
Lesson 5 Cell Cycle
Objectives: 1.2.2, 1.1.3, 4.2.1
How do multicellular eukaryotes replace damaged cells and how do single
cellular prokaryotes and eukaryotes reproduce?
Cell Division: The process by which a “parent cell” divides to form two or
more new “daughter cells”.
Cell Cycle: The continuous process in which individual cells grow, make
copies of their chromosomes (aka c’somes), and then divide to form
daughter cells.
The Cell Cycle
Interphase
• G1 Phase- Cells grow to mature size
• Longest phase of the cell cycle (18-20 hours).
• S Phase- Cell’s DNA is copied
• G2 Phase- Cell prepares for cell division
• Shortest phase of the cell cycle
Mitosis
• M Phase of Cell Cycle
• Division of the nucleus during cell division.
• Number of c’somes is same in mother and daughter cells
• Used for homeostasis/cell maintenance and asexual reproduction by
plants, and unicellular eukaryotes.
Prophase
• First phase of mitosis.
• Nuclear envelope dissolves.
• DNA shortens and tightens into c’somes.
• Spindle fibers form from centrioles and drag c’somes to ends of
cell.
• Two copies of c’somes form, each one is called a chromatid.
– Chromatids are connected by a centromere, which creates the
‘x’ shape.
Metaphase
• Second phase of mitosis.
• C’somes visible w/ a light microscope for the first time.
• Spindles move c’somes to center of the cell, line them up, and
hold them in place.
•
Anaphase
• Third phase.
• Chromatids split and are pulled by spindles to opposite poles of
the dividing cell.
• Once they separate, they are now individual chromosomes.
Telophase
• Fourth phase.
• C’somes reach opposite ends of the cell.
• Nucleolus and nuclear envelope reform around c’somes.
• The spindle fibers dissolve.
Cytokinesis (New Cell is Complete)
• Cytoplasm divides and splits at the Cleavage Furrow: Area
of the membrane that pinches to divide one cell to become
two. Note in plants, a Cell Plate develops and divides the
two new cells.
Assign Cell Cycle Problem Set
Assign Mitosis Problem Set
Assign Onion Root Tip Online Lab
http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html
Key Words
Cell division
Parent cell
Daughter cell
Cell cycle
Interphase
Mitosis
Prophase
Sister chromatids
Centromere
Metaphase
Anaphase
Telophase
Cytokinesis
Asexual reproduction