CELL CYCLE – INTERPHASE, MITOSIS, CYTOKINESIS
What are the 3 reasons why cells reproduce? Growth, Repair, & Replacement
Why would a cell divide?

As cells absorb nutrients and get larger, the volume of the cell increases faster than the surface area

This means that a cell can no longer absorb nutrients and get rid of wastes fast enough to support its demands
(volume)

So what’s a cell to do? Solution: divide in 2!
Cell division is a type of asexual reproduction!
Cell Cycle has 3 stages:
1) INTERPHASE
2) MITOSIS
-Prophase
-Metaphase
-Anaphase
-Telophase
3) CYTOKINESIS
INTERPHASE
•
Longest phase of the cell cycle (90% of time in Interphase)
•
Cell grows & makes proteins
•
Replicates its DNA and chromosomes
•
Makes organelles for division, like centrioles
Chromosomes:
-Inside nucleus
-Genetic information (DNA)
-After S phase = 2 sister chromatids
-There are different numbers of
chromosomes in different species.
MITOSIS = Division of the nucleus
Prophase  Metaphase  Anaphase  Telophase
1ST STAGE OF MITOSIS: PROPHASE
•
Chromatin condenses into chromosomes.
•
Nuclear envelope breaks down
•
Centrioles separate to opposite sides of the cell
•
Spindle begins to form between centrioles (made of
microtubules)
2ND STAGE OF MITOSIS: METAPHASE
•
Chromosomes line up at the center of the cell (meta means “middle”)
•
Spindle fibers attach to each sister chromatid at its centromere
3RD STAGE OF MITOSIS: ANAPHASE
•
Sister chromatids separate and the centromeres divide
•
Pulled apart by the shortening of the spindle fibers
•
Sister chromatids move to opposite poles of the cell
4th STAGE IN MITOSIS: TELOPHASE
•
Chromosomes begin to uncoil and become chromatin
•
Nuclear envelope begins to form around genetic material (chromatin).
•
2 distinct nucleuses are forming!
AFTER MITOSIS: CYTOKINESIS
•
Cytoplasm pinches in half
•
Two daughter cells are formed with identical genetic information.
•
Cell cycle starts all over again!
WHAT HAPPENS IF CELLS MULTIPLY UNCONTROLLABLY?
CANCER! = uncontrolled cell growth leading to masses of cells called tumors