The Cell Cycle
Is the process by which cells divide into 2 daughter cells
Cells do this to prevent from becoming to largeRecall…why don’t cells grow to be large?
Cell division
If a cell didn’t prepare before it divided, would it be able to survive?NO
Before a cell can divide it MUST:1. Make a copy of the DNA, this way each cell
can have a complete set2. Have extra of most organelles so that each
of the daughter cells will be functional
Preparation before division
Usually is stored in the form of chromatinChromatin carries all of an
organisms genetic informationAre unwound, non-visible strands
of DNA
Condenses to chromosomes/ chromatids before the cell dividesChromatids and chromosomes
are tightly wound up DNA that is visible
DNA
Before a cell divides, each chromosome is copied and when they condense into chromatids, there are 2 identical copiesThese are called Sister ChromatidsThe sister chromatids are connected together
by a centromere
Sister Chromatids
Is a series of events that a cell undergoes as it grows and divides
The four main steps are1. Growing2. Preparing for Dividing3. Dividing into 2 daughter cells4. Starting at step 1 again
The cell cycle
The 2 major phases of the cell cycle are1. Interphase—this is the period of growth
that a cell undergoes, the time when it is NOT dividingIt also prepares to divide during this time by
making a copy of the DNA2. Mitosis—this is the time when a cell is
actively dividingIt consists of 4 steps, plus cytokinesis
The cell cycle
The nuclear envelope breaks downChromatin condenses into the
chromosomes. Centrioles separate to opposite ends of
the cell.Mitotic spindle begins to form.
Mitosis Step 1 –Prophase
Chromosomes line up at the equator to the cell
The spindle fibers connect to the centromeres of each sister chromatid
Mitosis Step 2 –Metaphase
Centromeres joining the sister chromatids together split apart
The chromatids are pulled to opposite sides of the cell
Mitosis Step 3—Anaphase
Chromosomes begin to decondenseThe nuclear envelope reforms (this time there
is 2, one on each side)The spindle breaks apart
Mitosis Step 4 –Telophase
Means to divide the cell, so it is after mitosis and the cell splits into 2 independent cells
In animals, the cells suck in and then “pinch off”
In plants, a cell plate is formed that gradually turns into a new cell wall
Cytokinesis
Are a class of hormones that control the cells cycleThey decide when cells are to divide and when
the are NOT to divide
Cancer is considered UNCONTROLLED cell division and can lead to serious problems
Cyclins