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