1. The Cell Cycle Lesson Objectives: Explain why cells need to divide.
List the stages of the cell cycle and explain what happens in each stage.
List the stages of Mitosis and explain what happens at each stage.

2. Quick Review What is the cell theory?
In what part of your cells is the genetic information located?

3. Vocabulary Sexual Reproduction Budding Mitosis Cell Cycle Mitosis
Parent cell
Prophase
Telophase

4. Asexual reproduction produces offspring that are identical to the parent.
Budding - a form of asexual reproduction in which a new organism grows on another one. The new organism remains attached as it grows, separating from the parent organism only when it is mature.
Mitosis – division of the nucleus
Sexual reproduction produces offspring that have genetic information from two parents.
Fertilization – sex cells if different organisms if the same species combine to produce a new organism.
Meiosis

5. Why Cells Divide
Think about humans. A sperm cell fertilizes and egg, which makes the first cell the forms a human.
How many cells is a human made up of?
Think about the cell theory…all cells must come from existing cells.
From the one initial fertilized cell, a baby will develop.
But how does this one cell turn into the trillions that make up a human?
The original cell divides into 2 cells. Then those 2 cells divide again giving a total of 4 cells. Then those 4 cells divide giving a total of eight cells, ect.

6. Embryo Division Diagram

7. Other Reasons Cell Division is Necessary
To grow and develop, people must form new cells.
Cell division is needed to repair damaged cells. (ie: when you skin your knee)
Cells wear out over time and must be replaced.

8. The Cell Cycle
The cell cycle is the life cycle of a cell, with cell division at the end of the cycle.
These steps can be divided into 3 main components:
Interphase- the 1st stage where the cell mostly performs is “everyday” functions.
Mitosis- the 2nd stage when the cell prepares to become 2 cells.
Cytokinesis- the 3rd stage when the cell actually divides into 2 separate cells.
The original cell is called the parent cell. Once the cell divides into 2 identical cell these cells are called daughter cells.

9. Phase 1 of the Cell Cycle - Interphase
Most of the cell cycle consists of interphase, the time between cell divisions.
Stage 1: Interphase (21 hours)
Interphase is the longest of the 3 stages of the Cell Cycle
Interphase is divided into 3 stages:
G1 (1st gap) – the cell doubles in size and doubles the number of organelles
S phase (synthesis) – the DNA is replicated (an identical copy of all the cell’s DNA is made)
G2 (2nd gap) – Proteins are synthesized that will help the cell divide.
The cell begins to grow & enlarge during all 3 stages of Interphase
At the end of interphase, the cell is ready to enter mitosis.

11. Phase 2 of the Cell Cycle - Mitosis
During mitosis, the nucleus of the cell divides.
2 nuclei must form so that when the cell divides into 2 daughter cells each cell has its own nucleus.
To begin mitosis, the DNA in the nucleus wraps around proteins to form chromosomes.
Different organisms have a unique number of chromosomes.
After the DNA is replicated during the S phase of Interphase, each chromosomes has 2 identical copies of DNA which are called sister chromatids.

12. Mitosis continued Stage 2: Mitosis (<50 minutes)
During Mitosis, 2 nuclei are created and 1 copy of the DNA created during Interphase is distributed to each of the nuclei.
This process is divided into 4 primary phases:
Phase 1: Prophase – the chromosomes condense so that you can see them under a microscope
Phase 2: Metaphase – the chromosomes line up in the MIDDLE of the cell.
Phase 3: Anaphase – the 2 sister chromatids of each chromosome separate (pull APART)
Phase 4: Telophase – the spindle dissolves and nuclear membranes form around the chromosomes.

13. http://www. google. com/imgres

15. Phase 3 of the Cell Cycle - Cytokinesis
Cytokinesis is when the cytoplasm of the cell divides, producing 2 separate cells.
Stage 3: Cytokinesis (< 15 minutes)
The cytoplasm divides.
The 1st sign of cleavage is the appearance of a cleavage furrow.
A cleavage furrow is shallow groove in the cell surface near the old metaphase plate.
2 new cell membranes form around the 2 new cells.
The new cells have an identical set of chromosomes and half of the organelles.

16. The Cell Cycle

17. Review
In what phase of mitosis are chromosomes moving towards opposite sides of the cell?
In what phase of mitosis do the duplicated chromosomes condense?
What stage of the cell cycle is the longest?
What is the term for the division of the cytoplasm?
What happens during the S stage of interphase?