IN THIS PROJECT, YOU WILL BE ABLE TO: Explain cell division, growth, and development as a consequence of an increase in cell number, cell size, and/or cell products. Explain that complex interactions among the different kinds of molecules in the cell cause distinct cycles of activities, such as growth and division. Explain that gene mutation in a cell can result in uncontrolled cell division called cancer. Also know that exposure of cells to certain chemicals and radiation increases mutations and thus increases the chance of cancer.

Watch this video on the cell cycle if you need more help: The cell cycle is the sequence of events that takes place in a cell that leads to cell division. THE CELL CYCLE Watch this video on the cell cycle if you need more help: https://www.dropbox.com/s/u83r5fhqs4mdqz7/cell-cycle-an-animation.mp4

THE CELL CYCLE The cell cycle has 4 main purposes. Cell Growth Interphase Chromosome Replication Preparation for Division Cell Division Mitosis

CELL CYCLE PHASES It consists of four major phases and three major checkpoints. G1 - Phase G1 - Checkpoint S-Phase G2 - Phase G2 - Checkpoint Mitosis M - Checkpoint Cell Growth Chromosome Replication Mitosis Preparation Cell Division

CHECKPOINTS Checkpoints occur 3 times during the cell cycle. They are ESSENTIAL to cell replication!! During these checkpoints the “supervisor” proteins called Cyclin Dependent Kinases (CDKs) check through the cells for problems or mistakes.

CYCLIN DEPENDENT KINASES If the CDKs find a problem it is also their job to fix it. These problems can be mutations, lack of growth, poor replication, etc. The proteins can do any number of things to fix the problems... IF they do NOT fix them, horrible things can happen. Missing Limbs Down syndrome Muscular Dystrophy Cancer Tumors Many more...

G1 PHASE & CHECKPOINT G1 - Phase G1 - Checkpoint Cells do most of their growing during this phase. The cells increase in size and synthesize new proteins and organelles (golgi apparatus, ribosomes, etc). G1 - Checkpoint During this checkpoint the CDKs are checking to make sure that the cell is the right size in order to continue on through the cell cycle.

The S-phase follows the G1-phase Chromosomes are replicated and DNA synthesis takes place. This creates and second set of DNA so the cell now contains 92 chromosomes instead of 46. Key proteins associated with the chromosomes are also synthesized

G2 PHASE G2 - Phase G2 - Checkpoint The rest of the proteins and organelles are duplicated. REMEMBER you are building the necessary components for a second cell to be built. This means you must have two of everything!! G2 - Checkpoint Now that everything has been duplicated, the checkpoint makes sure all the organelles and DNA have been duplicated correctly.

M PHASE The M phase, or mitosis, has 4 phases: prophase metaphase anaphase telophase Depending on the type of cell, the four phases of mitosis may last anywhere from a few minutes to several days

M-PHASE CHECKPOINT After the chromosomes are aligned along the equatorial plate/center line there is another checkpoint. This checkpoint looks for the separation of the chromosomes and organelles. It makes sure that one of everything is on either side of the cell so that when it the two new cells are created and separated, each has a single copy.

REGULATING THE CELL CYCLE One of the most amazing aspects of cell behavior is how carefully cell growth and cell division are controlled. Not all cells move through the cell cycle at the same rate. In the human body, most muscle cells and nerve cells do not divide at all once they have developed. On the other hand, the cells of the skin and digestive tract grow and divide often and rapidly throughout life.

CONTROLS ON CELL DIVISION Typically, cells continue to grow until they come in contact with other cells. When they hit other cells they stop growing. Scientists have placed cells within a petri dish and adding nutrient broth, which feeds the cells. The cells will grow until they form a thin layer covering the bottom of the dish.

CONTROLS ON CELL DIVISION If cells are removed from the center of the dish, the cells bordering the open space will begin dividing until they have filled the empty space. This shows that the controls of cell division can be turned on and off. This also happens within the human body! Think of an injury like a cut to the skin or a broken bone. Cells at the edges of the injury are stimulated to divide rapidly, which produces new cells and starts the healing process. The rate of cell division slows and the controls of growth are restored when everything returns to normal.

CELL CYCLE REGULATORS In the early 1980’s, biologists found a substance that would “tell” cells when it was time to divide, duplicate their chromosomes, or enter another phase of the cycle. Cells in mitosis contain a protein that when injected into a nondividing cell, would cause a mitotic spindle to form. They named it cyclin, because it seemed to regulate the cell cycle. There are two types of regulatory proteins: those that occur inside the cell and those that occur outside the cell.

INTERNAL REGULATORS Internal regulators- proteins that respond to events inside the cell. These allow the cell cycle to proceed only when certain processes have happened inside the cell. Examples: Several regulatory proteins make sure that a cell does not enter mitosis until all its chromosomes have been replicated. Other regulatory proteins prevent a cell from entering anaphase until all its chromosomes are attached to the mitotic spindle.

EXTERNAL REGULATORS External regulators- proteins that respond to events outside the cell and direct cells to speed up or slow down the cell cycle. Growth factors : They stimulate the growth and division of cells, and are very important during embryonic development and wound healing. These signals prevent excessive cell growth and keep the tissues of the body from disrupting on another.

UNCONTROLLED CELL GROWTH Cell growth is regulated so carefully because the consequences of uncontrolled cell growth in multicellular organisms is very severe. Cancer is an example in which the body’s own cells lose the ability to control growth. Cancer cells do not respond to the signals that regulate the growth of most cells. Watch this video to see the difference between normal cells and cancer cells: https://www.dropbox.com/s/yx4r1bgosvnnvh2/control-of-cell- division.mp4