Chapter 10 – Cell Division

Limits to Cell Growth The bigger a cell gets The more nutrients it must bring in. More waste products must get out. It becomes very hard to move the material in and out of the cell.

Growing Cell

https://www.youtube.com/watch?v=1cVZBV9tD-A

Cell Division Process in which a cell divides into two new daughter cells. Happens before the cell gets too big. Before a cell can divide, it must first copy all of the DNA so each daughter cell can have a copy.

Chromosomes Made of DNA. The DNA carries the genetic information and proteins. Each type of organism has a specific number of chromosomes. Ex: humans: 46, carrots: 18, fruit flies: 8.

Can chromosomes split in 2? Can a human bone, muscle, or skin cell with 46 chromosomes split into 2 new chromosomes with 23 chromosomes each? Can a carrot cell split into 2 new cells with 9 chromosomes each? ABSOLUTELY NOT!!!!! Each new cell would only get ½ of the information it needs to survive.

Actual Process Before a cell can divide, information inside (DNA) must be copied Each new cell gets a full set of instructions.

Nuclear Material When a cell is not actively dividing, chromosomes are not visible under a microscope. What you would see is a mass of genetic material called chromatin. Once cell starts dividing, the chromatin organizes into chromosomes.

Chromatids When the chromosomes are copied, it consists of 2 chromatids. Each chromatid is one of two identical “sister” parts of a duplicated chromosome.

Centromere The part at which 2 chromatids are attached, usually near the middle.

Cell Cycle Series of events that cells go through as they grow and divide. The end result: 2 new daughter cells, which each begin a cell cycle of their own.

Interphase In-between period of growth. The cell is in the preparation stage to divide.

Mitosis 4 phases: prophase, metaphase, anaphase, telophase. These can take a few minutes, or a few days.

https://www.youtube.com/watch?v=b5JnwZbVezw

Cell growth Time Within the Same Organism Different types of cell within the same organism divide at different rates. Muscle and nerve cells don’t even divide. Skin cells and cells in the digestive system divide rapidly.

Controls on Cell Division Where there is a gap, cells will divide. Ex: cut or injury, which help in healing. When healing is complete, the cells divide more slowly.

Cell Cycle Regulators Certain proteins regulate when a cell needs to divide. These are called cyclins.

Internal regulator: proteins that respond to things happening inside the cell. The monitor the stages of cell division and either speed it up or slow it down. examples: several proteins check to make sure that all of the chromosomes have replicated before mitosis can occur. Another type stops anaphase until the spindle fibers have attached to the chromosomes.

External regulators: They respond to events outside of the cell External regulators: They respond to events outside of the cell. They direct the cell to speed up or slow down the cell cycle. Growth factors are important in embryonic development and wound healing. Some stop the cell from excessive growth. Others are found on the surface of neighbor cells which cause the cell to slow down or stop replicating to prevent excess growth and keeps body tissue from disrupting each other.

Mitosis going wrong

Cancer cells The cell loses the ability to control growth. They don’t respond to the signals that regulate the growth of most cells, so they keep dividing and form masses called tumors. Some of these cancer cells can break loose and spread to other parts of the body and disrupt the cells in the new area.

Causes of cancer Smoking tobacco, radiation exposure, viral infection.

Stem cells Cells in the body which can become any type of cell. Once it becomes a specific type it can’t be changed into any other type. They are found in developing embryos, some are in bone marrow. There is hope that stem cells can be used to reverse brain and spinal cord injuries in people.

Chapter Mystery PET SHOP ACCIDENT: An assistant in a pet shop accidently put a small and large salamander in the same tank. The large one bit off the limbs of the small one. The assistant put the small one in its own tank. She thought it would die, but instead, day by day something happened, which was amazing.

Question On a separate piece of paper, predict what happened to the small salamander, which lost its limbs. (Remember what we just learned).

Clue #1 As its wound heals, the salamander’s body cells are dividing to repair the damage. In what way is this type of cell division similar to asexual reproduction?

Clue #2 How would you expect the salamander’s wound to affect the cell cycle in the cells around the wound?

Clue #3 How might regulatory proteins be involved in wound healing in the salamander? (Internal, external, or both). (How do regulators ensure that some types of tissues do not grow faster than others?)

Clue #4 Some adult salamander cells never completely differentiate. What ability do these cells retain? (Tissues in a salamander’s limb include: bone, blood, and nerve).

ANSWER About a month after the accident, the salamander was growing a new limb. These animals are one of only a few vertebrates that can completely regenerate a complete limb).

How it works Week 1: Dedifferentiation: Cells such as muscle and nerve cells lose their characteristics that make them specialized. Week 2: These dedifferentiated cells migrate to the wounded area and form a blastema (growing mass of undifferentiated cells). Week 3: Redifferentiation: These cells then become specialized and form the type of cells needed to grow a new limb.

NGSS HS-LS1-4 HS-LS3-1 -LS1.A -LS1.B -LS3.A -LS3.B