CELLULAR REPRODUCTION

 Students know and understand the characteristics and structure of living things, the processes of life, and how living things interact with each other and their environment.  Benchmark 3.10: Cell reproduction/division has various processes and purposes (mitosis, meiosis, binary fission)  Assessment objective 3.10a: Compare and contrast the purposes and processes of mitosis, meiosis, and binary fission.

 It was once thought that some nonliving things could give rise spontaneously to living things.  Aristotle ( ) and others believed that living organisms could develop from non-living materials. Aristotle  1688: Francesco Redi ( ) was an Italian physician who refuted the idea of spontaneous generation by showing that rotting meat carefully kept from flies will not spontaneously produce maggots.Francesco Redi  1861: Louis Pasteur's ( ) famous experiments with swan-necked flasks finally proved that microorganisms do not arise by spontaneous generation.Louis Pasteur's

 Cell reproduction occurs when parent cells divide.  Cells divide rather than grow really big because as the volume of cytoplasm increases, the surface area of the plasma membrane can’t keep up and eventually the cell would either starve from lack of nutrients or poison itself because of excess wastes.  Cells stop growing or reproduce before either of those things happens.

 A cell’s activity is regulated by DNA which is organized into hereditary units called genes.  The genes code for RNA and protein.  DNA is organized and packaged into structures called chromosomes.  Prokaryotic cells have a single circular molecule of DNA. What is a prokaryotic cell?  Eukaryotic cells have many more genes. A human cell contains 46 separate, linear DNA molecules that are packaged into 46 chromosomes.

 DNA and proteins make up a substance called chromatin.  The first level of DNA packaging is done by 8 histones (proteins) that come together to form a histone core.  The structure made up of a histone core and the DNA around it is called a nucleosome.  Chromosomes exist as coiled or uncoiled nucleosomes. As the cell prepares to divide, the chromosomes condense even further so that the DNA molecules don’t get tangled up.

 Chromosomes are made up of two thick strands, called a chromatid, made up of a single DNA molecule.  Identical pairs, called sister chromatid are held together in the middle by a centromere.  During cell division, the sisters are separated at the centromere, then each ends up in a daughter cell, that way each cell has the same genetic material. Chromatin, chromosomes and DNA subunits. 3:45 DNA SONG!!!!

 Three types of cell division  Prokaryotic is binary fission—the DNA molecule is attached to the inner cell membrane. It builds a cell membrane between the two copies of DNA while a new cell wall forms around the membrane, squeezing the cell and pinching off two daughter cells.  Mitosis and Meiosis are eukaryotic and more complex.

 Interphase and Mitosis make up the cell cycle.  Interphase is the non- reproducing phase of cell life.  Mitosis is the reproductive phase of a cell’s life.  Most of the cell’s life is spent in interphase.

 Interphase is the cell’s non-reproducing stage.  Cells spend most of their life in this phase.  During interphase, each chromosome and the DNA it contains makes exact copies.  Mitosis follows interphase.  Cell song (mitosis) Cell song (mitosis)

 The chromatin in the nucleus starts forming loops and condensing, growing shorter and thicker.  In animal cells, the two pairs of centrioles begin to separate and migrate to opposite poles of the cell.  Microtubules form between the two pairs of centrioles and form a football-shaped structure called a spindle.  All eukaryotic cells have spindles.

 The nuclear membrane disappears.  Chromosomes are double-stranded structures which shows that replication has occurred.  Each strand is a replica of the other and called a chromatid.  Two chromatids of a chromosome are called sister chromatids and are joined in the middle by a centromere.

 Chromosomes are scattered randomly in the area where the nucleus was.  They then move toward the spindle’s equator when the microtubules attached to each centromere change in length.

 The centromeres split and the two sister chromatids of each chromosome begin to separate from one another and move apart.

 The overlapping microtubules from each pole join and begin to lengthen as proteins are added.  The poles are pushed apart, and sister chromatids are pulled to opposite poles of the cell.  Each end of the cell has one set of single- stranded chromosomes.

 In animals, two cells are formed from the one as the cell begins to pinch together at the center and the microfilaments attached to the membrane contracts.  In cell walls (plants), a cell plate grows outward from the middle of the cell.  A nuclear envelope forms around the chromosomes at each pole of the cell. The chromosomes uncoil and change back to their original chromatin form.  The spindle dissolves and mitosis is complete.

 Cytokinesis follows the end of mitosis. After telophase, the process reverses and nucleoli reappear. The 2 nuclear membranes enclose each set of chromosomes.  The chromosomes become a mass of chromatin.  The cytoplasm is separated and two cells called daughter cells are formed.  Each daughter cell is about half the size of the original cell and have the same genetic material.  Both then enter the G 1 stage of interphase. Daughter cells

 Cell division is highly controlled by signals from proteins and other environmental signals.  Proteins control the phases of the cell cycle.  Proteins and other organs control cell growth and division.  Environmental conditions such as nutrient availability affect the cell cycle.

 G 1 : Cell checks surroundings to determine if conditions are favorable and the cell is healthy and large enough. If so, it enters the synthesis phase.  G 2 : Before mitosis, cell checks for any mistakes in the copied DNA. Enzymes correct mistakes. Proteins also check to see if the cell is large enough. Once everything checks out, the cell undergoes mitosis.  Mitosis: During metaphase, cell checks to make sure chromosomes are properly attached to spindle fibers to ensure equal distribution of genetic material to the daughter cells.

 Cancer is a group of severe and sometimes fatal diseases caused by uncontrolled cell growth.  Uncontrolled cell growth and division can result in masses of cells that invade and destroy healthy tissues.  DNA can cause the cell to respond improperly or to stop responding. If the cell cycle is not controlled, the defective cell divides to produce more defective cells that can eventually form a mass called a tumor.  Mitosis in cancer: 0:28 Mitosis in cancer: 0:28

 Benign tumors do not spread to other parts of the body and can often be removed by surgery.  A malignant tumor can spread through the body in a process called metastasis (1:00). metastasis (1:00)  Some cancers are treated with drugs in a procedure called chemotherapy as well as surgery or radiation therapy.  The best way to prevent cancer is to avoid things that can cause it such as ultraviolet light or chemicals found in products such as cigarettes.