Chapter 3 Cell Division 3 1 Cell division

Chapter 3: Cell Division 3. 1 Cell division occurs in all organisms 3. 2 Cell division is part of the cell cycle 3. 3 Both sexual and asexual reproduction involve cell division Before, you learned: Now, you will learn: Cells come from other cells How genetic material is organized in Cells take in and release energycells and materials About the functions of cell division In a multicellular organism, in multicellular organisms some cells specialize

Cell division n Occurs in all organisms, but performs different functions: Unicellular organisms reproduce through cell division n Multicellular organisms division is involved in: n Growth, development, repair n While cells themselves grow, organisms grow through cells dividing and producing new cells n

n http: //www. cancerquest. org/cancer-celldivision

Cell division occurs in all organisms n n Tissue culture is a method of biological research in which small samples of plant or animal tissues are transferred to a flask or dish in which they can continue to survive. Human tissue cultures are often grown as single layers of cells in a glass or plastic dish. Normal cells grow until a single layer of cells just touching each other covers the surface. When this occurs, cell division stops, a phenomenon known as contact inhibition. Cancer cells, however, do not display contact inhibition. After a single layer of cells is formed, cancer cells continue to divide, piling into mounds. One strain of cancer cells known as He. La cells has been continuously cultured since its isolation in 1951 from Henrietta Lacks, a patient who died of cervical cancer. Unlike normal cells, which eventually die, many cancer cells continue to divide.

animation n 1. In the human body, a group of cancer cells can form a mass of abnormal cells called a tumor. How is the loss of contact inhibition related to tumor formation 2. How are He. La cells different from normal cells? 3. Scientists often use tissue culture to test new drugs or to examine the effects of suspected cancer-causing chemicals. List possible advantages and disadvantages of using cultured cells instead of using humans.

n n n 1. The lack of contact inhibition in cancer cells enables these cells to continue to divide, which can result in the formation of a tumor. 2. He. La cells are cancer cells that will continue to divide. Normal cells will eventually stop dividing and die. 3. A possible advantage is that tissue culture can enable scientists to test new drugs or possible cancer-causing chemicals without the risk of causing injury or death to humans. Also, tissue culture probably costs less and is faster. A possible disadvantage might be that the use of tissue culture testing cannot reveal possible side effects within the body, nor can it examine how the rest of the human body would respond to the drug or chemical being tested.

n n Genetic Material of a Cell Contains information for cell growth Most contained in Deoxyribonucleic acid: DNA – a chemical n n Contains info for growth and functions Double helix: two strands of molecules

DNA • Everything the cells do is coded somehow in DNA • which cells should grow and when • which cells should die and when • which cells should make hair and what color it should be • Our DNA is inherited from our parents • We resemble our parents simply because our bodies were formed using DNA to guide the process the DNA we inherited from them.

Chromosomes n n DNA typically exists as a mass of loose strands DNA is duplicated (copied) n n n Becomes wrapped around proteins Compacted into chromosomes Chromosomes consist of two identical structures: chromatids: held together at center by centromere

Chromosomes n Species specific: Pattern and number of chromosomes formed is the same everytime a cell divides n Humans: 46 chromosomes n Fruit flies: 8; Corn: 20 n n Relationship of DNA and chromosomes?

Chromosomes n Answer: Chromosomes consist of compacted DNA

1. The four letters All genetic code is spelled out with just four chemical letters, or bases: adenine (A), thymine (T), cytosine (C) and guanine (G). These pair up, A with T and C with G. The human genome has between 2. 8 and 3. 5 billion base pairs. 2. DNA double helix The base pairs form the rungs of the 3. Genes ladder-like DNA double helix. Running up and down the ladder are the long As little as 3% of the total genome issequences of bases which are the code for made of genes - the rest is life. Each cell in the human body contains meaningless "junk". Genes are two metres (six feet) of DNA. special sequences of hundreds or thousands of base pairs that provide the templates for all the proteins which the body needs to produce.

6. Body 5. Nucleus and Cell The 46 chromosomes are held in the nucleus found in most cells in the human body. Nearly every cell in the body contains the full DNA code for producing a human. 4. Chromosomes The total number of genes is not known - estimates range from 30, 000 to 120, 000. However many there are, they, and all the junk DNA, are wrapped up into bundles called chromosomes. Every human has 23 pairs of chromosomes, one set from each parent. Each of the cells becomes specialised by obeying just some of the instructions in the DNA. Blood, muscle, bone, organs and so on result. The body is built from 100 trillion of these cells.

n n n 1. The four letters (A-T, C-G) 2. DNA double helix 3. Genes 4. Chromosomes 5. Nucleus and Cell 6. Body

Summary of DNA (from book) 1. 2. 3. 4. 5. DNA is the genetic material of a cell The DNA wraps around proteins A chromosome consists of two chromatids held together by a centromere Before a cell divides, the DNA becomes compacted into chromatids The nucleus is where DNA in all its forms is located

Cell Division in Multicellular Organisms n n n Essential for? Growth, development, repair A single cell becomes? Two cells Damaged cells replaced by healthy cells

Cell Division n Growth n Individual cells grow, but this is limited Due to surface to volume ratio (chapter 2) n As the cell grows, more processes are needed to function – demand for instructions from DNA increase, but amount of DNA remains constant n n n Number of cells increase through division Development n Cell division AND specialization n Same genetic material

Cell Division n Repair Cut skin? Skin cells make new cells to heal the wound n Cells age and die n n Some quicker than others Lose ~40, 000 skin cells per minute! n Brain cells live a long time n