What is the purpose of DNA? Where is DNA located? What is the name of the cycle by which cells divide? Why do living things need new cells?

C ELL D IVISION TOPIC: W HY C ELLS D IVIDE

T HE C ELL C YCLE ESSENTIAL QUESTIONS: 1. Why are cells relatively small? 2. What are the primary stages of the cell cycle? 3. What are the stages of Interphase?

W HY C ELLS M AKE M ORE C ELLS 1. Most cells go through a series of changes in order to maintain homeostasis. 2. Cells need to reproduce (divide) when their surface area can no longer supply the much larger volume with nutrients and get rid of wastes. Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume

V OCABULARY 1.Chromatin: the relaxed, uncoiled state of the chromosome 2.Chromatid: one of two identical “sister” parts of a duplicated chromosome 3.Chromosome: threadlike structures within the nucleus containing genetic information that is passed on from generation to generation 4.Centromere: chromosome region that joins 2 sister chromatids A: centromere chromo─ color ─soma: body ─id: self, body centro─ center ─mere: part B: chromatids

C HROMOSOMES 1. Chromosomes: made up of DNA & proteins 2. Carry the cell’s coded genetic information 3. Different organisms have a different number of chromosomes Fruit flies have 8 chromosomes in each body cell Frogs have 26 chromosomes in each body cell Humans have 46 chromosomes in each body cell

C ELL C YCLE 1. Cell cycle: a sequence of events between the time a cell divides to form two daughter cells & the time those two cells divide to form two new cells. 2.Consists of Interphase and M-phase (Mitosis & Cytokinesis ) 3.G 0 ─ cells that exit the cell cycle

I NTERPHASE : 3 P HASES 1. G 1 phase: Growth Phase a. Cell performs all life’s activities: protein synthesis, waste removal, organelle synthesis, etc. 2. S phase: DNA Replication a. DNA makes a copy of itself b. Produces 2 identical sets of chromosomes 3. G 2 phase: Preparation a. Cell produces centrioles & spindle fibers needed to move the chromosomes DNA replicates in order to ensure that each daughter cell receives an identical copy of DNA

M ITOSIS D ISCOVERED Walther Flemming first discovered mitosis in 1870 and reported his discovery of chromosomes and mitosis in Metaphase in a salamander cell drawn by Walther Flemming from a stained slide.

M ITOSIS R EVIEW 1. Two main stages of the M-phase a. Mitosis: division of the nucleus b. Cytokinesis: division of the cytoplasm 2. Produces 2 cells called daughter cells a. Cells are genetically identical 3. Mitosis is source of new cells for a. Growth b. Development c. Repair d. Replacement of old cells 4. Cells that go through mitosis: skin, bone, muscle, liver 5. Cells that RARELY go through mitosis: nerve cells Normal red blood cells only live for 120 days. Then they die & stem cells make new ones.

M ITOSIS 1.Described as movement of chromosomes 2.Continuous series of events 3.Divided into four phases so that it is easier to understand Cell Cycle

4 Steps of Mitosis: 1.PROPHASE (nucleus breaks down and chromosomes condense) 2.METAPHASE (chromosomes find their homologous partner and line up in the middle of the cell).

3.ANAPHASE (homologous chromosomes are pulled apart in opposite directions – forming chromatids) 4.TELOPHASE (nucleus begins to reform around the chromatids to make 2 new daughter cells.) CYTOKINESIS (the cytoplasm pinches off and separates to form the 2 new daughter cells). This step happens at the same time as Telophase.

D IPLOID VERSES H APLOID Di─double Haplo─single -oid:like 23 Sperm cell 23 Egg cell 46 Fertilized Egg cell Fertilization Haploid: 1n; 1 set of chromosomes The egg and sperm cell are haploid Diploid: 2n; 2 sets of chromosomes The fertilized egg cell is diploid Develops into All of the cells that make up the organism are diploid Each kind of cell: Skin Muscle Bone Nerve Are ALL DIPLOID

C ELL C YCLE C ONTROL S YSTEM

E XTERNAL R EGULATIONS 1. Anchorage dependence – cells must be anchored (attached) to something before they will divide (extracellular matrix) 2. Contact inhibition – cells stop dividing when they touch each other  Caused by growth factors – proteins secreted by some cells that signal nearby cells to begin dividing

C ONTACT I NHIBITION

C HECKPOINTS this checkpoint makes the decision about whether the cell should divide and enter S some cells never pass this point and are said to be in G 0 this checkpoint leads to mitosis this checkpoint occurs during metaphase and triggers the exit process of the M phase and entry to the G 1 phase critical point where stop and go-ahead signal can regulate the cell cycle

C ANCER C ELLS ( UNCONTROLLED CELL G ROWTH ) 1. Do not respond to check points and continue rapidly through the cell cycle. This results in masses of undefined cells called tumors. 2. Do not mature, and do not enter into G Are effectively “Immortal” – they will divide indefinitely if supplied with proper nutrients (HeLa cells )

L UNG C ANCER

W HAT I S C ANCER ? There are two general classes of genes that are usually involved in cancer proto-oncogenes these genes encode proteins that stimulate cell division mutations to these genes can cause cells to divide excessively when mutated, these genes become oncogenes tumor-suppressor genes these genes normally turn off cell division in healthy cells when mutated, these genes allow uncontrolled cell division

D AMAGED G ENES – P 53 Cancer results from damaged genes failing to control cell division one such gene, p53, affects the G 1 checkpoint its normal action is to detect abnormal DNA it prevents cell division of a cell with damaged DNA until the DNA is repaired or directs the cell to be destroyed if the damage cannot be fixed if this gene itself becomes damaged, it will allow damaged cells to divide unchecked