DNA Replication 1 Interphase preforming normal functions and preparing for cell division a Gap 1 G1 you are born in this phase with 46 chromosomes Each of these chromosomes has 1 strand of DNA one double helix i Cells are small metabolically active and growing b Synthesize S this stage comes right after G1 this is where all DNA is synthesized meaning the helixes are copied duplicated i Copies of every chromosome in the cell are made 1 DNA is pulled apart and a polymerase is used to make complimentary strands 2 The double helix splits and creates new halves for each strand a There are now 2 identical DNA molecules ii At the end of this phase there are 46 duplicated chromosomes which can also be called a sister chromatids 1 A centromere is the center of the sister chromatids 2 A single sister chromatid is one half of the duplicated molecule iii This is all done in the nucleus c Gap 2 G2 2 Mitosis division of cell separates the duplicated chromosomes of a cell into two identical nuclei Occurs in the division of somatic cells a Prophase the first stage of Mitosis i The chromosomes coil tightly around histones and get rid of the nuclear envelope by disintegrating it ii An array of microtubules called spindle fibers form and attach to the kinetochores the protein bound area of the centromere iii Spindle fibers extend between centriole pairs and chromatids connect to the spindle fivers b Metaphase the second stage of Mitosis i The spindle fibers line the chromosomes up in the middle of the cell ii Chromatids become aligned c Anaphase the third stage of Mitosis i The spindle fibers pull the sister chromatids apart and bring them to opposite poles of the cell ii The spindle fibers then depolymerize iii Centromere of each chromatid pair splits d Telophase the last stage of Mitosis i Each new cell prepares to return to interphase ii The nuclear membranes reform the nuclei enlarge and the chromosomes gradually uncoil 3 Cytokinesis the division of the cytoplasm into two daughter cells This usually begins with the formation of a cleavage furrow and continues throughout telophase The completion of this marks the end of cell division 4 Parent Cell G1 S G2 P M A T daughter cells 5 G0 some cells go on hiatus and enter a G0 phase This is a form of suspended animation where the cells exit the circle of duplicating and dividing They aren t dead or frozen they just take a leave of absence This is a quiet phase 6 Check points there are checkpoints to make sure the cell did what it was supposed to do properly If it is flagged the cell goes back and fixes it before moving on to the next step a Normal healthy cells listen to these regulators and if they don t form properly they drop out of the cell cycle and die b Cancer forms when the cells don t listen to the regulators and keep going or when they lose control over their division process 7 Contact inhibition when cells form a full sheet and meet their perimeter they stop forming They make one small thin layer a Cuts i If you get a cut the skin grows back only where the cut was and not beyond that b Tumor can also be referred to as neoplasm i A mass of cells that have grown out of control and have lost contact c Benign tumor not cancerous they can become malignant though d Malignant tumor this is invasive and starts to spread to the next tissue and take inhibition over i Metastasize is when parts of the original tumor break off and enter the blood stream of another body system then a new tumor can form elsewhere in the body ii Angiogenesis you can stimulate nearby blood vessel to sprout new blood vessels to feed the tumor These can feed on the tumor at your expense the energy you are generating causes it to grow Malignant tissue is essentially immortal because it has its own supply and will not age or die it just keeps growing iii Malignant tumors can copy the full chromosome and the full length of the telomere which allows them to never die 8 Cell Age cells know how old they are a Telomeres allow the cell to know their age i Every time DNA is copied the telomere shortens 1 Once the telomere is gone the cell dies Epithelial Tissues 1 Definition Epithelial tissue covers or lines other tissues It is the lining of cavities organs skin etc The tissue sits on a layer of fibers called the basement membrane which is used to separate the epithelial tissue from the tissue beneath it which is almost always connective tissue The top of the epithelial cell is the apex which faces the lumen emptiness a Sits on the basement membrane has numerous cell to cell junctions has a high rate of mitosis has sparse blood supply and it lines the lumen of viscera organs 2 Junctions used to hold the cells together a Tight junction a really tight junction that causes cells to fuse together to make it impermeable This is used to protect i Membranes bound tightly together by transmembrane proteins isolates waste in the lumen prevents passage of water and solutes b Gap junction little pores that line up perfectly with other pores to create a tunnel between cells This is used for communication between the cells i These only occur on the side not the apex or base ii Cells that don t need to communicate don t have these iii Embryos have a ton of gap junctions iv Transport proteins connexons allow for the movement of ions from cell to cell coordinate contractions in heart muscle c Spot Desmosomes the tissues interlink like they are holding hands to form a strong junction between two cells i CAMs and proteoglycans link the plasma membranes allows bending and twisting d Hemidesmosome occurs at the base of an epithelial cells it is used to anchor the cell to the basement membrane i Attaches a cell to the extracellular filaments in the basal lamina stabilizes position and anchors to underlying tissue 3 Classifying epithelia describe them by their shape and number of layers a simple squamous epithelium one layer of cells that are wider than they are tall i convenient for places that need diffusion ii blood vessels capillaries allow gas exchange b simple cuboidal epithelium one layer of cells that are square i Too thick for diffusion not thick enough for wear and tear ii Great for ducts of a gland found in kidneys c simple columnar epithelium one layer of cells that are taller than they are wide i Used when something needs to be shipped out brought in ii Secretes or absorbs d stratified squamous epithelium many layers of cells that are wider than they are Ideal for wear and tear not good for