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Biology is the only subject in which multiplication is the same thing as division… Making New DNA- Replication Making New Cells- Cell Cycle Where it all began… You started as a cell smaller than a period at the end of a sentence… And look at you now! How did you get from there to here?? Getting from there to here… • Going from egg to baby…. the original fertilized egg has to divide… and divide… and divide… and divide… Why do cells divide… • for reproduction – one celled organisms (clones) amoeba • for growth & development – from fertilized egg to multi-celled organism • for repair – replace cells that die from normal wear & tear or from injury starfish Dividing cells… • What has to be copied – DNA – organelles – cell membrane – lots of other molecules • enzymes plant cell animal cell Copying DNA • A dividing cell duplicates its DNA – creates 2 copies of all DNA – separates the 2 copies to opposite ends of the cell – splits into 2 daughter cells DNA cell nucleus But the DNA starts loosely wound in the nucleus If you tried to divide it like that, it could tangle & break Organizing & Packaging DNA DNA cell nucleus DNA has been “wound up” DNA in chromatin in everyday “working” cell cell nucleus 4 chromosomes in this organism DNA in chromosomes in cell getting ready to divide When is DNA replicated? Cell Cycle (Before Mitosis) • Interphase: cell copies DNA Copy DNA! DNA cell nucleus Overview of Cell Cycle interphase I.P.M.A.T.C prophase cytokinesis metaphase anaphase telophase Interphase • 90% of cell life cycle – cell doing its “everyday job” • produce RNA, synthesize proteins/enzymes – prepares for duplication if triggered I’m working here! Time to divide & multiply! Cell Cycle: Dividing DNA & Cells • INTERPHASE: cell copies DNA Copy DNA! DNA cell nucleus (interphase) Making new DNA • Copying DNA – replication – DNA starts as a double-stranded molecule • matching bases (A:T, C:G) – then it unzips… REPLICATION REPLICATION The process when DNA is copied. This results in 2 double stranded DNA molecules that are exact copies of each other. This has to occur before new cells can be formed in cell division (mitosis and meiosis). Replication Movie Steps of Replication 1. DNA strands separate. DNA Replication Strands “unzip” at the weak bonds between bases Steps of Replication 2.Free nucleotides base pair with strands. (A-T, C-G) Copying DNA Build daughter DNA strand use original parent strand as “template” add new matching bases DNA Polymerase Steps of Replication 3. 2 DNA molecules are formed. How many strands would that be? New copies of DNA Get 2 exact copies of DNA to split between new cells DNA polymerase DNA polymerase Why does Replication occur? To make NEW cells—every cell needs DNA to function. Cell Cycle/ Mitosis: Dividing DNA & Cells • PROPHASE: DNA winds into chromosomes – DNA is wound up into chromosomes to keep it organized Wind up! duplicated chromosomes cell nucleus (prophase) Cell Cycle/Mitosis: Dividing DNA & Cells • METAPHASE: Chromosomes line up – chromosomes line up in middle – attached to protein “cables” that will help them move Line up! duplicated chromosomes lined up in middle of cell (metaphase) Cell Cycle/Mitosis: Dividing DNA & Cells • ANAPHASE: Chromosomes separate – chromosomes split, separating pairs – start moving to opposite ends Separate! chromosomes split & move to opposite ends (anaphase) Cell Cycle/Mitosis: Dividing DNA & cells • TELOPHASE: Cell starts to divide – cells start to divide – nucleus forms again Divide! (telophase) Cell Cycle: Dividing DNA & Cells • CYTOKINESIS: DNA unwinds again – cells separate – now they can do their every day jobs Bye Bye! (cytokinesis) Cytokinesis differs in plant and animal cells. Animal cell Formation of cleavage furrow between new cells. Plant cell Formation of cell plate. New “daughter” Cells • Get 2 exact copies of original cells – same DNA – “clones” Mitosis in Whitefish Embryo Mitosis in Plant Cell onion root tip Cell Cycle Review Copy DNA Wind Up Bye-Bye! Line Up Separate Divide Any Questions?? Any Questions??