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Biology is the only subject in which multiplication is the same thing as division… Regents Biology 2006-2007 MITOSIS: Making New Cells Making New DNA Regents Biology Where it all began… You started as a cell smaller than a period at the end of a sentence… Regents Biology Getting from there to here… Going from egg to baby…. the original fertilized egg has to divide… and divide… and divide… and divide… Regents Biology Why do cells divide… One-celled organisms for reproduction asexual reproduction (clones) amoeba Multi-celled organisms for growth & development from fertilized egg to adult for repair & replacement replace cells that die from normal wear & tear or from injury Regents Biology starfish Dividing cells… What has to be copied DNA organelles cell membrane lots of other molecules enzymes Regents Biology 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 Regents Biology 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 chromosomes in everyday “working” cell cell nucleus 4 chromosomes in thisBiology organism Regents DNA in chromosomes in cell getting ready to divide Chromosomes of Human Female 46 chromosomes 23 pairs Regents Biology Chromosomes of Human Male 46 chromosomes 23 pairs Regents Biology Paired bases DNA structure double helix 2 sides like a ladder Bases match together A pairs with T A:T C pairs with G C:G Regents Biology phosphate sugar N base Watson and Crick Regents Biology Copying DNA Matching bases allows DNA to be easily copied Regents Biology Making new DNA Copying DNA replication DNA starts as a double-stranded molecule matching bases (A:T, C:G) then it unzips… Regents Biology DNA replication Strands “unzip” at the weak bonds between bases Regents Biology DNA replication DNA bases in nucleus Enzyme DNA polymerase adds new bases DNA polymerase Regents Biology Copying DNA Build daughter DNA strand use original parent strand as “template” add new matching bases synthesis enzyme = DNA polymerase DNA Polymerase Regents Biology New copies of DNA Get 2 exact copies of DNA to split between new cells DNA polymerase DNA polymerase Regents Biology Copied & Paired Up Chromosomes centromere Regents Biology Copying & packaging DNA When cell is ready to divide… copy DNA first, then… coil up doubled chromosomes like thread on a spool… now can move DNA around cell without having it tangle & break Regents Biology Copying DNA Coil DNA into compact chromosomes double-stranded human chromosomes ready for mitosis Regents Biology DNA must be duplicated… chromosomes in cell DNA in chromosomes cell nucleus 4 single-stranded chromosomes duplicated chromosomes duplicated chromosomes Biology chromosomes 4Regents double-stranded cell nucleus Mitosis: Dividing DNA & cells Stage 1: cell copies DNA Copy DNA! DNA cell nucleus Regents Biology (interphase) Mitosis: Dividing DNA & cells Stage 2: DNA winds into chromosomes DNA is wound up into chromosomes to keep it organized duplicated chromosomes Wind up! cell nucleus Regents Biology (prophase) Mitosis: Dividing DNA & cells Stage 3: 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 Regents Biology (metaphase) Mitosis: Dividing DNA & cells Stage 4: Chromosomes separate chromosomes split, separating pairs start moving to opposite ends Separate! chromosomes split & move to opposite ends Regents Biology (anaphase) Mitosis: Dividing DNA & cells Stage 5: Cell starts to divide cells start to divide nucleus forms again Divide! Regents Biology (telophase) Mitosis: Dividing DNA & cells Stage 6: DNA unwinds again cells separate now they can do their every day jobs Bye Bye! Regents Biology (cytokinesis) New “daughter” cells Get 2 exact copies of original cells same DNA “clones” Regents Biology Cell division in Animals Regents Biology Mitosis in whitefish embryo Regents Biology Mitosis in plant cell Regents Biology onion root tip Regents Biology Overview of mitosis interphase I.P.M.A.T.C. prophase Please Make Another Two Cells cytokinesis Regents Biology metaphase anaphase telophase