Biology is the only subject in which multiplication is the same thing as division…

MITOSIS: Making New Cells Making New DNA

Where it all began… You started as a cell smaller than a period at the end of a sentence…

Going from egg to baby…. the original fertilized egg has to divide… and divide… Getting from there to here…

Why do cells divide…  One-celled organisms  for reproduction  asexual reproduction (clones)  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 amoeba starfish

Dividing cells… What has to be copied – DNA – organelles – cell membrane – lots of other molecules enzymes animal cellplant cell

The Cell Cycle describes normal growth & division of cells Cells follow a set pattern of growth & division Time between divisions is called interphase and is divided into 3 stages – G1: growth of cell occurs – S: DNA replication occurs – G2: preparation for mitosis (cell division) occurs Cells then enter into mitosis and divide again

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  But the DNA starts loosely wound in the nucleus  If you tried to divide it like that, it could tangle & break nucleus cell DNA

Organizing & packaging DNA nucleus cell DNA nucleus cell 4 chromosomes in this organism DNA in chromosomes in everyday “working” cell DNA in chromosomes in cell getting ready to divide DNA has been “wound up”

Chromosomes of Human Female 46 chromosomes 23 pairs

Chromosomes of Human Male 46 chromosomes 23 pairs

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 phosphate sugarN base

Watson and Crick – discovered DNA

Making new DNA Copying DNA – replication – DNA starts as a double-stranded molecule matching bases (A:T, C:G) – then it unzips…

DNA replication Strands “unzip” at the weak bonds between bases

DNA replication DNA polymerase Enzyme – DNA polymerase – adds new bases DNA bases in nucleus

DNA Polymerase Copying DNA  Build daughter DNA strand  use original parent strand as “template”  add new matching bases  synthesis enzyme = DNA polymerase

New copies of DNA Get 2 exact copies of DNA to split between new cells – each made of one old strand & one new strand, called semiconservative replication DNA polymerase DNA polymerase

Copied & Paired Up Chromosomes centromere

Copying & packaging DNA Copying DNA Coil DNA into compact chromosomes When cell is ready to divide… – copy DNA first, then… – coil up doubled chromosomes like thread on a spool…the spools are proteins called histones now can move DNA around cell without having it tangle & break

double-stranded human chromosomes ready for mitosis

DNA must be duplicated… nucleus cell DNA in chromosomes nucleus cell duplicated chromosomes chromosomes in cell 4 single-stranded chromosomes duplicated chromosomes 4 double-stranded chromosomes

Mitosis: Dividing DNA & cells Interphase: cell copies DNA, organelles, grows in size & in animal cells centrioles appear nucleus cell DNA Copy DNA!

Mitosis: Dividing DNA & cells Prophase: DNA winds into chromosomes to keep it organized – centrioles move to opposite ends of animal cells – nuclear membrane disappears nucleus cell duplicated chromosomes Chromosomes Wind up!

Mitosis: Dividing DNA & cells Metaphase: Chromosomes line up in middle of cell – each chromosome is attached to spindle fiber from centriole that will help them move duplicated chromosomes lined up in middle of cell Chromosomes Line up!

Mitosis: Dividing DNA & cells Anaphase: Chromosomes separate – chromosomes split, separating pairs – start moving to opposite ends of cell chromosomes split & move to opposite ends Chromosomes Separate!

Mitosis: Dividing DNA & cells Telophase: Cell starts to divide – Chromosomes begin to uncoil – nucleus forms again – Cytokinesis begins to divide the two cells Cells Divide!

Mitosis: Dividing DNA & cells Cytokinesis: DNA is completely unwound again – cells separate – now they can do their every day jobs, return to interphase in cell cycle Time to Rest!

New “daughter” cells Get 2 exact copies of original cells – same DNA – “clones”

Cell division in Plants & Animals Cell Plate forms to separate the two cells & eventually becomes a cell wall

Mitosis in whitefish embryo

Mitosis in plant cell

onion root tip

Overview of mitosis interphaseprophase metaphaseanaphasetelophase cytokinesis I.P.M.A.T.C. P lease M ake A nother T wo C ells