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…

And now look at you… How did you get from there to here?

 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 DNA organelles organelles cell membrane cell membrane lots of other molecules lots of other molecules enzymesenzymes animal cellplant cell

Copying DNA  A dividing cell duplicates its DNA creates 2 copies of all DNA creates 2 copies of all DNA separates the 2 copies to opposite ends of the cell separates the 2 copies to opposite ends of the cell splits into 2 daughter cells 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”

The Problem (in eukaryotes)? If chromosomes (DNA molecules) were like pasta, which would be easier to pull apart into individual pieces A plate of tangled spaghetti Or a plate of macaroni? Eukaryotic DNA

Chromosomes of Human Female 46 chromosomes 23 pairs

Chromosomes of Human Male 46 chromosomes 23 pairs

Paired bases  DNA structure double helix double helix 2 sides like a ladder2 sides like a ladder  Bases match together A pairs with T A pairs with T A : TA : T C pairs with G C pairs with G C : GC : G phosphate sugarN base

Watson and Crick

Copying DNA  Matching bases allows DNA to be easily copied

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

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

DNA replication DNA polymerase  Enzyme DNA polymerase DNA polymerase adds new bases 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 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… copy DNA first, then… coil up doubled chromosomes like thread on a spool… coil up doubled chromosomes like thread on a spool… now can move DNA around cell without having it tangle & breaknow 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  Stage 1: cell copies DNA nucleus cell DNA Copy DNA! (interphase)

Mitosis: Dividing DNA & cells  Stage 2: DNA winds into chromosomes DNA is wound up into chromosomes to keep it organized DNA is wound up into chromosomes to keep it organized nucleus cell duplicated chromosomes Wind up! (prophase)

Mitosis: Dividing DNA & cells  Stage 3: Chromosomes line up chromosomes line up in middle chromosomes line up in middle attached to protein “cables” that will help them move attached to protein “cables” that will help them move duplicated chromosomes lined up in middle of cell Line up! (metaphase)

Mitosis: Dividing DNA & cells  Stage 4: Chromosomes separate chromosomes split, separating pairs chromosomes split, separating pairs start moving to opposite ends start moving to opposite ends chromosomes split & move to opposite ends Separate! (anaphase)

Mitosis: Dividing DNA & cells  Stage 5: Cell starts to divide cells start to divide cells start to divide nucleus forms again nucleus forms again Divide! (telophase)

Mitosis: Dividing DNA & cells  Stage 6: DNA unwinds again cells separate cells separate now they can do their every day jobs now they can do their every day jobs Bye Bye! (cytokinesis)

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

Cell division in Animals

Mitosis in whitefish embryo

Mitosis in plant cell

onion root tip

Importance???  Growth  Replacement/Repair  Cancer  Regeneration of…

Cancer?  Unregulated mitosis  Benign  Malignant/ metastasis  How does it begin?

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

Any Questions??