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Biology is the only subject in which multiplication is the same thing as division … Lesson 14b: Mitosis

Making New Cells Making New DNA

Where it all began… You start as a cell smaller than a period at the end of a sentence… And end up as a full grown adult with billions of cells!

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

Why do cells divide… for reproduction – one celled organisms (clones) for growth & development – from fertilized egg to multi-celled organism for repair – replace cells that die or are lost amoeba

The Cell Cycle G1 = Resting and Growth S = DNA is replicated G2 = Growth & Prep for Mitosis M = Mitosis (cell division)

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

Remember this? When a cell is ready to divide it must… – copy DNA first (DNA Replication), then… – coil up doubled chromosomes like thread on a spool… now can move DNA around cell without having it tangle & break Copying DNA Coil DNA into compact chromosomes

Copied & Paired Up Chromosomes centromere Single DNA strand Single DNA strand being duplicated Two new DNA strands linked by centromere making one doubled chromosome.

Cell Prepares to Divide nucleus cell DNA in chromosomes nucleus cell duplicated chromosomes chromosomes are duplicated 4 single-stranded chromosomes 4 duplicated chromosomes Centromeres link chromosomes

Mitosis: Dividing DNA & Cells Stage 1: DNA Replication occurs. nucleus cell DNA DNA is copied! INTERPHASE

Mitosis: Dividing DNA & cells Stage 2: DNA winds into chromosomes nucleus cell duplicated chromosomes Chromosomes are condensed! PROPHASE

Mitosis: Dividing DNA & cells Stage 3: Chromosomes line up in middle – attached to protein spindle fibers that will pull them apart. Chromosomes are lined up! METAPHASE

Mitosis: Dividing DNA & cells Stage 4: Chromosomes separate – chromosomes split, separating the pairs – start moving to opposite ends (poles) Chromosomes are separated! ANAPHASE

Mitosis: Dividing DNA & cells Stage 5: Cytokinesis – cells start to divide – nucleus forms again Cells Divide! TELOPHASE

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

Mitosis in whitefish embryo

Mitosis in plant cell

onion root tip

Overview of mitosis

Any Questions?? Virtual Lab 8 Mitosis in Plant Cells Virtual Lab 9 Comparing Mitosis in Plant and Animal Cells Draw, label and explain mitosis as shown on pages in your text.