Limits to Cell Growth ? Do cells grow larger to increase the size of the organism? NO!! Why? 1) DNA - cell parts rely on DNA for instructions - increase in size = more parts needing info * DNA has a limit on ability to send out instructions

2) Movement of Materials - increase in size = larger volume (inner space) less surface area (cell membrane) Therefore: - materials get crowded moving in/out of cell Example: 1cm x 1cm cell 3cm x 3cm cell Surface Area = 1cm x 1cm x 6 sides 3cm x 3cm x 6 = 6 cm2 = 54 cm2 Volume = 1cm x 1cm x 1cm 3cm x 3cm x 3cm = 1cm3 = 27 cm3 Ratio = 6 to 1 2 to 1

- Cell division increases the number of cells Solution - Cell division increases the number of cells which increases the organism’s size.

Biology is the only subject in which multiplication is the same thing as division… 2006-2007

MITOSIS: Making New Cells Making New DNA

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

And now look what can happen… 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…

Why do cells divide… One-celled organisms Multi-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 Unicellular organisms Cell division = reproduction Reproduces entire organism& increase population Multicellular organisms Cell division provides for growth & development in a multicellular organism that begins as a fertilized egg Also use cell division to repair & renew cells that die from normal wear & tear or accidents

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

Copying & packaging DNA When cell is ready to divide… copy DNA first, then… chromosomes COIL UP like thread on a spool… now can move DNA around cell without having it tangle & break Copying DNA Coil DNA into compact chromosomes

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

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

double-stranded human chromosomes ready for mitosis

Chromosomes of Human Female 23 pairs

Chromosomes of Human Male 23 pairs

Cell Cycle: Life Cycle of Cells Stage 1: cell copies DNA - period of growth & division of a cell DNA Interphase 3 Stages G1 phase- cell growth S phase- DNA replication G2 phase- new organelles cell nucleus

Cell Cycle

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

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

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

Mitosis: Dividing DNA & cells Stage 5: Cell starts to divide cells start to divide nucleus forms again Telophase - Animals - cell pinches in - Plants- cell plate forms

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

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

Cell division in Animals

Mitosis in whitefish embryo

Mitosis in plant cell

onion root tip

Please Make Another Two Cells I.P.M.A.T.C. Overview of mitosis interphase prophase Please Make Another Two Cells cytokinesis metaphase anaphase telophase

Any Questions??