Limits to Cell Growth Do cells grow larger

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: 1 cm x 1 cm cell 3 cm x 3 cm cell Surface Area = 1 cm x 6 sides = 6 cm 2 3 cm x 6 = 54 cm 2 Volume = Ratio = 1 cm x 1 cm = 1 cm 3 6 to 1 3 cm x 3 cm = 27 cm 3 2 to 1

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… Regents Biology 2006 -2007

MITOSIS: Making New Cells Making New DNA Regents Biology

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

And now look what can happen… Regents Biology 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… Regents Biology

Why do cells divide… § One-celled organisms 1. 2. for reproduction asexual reproduction (clones) amoeba § Multi-celled organisms 1. for growth & development § 2. from fertilized egg to adult for repair & replacement § Regents Biology replace cells that die from normal wear & tear or from injury starfish

Dividing cells… § What has to be copied DNA u organelles u cell membrane u lots of other molecules u § enzymes Regents Biology plant cell animal cell

Copying DNA § A dividing cell duplicates its DNA 1. 2. 3. 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

Copying & packaging DNA § When cell is ready to divide… 1. 2. copy DNA first, then… chromosomes COIL UP like thread on a spool… § Regents Biology now can move DNA around cell without having it tangle & break Copying DNA Coil DNA into compact chromosomes

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

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

double-stranded human chromosomes ready for mitosis Regents Biology

Chromosomes of Human Female 46 chromosomes 23 pairs Regents Biology

Chromosomes of Human Male 46 chromosomes 23 pairs Regents Biology

Cell Cycle: Life Cycle of Cells § Stage 1: cell copies DNA - period of growth & division of a cell DNA cell nucleus Regents Biology Interphase 3 Stages G 1 phase- cell growth S phase- DNA replication G 2 phase- new organelles

Cell Cycle

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

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

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

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

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

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

Any Questions? ? Regents Biology