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

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

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

4. 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

5. Dividing cells… What has to be copied DNA organelles cell membrane
lots of other molecules
enzymes
plant cell
animal cell

6. 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

7. Paired bases DNA structure Bases match together double helix
2 sides like a ladder
Bases match together
A pairs with T
A : T
C pairs with G
C : G
phosphate
sugar
N base

8. Copying DNA
Matching bases allows DNA to be easily copied

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

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

11. DNA replication Enzyme DNA polymerase adds new bases
DNA bases in nucleus
Enzyme
DNA polymerase
adds new bases
DNA
polymerase

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

13. New copies of DNA Get 2 exact copies of DNA to split between new cells
polymerase
DNA
polymerase

14. Copied & Paired Up Chromosomes
centromere

15. Copying & packaging DNA
When cell is ready to divide…
copy DNA first, 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

16. double-stranded human chromosomes
ready for mitosis

17. 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

18. Mitosis: Dividing DNA & cells
Stage 1: cell copies DNA
Copy DNA!
DNA
cell
nucleus
(interphase)

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

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

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

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

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

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

25. Mitosis in whitefish embryo

26. Mitosis in plant cell

27. onion root tip

28. 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

29. Any Questions??