1. MITOSIS: Making New Cells Making New DNA
The Cell Cycle
MITOSIS: Making New Cells Making New DNA

2. From one cell to many… Going from egg to organism…. and divide…
the original fertilized egg has to divide…
and divide…

3. 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

4. The Big Challenge Before division, a cell must make copies of
DNA
organelles
cell membrane
lots of other molecules
Enzymes
Each new daughter cell requires a complete set of genes.
Evenly divide these things between 2 new (daughter) cells

5. The Big Picture

6. Chromosomes of Human Female
23 pairs 6

7. 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
DNA starts loosely wound in the nucleus
If you tried to divide it like that, it could tangle & break

8. 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

9. 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

10. Some Chromosome Vocab Normal Cell Dividing Cell
duplicated
chromosomes
Chromatin – Loosely coiled DNA. Disorganized, but accessible to enzymes and proteins.
Centromere- region where chromatids are held together
Chromosome – made up of 2 sister chromatids. DNA has been replicated.

11. Paired bases DNA structure Complementary base pairing double helix
2 sides like a ladder
Complementary base pairing
A pairs with T
A : T
C pairs with G
C : G
phosphate
sugar
N base

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

13. DNA replication Copying DNA replication
DNA starts as a double-stranded molecule
matching bases (A:T, C:G)
then it unzips…
Helicase:
The unzipping
enzyme 13

14. DNA replication Enzyme DNA polymerase adds new bases
DNA bases in nucleus
Enzyme
DNA polymerase
adds new bases
DNA
polymerase 14

15. Copying DNA Build daughter DNA strand
use original parent strand as “template”
add new matching bases
synthesis enzyme = DNA polymerase
DNA
Polymerase 15

16. Copied & Paired Up Chromosomes
centromere

17. Copying DNA Semi-conservative
Each daughter strand is ½ original DNA, ½ new.

18. Copying DNA DNA Polymerase can only work in one direction: 5’  3’
Can only add new nucleotides onto the sugar end of previous one. 5’
Base 3’ 5’
Base 3’ 5’
Base 3’ 5’
Base

19. Copying DNA
Leading strand: synthesized in 5’  3’ direction (continuous synthesis)
Lagging strand: synthesized in 3’  5’ direction. (Okazaki fragments.)
DNA strands run in opposite directions – “anti-parallel”

20. 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 20

21. The Cell Cycle: the period from the beginning of one cell division to the beginning of the next cell division.
Interphase – between cell divisions. Most time of the cell cycle.
Produce materials for growth
Prepare for the next division
Mitosis
cell division

22. The Cell Cycle G0 phase: When cells are not dividing
Mature cells. Ex: nerve cell, liver cell
Can re-enter cell cycle if the correct signals are received.

23. Mitosis: Dividing DNA & cells
Stage 1: Prophase
DNA winds into chromosomes (keeps it organized)
Nuclear membrane breaks down
Spindle fibers form
cell
duplicated
chromosomes
nucleus

24. Mitosis: Dividing DNA & cells
Stage 2: Metaphase
chromosomes line up in middle
attached to spindle fibers that will help them move
duplicated chromosomes
lined up in middle of cell

25. Mitosis: Dividing DNA & cells
Stage 4: Anaphase
Spindle fibers shorten, Chromosomes separate
start moving to opposite ends
One complete set of cell’s DNA is now at each end of the cell.
chromosomes split & move to opposite ends

26. Mitosis: Dividing DNA & cells
Stage 5: Telophase
“reverse prophase”
Nuclear membrane forms
Chromosomes uncoil  chromatin
Mitotic spindle breaks down

27. Mitosis: Dividing DNA & cells
Stage 6: Cytokinesis
“cytoplasm splitting”
Membrane folds in at the center, forming a cleavage furrow
cells separate
now they can do their every day jobs
Identical Daughter Cells.

28. Mitosis & Cancer: When Making New Cells Goes Terribly Wrong!28

29. When is mitosis a good thing?
When you have to add or replace cells
growth & development
repair
replacement

30. When is mitosis a BAD thing
When cells reproduce & they are not needed
these cells take over organs, but don’t do the right job
they just keep making copies
cancer
damages organs

31. Control of the Cell Cycle
How does a healthy cell know when to divide?
Cyclins – proteins that regulate progression of a cell through the cell cycle.
Checkpoints – proteins detect problems at each step of the cell cycle. Initiate cell-cycle arrest if problems are detected
 DNA mutations, incorrect attachment of spindle fibers to centromere
Proto-oncogenes – Code for genes that initiate the cell cycle.
 Have the potential to become oncogenes: cancer-causing genes.
Tumor suppressor genes – code for proteins that arrest, monitor, or slow the cell cycle. 31

32. Control of the Cell Cycle
How does a healthy cell know when to divide?
Attachment requirement – cells must be able to attach to surrounding environment.
Space and nutrient requirements – cells will only divide when they have enough space and nutrition
Cancerous cells ignore these requirements 32

33. Control of the Cell Cycle
If DNA gets damaged, cells stop listening to correct instructions
mutations
Causes of mutations:
UV radiation
chemical exposure
radiation exposure
heat
cigarette smoke
pollution
age
Genetics
Viruses 33

34. Control of the Cell Cycle
Cells usually require an accumulation of several mutations before becoming cancerous
Mutations to proto-oncogenes
Become over-active
Mutations to tumor suppressor genes
Become inactive
This explains why cancer become more likely as a person gets older.
Genetic Predisposition: When a few mutations are inherited, it becomes more likely that cancer will develop. Fewer mutations still needed. 34

35. Tumors Benign tumor abnormal cells remain at original site as a lump
most do not cause serious problems & can be removed by surgery
Malignant tumor
cells leave original site
start more tumors
damage functions of organs throughout body 35

36. Treatments for cancers
Treatments kill rapidly dividing cells
chemotherapy
poisonous drugs that kill rapidly dividing cells
radiation
high energy beam kills rapidly dividing cells
localized 36