Download Divide!

Biology is the only subject in
which multiplication is the
same thing as division…
Making New DNA- Replication
Making New Cells- Cell Cycle
Where it all began…
You started as a cell smaller than
a period at the end of a sentence…
And look at you now!
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…
and divide…
and divide…
Why do cells divide…
• for reproduction
– one celled organisms (clones)
amoeba
• for growth & development
– from fertilized egg to multi-celled organism
• for repair
– replace cells that die from
normal wear & tear or from injury
starfish
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
DNA
cell
nucleus
 But the DNA starts
loosely wound in the
nucleus
 If you tried to
divide it like that,
it could tangle &
break
Organizing & Packaging DNA
DNA
cell
nucleus
DNA has been
“wound up”
DNA in chromatin in
everyday “working” cell
cell
nucleus
4 chromosomes
in this organism
DNA in chromosomes in cell
getting ready to divide
When is DNA replicated?
Cell Cycle (Before Mitosis)
• Interphase: cell copies DNA
Copy DNA!
DNA
cell
nucleus
Overview of Cell Cycle
interphase
I.P.M.A.T.C
prophase
cytokinesis
metaphase
anaphase
telophase
Interphase
• 90% of cell life cycle
– cell doing its “everyday job”
• produce RNA, synthesize proteins/enzymes
– prepares for duplication if triggered
I’m working here!
Time to divide
& multiply!
Cell Cycle: Dividing DNA & Cells
• INTERPHASE: cell copies DNA
Copy DNA!
DNA
cell
nucleus
(interphase)
Making new DNA
• Copying DNA
– replication
– DNA starts as a double-stranded
molecule
• matching bases (A:T, C:G)
– then it unzips…
REPLICATION
REPLICATION
The process when DNA is copied. This
results in 2 double stranded DNA
molecules that are exact copies of each
other. This has to occur before new cells
can be formed in cell division (mitosis and
meiosis).
Replication Movie
Steps of Replication
1. DNA strands
separate.
DNA Replication
Strands “unzip” at the weak bonds
between bases
Steps of Replication
2.Free nucleotides
base pair with
strands.
(A-T, C-G)
Copying
DNA
 Build daughter DNA
strand
use original parent
strand as “template”
 add new matching
bases

DNA
Polymerase
Steps of Replication
3. 2 DNA molecules
are formed. How
many strands would
that be?
New copies of DNA
Get 2 exact copies of DNA to split
between new cells
DNA
polymerase
DNA
polymerase
Why does Replication occur?
To make NEW cells—every cell needs
DNA to function.
Cell Cycle/ Mitosis:
Dividing DNA & Cells
• PROPHASE: DNA winds into
chromosomes
– DNA is wound up into chromosomes to
keep it organized
Wind up!
duplicated chromosomes
cell
nucleus
(prophase)
Cell Cycle/Mitosis:
Dividing DNA & Cells
• METAPHASE: 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)
Cell Cycle/Mitosis:
Dividing DNA & Cells
• ANAPHASE: Chromosomes separate
– chromosomes split, separating pairs
– start moving to opposite ends
Separate!
chromosomes split &
move to opposite ends
(anaphase)
Cell Cycle/Mitosis:
Dividing DNA & cells
• TELOPHASE: Cell starts to divide
– cells start to divide
– nucleus forms again
Divide!
(telophase)
Cell Cycle: Dividing DNA & Cells
• CYTOKINESIS: DNA unwinds again
– cells separate
– now they can do their every day jobs
Bye Bye!
(cytokinesis)
Cytokinesis differs in plant and animal
cells.
Animal cell
Formation of cleavage
furrow between new cells.
Plant cell
Formation of cell plate.
New “daughter” Cells
• Get 2 exact copies of original cells
– same DNA
– “clones”
Mitosis in Whitefish Embryo
Mitosis in Plant Cell
onion root tip
Cell Cycle Review
Copy DNA
Wind Up
Bye-Bye!
Line Up
Separate
Divide
Any Questions??
Any Questions??