Download DNA replication.

The
Cells
Life
of
Cycle
Cell Growth
• A cell is limited by its cell size
• The larger the cell the harder it is to move
through tissue and get nutrients
• In order to stay alive and not grow
continuously, the cell will divide
Reasons why to divide
• DNA
– Genetic information stored
– Found in the nucleus of the cell
– DNA would not be able to keep up with
demand of the cell
• Transport
– Rate decreases as the cell size increases
– Takes too long for nutrients and wastes to move
in and out of cell
Surface Area to Volume
• Surface Area
– Area on outside of cell where reactions can
occur
– As a cell increases, the surface area decreases
DNA Structure
• Monomer of DNA
is a nucleotide
– 5-carbon sugar
– Phosphorous group
– Nitrogenous base
• 4 Nitrogenous
bases in DNA
–
–
–
–
Adenine
Guanine
Thymine
Cytosine
DNA Structure
• Backbone of DNA is the
sugar and phosphate
• Nitrogenous bases stick out
of side to form latter rungs
– These bases are repeated
in a pattern that form our
genetic code
DNA Structure
• Chargaff’s Rule
– Scientist that discovered a peculiar trend
between the 4 bases
– Same percentage of Adenine as Thymine
– Same percentage of Guanine as Cytosine
• Scientists still not sure how they match up
though
DNA Structure
• Rosalind Franklin
– Scientist that worked with X-ray diffraction
– Used X-rays on a portion of DNA and the
results showed an X pattern
DNA Structure
• Watson & Crick
– Scientists that were
able to figure out what
Rosalind’s X-ray
pattern
– Result: DNA has a
double helix pattern
where the nitrogenous
bases face each other
DNA Structure
• DNA has a double helix pattern
– Looks like a ladder twisted up
• The sides of the ladder are the sugar
and phosphate and the rungs of the
ladder are the nitrogenous bases
paired up
• The adenine binds to thymine
• The guanine binds to cytosine
• This concluded Chargaffs’s rule 
base pairing
DNA and Chromosomes
• Prokaryotes
– Lack nucleus and organelles
– DNA floats as a circle in the
cytoplasm
• Eukaryotes
– 1000 times more DNA than
prokaryotes
– DNA is located in nucleus
– Specific number of
chromosomes
•
Ex: Humans have 46
chromosomes
DNA and Chromosomes
• DNA Length
– DNA is very long
– DNA is coiled up into a
very small space
because it is in
chromatin form
• Chromosome Structure
– Tightly packed
chromatin is wrapped
around small proteins
called histones
– When chromatin gets
super coiled you create
a chromosome
Chromosomes
•
•
•
•
Made up of our DNA
Holds genetic information
Tight coils or rod like structures
Organisms have a specific amount of
chromosomes.
– Humans have 46 chromosomes of DNA in
every somatic cell
Chromosome Structure
• Histones are proteins that DNA wraps around
to make the chromosome shape
• Chromosomes are made of two sister
chromatids
– Identical to each other
Chromosomes
• Centromeres are in the center of a chromosome
• Chromosomes are tightly coiled strings of DNA
called chromatin
• Chromatin is the string-like form of DNA
Chromosome Numbers
• A diploid cell contains 2 sets of each
chromosome
– Prefix di = 2
• A haploid cell contains only 1 set of each
chromosome
– Half of the total number
– Usually sex cells
Chromosome Numbers
• There is a specific number of chromosomes
in each organism
• Humans autosomes and sex chromosomes
• We have 2 sex chromosomes
– Either X or Y
• We also have 22 autosomes
– Which do not code for gender
Karyotype
•A karyotype is a lab picture of one
set of chromosomes
How Replication Occurs
• Enzymes help make new strands of DNA
– One enzyme “unzips” the DNA, separating the base pairs
– DNA polymerase adds new bases to pair up with the template
– This enzyme also proofreads to make sure everything matches
• What would be the matching bases to the part of DNA
shown below?
DNA Replication
• Each strand of DNA is
needed to be a template
for a new strand of DNA
to be produced
• Since you can use one
strand to make the other
side, they are said to be
complementary
Duplicating DNA
• Before mitosis occurs, DNA needs to be
duplicated first during interphase
• When DNA duplicates, its called
replication
• DNA molecules separates into two
strands, then produces two new
complementary strands following the
rules of base pairing
• Each strand serves as a template for the
new strand
Cell Division in Prokaryotes
• Prokaryotes
– No nucleus
– No organelles
– Ex: Bacteria
• Reproduction is VERY fast
– Copy DNA
– Split into two cells
• Cell division is called binary fission
Eukaryotic Cell Reproduction
• Eukaryotes
– Have a nucleus
– Have organelles
– Ex: Humans, plants
• Complex reproduction
– Everything needs to be controlled!
• Much longer process – about 18 hours!
Cell Reproduction
• A cell splits to make 2
identical copies
• If asexual reproduction
– Only 1 cell involved
• This occurs in 3 main stages
1. Interphase – Growth
2. Mitosis – Splitting of the cell
3. Cytokinesis – Splitting of the
cytoplasm
Interphase
• Cell growth
• 90% of cell’s life is
spent in interphase.
• 3 Part of Interphase:
–G1, S, G2
G1 Phase
• The cell is
growing
• The organelles
are doubling
S Phase
• Takes place when
cells are too big
• S = Synthesis of
DNA
• DNA is replicated so
there is a set for each
new cell
DNA replicates in Interphase so
the daughter cells exact copies of
the DNA
G2 Phase
• Cell growth again
• Replication of
organelles
• Last stage of
interphase
• Cell prepares for
cell division
•cell is not dividing
• cell is growing, performing
respiration, producing,
photosynthesizing, doing whatever
functions it is supposed to do
•At some point, the cell can’t
diffuse fast enough and that
signals the end of interphase
•At the very end of interphase, the
chromatin makes an exact copy of
itself in a process called DNA
replication.
How is DNA copied?
• Each cell has an protein called helicase
– Enzyme the unwinds the DNA making 2
identical strands
– http://www.youtube.com/watch?v=zdDkiRw1P
dU
Mitosis
• The part of a cell’s life cycle when
the cell divides it nuclear contents
into 2 nuclei which are identical
•Mitosis consists of 4 steps:
•Prophase
•Metaphase
•Anaphase
•Telophase
• all sub-cellular
organelles
disappear
• centrioles
separate and
move to opposite
poles
• chromatin
become
chromosomes
• centrioles shoot
off spindle
fibers (short
and long)
chromosomes
line up at the
equator
• centromere splits
•sister chromatids attach
to the short spindle fibers
•short spindle fibers
shorten and bring the sister
chromatids to opposite
poles.
• chromatids become
chromatin (one at each
pole)
• spindle disappears
• subcellular organelles
reappear
Cytokinesis
• Once mitosis has finished!
• Last stage of cellular reproduction
• This process is when the cytoplasm splits
apart
• There are now 2 identical cells
Cytokinesis in Plant Cells
• Cell plate forms at equator and grows out to
the cell wall
• Cell plate
Cytokinesis in Animal Cells
• Cell membrane pinches in at equator
• Cleavage furrow
Control of Cell
Division
• G1 Checkpoint
– Enzymes will kick in if cell is large enough and
conditions are favorable to reproduce
• G2 Checkpoint
– DNA repair enzymes will fix any mutations, if
checkpoint is passed mitosis will occur
• Mitosis checkpoint – if all is correct, the 2
daughter cells will enter G1 phase and start
over again
Uncontrolled
Mitosis
is
cancer.
When Control is Lost
• Enzyme proteins are not
functioning properly causing cell
to reproduce out of control
• Could cause cancer
• Cancer cells do not respond to
body’s signals that control
mechanisms
Compare/Contrast
How else can our body control
cancer?