Download DNA replication

DNA Structure and function
Journey into the cell
• Viruses – small
nonliving particle
that infects cells
• Not living because
it can not
reproduce without
infecting a host
cell.
• Made of a protein
head and genetic
material.
• Bacteriophage – virus
that infects and bacteria
(bacteria eater)
• Made up of DNA and a
protein coat.
• It injects it’s DNA into
into the bacteria cell.
• It tricks the bacteria
into thinking the viral
DNA is its own.
• Bacteria starts to make more viral DNA
and then the cell bursts.
• Hundreds of new viruses are released.
• A virus can take advantage because
DNA is the universal genetic code for all
living things.
• Viruses are usually specific in what cells
they attack.
• For example, bacteriophages attack
bacteria cells.
• Hepatitis is a
disease in which a
virus attack liver
cells in humans.
• HIV attacks Thelper cells of the
immune system
Characteristic of DNA
1. carry information from one generation to the
next.
2.puts that information to work by determining
the inheritable characteristics of an organism.
3. has to be easily copied since all the DNA is
replicated each time a cell divides.
DNA Structure:
• DNA is a long molecule
made of nucleotides.
Nucleotide
1. 5-carbon sugar
(deoxyribose),
2. nitrogenous base,
3. and a phosphate group.
Build a DNA molecule
http://www.zerobio.com/drag_gr9/DNA/dna.htm
This is considered to be one
nucleotide:
1. One 5-carbon sugar (deoxyribose),
2. One of the four nitrogenous bases,
3. and a phosphate group.
Nucleotides
• Nucleotide repeat
over and over to
make up one huge
DNA molecule
The Double Helix
• The sides are
repeating units of
sugar and
phosphate.
• The sugar being
deoxyribose
• The rungs of the
ladder are the four
bases: A, T, G and C
• Remember GCAT
• G bonds with C and A
bonds with T
• Hydrogen bonds holds
together the bases
This is called base
pairing.
First to see DNA
Rosalind Franklin used X-ray diffraction to
take a picture in the 1950s.
• She was able to see 2 strands of DNA in a
helix shape.
Double Helix
Watson and Crick built
the 3D double helix
model of DNA that we
use today
• They saw Rosalind
Franklin’s x-ray photo
to help guide them
• It showed the twisted
ladder.
Watson and Crick
• DNA is found inside the nucleus of
most cells.
• It is found in the form of chromosomes.
• Every time a cell divides, DNA must
make a copy of itself so that each cell
has an equal amount of DNA
Chromosomes to DNA
• Prokaryotic Cells =Lack nucleus and many
organelles found in eukaryotes
• DNA is found in cytoplasm
• Plasmid: circular DNA segment
• Eukaryotic Cells = DNA
is found in nucleus in
the form of
chromosomes.
• Number of
chromosomes varies
from one organism to
another
• Humans have 46,
• fruit flies has 8
• 1000X more DNA than
prokaryotic cells: more
complex.
CHROMOSOME STRUCTURE
• DNA in Eukaryotes is packed tight.
• Nucleus contains more than 6 feet
of DNA.
• Eukaryotic chromosomes have both
DNA and proteins packed together
to form a substance called
chromatin
• Chromatins consist of DNA that is
tightly coiled around proteins
called histones.
• Histones = proteins that DNA wrap
around.
DNA
Section 12-2
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
Go to
Section:
DNA Replication
DNA replication:
Every time a cell divides, DNA must
make a copy of itself.
Reason: so every cell has an equal
amount of DNA
46 chromosomes in humans.
Replication – duplicating or copying the DNA
before the cell divides.
How is it done?
1. Start with an original strand of DNA
2. DNA unzips between the paired bases and
the DNA separates into 2 strands
The hydrogen bond breaks between them
A--T
3. Each separated strand gets copied to make
two new strands.
• The new strands are complimentary
because they are formed according to
base rules.
• G-C, A-T
• Complimentary strands of DNA have
opposite bases.
Process:
1. Original DNA strand: ATATGGGCCATTT
TATACCCGGTAAA
2. Original strand unzips: ATATGGGCCATTT
TATACCCGGTAAA
3. Complimentary strands are created
ATATGGGCCATTT
TATACCCG…..
ATATGGGCC……
TATACCCGGTAAA
• You do this one:
TACCCGGCCCTTT
ATGGGCCGGGAAA
• Each strand of the double helix serves as
a templatefor the new strand.
• Template: model for the new DNA strand
Section 12-2
DNA REPLICATION
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
Nitrogenous
bases
New strand
Go to
Section:
Original
strand
REPLICATION
http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animatio
ns/dna_replication.htm
http://www.johnkyrk.com/DNAreplication.html
DNA replication interactive
• http://www.pbs.org/wgbh/aso/tryit/dna/#
In your own words:
• How is DNA replicated?
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