Please……
• Get out your notes from
yesterday
• Grab a sticky note from up front
• You’ll need a highlighter and
• Something to write with
The DNA Song
We love DNA made of nucleotides
Sugar, phosphate, nitrogen bases bonded
down each side
Oh!
Deoxribonucleic acid
RNA is ribonucleic acid
Adenine and Thymine make a perfect pair
Cytosine without guanine would feel very bare,
OI!!
Review of DNA
Review of DNA
The shape of a DNA strand is
called?
Double Helix
Review of DNA
What three parts make up a
nucleotide?
1. Nitrogenous base
2. Phosphate group
3. Simple sugar
Review of DNA
How many bases are there
and what are their names?
1.
2.
3.
4.
Adenine
Thymine
Guanine
Cytosine
Review of DNA
Which bases pair together?
1. Adenine &Thymine
2. Guanine&Cytosine
DNA Replication
Replication of DNA
• Before a cell can divide by
mitosis or meiosis, it must first
make a copy of its
chromosomes.
• The process of copying DNA is
called DNA replication.
Replication of DNA
• DNA replication
occurs during the
S Phase of
Interphase prior
to mitosis and
meiosis.
Replication of DNA
• During replication, each
strand serves as a pattern,
or template, to make a
new DNA molecule.
• Each parent strand
remains intact.
• Each new DNA molecule is
half old and half new.
There are 3
major steps
to DNA
Replication
Step 1 of DNA Replication
1. Before the DNA can
be copied, the DNA
helix must be
unwound. This
process is done by
an enzyme called
DNA helicase.
Step 1 of DNA Replication
•
•
DNA Helicase
breaks the
Hydrogen bonds
which “unzips” the
DNA.
The place where the
2 strands are
separated is call the
replication fork.
Step 2 of DNA Replication
At the replication
fork, enzymes called
DNA Polymerase
moves along each
strand of DNA and adds
complimentary bases.
• This continues until
the entire molecule
has been unzipped
and replicated.
2.
Step 3 of DNA Replication
3. Once the DNA
polymerase has copied the
entire DNA strand, they
detach. Each of the two DNA
strands has 2 parts. The
original half and the new
half.
Result?
• Each new strand formed is a
complement of one of the original
(parent) strands.
• This results in two DNA molecules that
are identical to the original.
• This occurs for ALL chromosomes.
What about Errors?
• Our DNA is continuously
checked for errors by the DNA
Polymerase.
Replication
of DNA
Prokaryotes vs. Eukaryotes
• Prokaryotes
– Have circular DNA. A
prokaryotes DNA is much
smaller than ours, and takes
much less time to replicate.
Because of this, prokaryotes
will have 2 replication forks,
one on each side of the
circle. When replication is
complete, the replication
forks will meet up with each
other
Prokaryotes vs. Eukaryotes
• Eukaryotes
– DNA is in one long strand. In order to
get all of this copied quickly, our
bodies use many replication forks,
which are all spaced out along the
DNA strand.