DNA Structure and DNA
Replication
How cells make a copy of their DNA
before they divide.
DNA--Deoxyribonucleic Acid
DNA contains thousands of genes
• Genes are the recipes for the proteins a cell makes.
• Proteins are made of Amino Acids.
• The sequence of the amino acids and the number of
amino acids determines the kind of protein.
• Change the order or number of amino acids and the
protein is different.
Protein
• DNA is used to create RNA
• RNA is used by ribosomes to make Protein
• DNA -> RNA -> Protein [central dogma]
• True for all organisms
DNA structure
DNA is made of nucleotides
There are 4 different types of
nucleotides in DNA
DNA is a double stranded molecule that twists as it is forms, this shapes is
called a double helix. This was discovered by Watson and Crick.
Joining nucleotides into DNA*
The sides of DNA ladder are made of alternating sugar and phosphate molecules.
The nitrogen bases form the steps in the DNA ladder.
The second strand*
Here the second strand is shown completing the DNA molecule.
Hydrogen bonds that join the nitrogen bases together are weak allowing the
DNA to be unzipped.
As new nucleotides are added the molecule takes on
the spiral or double helix shape.
Base pairing rules
Adenine pairs with Thymine
Cytosine pairs with Guanine
Replication the details and enzymes
Details
• DNA is unwound and unzipped by helicase.
• Primase adds RNA nucleotides to one of the two split DNA strands priming
it to receive DNA Polymerase.
• DNA Polymerase lll attaches to the primer and begins adding nucleotides
to the first strand using base pairing rules, know as the leading strand.
• Base pairing rules are A bonds to T and C bonds to G
• The second DNA strand is replicated in the reverse direction from the first
strand and is know as the lagging strand.
• After the leading strand has replicated some distance more RNA primer
and DNA Polymerase lll are added to the second DNA strand.
• Nucleotides are added to this strand in the opposite direction forming
short segments of DNA called Okazaki fragments.
• The enzyme DNA Polymerase l replaces the primer with DNA nucleotides
and the enzyme ligase joins the many Okazaki fragments together,
completing the second DNA strand.
DNA Replication Videos
http://www.dnatube.com/video/3448/DNAReplication-Video
• http://www.dnatube.com/video/335/Animate
d-DNA-Replication
• http://www.dnatube.com/video/365/DNAReplication