DNA
What is DNA?
• Nucleic acid polymer made by a sequence
of nucleotides
What is a nucleotide?
• Smaller that makes up a nucleic acid
• Has three parts:
1. Sugar (deoxyribose)
2. Phosphate group
3. 1 of 4 nitrogen bases
DNA
What are the 4 nitrogen
bases?
1. Adenine (A)
2. Guanine (G)
3. Cytosine (C)
4. Thymine (T)
**ALL organisms have
the same 4 nucleotides
DNA
What is DNA’s structure?
• Made of 2 strands
• Strands are twisted like a spiral staircase/twisted
ladder
• This is called a DOUBLE HELIX
How are the sides of ladder formed?
• by the bonding of the sugar from one nucleotide
to the phosphate group of another nucleotide
How are the steps of the ladder formed?
By the bonding of one nucleotide N-base on strand
#1 to another nucleotides N-base on strand #2
Purines
Adenine
Pyrimidines
Guanine
Cytosine
Phosphate
group
Thymine
Deoxyribose
DNA Structure Diagram
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
DNA
DNA
How the nucleotide N-bases pair up?
• Adenine to Thymine ONLY (A-T)
• Guanine to Cytosine ONLY (G-C)
If all organisms have the same four
nucleotides, then how do we get so
many different organisms?
• The sequence of the nucleotides is
different for each organisms DNA strand
• The more similar the sequence the more
similar the organism
What is the Human Genome Project?
• A project where scientists are trying to
figure out the entire sequence of a human
DNA strand
• This will map out the genes for a human
• They can use this to find cures or
treatments for genetic disorders and some
cancers
1
DNA
DNA in Chromosomes
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
DNA Replication (Drawing)
What is DNA replication?
• How DNA will make a copy of itself to put into
each new cell which is made
How does it work?
• The 2 strands of DNA unzip by an enzyme
• Free floating nucleotides in that enzyme will
attach to the newly detached nucleotides on both
DNA strands
• The enzyme will run through the entire DNA
strand
• Result: 2 new DNA molecules
**Each new DNA molecule has one original
strand and one new complementary strand
DNA Replication Diagram
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Original
strand
2