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DNA
DeoxyriboNucleic Acid
DNA is the Genetic Material of Chromosomes
http://www.pbs.org/wgbh/nova/
genome/program.html
Instructions for a human 3:40
Levels of Structure
• Chromosomes are long DNA molecules packed
together
• DNA is composed of 2 strands
• Each strand is a long string of nucleotides
Journey into DNA
http://www.pbs.org/wgbh/nova/
genome/dna.html#
DNA is the blueprint
• Contains the codes
for what makes us…
us
• We are really just
scratching the
surface in
understanding the
ways DNA works
Some basics about DNA
• We have a lot of it- every cell
contains about 6.5 feet of
DNA (if you were to run each
molecule end to end)
• The total length of DNA in our
body would go the sun and
back
– 70 times!
Our Understanding of It Is Changing
Rapidly
Old View
New View
• DNA is mostly genes • <1% of DNA are
actually coding
• Each segment of
genes
DNA is a gene that
codes for a protein
• The rest controls the
expression of genes
• Rest of DNA is “junk”
or play as-of-yet
undiscovered roles
What We Have a Good Understanding Of
• The structure of DNA
(shape, how it is stored
etc.)
• How DNA is replicated
• How proteins are made
from genes
• The sequence of DNA
What We Barely Understand
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What causes genes to be activated or expressed
What the 99% of DNA does or why it’s there
Genetic links in things like heart disease/cancer
How the environment affects our DNA
How DNA came to be, chromosome came to be
etc.
• Much, much more
Our Knowledge of DNA is Changing
RAPIDLY!
• Our understandings now is very different from
when I was in college which is different from
when I was in HS. Our understanding will
have changed if you take biology in college
The Structure of DNA (DEOXYRIBOSE
NUCLEIC ACID)
•
A. DNA is a macromolecules called
NUCLEIC ACIDS. The other type of
molecule in this category is RNA.
Remember…
• Since DNA is a macromolecule (POLYMER), it
is really made of many (in this case billions)
smaller molecules (MONOMERS!) put
together. The DNA monomer is the
individual NUCLEOTIDE.
Nucleotide
• A single piece of the
DNA strand
• Made of 3 parts
– Deoxyribose
(sugar)
– Phosphate
– Base (A,G,C or T)
DNA Nucleotides
Purines
Adenine
Guanine
Phosphate
group
Pyrimidines
Cytosine
Thymine
Deoxyribose
The backbone of 1 strand
• Alternates between
the sugar
(deoxyribose) and
the phosphate group
• The base sticks out
into the middle
Double-Stranded
• The bases hydrogen bond with
each other to hold the strands
together
• The base from one strand
bonds with the base from the
other forming a
complementary base pair
a. ADENINE bonds with
THYMINE
b. GUANINE bonds with
CYTOSINE
Figure 12–7 Structure of DNA
Section 12-1
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
DNA Structure
• Theorized to be a
double helix
consisting of 2
strands wrapped
around each other
• Discovered by
Watson and Crick
AND Rosalind
Franklin
Rosalind Franklin
• Provided the
scientific evidence
that allowed Watson
and Crick to suggest
the double helix
• Often goes
uncredited and
since she had died –
couldn’t share in the
Nobel prize
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What about the structure of DNA makes us
unique???
– ORDER OF BASE PAIRS
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http://www.pbs.org/wgbh/nova/genome/program.html genetic variation (6:33)
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What You Should Know about DNA
structure
The basic structure of a nucleotide
The basic structure of DNA
How DNA and RNA differ
Base-pair rules
How the structure suggests a
replication method