DNA contains the genetic instructions that determine traits in living organisms. It is made up of nucleotides that form a double helix structure. Key discoveries included Griffith discovering a transforming principle in bacteria, Franklin's X-ray crystallography of DNA, and Watson and Crick describing the double helix structure and complementary base pairing of A-T and G-C. DNA replicates semiconservatively prior to cell division and its sequence of bases provides the code for building proteins through transcription and translation.

1. 3/31/2014
1
WARM-UP #7
DNA
(Deoxyribonucleic Acid)
Genetic material of cells…
• GENES – units of genetic material that
CODES FOR A SPECIFIC TRAIT
• Called NUCLEIC ACIDS
• DNA is made up of repeating molecules
called NUCLEOTIDES

2. 3/31/2014
2
DNA Nucleotide
O
O=P-O
O
Phosphate
Group
N
Nitrogenous base
(A, G, C, or T)
CH2
O
C1
C4
C3 C2
5
Sugar
(deoxyribose)
A HISTORY OF DNA
• Discovery of the DNA double helix
A. Frederick Griffith – Discovers that a factor
in diseased bacteria can transform harmless
bacteria into deadly bacteria (1928)
B. Rosalind Franklin - X-ray photo of DNA.
(1952)
C. Watson and Crick - described the
DNA molecule from Franklin’s X-ray.
(1953)
SEE p. 292-293
Watson & Crick proposed…
•DNA had specific pairing between the
nitrogen bases:
ADENINE – THYMINE
CYTOSINE - GUANINE
•DNA was made of 2 long stands of
nucleotides arranged in a specific
way called the “Complementary Rule”

3. 3/31/2014
3
DNA Double Helix
Nitrogenous
Base (A,T,G or C)
“Rungs of ladder”
“Legs of ladder”
Phosphate &
Sugar Backbone
DNA Double Helix
P
P
P
O
O
O
1
2
3
4
5
5
3
3
5
P
P
P
O
O
O
1
2 3
4
5
5
3
5
3
G C
T A
Nitrogenous Bases
• PURINES
1. Adenine (A)
2. Guanine (G)
• PYRIMIDINES
3. Thymine (T)
4. Cytosine (C) T or C
A or G

4. 3/31/2014
4
Chargaff’s Rule
• Adenine must pair with Thymine
• Guanine must pair with Cytosine
• Their amounts in a given DNA molecule will be
about the same.
G C
T A
BASE-PAIRINGS
C
G
H-bonds
T A
Genetic Diversity…
• Different
arrangements of
NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among
living organisms.

5. 3/31/2014
5
The Code of Life…
• The “code” of the chromosome is the
SPECIFIC ORDER that bases occur.
A T C G T A T G C G G…
DNA is wrapped tightly around
histones and coiled tightly to form
chromosomes
See p. 297
DNA Replication
• DNA must be copied
• The DNA molecule produces 2
IDENTICAL new complementary
strands following the rules of
base pairing:
A-T, G-C
•Each strand of the
original DNA serves as
a template for the new
strand See p. 298

6. 3/31/2014
6
DNA Replication
• Semiconservative
Model:
1. Watson and Crick
showed: the two strands
of the parental molecule
separate, and each
functions as a template
for synthesis of a new
complementary strand.
. Parental DNA
DNA Template
New DNA
1. Why is replication necessary?
2. When does replication occur?
3. Describe how replication works.
4. Use the complementary rule to
create the complementary
strand:
A---?
G---?
C---?
T---?
A---?
G---?
A---?
G---?
C---?
A---?
G---?
T---?
Replication Quiz
1. Why is replication necessary?
So both new cells will have the correct
DNA
2. When does replication occur?
During interphase (S phase).
3. Describe how replication works.
Enzymes unzip DNA and complementary
nucleotides join each original strand.
4. Use the complementary rule to
create the complementary strand:
A---T
G---C
C---G
T---A
A---T
G---C
A---T
G---C
C---G
A---T
G---C
T---A
Replication Quiz

7. 3/31/2014
7
(1961) Watson & Crick proposed…
• …DNA controlled cell function by
serving as a template for PROTEIN
structure.
• 3 Nucleotides = a triplet or CODON
(which code for a specific AMINO ACID)
See p.303
• AMINO ACIDS are the building blocks
of proteins.
DNA Transcription
• DNA can “unzip”
itself and RNA
nucleotides match
up to the DNA
strand.
• Both DNA & RNA
are formed from
NUCLEOTIDES and
are called NUCLEIC
acids.
See p.301
DNA Translation
• The cell uses
information from
“messenger” RNA
to produce proteins
See p.304-305
We will
discuss details
of this on a
later date

8. 3/31/2014
8
Transcription/Translation Quiz
1. Why is transcription necessary?
2. Describe transcription.
3. Why is translation necessary?
4. Describe translation.
5. What are the main differences
between DNA and RNA.
6. Using the chart on page 303,
identify the amino acids coded for by
these codons:
UGGCAGUGC
1. Why is transcription necessary?
Transcription makes messenger RNA (MRNA)
to carry the code for proteins out of the
nucleus to the ribosomes in the cytoplasm.
2. Describe transcription.
RNA polymerase binds to DNA, separates the
strands, then uses one strand as a template to
assemble MRNA.
3. Why is translation necessary?
Translation assures that the right amino acids
are joined together by peptides to form the
correct protein.
4. Describe translation.
The cell uses information from MRNA to
produce proteins.
5. What are the main differences between
DNA and RNA.
DNA has deoxyribose, RNA has ribose;
DNA has 2 strands, RNA has one strand;
DNA has thymine, RNA has uracil.
6. Using the chart on page 303, identify the
amino acids coded for by these codons:
UGGCAGUGC
tryptophan-glutamine-cysteine

9. 3/31/2014
9
AMAZING DNA FACTS…
• DNA from a single human
cell extends in a single
thread for almost 2 meters
long!!!
• It contains information
equal to some 600,000
printed pages of 500 words
each!!!
(a library of about 1,000 books)
LET’S REVIEW DNA…
LM p.44
1. List the conclusions Griffith & Avery,
Hershey & Chase drew from their
experiments.
2. Summarize the relationship between
genes & DNA.
3. Describe the overall structure of the
DNA molecule.
4. What are the 4 kinds of bases?