1. DNA contains the genetic instructions that determine traits in organisms. 2. DNA is made up of nucleotides containing phosphate groups, sugars, and one of four nitrogenous bases (adenine, guanine, cytosine, thymine). 3. Watson and Crick discovered that DNA takes the shape of a double helix with the bases on the inside paired in a specific way (adenine-thymine and cytosine-guanine).

1. DNA
(Deoxyribonucleic Acid)

2. 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

3. DNA Nucleotide
Phosphate
Group
O 5
O=P-O CH2
O
O
N
Nitrogenous base
C4 C1 (A, G, C, or T)
Sugar
(deoxyribose)
C3 C2

4. A HISTORY OF DNA
SEE p. 292-293
• 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)

5. 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”

6. DNA Double Helix
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone

7. DNA Double Helix
5 O 3
3 O
P 5 P
5 O
1 G C 3
2
4 4
2 1
3 5
O
P P
5
T A 3
O
O
5
P 3 P

8. Nitrogenous Bases
• PURINES
1. Adenine (A)
2. Guanine (G)
A or G
• PYRIMIDINES
3. Thymine (T)
4. Cytosine (C) T or C

9. 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.
T A G C

10. BASE-PAIRINGS
H-bonds
G C
T A

11. Genetic Diversity…
• Different
arrangements of
NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among
living organisms.

12. 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…

13. See p. 297
DNA is wrapped tightly around
histones and coiled tightly to form
chromosomes

14. 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

15. 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. DNA Template
Parental DNA
. New DNA

16. Replication Quiz
1. Why is replication necessary? A---?
G---?
2. When does replication occur? C---?
T---?
3. Describe how replication works. A---?
G---?
4. Use the complementary rule to A---?
create the complementary G---?
strand: C---?
A---?
G---?
T---?

17. Replication Quiz
A---T
1. Why is replication necessary? G---C
So both new cells will have the correct C---G
DNA
T---A
2. When does replication occur?
A---T
During interphase (S phase).
G---C
3. Describe how replication works.
A---T
Enzymes unzip DNA and complementary
nucleotides join each original strand. G---C
4. Use the complementary rule to C---G
create the complementary strand: A---T
G---C
T---A

18. (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.

19. DNA Transcription
• DNA can “unzip”
itself and RNA
nucleotides match
up to the DNA
strand. See p.301
• Both DNA & RNA
are formed from
NUCLEOTIDES and
are called NUCLEIC
acids.

20. 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

21. 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

22. 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.

23. 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

24. 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)

25. 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?