1. DNA – The Genetic Material
Chapter 9
DNA – The Genetic Material

2. EARLY DISCOVERIES…
Fred Griffith – trying to develop a vaccine for pneumonia …..TRANSFORMATION

3. Oswald Avery….
Discovered that the substance absorbed by the harmless bacteria was DNA…
DNA is the Transformation factor!

4. Hershey – Chase Experiment studies bacteriophages…

5. Discovering DNA:
Erwin Chargaff found
that the amount of Adenine always equals the amount of Thymine !....AND that Guanine amounts always equaled Cytosine.
Rosaline Franklin and Maurice Wilkins –X-Ray diffraction shows DNA is a coiled helix

6. staircase…..Nobel prize 1950
Francis Crick and James Watson
Discovered the 3-dimensional structure of DNA……. Showing base pairing in a double helical
staircase…..Nobel prize 1950

7. Structure of DNA Nucleotides: (3 parts):
I. DNA: (Deoxyribonucleic Acid)
Building blocks called…
Nucleotides: (3 parts):
1.Deoxyribose (simple sugar)
2.Phosphate Group
3.Nitrogen Base(A, C, T or G)
ADENINE
CYTOSINE
THYMINE
GUANINE

8. BASE PAIRING PURINES – ADENINE AND GUANINE PYRIMIDINES
- THYMINE AND CYTOSINE
ADENINE – HYDROGEN BOND – THYMINE
GUANINE – HYDROGEN BOND - CYTOSINE

9. THE SIDES OF THE DNA MOLECULE
PHOSPHATE
DEOXYRIBOSE SUGAR
PHOSPHATE
DEOXYRIBOSE SUGAR
PHOSPHATE

11. DNA =
2 strands of nucleotides joined by hydrogen bonds between the bases forms a
“DOUBLE HELIX” or
twisted ladder

12. A. DNA Replication:
Each organism has its unique nucleotide sequence in its DNA --->from parents
DNA must be copied
for cell division
(Replication)

13. Enzymes called DNA Helicases break bonds between bases - DNA “unzips”
STEPS IN
DNA REPLICATION:
Enzymes called DNA Helicases break bonds between bases - DNA “unzips”

14. 2 new strands formed and rewind (identical to original DNA)
Free nucleotides in pair up with exposed bases guided by DNA Polymerases.
2 new strands formed and rewind
(identical to original DNA)
Free nucleotides

15. …….How proteins
are made !!

16. II. PROTEIN SYNTHESIS:
20 Different amino acids
3 Nitrogen bases code for 1 amino acid = CODON
“Triplet code” - 64 different codons (3 stop codons) ---> 20 amino acids
Order of bases in DNA determines type and order of amino acids in protein
Code is universal among all organisms = common ancestor

17. Transcription takes place in the nucleus!
A. TRANSCRIPTION: Getting DNA to make a m RNA ….which carries the sequence for a particular polypeptide chain!
DNA IS IN THE NUCLEUS
Transcription takes place in the nucleus!
RNA structure differs from DNA:
Single strand of nucleotides
Ribose - simple sugar
Bases - uracil instead of thymine U -- A
A, U, C, G

18. STEPS OF TRANSCRIPTION:
1. DNA makes complimentary copy of mRNA (using U in place of T)
2. mRNA carries code out of nucleus into cytoplasm where ribosomes are located!

19. B. TRANSLATION: Interpreting the code from the mRNA - on the ribosomes.
tRNA (transfer) carries amino acids and bring them to ribosomes to be assembled into proteins
The order of amino acids determines the type of polypeptide assembled. (protein)

21. tRNA has anticodon (3 bases that code for a specific amino acid)
tRNA matches its anticodon with the mRNA codon and drops off its amino acid to bond with the next amino acid
Continues until a “stop codon” is reached