1. DNA
The molecule of Life

2. Nucleic Acids Ribonucleic acid (RNA) Single stranded Builds proteins
Acts as enzymes
Three types
mRNA
tRNA
rRNA

3. DNA DNA is often called the blueprint of life
Nucleic acids store and transmit hereditary information
In simple terms it contains the instructions for making proteins in the cell.

4. DNA by the numbers Each cell has about 2 meters of DNA.
The average human has 75 trillion cells.
The average human has enough DNA to go from the earth to the sun more than 400 times.
DNA has a diameter of only meter.
The earth is 150 billion meters
or 93 million miles from
the sun.

5. The Shape of the Molecule
DNA is a very long polymer.
The basic shape is like a twisted ladder or spiral staircase.
This is called a double helix.

6. DNA STRUCTURE Adenosine Mono Phosphate (AMP)OH HO
Phosphate
NH2 N
Base - H+ OH O
CH2
Sugar H 2’ 3’ 4’ 5’ 1’
Nucleotide OH

7. DNA Structure Sugar Base OH O CH2 H P O OH HO
Phosphate
The outer parts of the ladder are made of sugars and phosphates.
The steps of the ladder are made of pairs of nitrogen bases.
NH2 N
Base

8. Four Nitrogenous Bases
DNA
Four Nitrogenous Bases
Cytosine C
Thymine T
Adenine A
Guanine G

9. One Strand of DNA phosphate nucleotide base sugar
One strand of DNA is a polymer of nucleotides.
One strand of DNA has many millions of nucleotides.
The backbone of the molecule is alternating phosphate and deoxyribose, a sugar.
The teeth are nitrogenous bases.

10. Two Types of Bases in DNA
Purines are double ring bases. N
Adenine
NH2
NH2 O N NH
Guanine

11. Two Kinds of Bases in DNA
NH2
Cytosine
Pyrimidines are single ring bases.
Uracil
(RNA)
CH3 N O NH
Thymine
(DNA)
Uracil is found in RNA (more later)

12. Nitrogenous bases Pyrimidines
Nucleotide Bases CH
Uracil (in RNA) U
Ribose (in RNA)
Nitrogenous bases Pyrimidines C N O H
NH2 HN
CH3
Cytosine
Thymine (in DNA) T HC NH
Adenine A
Guanine G
Purines
HOCH2 OH
Pentose sugars
Deoxyribose (in DNA) 4’ 5” 3’ 2’ 1’
Pyrimidines
C = Cytosine
T = Thymine
U = Uracil
Purines
A = Adenine
G = Guanine

13. Two Stranded DNA
Remember, DNA has two strands that fit together something like a zipper.
The teeth are the nitrogenous bases but why do they stick together?

14. Hydrogen Bonds + - - + CH3 H Thymine Adenine N N H O
The bases attract each other because of hydrogen bonds.
Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.
CH3 N O H + -
Thymine N H - +
Adenine

15. 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

16. The Code of Life… A T C G T A T G C G G…
The “code” of the chromosome is the SPECIFIC ORDER in which the bases occur.
A T C G T A T G C G G…

17. DNA Structure Determination
Edwin Chargaff
1949 biochemist
Showed that the amount of A=T and G=C
Wilkins and Franklin
1952 X-ray picture of DNA
Watson and Crick
1953 proposed a 3-D model accounting for the data.

18. The Watson - Crick Model Of DNA
T A
G C
C G
G C
T A
The Watson - Crick Model Of DNA
3.4 nm
1 nm
Minor
groove
Major
groove
0.34 nm

19. DNA Replication The preparation of exact copies of a molecule.
DNA replication is essential for life
It allows organisms to create copies of themselves.
DNA is wrapped tightly around histones and coiled tightly to form chromosomes

20. Why is accuracy of Nucleotide sequence in the DNA of a gene important?
Nucleotide sequence in messenger RNA (mRNA) Transcription Nucleotide sequence in a protein (tRNA) Translation
Structure and function of the protein
Form and function
Characteristics or traits (normal health or problems)

21. DNA Replication A-T G-C
DNA must be copied to produce 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

22. DNA Replication Semi-conservative Model:
Meselson and Stahl 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

23. Uses energy from ATP to unwind the DNA by breaking the Hydrogen bonds
SSB
Areas where the DNA separates are called replication forks

24. Schematic representation of DNA Polymerase
Structure resembles a human right hand
Template DNA thread through the palm
Thumb and fingers wrapped around the DNA
Polymerase has “proofreading” role
Backtrack and correct errors
Only about one error per billion nucleotides

25. Multiple Replication Forks During Eukaryotic DNA Synthesis