1. DNA
The Secret Code

2. Genes Genes are known to:
Carry information from one generation to the next.
Put that information to work by determining the heritable characteristics of organisms.
Be easily copied, because all of a cell’s genetic information is replicated every time a cell divides.

3. Central Dogma of Molecular Biology!
Scientists call this the:
DNA
DNA
Central Dogma of Molecular Biology!
RNA
RNA
Protein
Protein

4. How do we know that all of our genetic information comes from DNA?
Thanks to many scientists and many experiments over the last ≈ 90 years.
Let’s take a look…….

5. Who helped?
In 1928: Griffith accidentally discovered a process called Transformation that turned non-deadly bacteria into deadly pneumonia causing bacteria.
In 1944: Avery, McCarty, and MacLeod Repeated Griffith’s Experiment
Discovered DNA was the transformation factor.

6. Who helped?
In 1952: Hershey-Chase experimented with bacteria and bacteriophages. Showed DNA was what entered the bacteria and caused disease.

7. DNA carries the genetic code!
Now we know!
DNA carries the genetic code!
But, how do we know how it works?

8. DNA’s Structure was the key!
How did DNA:
1. Store information?
2. Duplicate itself easily?
DNA’s Structure was the key!

9. The Race to Discover DNA’s Structure
Why do you think the bases match up this way?
1950
Chargaff’s Rule: Equal amounts of Adenine and Thymine, and equal amounts of Guanine and Cytosine
Purine + Purine = Too wide
Pyrimidine + Pyrimidine = Too Narrow
Erwin Chargaff
Purine + Pyrimidine = Perfect Fit from X-ray data

10. The Race to Discover DNA’s Structure
X-Ray diffraction image of DNA taken by Franklin in 1951
Maurice Wilkins
Rosalind Franklin

11. The Race to Discover DNA’s Structure
1953
Compiled data from previous scientists to build a double-helical model of DNA
James Watson
Francis Crick

12. DNA Deoxyribonucleic Acid (polymer) Nucleotide
A long molecule made up of units (monomers) called nucleotides.
Three components:
5-carbon sugar: Deoxyribose
A phosphate group
A nitrogenous base
DNA
Nucleotide

13. DNA Structure Called a double helix
Backbone (sides) : carbon sugar and phosphate groups
Rungs: nitrogenous bases held together with hydrogen bonds

14. Nitrogenous bases Our alphabet has 26 letters
Can create many different words  many different sentences  billions of different books of information.
DNA alphabet has 4 letters (bases)
A, T, C, and G
Create 3 letter words  Amino acids  proteins  billions of different organisms

15. Nitrogenous bases Remember Chargaff’s Rule?
Purines:
Adenine
Guanine
Pyrimidines:
Thymine
Cytosine

16. DNA Replication The double helix did explain how DNA copies itself
We will study this process, DNA replication, in more detail

17. DNA Replication
The “parent” molecule has two complementary strands of DNA.
Each is base paired by hydrogen bonding with its specific partner (Chargaff’s rule):
A with T
G with C

18. DNA Unzips
The first step in replication is the separation of the two strands. (Must unwind DNA before separating)
An enzyme called DNA helicase unwinds and unzips DNA

19. New nucleotides added
Each parental strand now serves as a template that determines the order of the bases along a new complementary strand. (bases always added 5’ to 3’)
an enzyme called DNA polymerase adds the bases

20. Gaps are closed
The nucleotides are connected to form the sugar-phosphate backbones of the new strands.
Enzyme DNA ligase closes the gaps.
Each “daughter” DNA molecule consists of one parent strand and one new strand….semi-conservative model

21. Reviewing DNA Replication
And One more…..
And another…

22. COOL!!!!
A single strand of DNA (one chromosome) is about 2 inches long when uncoiled.
Each human cell contains 46 chromosomes (6 to 7 feet of DNA)
Your nucleus is only about inches in diameter…..and you can fit that 6 ft of DNA in there?
Your body contains trillion of cells.

23. There’s more!
All of your DNA (when uncoiled and tied together) would be 67 billion miles long!
THAT’S 150,000 round trips to the moon!
OR 70 round trips to the sun!!!
It takes about 8 hours for one of your cells to copy all of its DNA.
Our entire DNA sequence is called a Genome…and there is an estimated 3,200,000,000 DNA bases
This would take up about 3GB of storage

24. And more!
If you could type 60 wpm, 8 hours/day…it would take you 50 years to type the bases of your DNA
99.6% of our DNA is the same as somebody else’s DNA…it is the 0.01% that makes you who you are!
98% of your DNA doesn’t actually code for anything….it is called “junk” DNA.
You have roughly 20,000 genes that can build up to 100,000 different proteins