2. Chapter 5. Macromolecules: Nucleic Acids

3. Nucleic Acids Function: Examples: Structure:
store & transmit hereditary information
Examples:
RNA (ribonucleic acid)
DNA (deoxyribonucleic acid)
Structure:
monomers = nucleotides

4. Nucleotides 3 parts nitrogen base (C-N ring) pentose sugar (5C)
ribose in RNA
deoxyribose in DNA
PO4 group

5. Types of nucleotides 2 types of nucleotides different Nitrogen bases
purines
double ring N base
adenine (A)
guanine (G)
pyrimidines
single ring N base
cytosine (C)
thymine (T)
uracil (U)

6. Building the polymer

7. Nucleic polymer Backbone sugar to PO4 bond phosphodiester bond
new base added to sugar of previous base
polymer grows in one direction
N bases hang off the sugar-phosphate backbone
Why is this important?

8. RNA & DNA RNA DNA single nucleotide chain double nucleotide chain
N bases bond in pairs across chains
spiraled in a double helix
double helix 1st proposed as structure of DNA in 1953 by James Watson & Francis Crick

9. Pairing of nucleotides
Nucleotides bond between DNA strands
H bonds
purine :: pyrimidine
A :: T
2 H bonds
G ::: C
3 H bonds
The 2 strands are complementary.
One becomes the template of the other & each can be a template to recreate the whole molecule.
Why is this important?

10. Information polymer Function series of bases encodes information
like the letters of a book
stored information is passed from parent to offspring
need to copy accurately
stored information = genes
genetic information
All other biomolecules we spoke about served physical or chemical functions. DNA & RNA are information storage molecules.
DNA well-suited for an information storage molecule:
chemically stable
stores information in the varying sequence of nucleotides (the genetic code)
its coded sequence can be copied exactly by the synthesis of complementary strands; easily unzipped & re-zipped without damage (weak H bonds)
damage to one strand can be repaired by addition of bases that match the complementary strand

11. Isn’t this a great illustration!?

12. Why is it important that the strands are bonded by H bonds?
DNA molecule
Double helix
H bonds between bases join the 2 strands
A :: T
C ::: G
Why is it important that the strands are bonded by H bonds?
H bonds = biology’s weak bond
• easy to unzip double helix for replication and then re-zip for storage
• easy to unzip to “read” gene and then re-zip for storage

13. Copying DNA Replication 2 strands of DNA helix are complementary
have one, can build other
have one, can rebuild the whole
why is this a good system?
when in the life of a cell does replication occur?
when cells divide, they must duplicate DNA exactly for the new “daughter” cells
Why is this a good system?
mitosis
meiosis

14. DNA replication
“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”
James Watson
Francis Crick
1953
The greatest understatement in biology!

15. Watson and Crick … and others…
1953 | 1962
Watson and Crick … and others…
Discovered & published in 1953
Nobel Prize in 1962:
Watson, Crick, Wilkins

16. 1953 | 1962
Maurice Wilkins… and…

17. Rosalind Franklin ( )
A chemist by training, Franklin had made original and essential contributions to the understanding of the structure of graphite and other carbon compounds even before her appointment to King's College. Unfortunately, her reputation did not precede her. James Watson's unflattering portrayal of Franklin in his account of the discovery of DNA's structure, entitled "The Double Helix," depicts Franklin as an underling of Maurice Wilkins, when in fact Wilkins and Franklin were peers in the Randall laboratory. And it was Franklin alone whom Randall had given the task of elucidating DNA's structure. The technique with which Rosalind Franklin set out to do this is called X-ray crystallography. With this technique, the locations of atoms in any crystal can be precisely mapped by looking at the image of the crystal under an X-ray beam. By the early 1950s, scientists were just learning how to use this technique to study biological molecules. Rosalind Franklin applied her chemist's expertise to the unwieldy DNA molecule. After complicated analysis, she discovered (and was the first to state) that the sugar-phosphate backbone of DNA lies on the outside of the molecule. She also elucidated the basic helical structure of the molecule.
After Randall presented Franklin's data and her unpublished conclusions at a routine seminar, her work was provided - without Randall's knowledge - to her competitors at Cambridge University, Watson and Crick. The scientists used her data and that of other scientists to build their ultimately correct and detailed description of DNA's structure in Franklin was not bitter, but pleased, and set out to publish a corroborating report of the Watson-Crick model. Her career was eventually cut short by illness. It is a tremendous shame that Franklin did not receive due credit for her essential role in this discovery, either during her lifetime or after her untimely death at age 37 due to cancer.

18. Interesting note… Ratio of A-T::G-C affects stability of DNA molecule
2 H bonds vs. 3 H bonds
biotech procedures
more G-C = need higher T° to separate strands
high T° organisms
many G-C
parasites
many A-T (don’t know why)
At the foundation of biology is chemistry!!

19. Another interesting note…
ATP Adenosine triphosphate
modified nucleotide
adenine ribose + Pi + Pi + Pi + +

20. Macromolecule Review

21. Carbohydrates Structure / monomer Function Examples monosaccharide
energy
raw materials
energy storage
structural compounds
Examples
glucose, starch, cellulose, glycogen
glycosidic bond

22. Lipids Structure / building block Function Examples
glycerol, fatty acid, cholesterol, H-C chains
Function
energy storage
membranes
hormones
Examples
fat, phospholipids, steroids
ester bond (in a fat)

23. Proteins Structure / monomer Function Examples amino acids
levels of structure
Function
enzymes u defense
transport u structure
signals u receptors
Examples
digestive enzymes, membrane channels, insulin hormone, actin
peptide bond

24. Nucleic acids Structure / monomer Function Examples nucleotide
information storage & transfer
Examples
DNA, RNA
phosphodiester bond