2. Nucleic Acids

3. Nucleic Acids Are Essential For
Information Transfer in Cells
• Information encoded in a DNA molecule is
transcribed via synthesis of an RNA molecule
• The sequence of the RNA molecule is "read"
and is translated into the sequence of amino
acids in a protein.

4. Replication
DNA replication yields two
DNA molecules identical to the
original one, ensuring transmission
of genetic information to daughter
cells with exceptional fidelity.
Transcription
The sequence of bases in DNA is
recorded as a sequence of
complementary bases in a singlestranded mRNA molecule.

5. Translation
Three-base codons on the
mRNA corresponding to
specific amino acids direct the
sequence of building a protein.
These codons are recognized by
tRNAs (transfer RNAs)
carrying the appropriate amino
acids. Ribosomes are the
“machinery” for protein
synthesis.

6. 
First discovered in 1869 by Miescher.

Found as a precipitate that formed when extracts
from nuclei were treated with acid.

Compound contained C, N, O, and high amount of
P.

Was an acid compound found in nuclei therefore
named nucleic acid

7. 
1944 Oswald, Avery, MacLeod and McCarty
demonstrated that DNA is the molecule that carrier
genetic information.

1953 Watson and Crick proposed the double helix
model for the structure of DNA

8. 
Nucleic acids are long polymers of nucleotides.

Nucleotides contain a 5 carbon sugar, a weakly
basic nitrogenous compound (base), one or
more phosphate groups.

Nucleosides are similar to nucleotides but have
no phosphate groups.

9. Pentoses of Nucleotides
• D-ribose (in RNA)
• 2-deoxy-D-ribose (in DNA)
• The difference - 2'-OH vs 2'-H
• This difference affects secondary structure
and stability

13. • Base is linked via a b-N-glycosidic bond
• The carbon of the glycosidic bond is anomeric
• Named by adding -idine to the root name of a
pyrimidine or -osine to the root name of a purine
• Conformation can be syn or anti
• Sugars make nucleosides more water-soluble than
free bases

16. Anti- conformation predominates in
nucleic acid polymers

17. Phosphate ester of nucleosides

19. Other Functions of Nucleotides
• Nucleoside 5'-triphosphates are carriers of
energy
• Bases serve as recognition units
• Cyclic nucleotides are signal molecules and
regulators of cellular metabolism and
reproduction

20. 
ATP is central to energy metabolism

GTP drives protein synthesis

CTP drives lipid synthesis

UTP drives carbohydrate metabolism

21. 
Nucleotide monomers are joined by 3’-5’ phosphodiester
linkages to form nucleic acid (polynucleotide) polymers

22. 
Nucleic acid backbone takes on extended
conformation.

Nucleotide residues are all oriented in the same
direction (5’ to 3’) giving the polymer
directionality.

The sequence of DNA molecules is always read in
the 5’ to 3’ direction

23. •Guanine pairs with
cytosine
•Adenine pairs with
thymine

24. Base compositions experimentally
determined for a variety of organisms

25. H-bonding of adjacent antiparallel DNA
strands form double helix structure

26. 
Distance between the 2 sugar-phosphate backbones
is always the same, give DNA molecule a regular
shape.

Plane of bases are oriented perpendicular to
backbone

Hydrophillic sugar phosphate backbone winds
around outside of helix

27. 
Noncovalent interactions between upper and lower
surfaces of base-pairs (stacking) forms a closely
packed hydrophobic interior.

Hydrophobic environment makes H-bonding
between bases stronger (no competition with
water)

Cause the sugar-phosphate backbone to twist.

28. Hydrophobic
Interior with base pair
stacking
Sugar-phosphate
backbone

29. 
Right handed helix

Rise = 0.33
nm/nucleotide

Pitch = 3.4 nm / turn

10.4 nucleotides per
turn

Two groves – major and
minor

30. 
Within groves,
functional groups on
the edge of base pairs
exposed to exterior

involved in interaction
with proteins.

31. 
Hydrophobic interactions – burying hydrophobic
purine and pyrimidine rings in interior

Stacking interactions – van der Waals interactions
between stacked bases.

Hydrogen Bonding – H-bonding between bases

32. 
Charge-Charge Interactions – Electrostatic
repulsions of negatively charged phosphate
groups are minimized by interaction with cations
(e.g. Mg2+)