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.
DNA replication yields two
DNA molecules identical to the
original one, ensuring transmission
of genetic information to daughter
cells with exceptional fidelity.
The sequence of bases in DNA is
recorded as a sequence of
complementary bases in a singlestranded mRNA molecule.
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
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
Was an acid compound found in nuclei therefore
named nucleic acid
1944 Oswald, Avery, MacLeod and McCarty
demonstrated that DNA is the molecule that carrier
1953 Watson and Crick proposed the double helix
model for the structure of DNA
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.
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
• 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
Anti- conformation predominates in
nucleic acid polymers
Other Functions of Nucleotides
• Nucleoside 5'-triphosphates are carriers of
• Bases serve as recognition units
• Cyclic nucleotides are signal molecules and
regulators of cellular metabolism and
ATP is central to energy metabolism
GTP drives protein synthesis
CTP drives lipid synthesis
UTP drives carbohydrate metabolism
Nucleotide monomers are joined by 3’-5’ phosphodiester
linkages to form nucleic acid (polynucleotide) polymers
Nucleic acid backbone takes on extended
Nucleotide residues are all oriented in the same
direction (5’ to 3’) giving the polymer
The sequence of DNA molecules is always read in
the 5’ to 3’ direction
•Guanine pairs with
•Adenine pairs with
Base compositions experimentally
determined for a variety of organisms
H-bonding of adjacent antiparallel DNA
strands form double helix structure
Distance between the 2 sugar-phosphate backbones
is always the same, give DNA molecule a regular
Plane of bases are oriented perpendicular to
Hydrophillic sugar phosphate backbone winds
around outside of helix
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
Cause the sugar-phosphate backbone to twist.
Interior with base pair
Right handed helix
Rise = 0.33
Pitch = 3.4 nm / turn
10.4 nucleotides per
Two groves – major and
functional groups on
the edge of base pairs
exposed to exterior
involved in interaction
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
Charge-Charge Interactions – Electrostatic
repulsions of negatively charged phosphate
groups are minimized by interaction with cations