BCHM-3050 Lecture Notes - Lecture 3: Heterocyclic Compound, Pyrimidine, Purine
19 May 2018
School
Department
Course
Professor
Nucleic acid: two types
DNA: deoxyribonucleic acid
Base pair
○
Has H group
○
•
RNA: ribonucleic acid
Has nucleobase
○
Has two OH groups
○
•
Phosphodiester link forms b/w two sugars residue
•
Ribose: heterocyclic ring
Has nucleobase or heterocyclic base
○
•
Deoxyribose: lacks hydroxyl group
•
Polynucleotides: polymers of nucleotides
Two features
Has sense of directionality (one end is 5' phosphate and other
end is unreacted 3' hydroxyl group)
§
Has individuality aka nucleotide sequence
§
○
•
Oligonucleotides: small polymers w a few residues
•
Ribozymes: RNA molecules capable of catalyzing chemical rxns
•
Nucleobases
Nucleobase or base: attach to first carbon position of deoxyribose and
ribose sugar
Purine: two ringed
○
Pyrimidine : single ringed
○
•
Bases are derivatives of purines and pyrimidines and are:
Heterocyclic
○
Aromatic
○
Planar
○
•
Adenine
(A):
C5H5N5
Guanine (G):
C5H5ON5
Thymine (T):
C5H6O2N2
Uracil (U):
C4H4O2N2
Cytosine C:
C4H5ON3
Purine
•
Comple
mentary
to uracil
and
thymine
•
Form
basis for
energy
currency
molecul
e of
ATP
•
Purine
•
Complementa
ry to cytosine
•
Form max of
3 hydrogen
bonds
On
carbony
l and
two
amino
groups
○
•
Pyrimidine
•
Can form
thymine
dimer in
DNA
Causes
skin
cancer
○
•
Complement
ary to
adenine
•
Pyrimidine
•
Replaces
thymine in
RNA
•
Complement
ary to
adenine
•
Pyrimidine
•
Complementa
ry to guanine
Forms
max of
3
hydroge
n bonds
○
•
Methylation:
role in
transcriptiona
l regulation
•
Nucleosides
Nucleoside = free base + sugar (ribose or deoxyribose)
Glycosidic bond: bond b/w first carbon of sugar and base nitrogen
○
•
Purine nucleoside: -sine
•
Pyrimidine nucleoside: -dine
•
Phosphate linkage
HPO42- : predominates homeostasis
Bonded to hydroxyl group on sugar
Hydroxyl: -OH
§
○
•
HPO42- + nucleoside = nucleotide
•
Properties of Nucleic acid
Nucleotide: strong acids
Have negative charges due to phosphate backbone
○
BUT different nucleotides have different net charges
○
•
Bases can convert into tautomeric form
Tautomer: structural isomers that differ in location of double bonds
and hydrogen atoms
G, T and U => isomerize to enol forms
§
A and C => isomerize to imino form
§
○
•
Bases absorb light strongly in UV region of spectrum
Absorption depends on pH
○
Strong absorbance used for determination of nucleic acids
○
•
Metastability: metastable compounds are thermodynamically favored to
break down but do so slowly
•
Nucleases: break down DNA and RNA
•
Chapter 4: Nucleic acid
Saturday, May 19, 2018
7:14 PM
