purines and pyrimidines. purine and pyrimidine are the names of the parent compounds of two types of...
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Purine and Pyrimidine are the names of the Purine and Pyrimidine are the names of the parent compounds of two types of nitrogen-parent compounds of two types of nitrogen-containing heterocyclic aromatic compounds.containing heterocyclic aromatic compounds.
PyrimidinePyrimidine PurinePurine
NN
NN NNHH
NN
NNNN 11
22
3344
5577
88
99
11
22
33
44
55
6666
Important PyrimidinesImportant PyrimidinesPyrimidines that occur in Pyrimidines that occur in DNADNA::
Cytosine and Thymine. (Cytosine and Thymine. (CC & & TT))
Pyrimidines in Pyrimidines in RNARNA::
Cytosine and Uracil. (Cytosine and Uracil. (CC & & UU)) HHNN
NNHH
OO
OO
UracilUracil
HHNN
NNHH
OO
OO
CHCH33
ThymineThymine
HHNN
NNHH
NNHH22
OO
CytosineCytosine
Important PurinesImportant Purines
Adenine and Guanine are the principal purines Adenine and Guanine are the principal purines of both DNA and RNA.of both DNA and RNA.
AdenineAdenine
NN
NN
NNHH22
NN
NNHH
GuanineGuanine
OO
HHNN
NNHH
NN
NN
HH22NN
NucleosidesNucleosides
A A nucleosidenucleoside is a pyrimidine or purine N- is a pyrimidine or purine N-glycoside of D-ribofuranose or 2-deoxy-D-glycoside of D-ribofuranose or 2-deoxy-D-ribofuranose.ribofuranose.
The purine or pyrimidine part of a nucleoside is The purine or pyrimidine part of a nucleoside is referred to as a referred to as a purine or pyrimidine purine or pyrimidine BaseBase..
Pyrimidine nucleosidesPyrimidine nucleosides NNHH22
HOHO OHOH
OOHOCHHOCH22
OO
NN
NN
Cytidine occurs in RNA; Cytidine occurs in RNA; its 2-deoxy analog occurs in DNAits 2-deoxy analog occurs in DNA
CytidineCytidineCytidineCytidine
Pyrimidine nucleosidesPyrimidine nucleosides OO
NN
NNHH
OO
HOHO
OO
HH33CC
HOCHHOCH22
Thymidine occurs in DNAThymidine occurs in DNA
ThymidineThymidineThymidineThymidine
Pyrimidine nucleosidesPyrimidine nucleosides
HOCHHOCH22
OO
NN
NNHH
OO
OHOHHOHO
OO
Uridine occurs in RNAUridine occurs in RNA
UridineUridineUridineUridine
Purine nucleosidesPurine nucleosides
Adenosine occurs in RNA; Adenosine occurs in RNA; its 2-deoxy analog occurs in DNAits 2-deoxy analog occurs in DNA
HOCHHOCH22 OO
OHOHHOHO
NN
NN
NN
NHNH22
NN
AdenosineAdenosineAdenosineAdenosine
Purine nucleosidesPurine nucleosides
Guanosine occurs in RNA; Guanosine occurs in RNA; its 2-deoxy analog occurs in DNAits 2-deoxy analog occurs in DNA
HOCHHOCH22
NN
NHNH
OO
OO
HOHO
NN NHNH22
NN
OHOH
GuanosineGuanosineGuanosineGuanosine
NucleotidesNucleotides
Nucleotides are phosphoric acid Nucleotides are phosphoric acid esters of Nucleosides.esters of Nucleosides.
Adenosine 5'-Monophosphate (AMP)Adenosine 5'-Monophosphate (AMP)
Adenosine 5'-monophosphate (AMP) is also Adenosine 5'-monophosphate (AMP) is also called 5'-adenylic acid.called 5'-adenylic acid.
OCHOCH22PPHOHO
OO
HOHO
OO
OHOHHOHO
NN
NN
NN
NHNH22
NN
5'5'
1'1'
2'2'3'3'
4'4'
Adenosine Diphosphate (ADP)Adenosine Diphosphate (ADP)
OOPP
OO
HOHO
HOHO
OCHOCH22PP
OO
HOHO
OO
OHOHHOHO
NN
NN
NN
NHNH22
NN
Adenosine Triphosphate (ATP)Adenosine Triphosphate (ATP)
ATP is an important molecule in several ATP is an important molecule in several biochemical processes including:biochemical processes including:
energy storage.energy storage.
OOPP
OO
HOHO
OO
OCHOCH22PP
OO
HOHO
OO
OHOHHOHO
NN
NN
NN
NHNH22
NN
PP
OO
HOHO
HOHO
Nucleic AcidsNucleic Acids
Nucleic acids first isolated in 1869 (Johann Nucleic acids first isolated in 1869 (Johann Miescher)Miescher)
Oswald Avery discovered (1945) that a Oswald Avery discovered (1945) that a substance which caused a change in the substance which caused a change in the genetically transmitted characteristics of a genetically transmitted characteristics of a bacterium was DNA.bacterium was DNA.
Scientists revised their opinion of the function of Scientists revised their opinion of the function of DNA and began to suspect it was the major DNA and began to suspect it was the major functional component of genes.functional component of genes.
Composition of DNAComposition of DNA
Erwin Chargaff (Columbia Univ.) studied DNAs Erwin Chargaff (Columbia Univ.) studied DNAs from various sources and analyzed the from various sources and analyzed the distribution of purines and pyrimidines in them.distribution of purines and pyrimidines in them.
The distribution of the bases adenine (A), The distribution of the bases adenine (A), guanine (G), thymine (T), and cytosine (C) guanine (G), thymine (T), and cytosine (C) varied among species.varied among species.
But the total purines (A and G) and the total But the total purines (A and G) and the total pyrimidines (T and C) were always equal.pyrimidines (T and C) were always equal.
Moreover: %A = %T, and %G = %CMoreover: %A = %T, and %G = %C
Composition of Human DNAComposition of Human DNA
Adenine (A) 30.3%Adenine (A) 30.3% Thymine (T) 30.3%Thymine (T) 30.3%
Guanine (G) 19.5%Guanine (G) 19.5% Cytosine (C) 19.9%Cytosine (C) 19.9%
Total purines: 49.8%Total purines: 49.8% Total pyrimidines: 50.1%Total pyrimidines: 50.1%
For example:For example:
PurinePurine PyrimidinePyrimidine
Base PairingBase Pairing
A and T are present in equal amounts in DNA A and T are present in equal amounts in DNA because of complementary hydrogen bonding.because of complementary hydrogen bonding.
2-deoxyribose2-deoxyribose
N
NN
N N
H
H
N
N
O CH3
O
H
2-deoxyribose2-deoxyriboseAA TT
Base PairingBase Pairing
Likewise, the amounts of G and C in DNA were Likewise, the amounts of G and C in DNA were equal because of complementary hydrogen equal because of complementary hydrogen bonding.bonding.
N
NN
N O
NH
H
H
N
N
N
O
HH
2-deoxyribose2-deoxyribose
2-deoxyribose2-deoxyribose
GG CC
The DNA DuplexThe DNA Duplex
A double-stranded structure for DNA in which a A double-stranded structure for DNA in which a purine or pyrimidine base in one chain is purine or pyrimidine base in one chain is hydrogen bonded to its complement in the hydrogen bonded to its complement in the other.other.
••Gives proper ratios (A=T and G=C)Gives proper ratios (A=T and G=C)
••Because each pair contains one purine and Because each pair contains one purine and one pyrimidine, the A---T and G---C distances one pyrimidine, the A---T and G---C distances between strands are approximately equal. between strands are approximately equal.
Two antiparallel Two antiparallel strands of DNA strands of DNA are paired by are paired by hydrogen bonds hydrogen bonds between purine between purine and pyrimidine and pyrimidine bases.bases.
O
O
ĞO
ĞO
ĞO
O
O
O
O
OP
O
O
P O
OO
P O
OO
O
O
OĞ
OĞ
OĞ
O
O
O
O
O P
O
O
PO
OO
PO
OO
C G
AT
AT
CG
3'
5'
5'
5'
5' 5'
5'
5'
5'
3'
3'3'
3'3'
3'
3'
DNA is coiledDNA is coiled
A strand of DNA is too long (about 3 cm in length).A strand of DNA is too long (about 3 cm in length).
To fit inside a cell, it is coiled.To fit inside a cell, it is coiled.
Efficient coiling of DNA is accomplished with the Efficient coiling of DNA is accomplished with the aid of proteins called aid of proteins called histoneshistones..
DNA winds around histone proteins to form DNA winds around histone proteins to form nucleosomes.nucleosomes.
Three main types of RNA :Three main types of RNA :
1- Messenger RNA1- Messenger RNA (mRNA): (mRNA):
Transfers DNA code to ribosomes for translation.Transfers DNA code to ribosomes for translation.
2- Transfer RNA2- Transfer RNA (tRNA): (tRNA):
Brings amino acids to ribosomes for protein Brings amino acids to ribosomes for protein synthesis.synthesis.
3- Ribosomal RNA3- Ribosomal RNA (rRNA): (rRNA):
Ribosomes are made of rRNA and protein.Ribosomes are made of rRNA and protein.
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