chemistry of nucleosides, nucleotides & nucleic acid
TRANSCRIPT
Chemistry of Nucleosides, Nucleotides
& Nucleic acid
Dr.Almoeiz Yousif MS.c.,Ph.D.,MEE
Nucleosides
•Nucleosides composed only of base and sugar.
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N. Base Sugar
Nucleotides
• nucleotides define as a monomer of Nucleic acids ( DNA & RNA).
• Nucleotides are intracellular molecules having the following structure:
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N.Base Sugar Phosphate
Nitrogenous Bases
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The nitrogenous bases are either purine or pyrimidine
Pyrimidine bases
•A pyrimidine bases -containing, a single six
membered ring.
•Numbering is clockwise
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Pyrimidine bases
•There are three pyrimidines commonly found in
nucleic acids: Fr
iday
, Ap
ril 2
4, 2
02
0
7
Uracil
Thymine Cytosine
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Uracil Thymine Cytosine
Pyrimidine bases
•The pyrimidines in DNA are cytosine (C) and thymine (T).
•The pyrimidines in RNA are cytosine ( C) and uracil (U).
•Cytosine can be found in DNA and RNA.
•Thymine is found only in DNA, while uracils are found only in RNA.
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Purines
• Purines consist of linked five - membered and six- membered rings.
•Numbering is anticlockwise
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Purines
•There are two purines commonly found in
Nucleic acids.
•Each can be found in nucleic acid.
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Purines
• Other purine bases produce during metabolism, present in free state in cells:
1. Hypoxanthine.
2. Xanthine.
3. Uric acid. (end product of Adenine & Guanine catabolism)
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Sugars
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• The sugars enter in the nucleotides are Pentose sugars (5-Carbon sugars)
Sugars
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• DNA and RNA have different sugars.
• RNA nucleotides or Ribonucleotides , contain ribose sugar
which have a hydroxyl group in both the 2, and 3 – position of
the sugar ring.
Sugars
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• DNA nucleotides or deoxyribonucleotides have 2-
deoxyribose sugars.
•These sugars have only a single hydroxyl group in the 3
position of the sugar ring.
Phosphate Groups
• A nucleotide contain a single phosphate group, which is a strong acid that gives nucleic acids their acidity.
• Phosphates can be attached through the oxygen of the hydroxyl group of either C3 or C5 atoms of the sugar.
• It is more commonly attached to C5.
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Nucleosides
• Result from linking one of the sugars with a purine or pyrimidine base through
an N-glycosidic linkage.
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Nucleotides • Nucleotides are phosphorylated nucleosides
• Result from linking one or more phosphates with a nucleoside onto OH group 5’ end of the sugar.
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Nucleosides and nucleotides
Naming Conventions
•Nucleosides:
•Purine nucleosides end in “-sine”
•Adenosine, Guanosine.
•Pyrimidine nucleosides end in “-dine”
• Thymidine, Cytidine, Uridine
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Naming Conventions
•Nucleotides:
• Start with the nucleoside name from above and add “mono-”, “di-”, or “triphosphate”
•Adenosine Monophosphate, Cytidine Triphosphate, Deoxythymidine Diphosphate
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Purine Base Nucleoside Nucleotide
Adenine (A) Adenosine Adenosine mono phosphate
(AMP, ADP,ATP)
Guanine (G) Guanosine Guanosine Mono P.
(GMP)
Xanthine Xanthosine Xanthosine Mono
Phosphate
Hypoxanthine Inosine Inosine Mono Phospate
Pyrimidine Base Nucleoside Nucleotide
Cytosine (C) Cytidine CMP
Uracil (U) Uridine UMP
Thiamine (T) Thymidine TMP
Functions of Nucleotides
1. They enter in the structure of nucleic acid, ( DNA , RNA).
2. Nucleoside Triphosphates are major biologic transducer of free energy (ATP,
GTP).
3. Important components of coenzymes
FAD, NAD+ and Coenzyme A.
4. Acts as a second messenger, (c-AMP, c GMP).
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Functions of Nucleotides
5. UDP- glucoronic acid is donor for conjugation reactions
that form urinary glucornide conjugates for biluribin or
drugs as aspirin
6. Cytosine derivatives CTP, is involved in synthesis
ceramide.
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Nucleic acid Chemistry
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What Are Nucleic Acids?
• Nucleic acids are polynucleotides: linear polymers of nucleotides
linked 3 to 5 by phosphodiester bridges .
• They are formed as 5-nucleoside monophosphates
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• Polymers of ribonucleotides are named ribonucleic acid, or RNA.
• Deoxyribonucleotide polymers are called deoxyribonucleic
• acid, or DNA.
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Phosphodiester Bond
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Base pairs
• In Nucleic acids, there is base pairing
• It’s a Complementarity (T=A, C=G)
• Purines always base-pair with pyrimidines
• Cytosine hydrogen bonds with guanine
• Thymine hydrogen bonds with adenine or uracil
• Due to distancing and proximity of unshared pairs and
hydrogens
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GC base pair
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N
N
N
NH
O
N HR
H
Guanine
NN
O
N
H
H
R
-- -- --
-- -- --
-- -- --
cytosine
3 H- bonds
AT base Pair
N
N
N
N
N H
H
R
adenine
NNH
O
O
R
-- -- --
-- -- -- --
thymine
2 H-bonds
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Base Pairs
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Pyrimidines
NH2
O
N
N NH
N
Guanine
N
N
Adenine
N
N
NH2
N O
NH2
N O
NH2
N
Cytosine
Purines
Uracil (RNA)
CH3
N O N
O
NH
N O N
O
NH
Thymine (DNA)
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- +
+
+
-
-
Base Pairing Guanine And Cytosine
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+
- Thymine
-
+ Adenine
Base Pairing Adenine And Thymine
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Base Pairing Adenine And Cytosine
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-
+
-
Base Pairing Guanine And Thymine
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+
+
-
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H
P
O
HO
O
O
CH2
H OH
P
O
O
HO
O
O
CH2
H
P
O
OH
HO
O
O
CH2
NH2
N
N
N
N
O
O
NH2 N
NH
N
N
N O
NH2
N
D
N
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O H
P
O
HO
O
O
CH2
HO
H
H
P HO
O
O
CH2
O
O
H
H2O
H OH
P
O
HO
O
O
CH2
H2O
5’Phosphate group
3’Hydroxyl group
5’Phosphate group
3’Hydroxyl group
Because of specific base paring, any single stranded sequence of DNA or RNA can be used as a template for production of the complimentary strand
DNA structure
• B-DNA is most common
• Antiparallel
• bases inside • Hydrophobic
• Perpendicular to helix
• stands complementary • Very important for information transfer
• Each strand a template for the other.
• right handed
• major and minor groove
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Forms of DNA
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Denaturation and Renaturation
• Heating double stranded DNA can overcome the hydrogen bonds
holding it together and cause the strands to separate resulting in
denaturation of the DNA
• When cooled relatively weak hydrogen bonds between bases can
reform and the DNA renatures
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Double stranded DNA
TACTCGACATGCTAGCAC ATGAGCTGTACGATCGTG
Double stranded DNA TACTCGACATGCTAGCAC
ATGAGCTGTACGATCGTG
Denatured DNA
Single stranded DNA
RNA
• codes for protein
• no consistent secondary structure
• single stranded
• Ribose instead of deoxyribose
• Thymine (T) replaced by Uracil
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. Three Types of RNA
•mRNA
• carries genetic information to the ribosomes
• rRNA
• , along with protein, makes up the ribosomes
• tRNA
• transfers amino acids to the ribosomes where proteins are synthesized
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DNA versus RNA
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DNA RNA
Double-stranded Single-stranded
Holds information Transfers information
A pairs with T A pairs with U (if paired)
C pairs with G C pairs with G (if paired)
Sugar is deoxyribose; lacks OH
at carbon 2
Sugar is ribose; has OH at
carbon 2
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