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8/2/2019 Nucleotides and Nucleic Acids 3(1)
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Nucleotides and Nucleic Acids
Learning objectives:
Define and classify nucleotides and nucleoside.
Define and classify nucleic acids.
Differentiate between the types of RNA and the role of each one.
Discuss the functions of important nucleotides.
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Selected References General, Organic and Biochemistry; 5th edition, Denniston et al.,
2007; McGraw-Hill, New York. Chapter 20, Page: 667 674.
Biochemistry 5th edition, Stryer et al., Chapter 5, Page: 117 125.
The medical Biochemistry home page @
http://themedicalbiochemistrypage.org/nucleic-acids.html
Nucleotide Structure wikipedia @
http://en.wikipedia.org/wiki/Nucleotide
Nucleic acid Structure wikipedia @
http://en.wikipedia.org/wiki/Nucleic_acid
The Structure of Nucleic Acids @
http://www.vivo.colostate.edu/hbooks/genetics/biotech/basics/nastruct.html
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Lecture outlines
Introduction
Nucleotide structure
Nitrogenous bases
Pentose sugar
Phosphate group
Nucleotides in DNA and RNA
Structure of Nucleic Acids
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NUCLEOTIDES
Nucleotides may be considered one of the most important
metabolites of the cell.
Nucleotides are the building units of the nucleic acids of the cell,
RNA and DNA.
They also are required for numerous other important functions
within the cell.
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Question
What are the important derivatives of
nuc eotides and w at are t eir unctions?
What are the types of RNA and what is the role of
each one?
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NUCLEIC ACIDS
Anucleic acid is a macromolecule composed of chains ofmonomeric nucleotide.
y y g
within cells.
The most common nucleic acids are:
DNA: deoxyribonucleic acid
RNA: ribonucleic acid (e.g., some viruses)
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NUCLEIC ACIDS Consist of chemically linked sequences of nucleotides
Nitrogenous base
Pentose sugar 5-carbon (ribose or deoxyribose)
Phosphate group
Sugar
Base
PO4
NucleosidesPhoshate group + = Nucleotides
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Nitrogenous Bases
Two types of bases: Purines are fused five- and six-membered rings
Pyrimidines are six-membered rings
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Purine Bases
H H
Adenine, A Guanine, G
DNA & RNA
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Pyrimidine Bases
Cytosine, C Thymine, T
H H H
Uracil, U
RNA DNA
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Nitrogenous Bases
Purines
Adenine A DNA RNA
Guanine G DNA RNA
Pyrimidines
Cytosine C DNA RNA
Thymine T DNA ------
Uracil U ------- RNA
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Sugars
O OHCH2HO HO O OHCH2
OHOH OH
ribose deoxyribose
(no O)
RNA DNA
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Nucleosides in RNA
Base Sugar Nucleoside
Guanine (G) ribose Guanosine
Cytosine (C) ribose Cytidine
Uracil (U) ribose Uridine
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Nucleosides in DNA
Base Sugar Nucleoside
Adenine (A) Deoxyribose Deoxyadenosine
Guanine (G) Deoxyribose Deoxyguanosine
Cytosine (C) Deoxyribose Deoxycytidine
Thymine (T) Deoxyribose Deoxythymidine
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Nucleotide
NucleosidesPhosphate group + = Nucleotides
Example
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Nucleotides in RNA and DNA
RNA
AMP adenosine monophosphateGMP guanosine monophosphate
CMP cytidine monophosphate
UMP uridine monophosphate
DNA
dAMP Deoxyadenosine monophosphatedGMP Deoxyguanosine monophosphate
dCMP Deoxycytidine monophosphate
dTMP Deoxythymidine monophosphate
16
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Structure of Nucleic Acids
Polymers of four nucleotides Linked by alternating sugar-phosphate bonds
RNA: ribose and A, G, C, U
: eoxyr ose an , , ,
nucleotide nucleotide nucleotide nucleotide
17
P sugar
base
P sugar
base
P sugar
base
P sugar
base
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Nucleic Acid Structure
3,5-phosphodiester bond
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Nucleic Acid Structure
O
N
N
NH2
O
CH2OP
O
-
O-
CMP
-N-glycosidic bond
OH
O
N
N
NH2
CH2OP
O
O-
OH
O
N
N
AMP
3
5
3,5-phosphodiester bond
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Structure of Nucleic Acids
base base base
g g g
5p OH3
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DNA: Helix5
53
3
DNA is double-stranded (two strands of nucleotides).
The strands run in opposite directions (antiparallel).
5 3
3OH p5
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Complementary Base Pairs
In the DNA double helix, purines and pyrimidines face
each other
The two polynucleotide chains in the double helix are
connec e y y rogen on s e ween e ases
(maintain and hold the double-helix structure)
Watson-Crick base-pairing rules
A T
G C
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Complementary Base Pairs
Two H bonds for A-T
Three H bonds for G-C
24
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Double Helix of DNA
55
3
3
Double-stranded (ds) DNA takes theform of a right handed helix with
approximately 10 base pairs per turn
of the helix.
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Double Helix of DNA
26
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Complementary Base Pairs
Since one strand of DNA is complementary to the
other, genetic material can be accurately
for the synthesis of the other
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Question
Write the complementary base sequence forthe matching strand in the following DNAsection:
-A-G-T-C-C-A-A-T-G-C-
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Answer
Write the complementary base sequence forthe matching strand in the following DNAsection:
-A-G-T-C-C-A-A-T-G-C-
-T-C-A-G-G-T-T-A-C-G-
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RNA Structure
RNAs are usually singlestranded.
Many RNA molecules have
secondary structure in whichintramolecular loops areformed by complementary
base pairing.
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RNA Structure
Base pairing in RNA
follows exactly the sameprinciples as with DNA:
duplex formation areantiparallel to one another,and
the base pairs that formare A-U and G-C.
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Question
What are the types of RNA and what is the role of
each one?What are the important derivatives of
nucleotides and what are their functions?
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important functions of nucleotides
These functions include:
1. serving as energy stores for future use in phosphate transferreactions. These reactions are predominantly carried out by
ATP.
2. forming a portion of several important coenzymes such asNAD+, NADP+, FAD and coenzyme A.
3. serving as mediators of numerous important cellularprocesses such as second messengers in signal transductionevents. The predominant second messenger is cyclic-AMP(cAMP), a cyclic derivative of AMP formed from ATP.
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important functions of nucleotides
4. controlling numerous enzymatic reactions through
allosteric effects on enzyme activity.
. servin as activated intermediates in numerous
biosynthetic reactions. These activated intermediates
include S-adenosylmethionine (S-AdoMet) involved in
methyl transfer reactions as well as the many sugarcoupled nucleotides involved in glycogen and
glycoprotein synthesis.
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Adenosine Derivatives
The most common adenosine derivative is the cyclic form,
3'-5'-cyclic adenosine monophosphate, cAMP.
This com ound is a ver owerful second messen er
involved in passing signal transduction events from the
cell surface to internal proteins, e.g. cAMP-dependent
protein kinase (PKA).PKA phosphorylates a number of proteins, thereby,
affecting their activity either positively or negatively.
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Adenosine Derivatives
Cyclic-AMP is also involved in the regulation of ion channels
by direct interaction with the channel proteins, e.g. in the
activation of odorant receptors by odorant molecules.
Formation of cAMP occurs in response to activation of receptorcoupled adenylate cyclase. These receptors can be of any
type, e.g. hormone receptors or odorant receptors.
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Adenosine Derivatives
S-adenosylmethionine is a form of "activated"
methionine which serves as a methyl donor in
propylamine in the synthesis of polyamines.
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Guanosine Derivatives
A cyclic form of GMP (cGMP) also is found in cells involved as a
second messenger molecule. In many cases its' role is toantagonize the effects of cAMP.
Formation of cGMP occurs in response to receptor mediated signals
similar to those for activation of adenylate cyclase. However, in thiscase it is guanylate cyclase that is coupled to the receptor.
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Questions ? ? ?
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