Nucleotides and Nucleic Acids 3(1)

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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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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base base base

g g g

5p OH3


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DNA: Helix5

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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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Two H bonds for A-T

Three H bonds for G-C

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Double Helix of DNA

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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

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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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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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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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Nucleotides and Nucleic Acids 3(1)

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