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1A Nucleosides—Joining a Monosaccharide and a Base

1A Nucleosides—Joining a Monosaccharide and a Base

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684



NUCLEIC ACIDS AND PROTEIN SYNTHESIS



NH2



O



O



4

5

6



CH3



N3



N



2



N

1



N

H



pyrimidine

(parent compound)



NH

O



cytosine

C



NH



N

H



O



uracil

U



N



O



6



5



8

9N

H



O



thymine

T



NH2

7



N

H



4 N

3



N1



N



2



N

H



N

N



adenine

A



purine

(parent compound)



N



NH



N

H



N



NH2



guanine

G



Uracil (U) occurs only in RNA, while thymine (T) occurs only in DNA. As a result:

• DNA contains the bases A, G, C, and T.

• RNA contains the bases A, G, C, and U.



A nucleoside is formed by joining the anomeric carbon of the monosaccharide with a nitrogen atom of the base. A nucleoside is an N-glycoside, because it is a nitrogen derivative of the

glycosides discussed in Chapter 20. Primes (') are used to number the carbons of the monosaccharide in a nucleoside, to distinguish them from the atoms in the rings of the base.

NH2

N



NH2

HOCH2



OH



O



OH



+



1

N

H



join



OH



D-ribose



HO



N



5'

CH2



N



O



1

1'



4'

3'



O



2'

OH



OH



O

N-glycoside



cytidine

a ribonucleoside



cytosine

C



NH2

N



NH2

HOCH2



O



N



OH



OH

D-2-deoxyribose



N



+

join



HO



CH2



O



9N

1'



9N

H



N

N

N-glycoside



N



adenine

A



OH

deoxyadenosine

a deoxyribonucleoside



With pyrimidine bases, the nitrogen atom at the 1 position bonds with the 1' carbon of the sugar.

With purine bases, the nitrogen atom at the 9 position bonds with the 1' carbon of the sugar. For

example, joining cytosine with ribose forms the ribonucleoside cytidine. Joining adenine with

2-deoxyribose forms the deoxyribonucleoside deoxyadenosine.



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NUCLEOSIDES AND NUCLEOTIDES



685



Nucleosides are named as derivatives of the bases from which they are formed.

• To name a nucleoside derived from a pyrimidine base, use the suffix -idine (cytosine →

cytidine).

• To name a nucleoside derived from a purine base, use the suffix -osine (adenine →

adenosine).

• For deoxyribonucleosides, add the prefix deoxy-, as in deoxyadenosine.



SAMPLE PROBLEM 22.1



Identify the base and monosaccharide used to form the following nucleoside, and then name it.

O

CH3

NH

HO



CH2



N



O



O



OH



ANALYSIS



• The sugar portion of a nucleoside contains the five-membered ring. If there is an OH group

at C2', the sugar is ribose, and if there is no OH group at C2', the sugar is deoxyribose.

• The base is joined to the five-membered ring as an N-glycoside. A pyrimidine base has one

ring, and is derived from either cytosine, uracil, or thymine. A purine base has two rings,

and is derived from either adenine or guanine.

• Nucleosides derived from pyrimidines end in the suffix -idine. Nucleosides derived from

purines end in the suffix -osine.



SOLUTION



O

CH3

NH

HO



CH2



N



O



O



from thymine



The sugar contains no OH at C2', so it is derived

from deoxyribose. The base is thymine. To name

the deoxyribonucleoside, change the suffix of

the base to -idine and add the prefix deoxy; thus,

thymine → deoxythymidine.



2'



OH



no OH group

deoxyribose



PROBLEM 22.1



Identify the base and monosaccharide used to form the following nucleosides, and then assign

names.

O



O

N



NH



a.



HO



CH2



OH



PROBLEM 22.2



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N



O



OH



O



b.



HO



CH2



O



N



NH

N



NH2



OH



Draw the structure of guanosine. Number the carbon atoms in the monosaccharide. Classify the

compound as a ribonucleoside or a deoxyribonucleoside.



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686



NUCLEIC ACIDS AND PROTEIN SYNTHESIS



22.1B



NUCLEOTIDES—JOINING A NUCLEOSIDE

WITH A PHOSPHATE



Nucleotides are formed by adding a phosphate group to the 5'-OH of a nucleoside. Nucleotides are named by adding the term 5'-monophosphate to the name of the nucleoside from which

they are derived. Ribonucleotides are derived from ribose, while deoxyribonucleotides are

derived from 2-deoxyribose.

NH2

N



Add phosphate here.

O

−O



P



NH2



HO

O−



5'

CH2



N



O



N



O

−O



O



P



O



5'

CH2



N



O



OH



phosphate



OH



OH



cytidine

a ribonucleoside



OH



cytidine 5'-monophosphate

a ribonucleotide



NH2

N



Add phosphate here.



−O



P



HO

O−



CMP



O−



O−



O



O



5'

CH2



O



N



NH2



N

N



−O



P

O



O−



N



O

O



O



N



N

N



dAMP







OH



phosphate



5'

CH2



OH

deoxyadenosine 5'-monophosphate

a deoxyribonucleotide



deoxyadenosine

a deoxyribonucleoside



Because of the lengthy names of nucleotides, three- or four-letter abbreviations are commonly

used instead. Thus, cytidine 5'-monophosphate is CMP and deoxyadenosine 5'-monophosphate

is dAMP.

Figure 22.1 summarizes the information about nucleic acids and their components learned thus

far. Table 22.1 summarizes the names and abbreviations used for the bases, nucleosides, and

nucleotides needed in nucleic acid chemistry.





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FIGURE 22.1 Summary of the Components of Nucleosides, Nucleotides,

and Nucleic Acids



Type of Compound



Components



Nucleoside



• A monosaccharide + a base

• A ribonucleoside contains the monosaccharide ribose.

• A deoxyribonucleoside contains the monosaccharide 2-deoxyribose.



Nucleotide



• A nucleoside + phosphate = a monosaccharide + a base + phosphate

• A ribonucleotide contains the monosaccharide ribose.

• A deoxyribonucleotide contains the monosaccharide 2-deoxyribose.



DNA



• A polymer of deoxyribonucleotides

• The monosaccharide is 2-deoxyribose.

• The bases are A, G, C, and T.



RNA



• A polymer of ribonucleotides

• The monosaccharide is ribose.

• The bases are A, G, C, and U.



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NUCLEOSIDES AND NUCLEOTIDES



687



TABLE 22.1

Base



Names of Bases, Nucleosides, and Nucleotides

in Nucleic Acids



Abbreviation



Nucleoside



Nucleotide



Abbreviation



DNA

Adenine



A



Deoxyadenosine



Deoxyadenosine 5'-monophosphate



dAMP



Guanine



G



Deoxyguanosine



Deoxyguanosine 5'-monophosphate



dGMP



Cytosine



C



Deoxycytidine



Deoxycytidine 5'-monophosphate



dCMP



Thymine



T



Deoxythymidine



Deoxythymidine 5'-monophosphate



dTMP



Adenine



A



Adenosine



Adenosine 5'-monophosphate



AMP



Guanine



G



Guanosine



Guanosine 5'-monophosphate



GMP



Cytosine



C



Cytidine



Cytidine 5'-monophosphate



CMP



Uracil



U



Uridine



Uridine 5'-monophosphate



UMP



RNA



Di- and triphosphates can also be prepared from nucleosides by adding two and three phosphate groups, respectively, to the 5'-OH. For example, adenosine can be converted to adenosine

5'-diphosphate and adenosine 5'-triphosphate, abbreviated as ADP and ATP, respectively. We

will learn about the central role of these phosphates, especially ATP, in energy production in

Chapter 23.

NH2

O

−O



P

O−



N



O

O



P



O



5'

CH2



N



O



NH2



N

N



O

−O



O−



P



O

O



O−

OH



P



O



O−



O



P



CH2



N



O



N

N



O−



OH



OH



adenosine 5'-diphosphate

ADP



SAMPLE PROBLEM 22.2



N



O



OH



adenosine 5'-triphosphate

ATP



Draw the structure of the nucleotide GMP.



ANALYSIS



Translate the abbreviation to a name; GMP is guanosine 5'-monophosphate. First, draw the

sugar. Since there is no deoxy prefix in the name, GMP is a ribonucleotide and the sugar is

ribose. Then draw the base, in this case guanine, bonded to C1' of the sugar ring. Finally, add

the phosphate. GMP has one phosphate group bonded to the 5'-OH of the nucleoside.



SOLUTION

Add phosphate here.

HO



O



Add base here.

CH2



O



N



O



OH

−O



P



O



5'

CH2



N



O



1'



O−

OH



NH

N



NH2



OH

OH



OH



ribose

guanosine 5'-monophosphate

GMP



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