Nucleotides (1)

7/29/2019 Nucleotides (1)

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One of the important specialized pathways of a number ofamino acids is the synthesis of purine and pyrimidinenucleotides. These nucleotides are important for a number ofreasons. Most of them, not just ATP, are the sources of energythat drive most of our reactions.


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There are two kinds of nitrogen-containing bases:

Purines consist of a six-membered and a five-membered nitrogen-containing ring, fused together.

Pyridmidines have only a six-membered nitrogen-containingring. There are 4 purines and 4 pyrimidines that are of concern

to us.


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Adenine = 6-amino purine

Guanine = 2-amino-6-oxy purineHypoxanthine = 6-oxy purine

Xanthine = 2,6-dioxy purine


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Adenine and guanine are found in both DNA and RNA.

Hypoxanthine and xanthine are not incorporated into the nucleic

acids as they are being synthesized but are important

intermediates in the synthesis and degradation of the purine

nucleotides.


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Uracil = 2,4-dioxy pyrimidine

Thymine = 2,4-dioxy-5-methyl pyrimidine

Cytosine = 2-oxy-4-amino pyrimidine

Orotic acid = 2,4-dioxy-6-carboxy pyrimidine


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Cytosine is found in both DNA and RNA. Uracil is found

only in RNA. Thymine is normally found in DNA. Sometimes

tRNA will contain some thymine as well as uracil.


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If a sugar, either ribose or 2-deoxyribose, is added to anitrogen base, the resulting compound is called a nucleoside.Carbon 1 of the sugar is attached to nitrogen 9 of a purine base

or to nitrogen 1 of a pyrimidine base.

The names of purine nucleosides end in -osine and thenames ofpyrimidine nucleosides end in -idine.


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Adenosine

Guanosine

Inosine - the base in inosine is hypoxanthineUridine

Thymidine

Cytidine


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Adding one or more phosphates to the sugar portion of a

nucleoside results in a nucleotide. Generally, the phosphate is inester linkage to carbon 5' of the sugar. If more than one

phosphate is present, they are generally in acid anhydride

linkages to each other.


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AMP = adenosine monophosphate = adenylic acid

CDP = cytidinediphosphate

dGTP = deoxyguanosine triphosphate

dTTP = deoxy thymidine triphosphate (more commonly

designated TTP)

cAMP = 3'-5' cyclic adenosine monophosphate


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Four deoxynucleotides:

A (adenine)

G (guanine)

T (thymine)

C (cytosine)


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The denaturation of DNA is USED to analyse its

structure

Double-stranded structure of DNA can

be separated in two component strands.

Concomitant with this denaturation of

the DNA molecules is an increase in the

optical absorbance of the purine and

pyrimidine bases.


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Renaturation of DNA requires Base Pair Matching

Separated strands of DNA will

renature or reassociate, whenappropriate physiologic

temperature and salt

conditions are achieved.


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RNA INVOLVED IN SOME ASPECT OF PROTEIN SYNTHESIS

Cytoplasmic RNA molecules that

serves as templates for protein

synthesis that transfers geneticinformation from DNA to protein-

synthesizing machinary are designated

messenger RNAs, or mRNAs.


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RNA DNA

Contains the sugar

ribose

contains the slightly

different

sugar deoxyribose

RNA has the

nucleobase uracil contains thymine

single-stranded Double-stranded


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Adenine and guanine are purines, cytosine,

and uracil are pyrimidines. A phosphate group

is attached to the 3' position of one ribose and

the 5' position of the next.


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This results in a very deep and narrow major grooveand a shallow and wide minor groove.A second

consequence of the presence of the 2'-hydroxyl group

is that in conformationally flexible regions of an RNA

molecule it can chemically attack the adjacent

phosphodiester bond to cleave the backbone.

Nucleotides (1)

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