Nucleotide; is made of; a sugar, a base and a phosphate group;

  • A phosphate group( PO3-4 );
  • A pentose sugar (pent=5; ie a sugar molecule made of 5 carbon atoms); is either;

-Deoxyribose sugar in DNA; OR

-Ribose sugar in RNA;

In DNA nucleotides; the deoxyribose sugar ( a 5-carbon sugar) and phosphate are same; but the nitrogen base in each nucleotide could be either; A or C or G or T.

In RNA nucleotides; the ribose sugar (a 5-carbon sugar); and phosphate are same; but the nitrogen base in each nucleotide could be either;  A or C or G or U.

Note; Like in proteins, DNA and RNA have Nitrogen and that’s why metabolic wastes from them are called nitrogenous wastes= urea/uric acid from protein and s

One pentose sugar plus nitrogenous base=nucleoside;
N-base joins to the sugar molecule at 1’ carbon atom by; a glycoside bonds;

NUCLEOSIDES;= one pentose sugar +  a nitrogenous base;

  • Ribose sugar plus a nitrogen base= ribonucleoside/riboside ;(are found in RNA)

Eg; -Ribose + adenine =adenosine;  (R-A)
-Ribose + guanine=guanosine ;(R-G)
-Ribose + cytosine=cytidine ;(R-C)
– Ribose + Uracil=uradine ;(R-U)
Uracil only forms a nucleoside with ribose sugar;

  • Deoxyribose plus a nitrogen base=deoxyribonucleoside/deoxyriboside;(are found in DNA)

Eg; -Deoxyribose + adenine=deoxyadenosine; (D-A)
– Deoxyribose + guanine=deoxyguanosine; (D-G)
– Deoxyribose + cytosine=deoxycytidine; (D-C)
– Deoxyribose + thymine= deoxythymine; (D-T)
Thymine only forms a nucleoside with deoxyribose sugar;

Note; sometimes the nucleotides are represented just by the first letter of the base present on it when drawing a nucleotide polymer. I.e. just A, G , C, T  or  U

A nucleotide= nucleoside +  a phosphate (=nucleoside monophosphate);

(The phosphate joins to nucleoside sugar at 5’ atom a by covalent ester bond to form a nucleotide);


  • Ribonucleotide /ribotide=nucleotide whose sugar is  ribose sugar; are RNA monomers;

     (Nucleoside monophosphate whose sugar is a ribose);

Eg -adenylic acid/ adenosine monophosphate=AMP;
-Guanylic acid/guanosine monophosphate=GMP
-Cytidylic acid/cytidine monophosphate=CMP;
-Uridylic acid/ uradine monophosphate=UMP

  • Deoxyribonucleotide (DNA)/ deoxyribotide =nucleotide whose sugar is deoxyribose sugar;(nucleoside monophosphate whose pentose sugar is deoxyribose); are DNA monomers;

Eg -Deoxyadenylic acid/deoxyadenosine monophosphate=dAMP;
-Deoxyguanylic acid/deoxyguanosine monophosphate=dGMP;
-Deoxycytidylic acid/deoxycytidine monophosphate=dCMP;
-Deoxythymidylic acid/ deoxythymine monophosphate=dTMP;

Note; –Nucleotides are the monomers of DNA and RNA chains and are joined together by their phosphate groups through covalent ester bonds;

-Both glycosidic & ester bonds formations involve removal of water molecule=condensation reaction;
-DNAs and RNAs are polymers while nucleotides are their monomers);

Sketching DNA structure;

Remember nucleotides can be represented just by the first letter of the base present on them.
T if thymine is the one present; or C if cytosine; or A if adenine; or G if guanine is the base present.
In one DNA strand; C joins to G;  A joins to T ; (Remember instead of T we have U when dealing with RNAs)

Note; normally two strands of DNAs hydrogen-bond to form DNA Double Helix; which then twists like a  spiral  staircase. RNAs are made of single strands;




Higher nucleotides;

Free nucleotides may have up to 3 phosphate groups eg Adenosine Diphosphate (ADP), Adenosine Triphosphate, (ATP),
Guanosine di-phosphate (GDP), Guanosine Triphosphate (GTP) etc;
These free existing nucleotides with more than one phosphate=higher nucleotides;
Here the 2nd and 3rd phosphates are attached against repulsive forces between similar charged phosphate radicals;
3rd phosphate bond of higher nucleotide yields 8.9 kcal and 2nd 6.5kcal per mole;
These are more than most covalent bonds;
Phosphate bonds of higher nucleotides=high energy bonds; &can be hydrolysed to release the energy;
Higher nucleotides function as energy carriers eg ATP;
Nucleotides of vitamins =coenzymes;
Are formed by replacing a nucleotide’s nitrogen base with some vitamin;
Eg two B-complex vitamins;
Nicotinamide and flavin parts of riboflavin (riboflavin=vitamin B2;

Nicotinamide and flavin parts of riboflavin (riboflavin=vitamin B2;

Vitamin Nucleotide Components
Nicotinamide(Vitamin B3) Nicotinamide adenine dinucleotide, NAD+Nicotinamide adenine dinucleotide phosphate, NADP+(coenzymes in hydrogen transport) Nicotinamide-ribose-phosphate-ribose-adenine.Nicotinamide-ribose-phosphate-phosphate-phosphoribose-adenine
Riboflavin(vitamin B2) Flavin mononucleotide (FMN)Flavin adenine dinucleotide, (FAD)(flavoproteins in oxidative phosphorylation) Riboflavin-phosphateRiboflavin-phosphate-phosphate-ribose-adenine



Functions of nucleotides e.g.

  • Form nucleic acids (RNA and DNA) by polymerisation;
  • Higher nucleotides especially ATP store energy in their high energy phosphate bonds which is hydrolysed to release energy for driving energy-dependent cellular reaction;
  • Nicotinamide and riboflavin nucleotides act as co-enzymes for oxidising enzymes;


Nucleic acids; as genetic materials;- (DNAs and RNAs)
Are the largest macromolecules in living-things?
DNA is the genetic code in living things while RNA is genetic code in some viruses like tobacco mosaic virus, TMV;
DNA is the main genetic materials in organisms while RNAs performs functions of a messenger and adapter;

Functions of a genetic material;

  • Blue-print for construction of organisms; In sexual reproduction genetic material in fertilized egg helps in development of the Zygote to embryo and eventually to adult organism;
  • Allows organism to survive in its environment;

Example; it provides blue-print for synthesis of necessary enzymes needed for food metabolism;
To fulfil these roles, a genetic material should have following properties;
Information; it must have necessary instructions to construct entire organism
Transmission; it must be able to be passed to next generation of organisms, or of cells through reproduction;
Replication; for transmission to occur it must be able to be accurately copied;
This is only seen in RNAs and DNAs; but not in any other biomolecules like proteins;
Variation; should be able to mutate and the mutant genetic material should be in a position to be stably inherited;

Variations allow organisms to colonise different habitats and utilise different resources;
Natural selection acts on inheritable variations to bring speciation/evolution
New species may be adapted to colonising different habitats and utilise different resources
When organisms are able to colonise different habitats, potential completion between and
Among them is minimised; this increases survival chances of different species;

Relative stability; though some mutations lead to good variations, genetic material should be fairly stable and shouldn’t easily change eg with change in age, or physiology   in organism;

Reasons why RNAs are less stable than DNAs

  • RNA is less stable in high temperature due to 2’- OH group in each nucleotide;
  • RNA is catalytic and thus has become reactive;
  • RNA has Uracil instead of thymine;

RNA is less stable in high temperature due to 2’- OH group in each nucleotide;
RNA is catalytic and thus has become reactive;

Note; because RNAs are less stable, they mutate faster than DNAs;
That’s why viruses with RNAs as genome mutate faster; and have shorter life spans;

RNAs are better for transmission of genetic information;
While DNAs are better for storage of genetic information;


Functions of DNA

  • Carries all hereditary in formation in organisms and some viruses;
  • It transfers this information from one generation to next through unique property of replication; (Replication=; copying of DNA strand)
  • It gives rise to RNAS through transcription;
  • It uses these RNAs to direct synthesis of biomolecules like proteins eg enzymes, lipids, vitamins, hormones
  • Controls cell different functions of diffent cell parts, and cell specialisation;
  • Contributes to variation through; Formation of new gene combinations (gene re-combinations) due to crossing over during cell division;
  • Contributes to evolution through stable mutations;Mutation; leads to heritable variations upon which natural selection works;

Functions of RNAs

  • Involved in expression of genetic code of DNA by helping in forming proteins according to in information on DNA;
  • Segment of DNA called gene is transcribed into RNA and ultimately results in formation of a functional product; (Transcription begins at promoter and ends at terminator DNA)Structural genes (are over 90%) are transcribed to mRNA which help in a protein synthesis;
    Non-structural genes are transcribed to rRNA or tRNA ; provide arena for protein synthesis
  • mRNA carry instruction for protein synthesis from DNA to ribosome;translation; formation of polypeptide on a ribosome using information on the mRNA;
  • rRNA forms part of ribosome, helps in correctly locating mRNA on ribosome surface;
  • tRNAs help in transferring amino acids from cytoplasm to the mRNA on ribosome during protein synthesis;
  • RNA is the genetic material in some viruses like HIV, and tobacco mosaic virus (TMV);
  • RNA-primer is used during DNA replication;
  • Some RNAs like ribozymes, ribonuclease act as enzymes;
  • RNA helps in folding of DNA into a Nucleoid;

Nucleosome; highly packaged units of 146 nucleotide base pairs of DNA + 8  positively charged proteins called histones; these are connected by linker DNA regions; in a chromosome
Chromatin; the whole

DNA-protein complex that makes eukaryotic chromosomes;

Nuclear chromatin;/nuclear reticulum; darkly stained network of long fine threads of Nucleosomes;
Karyotype; photographic presentation of chromosomes, from largest to smallest, in an actively dividing cell ;(they appear as duplicated condensed sister chromatids);

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