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;

gen2
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
Sustainably
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;
Thus;

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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