NUCLEIC ACIDS AND TYPES/FORMS OF NUCLEIC ACIDS

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NUCLEIC ACIDS AND TYPES/FORMS OF NUCLEIC ACIDS

 

“NUCLEIC ACIDS AND TYPES/FORMS ”  Nucleic acids are the hereditary determinants of living organisms I.e. they determine the genetics of the cell. The cells that make up the human body have nucleic acids that instruct the cell on how to function.  The term nucleic acid is the general name for DNA and RNA. They are the macromolecules present in most living cells either in the free state or bound to proteins as nucleoproteins (which are made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base).

If the sugar is a compound ribose, the polymer is RNA (ribonucleic acid); if the sugar is derived from ribose as deoxyribose, the polymer is DNA (deoxyribonucleic acid).

Nucleic acids are biopolymers of high molecular weight with mononucleotides as their repeating units.

take the course

 

NUCLEIC ACIDS AND TYPES/FORMS

TYPES/FORMS of NUCLEIC ACIDS

 

There are two forms of nucleic acids, Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The bulk of DNA is found in chromosomes in the nucleus of eukaryotic cells, although some is also present in mitochondria and chloroplasts.

 

Upon hydrolysis, under different sets of conditions, the two nucleic acids yield three components:

  • Phosphoric acid
  • A pentose sugar and
  • Nitrogenous bases

 

NUCLEIC ACIDS AND TYPES/FORMS

The structural component of RNA and DNA

Components RNA DNA
Acid Phosphoric acid Phosphoric acid
Pentose sugar D-ribose D-2-deoxyribose
Nitrogenous bases
Purines Adenine Adenine
Guanine Guanine
Pyrimidines Cytosine Cytosine
       Uracil Thymine

 

PHOSPHORIC ACID

The molecular formula of phosphoric acid is H3PO4

 

PENTOSE SUGAR   “NUCLEIC ACIDS AND TYPES/FORMS”

The sugars found in nucleic acids are pentose sugars; a pentose sugar has five carbon atoms. Ribose, found in RNA, is a “normal” sugar, with one oxygen atom attached to each carbon atom. Deoxyribose, found in DNA, is a modified sugar, lacking one oxygen atom (hence the name “deoxy”). This difference of one oxygen atom is important for the enzymes that recognize DNA and RNA because it allows these two molecules to be easily distinguished inside organisms.

 

 

NITROGENOUS BASES  NUCLEIC ACIDS AND TYPES/FORMS”

The two types of nitrogenous bases found in nucleic acids are Purine and Pyrimidine.

All nitrogenous bases have a six-sided ring with 4 carbon atoms and 2 nitrogen atoms. A purine has an additional 5-sided ring, created by 1 more carbon and 2 more nitrogen atoms. A pyrimidine has only 1 six-sided ring.

or

Guanine and adenine are double-ringed purine molecules

Cytosine, thymine and uracil are single-ringed pyrimidine molecules

 

Thymine and uracil are chemically similar molecules – thymine is present in DNA, while uracil is used in RNA

SUGAR–PHOSPHATE BACKBONE

The sugar-phosphate backbone forms the structural framework of nucleic acids, including DNA and RNA. This backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule and always reads from 5′ to 3′.

DNA and RNA are composed of nucleotides that are linked to one another in a chain by chemical bonds, called ester bonds, between the sugar base of one nucleotide and the phosphate group of the adjacent nucleotide. The sugar is the 3′ end, and the phosphate is the 5′ end of each nucleotide. The phosphate group attached to the 5′ carbon of the sugar on one nucleotide forms an ester bond with the free hydroxyl on the 3′ carbon of the next nucleotide. These bonds are called phosphodiester bonds, and the sugar-phosphate backbone is described as extending, or growing, in the 5′ to 3′ direction when the molecule is synthesized. Phosphates carry a negative charge; thus, DNA and RNA strands have an overall negative charge continue reading

 

 

NUCLEOSIDES AND NUCLEOTIDES “NUCLEIC ACIDS AND TYPES/FORMS”

 

Nucleosides are compounds in which nitrogenous bases (purines and pyrimidines) are conjugated to the pentose sugars (ribose and deoxyribose) by a β–glycosidic linkage (C-1 of sugar and the hydrogen atom of N-9 (purines) or N-1 (pyrimidine)). Examples of nucleosides include cytidine, uridine, adenosine, guanosine, thymidine and inosine.

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Nucleotides are formed when one or more phosphate groups are attached to C-5′ of a nucleoside. Nucleotides are energy-rich substances that drive metabolic processes in cells. They serve as chemical signals, key links in cellular systems that respond to hormones and other extracellular stimuli and are structural components of a number of enzyme cofactors and metabolic intermediates.

 

Parts of a nucleotide

NUCLEIC ACIDS AND TYPES/FORMS

Base Nucleoside Nucleotides
Adenine Adenosine

(Deoxyadenosine)

AMP (dAMP) ADP

(dADP)

ATP (dATP)
Guanine Guanosine

(Deoxyguanosine)

GMP (dGMP) GDP (dGDP) GTP (dGTP)
Cytosine Cytidine

(Deoxycytidine)

CMP (dCMP) CDP

(dCDP)

CTP (dCTP)
Uracil Uridine

(Deoxyuridine)

UMP (dUMP) UDP (dUDP) UTP (dUTP)
Thymine Deoxythymidine (dTMP) (dTDP) (dTTP)

 

NUCLEIC ACIDS AND TYPES/FORMS

NUCLEOSIDE ANALOGUES AS DRUGS “NUCLEIC ACIDS AND TYPES/FORMS”

The two nucleoside analogues, 3’-azidodeoxythymidine (AZT) and 2’,3’-dideoxycytidine (DDC), have been therapeutically used for the treatment of acquired immune deficiency syndrome (AIDS) patients. The disease is caused by the human immunodeficiency virus (HIV), which is an RNA virus that requires a specific enzyme, an RNA-dependent DNA polymerase, for its replication. When given to AIDS patients, AZT and DDC are converted into their triphosphate forms, which can then compete with dTTP and dCTP, respectively, as substrates for DNA synthesis. When incorporated the analogues terminate DNA synthesis because the absence of a 3’-OH group in them prevents continued elongation of DNA molecule being synthesized. continue reading

 

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