Karaganda State Medical University. Chemistry department. Lecture on the topic: HETEROCYCLIC COMPOUNDS. NUCLEIC ACIDS. For the 1st year students of specialty “General medicine". Discipline: Chemistry. Lecturer: PhD, Associate Professor Vlassova Lenina. Karaganda 2014

Plan of the lecture: 1. The nucleic acid. 2. Nucleosides as structural components of nucleic acids. 3. Nucleotides as structural components of nucleic acids. 4. The structure of nucleic acids.

The objectives of the lecture: 1. Learning to understand the structure of nucleotides and nucleosides. 2. To be able to distinguish and know the names of the various nucleotides and nucleosides. 3. Know the features of the structure of RNA and DNA. 4. To be able to apply their knowledge to solve biochemical problems.

Introduction. There are two types of nucleic acids, namely deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Primarily, nucleic acids serve as repositories and transmitters of genetic information. Brief history. DNA was discovered in 1869 by Johann Friedrich Miescher, a Swiss researcher. The demonstration that DNA contained genetic information was first made in 1944, by Avery, Macleod and MacCary. Functions of nucleic acids. DNA is the chemical basis of heredity and may be regarded as the reserve bank of genetic information. DNA is exclusively responsible for maintaining the identity of different species of organisms over millions of years. Further, every aspect of cellular function is under the control of DNA. The DNA is organized into genes, the fundamental units of genetic information. The genes control the protein synthesis through the mediation of RNA, as shown below DNA  RNA  Protein

The interrelationship of these three classes of biomolecules (DNA, RNA and proteins) constitutes the central dogma of molecular biology or more commonly the central dogma of life.

Components of nucleic acids. The nucleic acid include residues of monosaccharides - D-ribose and 2-deoxy-D-ribose. Both monosaccharides present in the nucleic acids in the β-furanose forms.

General structure of nitrogen bases (A) Purine (B) Pyrimldine (The positions are numbered according to the international system).

All nucleic bases include bases of pyrimidine series - the uracil, thymine, cytosine, and purine series –the adenine and guanine.

Nucleosides. Nucleosides - N-glycosides are formed from nucleic bases (uracil, thymine, cytosine, adenine and guanine) and the ribose or deoxyribose. The chemical bond between the nucleobase and the carbohydrate residue is called a glycoside.

Nucleotides. Nucleotides - are esters of phosphoric acid, and nucleosides (nucleoside phosphates). The ester bond formed with phosphoric acid fnd OH group in position 5 / or 3 / of monosaccharide units. Depending on the nature of the monosaccharide residue nucleotides divided by the ribonucleotides (RNA structural elements), and deoxyribonucleotides (DNA structural elements.)

STRUCTURE OF NUCLEOTIDES.

The names of nucleotides include the name of the nucleoside showing the position it phosphoric acid residue. The abbreviated notation of nucleosides contains a designation nucleoside residue and mono-, di-or triphosphoric acid.

Table 1. Principal bases, nucleosides and nucleotides. Ribonucleoside Ribonucleotide (5'- monophosphate) Abbreviation Adenine (A) Adenosine Adenosine 5'-monophosphate or adenylate AMP Guanine (G) Guanosine Guanosine 5'-monophosphate or guanylate GMP Cytosine (C) Cytidine Cytidine 5'-monophosphate or cytidylate CMP Uracil (U) Uridine Uridine 5'-monophosphate or uridylate UMP

Deoxyribonucleotide (5'-monophosphate) Base Deoxyribonucleosid e Deoxyribonucleotide (5'-monophosphate) Abbreviation Adenine (A) Deoxyadenosine Deoxyadenosine 5'-monophosphate or deoxyadenylate dAMP Guanine (G) Deoxyguanosine Deoxyguanosine 5'-monophosphate or deoxyguanylate dGMP Cytosine (C) Deoxycytidine Deoxycytidine 5'-rnonophosphate or deoxycytidylate dCMP   Thymine (T) Deoxythymidine Deoxythymidine 5'-monophosphate or deoxythymidylate dTMP

Nucleotides are the monomeric units of the polymer chains which are built of nucleic acids.      Some nucleotides act as coenzymes and are involved in metabolism.

Nucleic acids The primary structure of the nucleic acid is a linear polymer chain, built of monomers - nucleotides linked 3/-5/-phosphodiester bonds.

The secondary structure of DNA. The secondary structure of DNA is a complex of two polynucleotide chains right twisted around a common axis so that the carbohydrate chain are outside the phosphate and nucleic bases directed inwards (Watson-Crick double helix).

Complementarity. Two DNA chains unequal in their composition but they are complementary. It is expressed that opposite the adenine (A) in a chain is always thymine (T) in the other chain, and opposite guanine (G) is always cytosine (C).

Complementary pairing A with T and G with C is due to hydrogen bonds Complementary pairing A with T and G with C is due to hydrogen bonds. Between A and T forms two hydrogen bonds between the T and C – three hydrogen bonds.

The complementary strands of DNA is the chemical basis of the most important functions of DNA - storage and transmission of genetic information.          There are three main types of cellular RNAs: - Transfer RNA (tRNA) - Matrix RNA (mRNA) - Ribosomal RNA (rRNA).

The functions of RNA. The matrix RNA is function as matrix protein synthesis in ribosome. Ribosomal RNA is serve as structural components of ribosomes. Transport RNA involved in transporting a-amino acids from the cytoplasm to the ribosomes and translation information in the nucleotide sequence of the mRNA sequence of amino acids in proteins.

Thank you for your attention.