Nucleic acids.pdf

Almaaqal University Medical Chemistry Collage of Dentistry Nucleic Acids Dr/ Wael Sobhy Darwish 1ST stage&2024  Nucleic acids Nucleic acids are large biomole...

Almaaqal University Medical Chemistry Collage of Dentistry Nucleic Acids Dr/ Wael Sobhy Darwish 1ST stage&2024  Nucleic acids Nucleic acids are large biomolecules that play essential roles in all cells and viruses. A major function of nucleic acids involves the storage and expression of genomic information, they determine the inherited characteristics of every living thing. The tow main classes of nucleic acids: 1- Deoxyribonucleic acid (DNA) encodes the information cells need to make proteins. 2- Ribonucleic acid (RNA), comes in different molecular forms that play multiple cellular roles, including protein synthesis. Each type of nucleic acid has a distinctive structure and plays a different role in our cells.  Nucleotide The building block of DNA and RNA called Nucleotides Nucleotides are linked together by covalent bonds called phosphodiester linkage. Structure of nucleotide Nitrogenous base Pentose sugar Phosphate group a- Purines Adenine & Guanine RNA b- Pyrimidine DNA Cytosine& Thymine & Uracil  Nucleotide Structure Nucleotides are linked together in DNA and RNA by phosphodiester bonds. These covalent bonds form between the 5' phosphate group of one nucleotide and the 3' hydroxyl group of the sugar of the next nucleotide. Nucleotide Structure  DNA&RNA DNA is composed of a phosphate-deoxyribose sugar backbone and the nitrogenous bases adenine (A), guanine (G), cytosine (C), and thymine (T). RNA has ribose sugar and the nitrogenous bases A, G, C, and uracil (U). A, C, G, U A, C, G, T  DNA Double Helix: DNA is made of two strands of nucleotides joined together by hydrogen bonding. Two DNA strands are twisted around each other to form an anti-parallel double helix Hydrogen bonding occurs as a result of complimentary base pairing. Hydrogen bonding always occurs between one pyrimidine and one purine. Adenine and Thymine pair up with double hydrogen bond (A=T). Cytosine and Guanine pair up with triple bond (GΞC).  Ribonucleic acid (RNA) RNA is a single-stranded nucleic acid polymer of the four nucleotides A, C, G, and U joined through a backbone of alternating phosphate and ribose sugar residues. It is the first intermediate in converting the information from DNA into proteins essential for the working of a cell. Some RNAs also serve direct roles in cellular metabolism. RNA is made by copying the base sequence of a section of double-stranded DNA, called a gene, into a piece of single-stranded nucleic acid. This process, called transcription is catalyzed by an enzyme called RNA polymerase.  Types of RNAs  There are three main classes of RNA molecules: 1. Messenger RNA (mRNA). 2. Transfer RNA (tRNA). 3. Ribosomal RNA (rRNA).  There are some other classes of RNA molecules: Small nuclear RNA (snRNA). Micro RNA (miRNA). Small interfering RNA (siRNA). Heterogeneous nuclear RNA (hnRNA).  mRNA tRNA rRNA Single and straight. Single (80 nucleotide). Globular shape. Copies DNA's instructions & Carries amino acids in the rRNA and protein make up the carries them to ribosomes for cytoplasm to ribosomes for large and small subunits of protein assembly. protein assembly. ribosomes. mRNA's base sequence is Reads mRNA codons and links Aids in moving ribosomes along translated into amino acid together correct sequence of A.A. mRNA strand, to make protein. sequence of protein. to make protein. Three consecutive bases on Three bases on tRNA complement Ribosomes are the site of mRNA called a codon (e.g. UAA, a codon on mRNA, called translation (making poly-peptides). CGC, AGU). anticodon.  Gene expression Gene expression is the process by which the genetic information stored in a gene is used to synthesize a functional protein. Proteins synthesis occurs in two steps : Transcription = DNA → RNA Translation = RNA → protein Transcription is the first step in gene expression. It involves copying a gene's DNA sequence to make an RNA molecule. Transcription is performed by enzymes called RNA polymerases.  Translation Translation is the process of translating the transcript (genetic information) from the mRNA into a specific sequence of amino acids in the growing chain of a polypeptide. Translation takes place on ribosomes The three general steps of translation are initiation, elongation, and termination. A codon is a sequence of three nucleotides in messenger RNA that determines the position of amino acids when a cell starts making proteins. An anticodon is a sequence of three nucleotides in transfer RNA that binds to a corresponding codon and designates a specific amino acid.  tRNA mRNA