Nucleic Acid Structure PDF

Nucleic acid Structure Dr. Ayaz K Mallick This PowerPoint is to illustrate the lectures and should not be used as a substitute for textbooks. You must read the recommended textbooks for complete understanding and preparation for the exams.  Learning objectives At the en...

Nucleic acid Structure Dr. Ayaz K Mallick This PowerPoint is to illustrate the lectures and should not be used as a substitute for textbooks. You must read the recommended textbooks for complete understanding and preparation for the exams.  Learning objectives At the end of the lectures, the students should be able to: Define nucleosides, nucleotides, and nucleic acid Classify and list the nitrogenous bases Describe the structure and properties of DNA Describe the structure of different types of RNA Outline the structural organization of DNA into a chromosome  Types of Nucleic acids NUCLEIC DNA (Deoxyribonucleic acid) ACID RNA (Ribonucleic acid) DNA RNA Nucleic acids are polymers of nucleotides Nucleic Acid = N N N N N N N N Structure of DNA and RNA nucleotides -DNA is a double stranded, helical polymer of deoxyribonucleotides (Helical means: like a coil) -RNA is a single stranded polymer ribonucleotides  Nucleotides Nucleotides are composed of a nitrogenous base linked to a pentose sugar to which at least one phosphate group is also attached N = NITROGENOUS BASE + PENTOSE SUGAR + PHOSPHATE GROUP(s) Nucleotide = Nitrogenous base (A/T/G/C/U) + pentose sugar (ribose/deoxyribose) + Phosphate group(s) Nucleoside= [Nitrogenous base + pentose sugar]  A A T U G G C C (DNA) (RNA) Pentose sugar Deoxyribose(in DNA) Ribose(in RNA) NUCLEOTI  Nitrogenous bases The nitrogenous bases are of 2 types: 1. Purines (9 membered ring) Adenine (A) Guanine (G) 2. Pyrimidines (6 membered ring) Thymine (T) Cytosine (C) Uracil (U)  DNA RNA 1. Nitrogenous bases 1. Nitrogenous bases found in found in DNA RNA:  Adenine  Adenine  Thymine  Uracil  Guanine  Guanine  Cytosine  Cytosine 2.Pentose sugar present is 2.Pentose sugar present is deoxyribose Ribose 3.DNA is double stranded 3.RNA is single stranded 4.DNA is a polymer of 4.RNA is a polymer of deoxyribonucleotides ribonucleotide 5’ 3’ 5’ 3’ 5’ 3’ 3’ 5’ 3’ 5’ 3’ 5’ Chemical structure of a nucleic acid  The phosphate (PO4) bridges the 3’ and 5’ positions of ribose sugar The linkage between the nucleotides is known as phosphodiester bond The terminal nucleotide whose C5’ is not linked to another nucleotide is called the 5’ end The terminal nucleotide whose C3’ is not linked to another nucleotide is called the 3’ end The sugar and phosphate are the backbone of DNA strands G-C Content and Melting Temperature (Tm) Melting temp: The temperature at which the double- stranded DNA is separated into single strands Melting temp. of DNA depends on the G-C content G-C bonding has 3 hydrogen bonds (stronger than A- T)  Structure of Deoxyribonucleic Acid (DNA)  The first structure of DNA was determined by James Watson and Francis Crick in 1953  DNA has a double helix structure  Three types of DNA  A- DNA  B- DNA (Watson-Crick model)  Z- DNA The Features of Watson-Crick DNA structure Two polynucleotide chains wind around a common axis to form a double helix The two strands are anti-parallel (run in opposite direction) Each strand is a right handed helix The nitrogenous bases are in the center of the double helix and the sugar-phosphate chains are on the sides The helix has 10 base pairs (bp) per turn The bases of both strands are held by hydrogen bonds. This is known as complementary base pairing [(A- T) and (G-C). Watson-Crick base 3-Dimensional structure pairing in DNA of DNA 2 hydrogen bonds are present between adenine and thymine 3 hydrogen bonds are present between guanine and cytosine Adenine (A) Thymine (T) Guanine (G) Cytosine (C)  Types of RNA mRNA (messenger tRNA (transfer RNA) RNA) Is clover leaf shaped Is linear shaped RNA Is involved in Is derived from DNA protein synthesis by transcription (Translation) mRNA carries the Transfers amino codon sequence for acid to growing protein synthesis protein chain rRNA (ribosomal RNA) Is involved in protein synthesis(translation) Is the place/site of protein synthesis- hence ribosmes are called protein factory of cell Ribosomes structure has 2 subunits (1 big and 1 small) Prokaryotes have 70s ribosomes Eukaryotes have 80s ribosomes  Chromosome Structure: DNA is packed into the nucleus as organized structure called chromosomes The DNA is wrapped around Histones to form nucleosomes which undergoes more folding to form chromosomes These nucleosomes are subunits of chromatin Histone is a positively charged protein rich in basic amino acid (arginine and lysine) Histones