DNA Structure and Analysis PDF

DNA Structure and Analysis Basic Molecular Genetics Nucleic Acids Nucleic Acids The largest and the most complex organic molecules. Friedrich Miescher who discovered nucleic acids in 1871. Nucleic acids were...

DNA Structure and Analysis Basic Molecular Genetics Nucleic Acids Nucleic Acids The largest and the most complex organic molecules. Friedrich Miescher who discovered nucleic acids in 1871. Nucleic acids were first isolated from the nucleus, hence the name. The heredity material found in cells Associated with the nuclear material of cells NUCLEIC ACIDS are macromolecules, found in all cells with molecular masses of over 100 million, which precipitate in the storage, transmission and translation of genetic information. Nucleic Acids Are constructed from a string of small molecules called Nucleotides. Nucleotides consist of a 5-carbon sugar (pentose), one or more phosphate groups, and a base containing nitrogenous rings. Nucleic Acids Two types Deoxyribonucleic Acid Ribonucleic Acid DNA Deoxyribonucleic Acid DNA stands for deoxyribose nucleic acid This chemical substance is present in the nucleus of all cells in all living organisms. DNA controls all the chemical changes which take place in cells. The kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA Deoxyribonucleic Acid Is responsible for all cellular activity. Directs the production of proteins. Is double stranded and helical. Is maintained by hydrogen bonds (weak bonds) Is very stable and can survive Temperatures as high as 70C High salt concentrations Acid environments Functions of the DNA DNA is a permanent storage place for genetic information. DNA controls the synthesis of RNA (ribonucleic acid). The sequence of nitrogenous bases in DNA determines the protein development in new cells. The function of the double helix formation of DNA is to ensure that no disorders occur. This is because the second identical strand of DNA that runs anti-parallel to the first is a back up in case of lost or destroyed genetic information. Ex. Down’s Syndrome or Sickle Cell Anemia.  The “Incredible Hulk” The “double muscle” phenotype commonly occurs due to defective splicing of the myostatin gene in animals. Myostatin is a protein that limits skeletal muscle development. Structures of DNA molecules DNA is a very large molecule made up of a long chain of sub-units The sub-units are called nucleotides Each nucleotide is made up of a sugar called deoxyribose a phosphate group -PO4 and an organic base Ribose and Deoxyribose Ribose is a sugar, like glucose, but with only five carbon atoms in its molecule Deoxyribose is almost the same but lacks one oxygen atom Both molecules may be represented by the symbol The bases The most common organic bases are: Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Nucleotides The phosphate The deoxyribose, and one of the bases PO4 Adenine Combine to form a nucleotide Base Types Purines Contain 2 nitrogenous rings: Adenine, and Guanine Base Types Pyrimidines Contain 1 nitrogenous ring Cytosine and Thymine in DNA Joined Nucleotides PO4 A molecule of DNA is formed by millions of nucleotides joined together in a long chain PO4 In fact, the DNA usually consists of a double strand of PO4 nucleotides PO4 The sugar-phosphate chains are on the outside and the strands are held together by chemical bonds between the sugar-phosphate + bases bases backbone Bonding The bases always pair up in the same way Adenine forms a bond with Thymine Adenine Thymine and Cytosine bonds with Guanine Cytosine Guanine Bonding PO4 PO4 adenine thymine PO4 PO4 cytosine guanine PO4 PO4 PO4 PO4 Pairing up: 2-Stranded DNA PO4 PO4 PO4 PO4 The paired strands are PO4 PO4 coiled into a spiral PO4 called PO4 PO4 A DOUBLE HELIX PO4 PO4 PO4 PO4 PO4 PO4 PO4 Pairing up: 2-Stranded DNA Hydrogen bonds between bases hold the strands together: A and T, C and G Hydrogen bond Ribbon model Partial chemical structure Computer model Figure 10.3D Rules for Base Pairings Adenine always pairs with Thymine in DNA (A-T) Guanine always pairs with Cytosine (G-C) and are stronger bonds. Nucleic Acid Strands Nucleic acids are polymers derived from nucleotides. As shown in Fig a, the backbone consists of repetitive [-phosphate- (deoxy)ribose-] units. Individual nucleotides are joined by phosphodiester linkages. Like proteins, nucleic acid chains have a polarity which is defined by the 5' Figure B and 3' ends of the sequence. By convention, the sequence of bases in a strand is written left-to- Figure A right from the 5' to 3' end (Fig. b). Pairing up: 2-Stranded DNA bases sugar-phosphate chain  Structure of Double-helical DNA Cellular DNA exists primarily in a right-handed double-helical form (Fig). The double helix contains two interwound, antiparallel DNA strands (see arrows). The strands are complementary and pair together via Watson-Crick base pairs (A.T; G.C). The backbones of the strands are located on the outside of the helix, while the bases are stacked inside. In the most common conformation of the double helix (DNA), ~10 bp occur per turn. DNA molecules contain wide (major) and narrow (minor) grooves in which parts of the bases are exposed to the outside. DNA binding proteins locate and interact with specific base sequences exposed in the grooves. A DIY model of part of a DNA molecule DNA is a Double-stranded Helix James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10.3A, B RNA Ribonucleic Acid Ribonucleic acid (RNA) is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate. RNA is very similar to DNA, but differs in a few important structural details: in the cell, RNA is usually single- stranded. Ribonucleic Acid It carries out the instructions encoded in DNA Remember DNA = blueprints for life… but “someone” has to be able to read those blueprints and get that info outside of the nucleus DNA in its “pure form” cannot leave the nucleus… Ribonucleic Acid Structure Made of nucleotides that have 3 components (very similar to DNA): Sugar (ribose) Phosphate group (phosphate + oxygen) Nitrogen base (A, U, C, G) Differences from DNA: Sugar is ribose Single stranded Contains uracil instead of thymine as one of the nitrogen bases Ribonucleic Acid Three types of RNA mRNA messenger tRNA transfer rRNA ribosomal Types of Ribonucleic Acid mRNA messenger Is complementary to one strand of DNA and functions to carry the genetic material from the chromosome to the ribosome. Transcription Carry copies of instructions from DNA for the purpose of assembling proteins Remember where proteins are assembled in the cell? Types of Ribonucleic Acid tRNA transfer Is responsible to transfer information from mRNA to rRNA. Translation Types of Ribonucleic Acid rRNA ribosomal Is associated with the ribosome and accepts information from tRNA and correlates the information to synthesize proteins. Protein Synthesis a molecular component of a ribosome Ribosomal RNA (rRNA) does not make proteins. It makes polypeptides (assemblies of amino acids) that go to make up proteins.