University:
Kentucky State University
Course:
BIO 307 | Genetics
Academic year:

2021
Views:

161

Pages:

21
Author:

Nicole Wang

Lecture # 2: Structure of Nucleic Acids I  Nucleic Acids: How Structure Conveys Information: SHEET NOTE - There are two types of nucleic acids: 1. deoxyribonucleic acid (DNA) 2. ribonucleic acid (RNA) We have three types of polymers, 1. Carbohydrates 2. Proteins 3. Nucleic Acids Note: lipids not polymers - Nucleic acids are polymers consisting of long chains of monomers called nucleotides. Today we will talk about the structure of Nucleic Acid - A nucleotide: consists of a nitrogenous base, a pentose sugar and a phosphate group. - 2 Lecture # 2: Structure of Nucleic Acids I  Pentose Sugars: - There are two related pentose sugars: - RNA contains ribose - DNA contains deoxyribose SHEET NOTE The really important difference is that RNA has an extra oxygen atom. This makes RNA less stable than DNA - 3 SHEET NOTE To understand the idea, do not memorize You might think that being unstable is a bad thing, but there are advantages. Organisms that need to change rapidly tend to use RNA as their genetic material. Viruses, such as influenza and HIV, choose RNA rather than the more stable alternative of DNA so they can change and keep one step ahead of the immune system of their hosts. Many factors contribute to the high mutation rates in RNA viruses, including the instability of RNA and the poor proof reading activity in the enzymes that replicate RNA . 4 Lecture # 2: Structure of Nucleic Acids I  Pentose Sugars: HOCH2 OH O Ribose 5’ HOCH2 O OH 4’ 1’ 3’ - OH 2’ The sugars have their carbon atoms numbered with primes to distinguish them from the nitrogen bases HOCH2 OH O Deoxyribose OH H 5 Lecture # 2: Structure of Nucleic Acids I  DNA structure: - DNA is the largest macromolecule in the cell. In eukaryotic cells, 99% of the cell DNA is present in linear form folded on itself several times to occupy small space within the chromosomes of the nucleus . - Each chromosome contains single DNA molecule. Small amounts of DNA (about 1%) are circular shape present inside the mitochondria. - The DNA can be described as a polymer of nucleotides (Polynucleotide).That is a long chain of repeating nucleotide units connected together strongly (by covalent bonds). 6 Lecture # 2: Structure of Nucleic Acids I  DNA structure: - The nitrogen bases are heterocyclic (combination of carbon and nitrogen atoms) present in the cell with 5 different types.  Two purines : adenine and guanine (with 9 atoms of 4 nitrogens and 5 carbons arranged in two rings)  Three pyrimidine: Cytosine, Thymine and Uracil having (6 atoms ring including 2 nitrogens and 4 carbons) 7 One episode two episodes 8 Lecture # 2: Structure of Nucleic Acids I SHEET NOTE  Nucleotides and Nucleosides: Nucleotide : - Nitrogeneous base - Pentose - Phosphate Nucleoside : - Nitrogeneous base - Pentose Nucleobase : - Nitrogeneous base - 9 Lecture # 2: Structure of Nucleic Acids I  DNA structure: SHEET NOTE Uracil -- RNA Thymine -- DNA - the pentose sugar connects to nitrogen base at carbon one from one direction and to phosphate group at carbon 5 of the other side - 10 SHEET NOTE Lecture # 2: Structure of Nucleic Acids I  Deoxyribonucleotides found in DNA: dA dG dT Principles of Genetics and molecular biology Dr. Ola AL-FAWARES dC 11 Lecture # 2: Structure of Nucleic Acids I  Deoxyribonucleotides found in DNA: 13 - The difference is - 2'-OH in ribose and 2'-H in deoxyribose 14 • In DNA, A, C, G, and T are linked by 3’-5’ ester bonds between deoxyribose and phosphate 15 - Lecture # 2: Structure of Nucleic Acids I  DNA structure: - In single polynucleotide chain of DNA (and similarly for RNA structure) the chain is made from covalent linkage of sugar phosphate backbone .In this arrangement the nitrogen bases are exposed freely to the inside of the backbone structure. Has polarity Has a Hydroplilic side Has a Hydrophobic side 16 Lecture # 2: Structure of Nucleic Acids I Two bond  DNA structure: SHEET NOTE Three bond Hydroplilic sid Hydroplilic side Hydrophobic side - 17 Lecture # 2: Structure of Nucleic Acids I  James Watson and Francis Crick, 1959: - In 1953 Watson and Crick noted that DNA consists of two polynucleotide strands, running in opposite directions ( antiparallel ) and coiled around each other in a double helix - Strands are held together by hydrogen bonds between specific pairs of bases - Adenine (A) and thymine (T) form strong two hydrogen bonds to each other but not to C or G - (G) and cytosine (C) form strong three hydrogen bonds to each other but not to A or T - won the 1962 Nobel Prize in Medicine for their discovery of the structure of DNA 18 - Fig. 9-8a, p.222 19 - Fig. 9-8b, p.222 20 Lecture # 2: Structure of Nucleic Acids I  G-C Content: SHEET NOTE Density Gradient Centrifugation ---Shows direct relationship between G=C content and density. • A=T, G=C, but AT≠GC • Generally GC~50%, but extremely variable • EX. • Slime mold~22% • Mycobacterium~73% • Distribution of GC is not uniform in genomes - 21 Lecture # 2: Structure of Nucleic Acids I  Opposite direction of DNA polynucleotide chains: - 5’ terminal: at one end of each DNA strand is a phosphate group linked to carbon atom 5 of deoxyribose - 3’ terminal: at one end of each DNA is a hydroxyl group attached to carbon atom 3 of deoxyribose. - The sequence is read from the free 5’-end using the letters of the bases, this example reads 5’—A—C—G—T—3’ - 22 Lecture # 2: Structure of Nucleic Acids I  ROSALIND FRANKLIN 1920-58 -Gave an idea that the structure of DNA is a helical structure. -Physical Chemistry & Xray crystallography expert -Died of ovarian cancer - 23

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