Nucleotides, Nucleic Acids and Heredity Bettelheim, Brown, Campbell and Farrell Chapter 25

Nucleic Acids--Intro Chromosomes contain genetic information –found primarily in nucleus Chromatin: tightly packed DNA and histones Chromosomes contain DNA and basic proteins (histones) –Can be seen during cell division Nucleic acids are responsible for genetic information

Introduction –Cells contain thousands of different proteins –How do cells know which proteins to synthesize? chromosomes) –First thought that transmission of hereditary information took place in the nucleus (in chromosomes) beginning late in 19 th century genes –Hereditary information thought to be in genes within the chromosomes histones nucleic acids –Chemical analysis of nuclei showed chromosomes are made up largely of proteins called histones and nucleic acids

Introduction deoxyribonucleic acids (DNA) –By the 1940s it became clear that deoxyribonucleic acids (DNA) carry the hereditary information –Other work in the 1940s demonstrated that each gene controls the manufacture of one protein –Thus, the expression of a gene in terms of an enzyme protein led to the study of protein synthesis and its control

Categories of Nucleic Acids Deoxyribonucleic Acid (DNA) Found in nucleus (in chromosomes) Contain genes which contain genetic information Ribonucleic Acid (RNA) Some found in nucleus (but not in chromosomes) Also found in cytoplasm

Both DNA and RNA contain –A Nitrogenous Base –Sugar –Phosphate Nucleoside contains just a base and a sugar Nucleotide contains all three components

Nucleic Acid Bases

Purine Bases Adenine Guanine

Pyrimidine Bases Cytosine Thymine Uracil

Pyrimidine/Purine Bases

DNA and RNA Bases DNA RNA AdenineAdenine ThymineUracil GuanineGuanine CytosineCytosine

Sugar Ribose2’-Deoxyribose

Both DNA and RNA contain –A Nitrogenous Base –Sugar –Phosphate Nucleoside contains just a base and a sugar Nucleotide contains all three components

Nucleoside

Nucleosides Nucleoside:Nucleoside: a compound that consists of D-ribose or 2-deoxy-D-ribose bonded to a purine or pyrimidine base by a  -N- glycosidic bond

Nucleotide

Nucleotides Nucleotide:Nucleotide: a nucleoside in which a molecule of phosphoric acid is esterified with an -OH of the monosaccharide, most commonly either the 3’ or the 5’-OH

Nucleotides –adenosine 5’-triphosphate (ATP) serves as a common currency into which energy gained from food is converted and stored

Structure of DNA and RNA Primary Structure:Primary Structure: the sequence of bases along the pentose-phosphodiester backbone of a DNA or RNA molecule –base sequence is read from the 5’ end to the 3’ end

Nucleic Acid - 1° Structure A schematic diagram of a nucleic acid

Fig ’,5’ phospho- diester linkage 3’ end of one sugar to phosphate to 5’ end of second sugar Each nonterminal phosphate has -1 charge

Pyrimidine Bases Cytosine Thymine Uracil

Fig. 24.3, p.602

Structure of DNA and RNA Primary Structure:Primary Structure: the sequence of bases along the pentose-phosphodiester backbone of a DNA or RNA molecule –base sequence is read from the 5’ end to the 3’ end

Nucleic Acid Structure DNA has a double helix structure –Phosphates on outside Complementary Base Pairs on inside RNA is single stranded –Messenger RNA (m-RNA) Transfer RNA (t-RNA) has some double stranded loops

DNA - 2° Structure Secondary structure:Secondary structure: the ordered arrangement of nucleic acid strands –Double helix model of DNA 2° structure was proposed by James Watson and Francis Crick in 1953 –Based on two primary sources of information Irwin Chargaff: A = T and C = G X-ray diffraction picture of DNA taken by Rosalind Franklin

Table 24.2, p.602 Irwin Chargaff: Base Composition in Many Different Species

p. 640 Rosalind Franklin

p. 640 James Watson & Francis Crick

Double helix:Double helix: –a type of 2° structure of DNA molecules in which two anti-parallel polynucleotide strands are coiled in a right-handed manner about the same axis

DNA – Double Helix Double helix: Two DNA strands Anti-parallel strands –One is 3’ to 5’ Other is 5’ to 3’ Strands are coiled in a right-handed helix about the same axis Backbone has alternating sugar and phosphate groups Complementary Base Pairs on inside of helix

The DNA Double Helix Each turn is 3.4 nm

Complementary Base Pairs DNA Base Pairs Double-Stranded A-T%A = %T C-G%C = %G RNA Base PairsSingle-Stranded A-U C-G

Complementary Base Pairs Must be one purine and one pyrimidine to fit properly Two purines too big Two pyrimidines too small Not every purine-pyrimidine pair forms naturally

Fig. 24.6, p.605

Complementary Base Pairs 2 H-bonds 3 H-bonds TA pair GC pair

Non-Complementary Base Pairs

Chains are anti-parallel

Fig. 24.5

Fig. 24.4

Higher Structure of DNA histones –DNA is coiled around proteins called histones –Histones are rich in the basic amine acids Lys and Arg, whose side chains have a positive charge –DNA molecules (with – charge) and histones (with + charge) attract each other and form units called nucleosomes –nucleosome: –nucleosome: a core of eight histone molecules around which the DNA helix is wrapped chromatin –nucleosomes are condensed into chromatin chromosomes –chromatin fibers are organized into loops and then bands in the superstructure of chromosomes

Chromosomes

DNA and RNA The three differences in structure between DNA and RNA are T U –DNA bases are A, G, C, and T; the RNA bases are A, G, C, and U 2-deoxy-D-ribose D-ribose –the sugar in DNA is 2-deoxy-D-ribose; in RNA it is D-ribose double stranded single- stranded –DNA is always double stranded; there are several kinds of RNA, all of which are single- stranded