Lecture 4.docx

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Biology - Biological Sciences
BSC 2010

Lecture 4 Concept 3.1 Nucleic Acids are Informational Macromolecules  Nucleic Acids are polymers specialized for storage, transmission, and use of genetic information.  DNA= deoxyribonucleic acid  RNA= ribonucleic acid  Monomers: nucleotides  Nucleotide: Pentose sugar + N-containing base + phosphate group  Nucleosides: Pentose sugar + N-containing base  Bases: o Pyrimidines- single rings o Purines- double rings  Sugars: o DNA contains deoxyribose o RNA contains ribose  Nucleotides have 3 components: o Base (can be pyrimidines or purines) o Ribose or deoxyribose o Phosphate  Nucleotides bond in condensation reactions to form phosphodiester linkages.  Nucleic acids grow in the 5′ to 3′ direction.  Oligonucleotides have about 20 monomers, and include small RNA molecules important for DNA replication and gene expression.  DNA and RNA are polynucleotides, the longest polymers in the living world.  ***Memorize Table 3.1 Distinguishing RNA from DNA*** o RNA:  Sugar: Ribose  Bases: Adenine, Cytosine, Guanine, Uracil  Strands: Single o DNA:  Sugar: Deoxyribose  Bases: Adenine, Cytosine, Guanine, Thymine  Strands: Double  Complementary base pairing: o adenine and thymine o always pair (A-T) o double bonded o cytosine and guanine o always pair (C-G) o triple bonded  Base pairs are linked by hydrogen bonds.  There are so many hydrogen bonds in DNA and RNA that they form a fairly strong attraction, but not as strong as covalent bonds.  Thus, base pairs can be separated with only a small amount of energy.  RNA is usually single-stranded, but may be folded into 3-D structures, by hydrogen bonding.  Folding occurs by complementary base pairing, so structure is determined by the order of bases.  DNA—two polynucleotide strands form a “ladder” that twists into a double helix.  Sugar-phosphate groups form the sides of the ladder, the hydrogen-bonded bases form the ru
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