BIOL 112 Chapter Notes - Chapter 4: Nucleic Acid Double Helix, Endergonic Reaction, Macromolecule

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6 Apr 2012
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Chapter 4 Notes
4.1 What is a Nucleic Acid?
- Nucleic Acids: - polymers made of nucleotides instead of amino acid monomers like proteins
- Nucleotides: consist of three parts: 1. A sugar: organic compound with a carboxyl
group and several OH- groups
- Two kinds of sugars: Ribose (OH on 2’)
Deoxyribose (H on 2’)
2. A nitrogenous base: attached at 1’ of sugar
Pyrimidines: Cytosine, Uracil, Thymine
Purines: Guanine, Adenine
3. Phosphate group: attached at 4’ of sugar
- Polymerization: nucleic acids form when nucleotides polymerize
Phosphodiester linkage: rxns = bond between phosphate group of one nucleotide
and the hydroxyl group on the sugar of another nucleotide
If the sugar is ribose = RNA, deoxyribose (always 5’ 3’)
Process needs energy, free energy of nucleotide monomers add 2 phosphate
groups to ribonucleotides or deoxynucleotides = triphosphates = phosphorylated
* Adding of 1+ phosphates = increase PE of substrate molecule = endergonic rxn
4.2 DNA Structure and Function
- Sugar phosphate backbone created by phosphodiester linkages, 4 nitrogenous bases extending out
- Double helix due to antiparallel strands (one runs 5’3’ and one 3’ 5’)
- Complementary Base Pairing: Purines with Pyrimidines, A-T (U in RNA) C-G
- Template Strand: strand of DNA transcribed by RNA polymerase to make complementary RNA/DNA
- Complementary Strand: newly synthesized strand of RNA/DNA has a base sequence that is
complementary to that of template strand (Coding Strand!)
- Is extremely stable (due to symmetry), less reactive than RNA (no 2’ hydroxyl)
- NOT an effective catalysis
4.3 RNA Structure and Function
- Two major differences between nucleic acids: 1. T does not exist, instead U 2. Ribose no Deoxyribose
- 2’ OH makes it much more reactive, tear the polymer apart
- Three hydrogen bonds between G-C and two form between A-U
- How does the secondary structure differ from DNA?: RNA spontaneously forms a hairpin (exergonic rxn
though requires energy h-bonds are favorable) due to h-bonds between the complementary bases on
the same strand not a different strand like DNA, ALSO short double helix
- ribozymes: an RNA molecule that catalyzes important chemical rxns, RNA can carry information like
DNA but can ALSO catalyze rxns = RNA is a macromolecule that can do both!