CAS BI 105 Lecture Notes - Lecture 15: Phosphodiester Bond, Nucleic Acid Double Helix, Cytosine
30 Apr 2018
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DNA Replication
DNA is the blueprint of life
•Universal molecule
•All cells and some viruses contain DNA
•Central Dogma
•DNA codes for proteins
•Cannot go directly to protein
•DNA —> RNA —> PROTEIN
Structure & Function
•Double helix structure makes DNA elegantly suited to its function
•Encodes and stores an enormous amount of information in a small amount of space
•Matching and structure helps to prevent mutation
•Double-stranded nature provides accurate template for reproduction
DNA Structure
•Chromatin - DNA found in an unwound/condensed form
•Chromatin involves a mixture of both DNA and the proteins it winds
around
•Not as coiled/condensed as in chromosome form BUT still has some
organization to it
DNA & RNA
•Composed of nucleotides (~ 3 billion of these)
•Two backbones (sugar-phosphate)
•Connected through hydrogen bonds to bases
•Equal spacing up and down the strands
•2 ring N always bonds with a 1 ring N
•4 nitrogenous bases (DNA)
•Adenine (A) (must bind with Thymine) - 2 hydrogen bonds
•Thymine (T) (must bind with Adenine) - 2 hydrogen bonds
•Guanine (G) (must bind with Cytosine) - 3 hydrogen bonds
•Cytosine (C) (must bind with Guanine) - 3 hydrogen bonds
•4 nitrogenous bases (RNA)
•Adenine (A)
•Uracil (U)
•Guanine (G)
•Cytosine (C)
•DNA & RNA - have very similar chemical structures
•Each nucleotide is joined to the next by a covalent phosphodiester bond between the sugar and
phosphate
*Ladder Analogy:
•Rungs = nitrogenous bases
•Sides = sugar-phosphates
•^side 1 = sugar THEN phosphate / side 2 = phosphate THEN sugar
Orientation of the backbone molecules are anti parallel
•(3 prime end and 5 prime end)
•has consequences for DNA replication
DNA Replication
•DNA is a 2 stranded molecule
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Document Summary
Dna is the blueprint of life: universal molecule, all cells and some viruses contain dna, central dogma, dna codes for proteins, cannot go directly to protein, dna > rna > protein. Dna structure: chromatin - dna found in an unwound/condensed form, chromatin involves a mixture of both dna and the proteins it winds around, not as coiled/condensed as in chromosome form but still has some organization to it. *ladder analogy: rungs = nitrogenous bases, sides = sugar-phosphates, ^side 1 = sugar then phosphate / side 2 = phosphate then sugar. Orientation of the backbone molecules are anti parallel: (3 prime end and 5 prime end, has consequences for dna replication. Stabilize newly single-stranded dna - single strand binding proteins: 3. Stabilize the helix ahead of the replication area - topoisomerase: 4. Build a tiny stretch of rna - primer (built by primase: 5.
