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Unformatted text preview: A pol 5’ primer 3’ 3’ 5’ 5’ 3’ DNA pol requires both a template strand AND a primer with a free 3’OH
30 31 Problem 2: If DNA pol can only move in a 5’-3’ direction, how does DNA pol synthesize DNA on the other template strand? Similar to Fig. 20.7
32 Answer: Lagging strand synthesis is discontinuous Okazaki fragments 33 So far
DNA pol synthesizes DNA directionally: 5’ to 3’ Requires a template and primer, to which it attaches new dNTPs Primase - RNA polymerase that synthesizes the RNA primers (11-12 nt that start with pppAG) for both lagging and leading strand synthesis DNA synthesis creates lagging and leading strand Lagging strand = small (~100-1000 bp) fragments = “Okazaki fragments” .
34 Problem 3: How do cells stitch together Okazaki fragments? 35 Answer: Okazaki fragments stitched together covalently by DNA Ligase DNA Ligase - joins the 5’ phosphate of one DNA molecule to the 3’ OH of another - using energy in the form of NAD (prok) or ATP (euk) - prefers substrates that are double-stranded, with only one strand needing ligation, and lacking gaps DNA ligase
photo courtesy: wikipedia 36 DNA Ligase Substrate Specificity 37 DNA ligase mechan...
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This note was uploaded on 04/10/2010 for the course BIO 51130 taught by Professor Moon during the Spring '09 term at University of Texas.
- Spring '09