07BIS1012013ReplicLect_7

The 3oh of the primer primes dna synthesis that this

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Unformatted text preview: that newly H-thymidine synthesized DNA was made in short pieces (1000 to 2000bp) on the lagging strand. BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 44 DNA Replication Fork (p. 241) BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 45 The Priming Problem ­ DNA polymerase cannot initiate DNA synthesis de novo. A 3'-OH template DNA de primer is required. primer 5’-P ­ ­ ­ P P P P HO-3’ 3’-OH ­ P P P P P P P P P P P P P -5’ Therefore, once the two strands of DNA have separated, a primer must Therefore, be added by a polymerase which can initiate de novo. de This enzyme is a special type of RNA polymerase called primase, the This primase the product of the dnaG gene of E. coli. dnaG E. Primase works in conjunction with collection of proteins called the Primase primosome to synthesize small (30 to 50 bases) RNA primers at the primosome replication fork. The 3'OH of the primer "primes" DNA synthesis. That this primer is RNA, and bears a 5' triphosphate on one end, creates That another problem. DNA ligase can not use such termini as substrates. Therefore, the primer must be first erased by the 5' to 3' exonuclease activity of DNA polymerase. activity BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 46 DNA Replication: Lagging Strand BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 47 DNA Ligase: Mechanism of Action O DNA Strand 3’ OH OP O 5’ DNA Strand O + LIGASE LIGASE PPi + ATP LIGASE AMP + 3’ DNA Strand DNA Strand OH 3’ + 5’ AMP LIGASE P P DNA Strand 5’ DNA Strand O OP O 5’ DNA Strand O LIGASE LIGASE + AMP BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodrigue...
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This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

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