Lecture 3 - 011509

Lecture 3 - 011509 - DNA Replication Lecture#3 MBOC old =...

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DNA Replication Lecture #3 MBOC old = 235-266 MBOC new = 263-295
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Concepts • When is DNA replicated? • What is a replication fork? • Is DNA replicated synchronously? • What is the immortal strand hypothesis?
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DNA and Chromatin Review • The nucleosome is the basic unit of the chromosome and it is composed of DNA and histone proteins • DNA + histone proteins + non histone proteins make up chromatin • Covalent modifications on histones are essential for cell identity and basic cell biology • When DNA is replicated the proteins associated with the DNA are also inherited into the daughter cell
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Cell Cycle Review
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What is DNA replication • The mechanism whereby DNA is duplicated in preparation for cell division • DNA replication requires a template strand and an enzyme for adding new nucleotides to the growing strand – DNA is always replicated from 5’ to 3’ • DNA replication requires DNA polymerase and it was first discovered in 1957.
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Origins of Replication • Replication in eukaryotic cells is initiated in one stage of the cell cycle. • In mammals S-phase lasts ~8 hours • By the end of S-phase each chromosome contains an associated sister chromatid joined at their centromeres • There are multiple origins of replication on a given chromosome • Given that the S-phase lasts ~8 hours, not all origins of replication are initiated at the same time.
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How was it determined that different regions of a chromosome were replicated at different times? - Cells were synchronized - Labeled with BrdU - Pulsed with thymidine during early, middle or late S-phase - Light colored regions are sites of new replication where one strand is Brdu+ and the other strand is Brdu- Traditional method
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Identifying origins of Replication by DNA microarray DNA is synchronized DNA replicated once gives a signal twice as high as unreplicated DNA For simplicity only one site of origin is shown here In reality yeast have hundreds of origins of replication DNA replication proceeds bidirectionally
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How are origins identified • In bacteria (prokaryotes) origins of replication are defined by a DNA sequence • In eukaryotes the model S. Cerevisiae (budding yeast) has been most productive in defining origins of replication. • This was originally done using a functional screen
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This note was uploaded on 03/30/2009 for the course MCDB 144 taught by Professor Dr.clarkanddr.lowry during the Spring '09 term at UCLA.

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Lecture 3 - 011509 - DNA Replication Lecture#3 MBOC old =...

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