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Lecture 6

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Biology 1001A
Tom Haffie

Lecture 6: -Genome full of junk DNA -Researchers define functional as anything that looks like anything that would ne expressed and therefore have said about 80% is functional; misconception -Maybe if it true but its not function to make US -Junk DNA is powerful evidence of evolution DNA Structure -Antiparallel means each of these single strands of DNA has a 3‘ end and a 5’ end -This gives the molecule a kind of direction -Those two strands fit together in opposite directions, such that at the end of the molecule one of the strans is a 3’ and is a 5’ ; antiparallel -Hydroxyl on the 3’ end -5’ end has a phosphate Replication is semi-conservative -This one molecule gives rise to 2 daughter molecules -See this in the mesosole experiment -The bases are being added to the 3’ end -centre; incoming nucleotide is there -Nucleotides are being added to the free 3’ end hydroxyl -Every DNA polymerase in the known universes extends the 3’ OH; only does this elongation B A Answer: B -Has to extend on the 3’ -Why the 3’? Because polymerase only knows how to extend the 3’ -All the proteins sticking together, called that a replisome -Replisome is active as a structure called the REPLICATION FORK -Replisome contains 2 molecules of DNA polymerase -2 polymerases are going continuously in a replisome just replicating both strands of the helix but we can only extend the 3’ end, that requires that the replisome to replicate one strand continuously and one discontinuously -Strands of parent DNA are going in opposite direction; antiparallel -Replication is therefore, semi-conservative and semi-discontinuous Replication “bubble” arises from two “forks” created at one “origin” -Recall in prokaryotes, chloroplasts and mitochondria have circular genomes -Replicate from one single site; one origin -Sends replication forks in both directions -This makes DNA replication semi-conservative, semi-discontinuous and bidirectional (goes both directions at the same time) -This creates a REPLICATION BUBBLE -BE ABLE TO DRAW A REPLICATION BUBBLE; be able to put in the primers, okazaki fragments, the 3’ and 5’ -Blue parts are primers which provide a 3’ OH for DNA polymerase to extent -Most circular (prokaryotic) genomes are relatively small, they can replicate from one bubble or origin -BUT ours is really big, we cant replicate from origin, not even one origin on each chromosome -Replisome FOR SURE DOES NOT go from one end of replisome to the other -Our chromosomes are replicated really quickly because they have multiple origins all along our chromosomes -Be able to DRAW THIS from understanding (functions, etc.) -Have forks going in both directions from multiple origins and replicates all the DNA quite quickly -Origins are sprinkled around, but there are specific sequences, so can tell by looking at the genome where the origin is but they're not in specific places -KNOW enzyme functions G1 S phase G2 Miototic Metaphase -G1 and then S phase in where the DNA replicates -G2 is when now the chromosome is composed of 2 molecules of DNA, these molecules are held together -After these molecules condense like crazy, they look like the metaphase stage
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