The ends of DNA molecules are replicated by a special mechanism. Limitations of DNA polymerase create problems for the linear DNA of eukaryotic chromosomes. The usual replication machinery provides no way to complete the 5 ′ ends of daughter DNA strands. o Repeated rounds of replication produce shorter and shorter DNA molecules. Prokaryotes do not have this problem because they have circular DNA molecules without ends. The ends of eukaryotic chromosomal DNA molecules, the telomeres, have special nucleotide sequences. Telomeres do not contain genes. Instead, the DNA typically consists of multiple repetitions of one short nucleotide sequence. o In human telomeres, this sequence is typically TTAGGG, repeated between 100 and 1,000 times. Telomeric DNA binds to protein complexes to protect genes from being eroded through multiple rounds of DNA replication. Telomeric DNA and specific proteins associated with it also prevent the staggered ends of the daughter molecule from activating the cell’s system for monitoring DNA damage. Telomeres become shorter during every round of replication.
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This note was uploaded on 01/04/2012 for the course BSC BSC1005 taught by Professor Orlando,rebecca during the Fall '10 term at Broward College.