Continuous and Discontinuous DNA Synthesis

Continuous and Discontinuous DNA Synthesis - • Most...

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Continuous and Discontinuous DNA Synthesis Continuous Because the 2 strands of a DNA molecule are antiparallel Only one template strand runs in a direction that allows DNA polymerase to make a continuous 5’ 3’ copy toward the replication fork Discontinuous DNA polymerase copies the other strand in short lengths Leading Strand The new DNA strand synthesized in the direction of DNA unwinding Lagging Strand New DNA strand synthesized discontinuously, in the direction opposite the DNA unwinding Enzymes Helicase, primase, polymerase I, polymerase III, and ligase Replication Bubbles Replication of Circular DNA Replication Bubbles and Multiple Origins Eukaryotic chromosomes have multiple origins- replication initiates and a replication bubble forms at each origin Forks eventually meet along the chromosomes Function of Telomeres Telomeres are nucleotide repeats at the end of the chromosome
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Unformatted text preview: • Most eukaryotic chromosomes are “protected” by a buffer of noncoding DNA (the telomere) consisting of short, repeating sequences (the telomere repeat) • When primer removed, it leaves a gap at the 5’ end of the new DNA strand • DNA polymerase can’t fill- causing the chromosome to shorten with each replication • With each replication, some telomere repeats are lost Telomerase • An enzyme that lengthens the telomere • Consists of proteins and an RNA molecule • Stops the shortening of telomeres by adding telomere repeats to chromosome ends • An RNA section binds to DNA and is the template for addition of telomere repeats o Active only in rapidly dividing embryonic cells, in germ cells- and in cancerous somatic cells o Generally not active in somatic cells, which have limited life span •...
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