Exam 11: DNA Replication and Recombination

Homologous recombination requires the formation of heteroduplex DNA consisting of one nucleotide strand from each of two homologous chromosomes. In the Holliday model, homologous recombination is accomplished through a single-strand break in the DNA, strand displacement, and branch migration. In the double-strand-break model, recombination is accomplished through double-strand breaks, strand displacement, and branch migration. -Why is recombination important?

Replication is semiconservative: each DNA strand serves as a template for the synthesis of a new DNA molecule. Meselson and Stahl convincingly demonstrated that replication in E. coli is semiconservative. -How many bands of DNA would be expected in Meselson and Stahl's experiment after two rounds of conservative replication?

A number of proteins have roles in recombination, including RecA, RecBCD, RuvA, RuvB, resolvase, single-strand-binding proteins, ligase, DNA polymerases, and gyrase. -What is the function of resolvase in recombination?

All DNA synthesis is 5^'\rightarrow3^' , meaning that new nucleotides are always added to the 3^' end of the growing nucleotide strand. At each replication fork, synthesis of the leading strand proceeds continuously and that of the lagging strand proceeds discontinuously -Discontinuous replication is a result of which property of DNA?

Eukaryotic DNA contains many origins of replication. At each origin, a multiprotein origin-recognition complex binds to initiate the unwinding of the DNA. -In comparison with prokaryotes, what are some differences in the genome structure of eukaryotic cells that affect how replication takes place?

After primers have been removed and replaced, the nick in the sugar-phosphate linkage is sealed by DNA ligase -Which bacterial enzyme removes the primers?

There are a large number of different DNA polymerases in eukaryotic cells. DNA polymerases $\alpha, \delta$ , and $\varepsilon$ carry out replication on the leading and lagging strands. Other DNA polymerases carry out DNA repair. Specialized translesion polymerases are used to bypass distortions of the DNA template that normally stall the main DNA polymerases. -Some of the eukaryotic DNA polymerases have a tendency to make errors in replication. Why would a cell use an error-prone DNA polymerase instead of one that is more accurate?

Replication is extremely accurate, with less than one error per billion nucleotides. This accuracy is due to the processes of nucleotide selection, proofreading, and mismatch repair. -Which mechanism requires the ability to distinguish between newly synthesized and template strands of DNA?

Replication is initiated at a replication origin, where an initiator protein binds and causes a short stretch of DNA to unwind. DNA helicase breaks hydrogen bonds at a replication fork, and singlestrand-binding proteins stabilize the separated strands. DNA gyrase reduces the torsional strain that develops as the two strands of double-helical DNA unwind. -Place the following components in the order in which they are first used in the course of replication: helicase, single-strand-binding protein, DNA gyrase, initiator protein.

The ends of eukaryotic chromosomes are replicated by an RNA- protein enzyme called telomerase. This enzyme adds extra nucleotides to the G-rich DNA strand of the telomere. -What would be the result if an organism's telomerase were mutated and nonfunctional?

Theta replication, rolling-circle replication, and linear replication differ with respect to the initiation and progression of replication, but all produce new DNA molecules by semiconservative replication -Which type of replication requires a break in the nucleotide strand to get started?

Primase synthesizes a short stretch of RNA nucleotides (primers), which provides a 3'-OH group for the attachment of DNA nucleotides to start DNA synthesis. -Primers are synthesized where on the lagging strand?