Concept explainers
In Step 6 of Fig. 6.27, the resolvase enzyme almost always cuts all four strands of DNA in the double Holliday junction intermediate: both blue strands and both red strands. Another way of stating this fact is that the enzyme cuts the DNA at Holliday junctions 1 and 2 in different ways, represented by the yellow arrows at junction 1 and the green arrows at junction 2 in the figure. But rarely, the resolvase enzyme instead cuts the DNA at both Holliday junctions in the same way (yellow arrows at both junctions or green arrows at both junctions). In other words, at both junctions, the same red strand and the same blue strand are cut. What would be the outcome of this rare resolvase enzyme behavior?
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ND STONY BROOK UNIVERSITY LOOSELEAF GENETICS: FROM GENES TO GENOMES
- The 3′ → 5′ exonuclease activity of Pol I excises only unpaired 3′-terminal nucleotides from DNA, whereas this enzyme’s pyrophosphorolysis activity removes only properly paired 3′-terminal nucleotides. Discuss the mechanistic signifi cance of this phenomenon in terms of the polymerase reaction.arrow_forwardAll known DNA polymerases catalyze synthesis only in the 5' → 3' direction. Nevertheless, during semiconservative DNA replication in the cell, they are able to catalyze the synthesis of both daughter chains, which would appear to require synthesis in the 3' → 5' direction on one strand. Explain the process that occurs in the cell that allows for synthesis of both daughter chains by DNA polymerasearrow_forwardSupercoiled DNA is slightly unwound compared to relaxed DNA and this enables it to assume a more compact structure with enhanced physical stability. Describe the enzymes that control the number of supercoils present in the E. coli chromosome. How much would you have to reduce the linking number to increase the number of supercoils by five?arrow_forward
- During the resolution of the two Holliday junctions, how many strands of DNA in total are broken during this process? Does the number differ depending on if this leads to recombination or non-recombination?”arrow_forwardIn the catalytic center of DNA polymerases, the presence of Mg2+ ions and aspartate residues close to these ions is required. What is the role of these aspartate residues that are found close to the magnesium ions? What is the role of the magnesium ions in the polymerization of nucleotides?arrow_forwardThe sequences of DNA bases below represent parts of the genes responsible for the production of one type of protein, an enzyme, produced by Botana curus and Species X, Y, and Z Under each DNA sequence, write the complementary messenger RNA base sequences that each of these gene fragments would produce. Note: Unlike during DNA replication, in the production of messenger RNA, the DNA base “A” specifies the RNA base “U.”. Use the universal genetic code table provided (see Universal Code attachment) to translate the messenger RNA base sequences into sequences of amino acids in the protein produced by each species. Write the sequences of amino acids under the messenger RNA sequences.arrow_forward
- The D1S80 locus is located on human chromosome 1 and is characterized by a repeating 16 base pair (bp) sequence. Alleles for this locus vary depending on the number of repeats present, thus affecting the size of the locus. The D1S80 locus also contains two conserved sequences, a 32bp sequence at one end and a 113bp sequence at the other end. If the DNA of an individual is targeted for D1S80 amplification, and one of the resulting amplicons is approximately 785bp in size, how many repeats would be present in this D1S80 allele? The amplicon of interest is indicated by a red arrow in the diagram below.arrow_forwardExplain why two bound metal ions at the palm domain of DNA polymerase play an important role during S phase.arrow_forwardWhich of the follwing enzymes adds incoming deoxyribonucleotid triphosphates to the 3' OH of the growing es/deoxyribonucleoside daughter strand in the 5'-3' direction?arrow_forward
- In the following sequence, a cytosine was deaminated and is now a uracil (underlined). 5’-GGTAUTAAGC-3’ a. Which repair pathway(s) could restore this uracil to cytosine? b. If the uracil is not removed before a DNA replication fork passes through, what will be the sequences of the two resulting double helices? Provide the sequences of both strands of both helices. Label the old and new strands and underline the mutation(s). c. Could the mismatch repair pathway fix the mutations you’ve indicated in part b? d. If the cell undergoes mitosis, and the replicated DNAs are distributed into the two daughter cells. Will 0, 1, or 2 daughter cells have a mutation in this sequence?arrow_forwardUsing the numbered sites on the DNA double helix strands below, where would the DNA Primer ACTTGCGA bind to for DNA Amplification?arrow_forwardSometimes DNA polymerase makes a mistake, and the wrong nucleotide is added to the growing DNA strand. With regard to pyrimidines and purines, two general types of mistakes are possible. The addition of an incorrect pyrimidine instead of the correct pyrimidine (e.g., adding cytosine where thymine should be added) is called a transition. If a pyrimidine is incorrectly added to the growing strand instead of purine (e.g., adding cytosine where an adenine should be added), this type of mistake is called a transversion. If a transition or transversion is not detected by DNA polymerase, a mutation is created that permanently changes the DNA sequence. Though both types of mutations are rare, transition mutations are more frequent than transversion mutations. Based on your understanding of DNA replication and DNA polymerase, offer three explanations why transition mutations are more common.arrow_forward
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