In E. coli, how does the mismatch repair system able to detect which of the two mismatched bases is "correct" and which is "incorrect?"
What will be an ideal response?
Ans: Both strands of E. coli DNA are methylated by a methylase coded by the dam gene. Specifically, the A in the sequence GATC is methylated. After replication, the template strand is methylated while the newly synthesized strand is not, so the repair system can recognize the methylated strand as the "correct" one. Eventually, however, Dam methylase will methylate the new strand as well.
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The covalent bond between a hydrogen atom and the oxygen atom in water is formed when:a
hydrogen gains an electron from oxygen. b. hydrogen and oxygen share an electron pair. c. hydrogen and oxygen both lose electrons from their outer shells. d. hydrogen and oxygen both gain electrons in their outer shells. e. hydrogen gains an electron from oxygen.
In most eumetazoans the innermost tissue layer during development is the
a. mesoderm. b. epiderm. c. mesoglea. d. endoderm. e. ectoderm.
Which of the following structures are NOT used by chemical synapses during signal transmission?
a. gap junctions b. ligand-gated receptors c. Ca2+ d. vesicles e. neurotransmitters
Assuming complete dominance, what is the expected ratio of genotypes of the offspring following the cross of two heterozygotes?
A. 1:1 B. 4:1 C. 1:2:1 D. 3:1