Answer:
A. “The DNA molecule is usually a double helix, with the sugar-phosphate backbones of the antiparallel polynucleotide strands on the outside of the helix. Hydrogen bonds between pairs of nitrogenous bases hold the two strands together. As illustrated here with symbolic shapes for the bases, adenine (A) can pair only with thymine (T), and guanine (G) can pair only with cytosine (C). Each DNA strand in this figure is the structural equivalent of the polynucleotide. A tRNA molecule has a roughly L-shaped structure, due to complementary base pairing of antiparallel stretches of RNA. In RNA, A pairs with U.” from Campbell Biology in Focus,3e, Chapter 3: Carbon and the Molecular Diversity of Life, Concept 3.6: Nucleic acids store, transmit, and help express hereditary information. Basically it is saying that DNA molecules are usually double helixes and double helixes consist of hydrogen bonds, for example adenine can only pair with thymine and guanine can only pair with cytosine, these two strands of sugar phosphate backbones are similar structure of polynucleotides. Then the tRNa molecules create a L-shape structure caused from the complementary base pairings, the adenine with thymine and guanine with cytosine.
“DNA polymerases proofread new DNA, replacing incorrect nucleotides. In mismatch repair, enzymes correct errors that persist. Nucleotide excision repair is a general process by which nucleases cut out and replace damaged stretches of DNA.”- from Campbell Biology in Focus,3e Concept 13.2: Many proteins work together in DNA replication and repair. It’s saying that DNA polymerases check new DNA for problems and replaces incorrect nucleotides. In a mismatch repair enzymes correct errors they keep on coming happening. Nucleotide excision repair is a process where nucleases cut out damaged DNA and completely replace them.
“Each strand is composed of nucleotides bonded together covalently between the phosphate group of one and the deoxyribose sugar of the next. From this backbone extend the bases.” - from Concepts of Biology – 1st Canadian Edition, chapter 9.1 The Structure of DNA. This means every DNA strand is composed of nucleotides covalently bonded with the phosphate group of one and the deoxyribose of another.
B. “It is traditional—and convenient—to represent DNA polymerase molecules as locomotives moving along a DNA railroad track, but such a model is inaccurate in two important ways. First, the various proteins that participate in DNA replication actually form a single large complex, a “DNA replication machine.” Many protein-protein interactions facilitate the efficiency of this complex. For example, by interacting with other proteins at the fork, primase apparently acts as a molecular brake, slowing progress of the replication fork and coordinating the placement of primers and the rates of replication on the leading and lagging strands. Second, the DNA replication complex may not move along the DNA; rather, the DNA may move through the complex during the replication process.”- from Campbell Biology in Focus,3e, chapter 13: The Molecular Basis of Inheritance Concept 13.2: Many proteins work together in DNA replication and repair. From this excerpt, we can understand the difference between leading and lagging strands because of the way they process DNA. In lagging the strands DNA discontinuously grows from Okazaki fragments while lending strands continuously grow through DNA replication.
Explanation:
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