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In his work with pneumonia-causing bacteria and mice, Griffith found that the protein coat from pathogenic cells was able to transform nonpathogenic cells. heat-killed pathogenic cells caused pneumonia. some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic. the polysaccharide coat of bacteria caused pneumonia. What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized? DNA polymerase can join new nucleotides only to the 3′ end of a preexisting strand. Helicases and single-strand binding proteins work at the 5′ end. The origins of replication occur only at the 5′ end. DNA ligase works only in the 3′ → 5′ direction. In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules? A = G A + G = C + T A + T = G + C A = C The elongation of the leading strand during DNA synthesis progresses away from the replication fork. occurs in the 3′ → 5′ direction. produces Okazaki fragments. depends on the action of DNA polymerase. In a nucleosome, the DNA is wrapped around polymerase molecules. ribosomes. histones. a thymine dimer. Which of the following sequences in double-stranded DNA is most likely to be recognized as a cutting site for a restriction enzyme?

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1. The correct answer is:  some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic

Griffith in his experiment used two related strains of bacteria (Streptococcus pneumonia), known as R and S and mice, trying to develop a vaccine against pneumonia.

• R strain-formed nonvirulent, rough-edged colonies  

• S strain- rounded and smooth colonies, with sugar protection coat, virulent

Mice that were injected with S strain developed pneumonia and died. But, when mice were injected with heat-killed S strain it did not cause disease in mice.The next part of experiment is the injection of combined harmless R bacteria with harmless heat-killed S bacteria. The result was that the mouse developed pnenumonia and in blood sample from the dead mouse, living S bacteria were found. From his experiment, Griffith concluded that injected together, R strain and S strain bacteria most likely “communicate”. The R-strain bacteria took "transforming principle" (we know today that this is genetic material DNA) from the heat-killed S bacteria which allowed them to "transform" into virulent bacteria.

2. The correct answer is: DNA polymerase can join new nucleotides only to the 3’ end of a preexisting strand.

DNA replication (or the synthesis of DNA) begins when the helicase unfolds the double-stranded DNA. The forked structure is formed and DNA synthesis by the DNA polymerase can start. DNA polymerase is an enzyme that works only in one direction-5' to 3' (new nucleotides are added only to the 3’ end), so it replicates the leading strand continuously. On the other hand, lagging-strand replication is discontinuous( Okazaki fragments are formed and later linked together).

3. The correct answer is A + G = C + T

This is according to Chargaff's rule which states that DNA should have a 1:1 ratio of pyrimidine and purine bases (the amount of guanine should be equal to cytosine and the same thing with adenine and thymine).

4. The correct answer is: depends on the action of DNA polymerase.

Elongation is the second stage of DNA replication process (the first one is initiation and the third one is termination). The main enzyme during this phase is DNA polymerase, which adds nucleotides on newly synthesized  polynucleotide strand. . DNA polymerase is an enzyme that works only in one direction-5' to 3' (new nucleotides are added only to the 3’ end). Only the nucleotide that is complementary to the template nucleotide can be added to new strand.

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