6. Nucleic acids and protein synthesis
A section of Biology, 9700
Listing 10 of 441 questions
A culture of bacteria was allowed to reproduce using nucleotides containing the heavy isotope of nitrogen (15N). After several generations, all of the bacterial DNA molecules contained heavy nitrogen. DNA was extracted from a sample of the culture, mixed with caesium chloride solution and spun at high speed in a centrifuge. In this process, DNA molecules of different masses separate into bands at different positions in the centrifuge tube. The heavier the DNA molecules, the closer to the bottom of the centrifuge tube that a band forms. The diagram shows the position of the DNA molecules containing heavy nitrogen in the centrifuge tube. K L M The culture of bacteria was then allowed to reproduce using nucleotides containing the light isotope of nitrogen (14N). DNA samples were taken and separated by centrifugation after the bacteria had divided once and again after the bacteria had divided twice. In which positions would the DNA be found after the cells had divided once and after the cells had divided twice?
9700_m18_qp_12
MCQ
2018
Paper 1, Variant 2
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Plant and animal cells carry out mitosis to form two genetically identical cells from one original cell. State other reasons why mitosis is important in both plants and animals. Plant cells require microtubules to form structures that are needed for mitosis. Name one of these structures. During the mitotic cell cycle, free nucleotides are used for the synthesis of both types of nucleic acid: RNA and DNA. Complete sentences A, B, C and D to provide information about nucleotides and the synthesis of nucleic acids. Write the correct term in the spaces provided in each sentence. A Each nucleotide has three main components: a group, a (5 carbon) sugar and a nitrogenous organic base. B The nitrogenous organic base of a nucleotide is either a purine or a . C In a DNA nucleotide, the sugar is deoxyribose and in an RNA nucleotide the sugar is . D The synthesis of RNA from a template strand of DNA is known as . A virus named Pandoravirus salinus was discovered in 2013 by French scientists. The virus was so large that the scientists initially thought that P. salinus was a bacterium. P. salinus was confirmed to be a virus after further research. List three key features of viruses. The dimensions of viruses are usually stated in nanometres . As P. salinus is so big, it has been described as 1 µm long and 0.5 µm wide. Convert the width of P. salinus to nanometres. width = nm
9700_m19_qp_22
THEORY
2019
Paper 2, Variant 2
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Questions Discovered
441