Chapter 11 Study Guide

Chapter 11 Study Guide - Study Guide 11 UNIT III...

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Study Guide 11 UNIT III: - Meiosis (and Genetic Variation) - Mendel & the Gene (linkage and crossing over) - How Do Genes Work ( DNA = genes; the genetic code) - DNA Synthesis. .. (Replication) - Transcription and Translation - Control of Gene Expression in Bacteria - Control of Gene Expression in Eukaryotes . The molecular basis of inheritance 1. By the 1920's, we knew that a) genes are aligned on chromosomes; b) the nucleus contains chromosomes; c) the nucleus is mostly protein, RNA and DNA; d) chromosomes are mostly protein and DNA; e) DNA is composed of the four nucleotides; f) proteins are composed of 20 amino acids. 2. A chance experiment by an investigator looking for a way to prevent a deadly influenza infection led to the discovery that bacterial cells can take up genetic molecules from the environment . Specifically, a harmless, mutant strain of otherwise deadly Streptococcus pneumonia cells could acquire the gene(s) for virulence from heat-inactivated wild-type cells (see Fig. 14.1 for the phenotypic difference between the virulent and benign cell colonies). The experiment, in which mice were injected with normal (deadly) wild type cells, virulent cells that had been heat inactivated, mutant harmless cells and a mixture of live mutant cells and heat inactivated virulent cells is shown in Fig. 14.2. Mice would die within 24 hr if injected with live virulent S. Pneumonia , or with the harmless cells mixed with heat-killed virulent cells. Clearly, the living harmless cells had been transformed by something they had taken up from the dead, virulent cells and then passed on to their progeny. The transforming principle was the genetic material. 3. The search for the identity of the transforming principle was helped along when it was found that you didn’t need a mouse for one bacterium to pick up genetic information from another (see below & Fig. 14.3 ): 4. This experiment says that DNA must be the transforming principle i.e., genetic material. But there was resistance to this conclusion. .. after all, how can such a simple polymer made up of only 4 monomers carry the information needed to make a living cell or organism?
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5. Since polypeptides consist of 20 different monomers (amino acids), many scientists thought that genes would be made of proteins, until the experiments of Hershey and Chase Fig. 14.5 ). a) Bacterial viruses ( bacteriophage , or phage for short) consist of only DNA and protein (no other kinds of molecules!). In fact, viruses are not alive, and are only active when they infect host cells. Viral infection occurs when the virus can reproduce inside the host cell. Hershey and Chase asked: “Is it viral DNA or viral protein that actually gets into host cells to cause infection?” b) They made radioactive viruses, allowing infection to occur in medium containing radioactive phosphorous or sulfur which would become part of DNA and protein, respectively ( WHY? ). c)
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Chapter 11 Study Guide - Study Guide 11 UNIT III...

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