Biology Homework Chapter 10: DNA Structure
Textbook assignment: Chapter 10: Molecular Biology of the Gene, sections 1-16.
- 10.1 The discovery of the genetic role of nuclear material belongs to Frederick Griffith, who was able to show that bacteria absorbed and expressed genetic material from another organism. The radioactive tracing experiments of Hershey and Chase led to the conclusin that DNA, not protein material inthe nucleus, contained the inherited genetic information passed from one generation to the next. [This is a truncated history of the discovery of DNA; more is covered in the Weblecture linked below.]
- 10.2 Review polymers (ch. 2). Be able to identify each part of a DNA or RNA monomer and explain the differences between DNA and RNA, and the primary characteristics of each of the four nitrogenous bases: thymine and cytosine (pyrimidines), and adenine and guanine (purines).
- 10.3 Study the diagrams of the double helix, and be able to explain why A always bonds with T and G with C (size, number of H-bonds). Our model for the double-strand DNA molecule comes from the work of Rosalind Franklin, who gathered the data, and Watson and Crick, who were able to explain it, during the early 1950s.
- 10.4 Because C and G always bond together, and A and T always bond together, either strand of DNA contains enough information to construct the entire helical form.
- 10.5 DNA is split by one set of enyzymes, then each strand is filled out with a matching strand by DNA polymerase. Because the polymerase can only "walk" the DNA strand in one direction, replication of the opposite-facing strand occurs in segments that are then fused together with DNA ligase. This process has important implications for genetic research.
- 10.6 A gene is the instruction set that allows a cell to create specific proteins and enzymes from the twenty available amino acids. A single strand of RNA contains the information for one of the strands of DNA in a gene segment.
- 10.7 Transcription is the process of creating an RNA copy of a DNA strand. Every three nucleotides or codon on the strand maps to a specific amino acid, or to a sequence that tells the RNA that it is at the end of a gene.
- 10.8 There are only twenty amino acids, but there are 43 = 64 possible combinations of 3 codons, each of which can have one of four possible values. In some cases, only one codon maps to a given amino acid; in others, 2, 3 or 4 codons all map to the same amino acid. This redundance provides some flexibility and lowers the risk (but does not eliminate it) of a mutation causing the wrong amino acid to be added to a protein chain.
- 10.9 The transcription process occurs when the enzyme RNA polymerase interacts with a DNA strand, temporarily splitting it at the H-Bonds between C and G or A and T, and creating an RNA copy of the sequence in the strand.
- 10.10 The completed messenger RNA or mRNA strand that will carry the sequence information is read in place in prokaryotic cells, which have no nuclear membrane. In eukaryotic cells, however, the RNA must be packaged so that it can survive passage through the nuclear membrane to the endoplasmic reticulum and ribosome complexes where protein manufacture will take place.
- 10.11 Transfer RNA or tRNA is an RNA-based complex that binds to the mRNA, "reads" it, and uses the codon information in the mRNA to create a polypeptide chain of the correct amino acids in the right order.
- 10.12 The tRNA complex is held within a structure called a ribosome which keeps all the parts -- tRNA, mRNA, proteins, and amino acids, in the right positions for the construction project.
- 10.13-10.14 The ribosomal structure reads through the mRNA package until it finds the start of the codon information it needs to make a protein. It then attaches initiator tRNA with the correct amino acid to the codon on the mRNA and shifts the initiator tRNA into a holding site while it does the same thing with the next codon. It switches the growing polypeptide chain from the earlier operation to the newest amino acid, then repeats the process. As the chain grows, it folds into its secondary and tertiary structure, ensuring that it will not break. At the end of the chain formation process, the ribosome releases the protein.
- 10.15 The flow of information stored in DNA is copied to RNA and manifested in the proteins created in the ribosome complex. Information does not flow back into the nucleus.
- 10.16 Mutations can occur that do change the order of the amino acids in the protein. The substitution of a nucleotide base can change a codon so that it programs a single incorrect amino acid into the chain. This may or may not affect the function of the protein. The deletion of a base shifts all subsequent bases in the sequence, programming completely different amino acids. A deletion usually corrupts the enzyme so that it can no longer function properly.
Read the following weblecture before chat: DNA Structure and Gene Inheritance
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
- No quiz yet: the Chapter Quiz opens when we finish the chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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