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Molecular Genetics Section 1: DNA: The Genetic Material Section 2: Replication of DNA Section 3: DNA, RNA, and Protein Section 4: Gene Regulation and Mutation Click on a lesson name to select. Click on a lesson name to select. Section 1 Molecular Genetics DNA: Discovery Frederick Griffith - 1928 Performed the first major experiment that led to the discovery of DNA as the genetic material REFUTED THAT PROTEIN WAS THE GENETIC MATERIAL – ANOTHER LARGE MOLECULE –DNA CARRIED GENETIC INFO Section 1 Molecular Genetics DNA: The Genetic Material Oswald Avery - 1944 Identified the molecule that transformed the R strain of bacteria into the S strain Concluded that when the S cells were killed, DNA was released R bacteria incorporated this DNA into their cells and changed into S cells. VERIFIED GRIFFITH’S EXPERIMENT Section 1 Molecular Genetics DNA: The Genetic Material Hershey and Chase - 1952 Used radioactive labeling to trace the DNA and protein Concluded that the viral DNA was injected into the cell and provided the genetic information needed to produce new viruses CONFIRMED THAT DNA IS THE GENETIC MATERIAL Section 1 Molecular Genetics DNA: The Genetic Material DNA Structure Nucleotides Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base Section 1 Molecular Genetics Section 1 Molecular Genetics DNA: The Genetic Material Erwin Chargaff 1950 Chargaff’s rule: C = G and T = A Section 1 Molecular Genetics DNA: The Genetic Material X-ray Diffraction Rosalind Franklin - 1951 X-ray diffraction data helped solve the structure of DNA Indicated that DNA was a double helix Section 1 Molecular Genetics DNA: The Genetic Material Watson and Crick - 1953 Built a model of the double helix that conformed to the others’ research 1. two outside strands consist of alternating deoxyribose and phosphate 2. cytosine and guanine bases pair to each other by three hydrogen bonds 3. thymine and adenine bases pair to each other by two hydrogen bonds Cambridge University, Cambridge Kings College, London Section 1 Molecular Genetics DNA: The Genetic Material DNA Structure DNA often is compared to a twisted ladder. Rails of the ladder are represented by the alternating deoxyribose and phosphate. The pairs of bases (cytosine–guanine or thymine–adenine) form the steps. Section 1 Molecular Genetics DNA: The Genetic Material Orientation On the top rail, the strand is said to be oriented 5′ to 3′. The strand on the bottom runs in the opposite direction and is oriented 3′ to 5′. Section 1 Molecular Genetics DNA: The Genetic Material Chromosome Structure DNA coils around histones to form nucleosomes, which coil to form chromatin fibers. The chromatin fibers supercoil to form chromosomes that are visible in the metaphase stage of mitosis. Section 2 Molecular Genetics Replication of DNA Semiconservative Replication Parental strands of DNA separate, serve as templates, and produce DNA molecules that have one strand of parental DNA and one strand of new DNA. • What is the complementary strand for the DNA segment ACTGGA? Section 2 Molecular Genetics Replication of DNA Unwinding DNA helicase, an enzyme, is responsible for unwinding and unzipping the double helix. RNA primase adds a short segment of RNA, called an RNA primer, on each DNA strand. Section 2 Molecular Genetics Replication of DNA Base pairing DNA polymerase continues adding appropriate nucleotides to the chain by adding to the 3′ end of the new DNA strand. Section 2 Molecular Genetics Section 2 Molecular Genetics Replication of DNA One strand is called the leading strand and is elongated as the DNA unwinds. The other strand of DNA, called the lagging strand, elongates away from the replication fork. The lagging strand is synthesized discontinuously into small segments, called Okazaki fragments. Section 2 Molecular Genetics Replication of DNA Joining DNA polymerase removes the RNA primer and fills in the place with DNA nucleotides. DNA ligase links the two sections. Section 2 Molecular Genetics Replication of DNA Comparing DNA Replication in Eukaryotes and Prokaryotes Eukaryotic DNA unwinds in multiple areas as DNA is replicated. In prokaryotes, the circular DNA strand is opened at one origin of replication. Section 3 Molecular Genetics Section 3 Molecular Genetics DNA, RNA, and Protein RNA Contains the sugar ribose and the base uracil instead of thymine Usually is single stranded Section 3 Molecular Genetics DNA, RNA, and Protein Messenger RNA (mRNA) Long strands of RNA nucleotides that are formed complementary to one strand of DNA Ribosomal RNA (rRNA) Associates with proteins to form ribosomes in the cytoplasm Transfer RNA (tRNA) Smaller segments of RNA nucleotides that transport amino acids to the ribosome Section 3 Molecular Genetics DNA, RNA, and Protein Transcription Through transcription, the DNA code is transferred to mRNA in the nucleus. DNA is unzipped in the nucleus and RNA polymerase binds to a specific section where an mRNA will be synthesized. Transcribe A C A G G A Section 3 Molecular Genetics DNA, RNA, and Protein RNA Processing The code on the DNA is interrupted periodically by sequences that are not in the final mRNA. Intervening sequences are called introns. Remaining pieces of DNA that serve as the coding sequences are called exons. DNA and Genes Section 3 Molecular Genetics DNA, RNA, and Protein The mRNA Code Experiments during the 1960s demonstrated that the DNA code was a three-base code. The three-base code in DNA or mRNA is called a codon. Section 3 Molecular Genetics DNA, RNA, and Protein Translation In translation, tRNA molecules act as the interpreters of the mRNA codon sequence. At the middle of the folded strand, there is a three-base coding sequence called the anticodon. Each anticodon is complementary to a codon on the mRNA. • According to the mRNA Genetic Code which amino acid sequence would most likely be determined by a section of DNA molecule with the base sequence: • A-C-A-G-G-A-T-C-A Section 3 Molecular Genetics DNA, RNA, and Protein One Gene— One Enzyme The Beadle and Tatum (1941) experiment showed that one gene codes for one enzyme. We now know that one gene codes for one polypeptide. Section 4 Molecular Genetics Gene Regulation and Mutation Eukaryote Gene Regulation Controlling transcription Transcription factors ensure that a gene is used at the right time and that proteins are made in the right amounts The complex structure of eukaryotic DNA also regulates transcription. Section 4 Molecular Genetics Gene Regulation and Mutation Hox Genes Hox genes are responsible for the general body pattern of most animals. Section 4 Molecular Genetics Gene Regulation and Mutation Mutations A permanent change that occurs in a cell’s DNA is called a mutation. Types of mutations Point mutation Insertion Deletion Section 4 Molecular Genetics THE BIG RAT CAT ATE THE WET BAT Section 4 Molecular Genetics Gene Regulation and Mutation Protein Folding and Stability Substitutions also can lead to genetic disorders. Can change both the folding and stability of the protein Section 4 Molecular Genetics Gene Regulation and Mutation Causes of Mutation Can occur spontaneously Chemicals and radiation also can damage DNA. High-energy forms of radiation, such as X rays and gamma rays, are highly mutagenic. Section 4 Molecular Genetics Gene Regulation and Mutation Body-cell v. Sex-cell Mutation Somatic cell mutations are not passed on to the next generation. Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring. Chapter Molecular Genetics Chapter Diagnostic Questions Which scientist(s) definitively proved that DNA transfers genetic material? A. Watson and Crick B. Mendel C. Hershey and Chase D. Avery 1. 2. 3. 4. A B C D Chapter Molecular Genetics Chapter Diagnostic Questions During which stage of the cell cycle does DNA replication take place? A. Growth B. Prophase C. Synthesis D. Mitosis 1. 2. 3. 4. A B C D Chapter Molecular Genetics Chapter Diagnostic Questions Name the small segments of the lagging DNA strand. A. ligase B. Okazaki fragments C. micro RNA D. helicase 1. 2. 3. 4. A B C D Chapter Molecular Genetics Chapter Diagnostic Questions Which is not true of RNA? A. It contains the sugar ribose. B. It contains the base uracil. C. It is single-stranded. D. It contains a phosphate. 1. 2. 3. 4. A B C D Chapter Molecular Genetics Section 1 Formative Questions The experiments of Avery, Hershey and Chase provided evidence that the carrier of genetic information is _______. A. carbohydrate B. DNA C. lipid D. protein 1. 2. 3. 4. A B C D Chapter Molecular Genetics Section 1 Formative Questions What is the base-pairing rule for purines and pyrimidines in the DNA molecule? A. A—G and C—T B. A—T and C—G C. C—A and G—T D. C—U and A—G 1. 2. 3. 4. A B C D Chapter Molecular Genetics Section 1 Formative Questions What are chromosomes composed of? A.chromatin and histones B. DNA and protein C. DNA and lipids D. protein and centromeres 1. 2. 3. 4. A B C D Chapter Molecular Genetics Section 2 Formative Questions The work of Watson and Crick solved the mystery of how DNA works as a genetic code. A. True B. False 1. 2. A B Chapter Molecular Genetics Section 2 Formative Questions Which is not an enzyme involved in DNA replication? A. DNA ligase B. DNA polymerase C. helicase D. RNA primer 1. 2. 3. 4. A B C D Chapter Molecular Genetics Section 3 Formative Questions Which shows the basic chain of events in all organisms for reading and expressing genes? A. DNA RNA protein B. RNA DNA protein 1. A C. mRNA rRNA tRNA 2. B 3. C D. RNA processing transcription 4. translation D Chapter Molecular Genetics Section 3 Formative Questions In the RNA molecule, uracil replaces _______. A. adenine B. cytosine C. purine D. thymine 1. 2. 3. 4. A B C D Molecular Genetics Chapter Section 3 Formative Questions Which diagram shows messenger RNA (mRNA)? A. C. B. D. 1. 2. 3. 4. A B C D Chapter Molecular Genetics Section 3 Formative Questions What characteristic of the mRNA molecule do scientists not yet understand? A. intervening sequences in the mRNA molecule called introns B. the original mRNA made in the nucleus called the pre-mRNA C. how the sequence of bases in the mRNA 1. molecule A 2. B codes for amino acids 3. C 4. D D. the function of many adenine nucleotides at the 5′ end called the poly-A tail Chapter Molecular Genetics Section 4 Formative Questions Why do eukaryotic cells need a complex control system to regulate the expression of genes? A. All of an organism’s cells transcribe the same genes. B. Expression of incorrect genes can lead to mutations. C. Certain genes are expressed more frequently than others are. 1. 2. 3. 4. A B C D D. Different genes are expressed at different times in an organism’s lifetime. Chapter Molecular Genetics Section 4 Formative Questions Which type of gene causes cells to become specialized in structure in function? A. exon B. Hox gene C. intron D. operon 1. 2. 3. 4. A B C D Chapter Molecular Genetics Section 4 Formative Questions What is a result of a mutation in a gene? A. cancer B. genetic disorder C. nonfunctional enzyme D. amino acid deficiency 1. 2. 3. 4. A B C D Chapter Molecular Genetics Section 4 Formative Questions Which is the most highly mutagenic? A. chemicals in food B. cigarette smoke C. ultraviolet radiation D. X rays 1. 2. 3. 4. A B C D Chapter Molecular Genetics Chapter Assessment Questions Look at the following figure. Identify the proteins that DNA first coils around. A. chromatin fibers B. chromosomes C. histones D. nucleosome 1. 2. 3. 4. A B C D Chapter Molecular Genetics Chapter Assessment Questions Explain how Hox genes affect an organism. A. They determine size. B. They determine body plan. C. They determine sex. 1. A 2. B D. They determine number of body segments. 3. C 4. D Chapter Molecular Genetics Chapter Assessment Questions Explain the difference between body-cell and sex-cell mutation. Answer: A mutagen in a body cell becomes part of the of the genetic sequence in that cell and in future daughter cells. The cell may die or simply not perform its normal function. These mutations are not passed on to the next generation. When mutations occur in sex cells, they will be present in every cell of the offspring. Chapter Molecular Genetics Standardized Test Practice What does this diagram show about the replication of DNA in eukaryotic cells? A. DNA is replicated only at certain places along the chromosome. B. DNA replication is both semicontinuous and conservative. C. Multiple areas of replication occur along the chromosome at the same time. D. The leading DNA strand is synthesized discontinuously. 1. 2. 3. 4. A B C D Chapter Molecular Genetics Standardized Test Practice What is this process called? A. mRNA processing B. protein synthesis C. transcription D. translation 1. 2. 3. 4. A B C D Chapter Molecular Genetics Standardized Test Practice What type of mutation results in this change in the DNA sequence? TTCAGG A. deletion B. frameshift C. insertion D. substitution TTCTGG 1. 2. 3. 4. A B C D Chapter Molecular Genetics Standardized Test Practice The structure of a protein can be altered dramatically by the exchange of a single amino acid for another. A. True B. False 1. 2. A B