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A.P. Biology Ch. 16
Chapter 16: The Molecular Basis of Inheritance
| Question | Answer |
|---|---|
| Why were proteins candidates for the genetic material of DNA? | Proteins were a class of macromolecules, which had great heterogeneity and specificity of function; therefore, they were considered more likely than nucleic acids until the 1940's. |
| How was the ability of DNA to transform bacteria discovered? | The experiments of Frederick Griffith, Oswald Avery, Maclyn McCarthy, and Colin MacLeod proved that DNA was the agent responsible for the transformation of bacteria. |
| What was Frederick Griffith's experiment? | In 1928, Frederick Griffith studied the effects of pathogenic (S) and nonpathogenic (R) Streptococcus pneumoniae, both heat-killed and living, on mice. |
| What were the results of Frederick Griffith's experiment? | Frederick Griffith observed that the living S cells, as well as the mixture of the heat-killed S cells and the living R cells, killed the mice; whereas, the heat-killed S cells and the living, R cells did not. |
| What conclusions could be drawn from Frederick Griffith's results? | Frederick Griffith concluded that an unknown, heritable substance from the dead S cells had allowed the R cells to form the capsules needed to transformed them into S cells. |
| Transformation | The change in genotype and phenotype due to the assimilation of external DNA by a cell. |
| What was Oswald Avery, Maclyn McCarthy, and Colin MacLeod's experiment? | Avery, McCarthy, and MacLeod deactivated two of the three candidates (DNA, Protein, and RNA) for the transforming agent at a time and tested the activated candidate's ability to transform living, nonpathogenic bacteria into pathogenic bacteria. |
| What were the results of Oswald Avery, Maclyn McCarthy, and Colin MacLeod's experiment? | Avery, McCarthy, and MacLeod observed that only DNA could transform the living, nonpathogenic bacteria into pathogenic bacteria. |
| What conclusions could be drawn from Oswald Avery, Maclyn McCarthy, and Colin MacLeod's results? | Avery, McCarthy, and MacLeod concluded that DNA was the transforming agent. |
| How was DNA's ability to program cells discovered? | The experiments of Alfred Hershey and Martha Chase demonstrated how viral DNA could program infected cells. |
| Bacteriophage | A virus that can infect bacteria. |
| Phage | Another name for a bacteriophage. |
| Virus | An organism consisting of a phage head, tail sheath, tail fiber, and DNA, which allows it to infect a host cell and take over the cell's metabolic machinery in order to reproduce. |
| What was Alfred Hershey and Martha Chase's experiment? | Hershey and Chase used radioactive sulfur and phosphorus to trace the fates of protein and DNA, respectively, of T2 phages that infected bacterial cells; therefore, they could see which of the molecules entered and reprogrammed the cells. |
| What were Alfred Hershey and Martha Chase's results? | Hershey and Chase observed that the proteins labeled with sulfur remained outside of the cells, but the DNA labeled with phosphorus entered the cells. |
| What conclusions could be drawn from Alfred Hershey and Martha Chase's results? | Hershey and Chase concluded that DNA functions as the genetic material of phage T2, and nucleic acids, instead of proteins, serve as the hereditary material, at least for viruses. |
| Why did Alfred Hershey and Martha Chase use phosphorus and sulfur in their experiment? | Hershey and Chase used phosphorus to label the DNA because most of the phosphorus in phage T2 is in its DNA; moreover, they used sulfur to label the protein because sulfur was incorporated only into the protein of phage T2. |
| What was Erwin Chargaff's experiment? | Chargaff analyzed the nitrogenous base composition of DNA in various organisms. |
| What were Erwin Chargaff's results? | Chargaff observed that the base composition of DNA varied between species, but was consistent within species, so that the percent of adenine was always equal to that of thymine, and the percent of cytosine was always equal to that of guanine. |
| How was a structural model for DNA discovered? | The structural model for DNA was a collaboration of the work of Rosalind Franklin, James Watson, and Francis Crick. |
| Double Helix | The double helix refers to the two, antiparallel, twisted strands that make up the DNA model. |
| How did Rosalind Franklin contribute to the discovery of the structural model of DNA? | Franklin took images of a DNA molecule using x-ray crystallography, which showed that DNA was a double helix with a specific width between the two strands that had sugar-phosphate backbones. |
| How did James Watson and Francis Crick finalize the structural model of DNA? | Watson and Crick used Franklin's images and Chargaff's rules to create a double helical model, in which the hydrophobic nitrogenous bases were on the inside, and the two strands are complementary. |
| What is the structural model of DNA? | The structural model of DNA consists of two antiparallel strands of nitrogenous bases (adenine, cytosine, guanine, and thymine), which are supported by a phosphate-sugar backbone and twist in a rightward, double-helical formation |
| How does the structural model of DNA explain Chargaff's rules? | The structural model of DNA pairs adenine with thymine and cytosine with guanine, so the ratios of the paired bases will be equal. |
| What is the basic model for the replication of DNA? | The parent DNA molecule has two complementary strands, which resemble a ladder, when the DNA is unwound, and are then separated to serve as templates for the new, complementary, daughter strands that result in two identical copies of the parent DNA. |
| Semiconservative Model | The model of DNA replication, in which, each of the daughter molecules will consist of one of the parent strands and a complementary daughter strand. |
| Conservative Model | The model of DNA replication in which the parent strands reform the parent molecule after the daughter strands form the new daughter molecule. |
| Dispersive Model | The model of DNA replication, in which each of the daughter molecules will contain a mixture of the old and new DNA within both strands. |
| How was the model of DNA replication discovered? | The experiment of Meselson and Stahl eliminated the dispersive and the conservative models of DNA replication. |
| What was Matthew Meselson and Franklin Stahl's experiment? | Meselson and Stahl cultured bacteria in a nitrogen medium, transferred the bacteria to a lighter nitrogen medium, and centrifuged the sample after two replications. |
| What were Matthew Meselson and Franklin Stahl's results? | Meselson and Stahl observed that the first replication produced a hybrid between the two medium colors, and the second replication produced both the lighter medium and the hybrid of the two. |
| What conclusions could be drawn from Matthew Meselson and Franklin Stahl's results? | Meselson and Stahl's results eliminated the conservative model after the first replication and the dispersive model after the second; therefore, the semiconservative model best represented DNA replication. |
| Origin of Replication | The special site at which DNA replication begins that are identified as short stretches of DNA having a specific sequence of nucleotides. |
| Replication Fork | The Y-shaped region at the end of the replication bubble, where the parental strands are unwound. |
| Helicase | The enzyme that untwists the parental strands at the replication fork, so they can be used as templates. |
| Singl-Strand Binding Protein | The protein that binds to the unpaired DNA strands and stabilizes them. |
| Primer | The short stretch of five to ten RNA nucleotides that is the initial nucleotide chain produced as a new strand during DNA replication and allows DNA nucleotides to be added at the 3' end. |
| Primase | The enzyme that synthesizes the RNA primer from a single nucleotide, which is paired with the parent DNA template. |
| DNA polymerase | The enzyme that catalyzes the synthesis of new DNA molecules by adding DNA nucleosides triphosphates to the 3' end of the preexisting RNA chain with the release of two phosphates. |
| Topoisomerase | The enzyme that breaks, swivels, and rejoins the DNA strands in order to help relieve the strain caused by the tighter twisting ahead of the replication fork. |
| Leading Strand | The DNA strand synthesized by DNA polymerase III in the mandatory 5' -> 3' direction, and it only requires one primer for synthesis. |
| Lagging Strand | The DNA strand that the DNA polymerase III synthesizes by working along the template strand in the opposite direction of the replication fork in order to maintain the mandatory 5'->3' direction. |
| Okazaki Fragment | A segment of the lagging strand that is synthesized discontinuously and must be primed separately. |
| DNA Ligase | The enzyme that joins the final nucleotide of the replacement DNA to the first DNA nucleotide of the Okazaki fragment. |
| Mismatch Repair | The condition in which enzymes remove and replace incorrectly placed nucleotides that have resulted from erroneous replication. |
| Nuclease | The enzyme that cuts out the segment of the DNA the contains the damage, then DNA polymerase and ligase can fill the gap. |
| Nucleotide Excision Repair | The DNA repair system through which DNA is distorted, excised, replenished with nucleotides by DNA polymerase, and the free end of the new DNA is sealed to the old DNA by DNA ligase. |
| Thymine Dimer | The molecule formed by the covalent linkage of thymine bases that are adjacent to the DNA strand, which cause the DNA to distort and interfere with replication. |
| Telomere | The special sequence of DNA found in eukaryotic chromosomal DNA molecules that do not contain genes and postpone the erosion of genes near the ends of the DNA molecules. |
| Telomerase | The enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells, restoring their original length and compensating for the shortening from DNA replication; however, it is not active in human somatic cells, protecting them from cancer. |
| How does the antiparallel arrangement of the double helix affect replication? | DNA polymerases can only add nucleotides to the 3', so the strand can only elongate in the 5'->3' direction, so the polymerase must work away from the replication fork. |
| DNA Polymerase I | The enzyme that replaces the RNA nucleotides of the primers with DNA versions individually at the 3' end of the adjacent Okazaki fragment. |
| Why can DNA replication not be modeled with locomotives moving along a railroad track? | The proteins involved in replication work as a single complex; the DNA moves along the replication complex; and the lagging strand loops back through the complex, so the DNA polymerase can quickly synthesize the Okazaki fragments and dissociate. |
| Bacterial Chromosome | The double-stranded, circular, DNA molecule associated with a small amount of protein that serves as the main component of the bacterial genome. |
| Eukaryotic Chromosome | The single, linear DNA molecule that is associated with a large amount of protein. |
| Nucleoid | The dense region of DNA in a bacterium that is not bounded by a membrane |
| Chromatin | The complex of DNA and protein that fits into the nucleus of a eukaryotic cell because of an elaborate, multilevel packaging system. |
| How is DNA packaged in eukaryotic cells? | DNA is packaged as a double helix, histones, nucleosomes, 30-nanometer fibers, looped domains, and metaphase chromosomes. |
| The Double Helix | The two strands of DNA are twisted into a double helical formation. |
| Histone | The protein responsible for the first level of DNA packaging in chromatin, and the most common types in chromatin are H2A, H2B, H3, and H4. |
| Nucleosome | The package of DNA, also known as "beads on a string" or 10-nm fiber, wound twice around a protein core that is made up of two molecules each of the four main histone types, so that the amino end (N-terminus or histone tail) extends from the nucleosome. |
| 30-Nanometer Fiber | The package resulting from interactions between the histone tails of one nucleosome, the linker DNA, nucleosomes on the other side, and a fifth histone (H1), which cause the 10-nm fiber to coil to 30-nm; this is prevalent in the interphase nucleus. |
| Looped Domains | The package formed, when the 30-nm fiber loops and attaches to a chromosomes scaffold made of proteins, a type os topoisomerase, and H1 molecules, to form a 300-nm fiber. |
| Metaphase Chromosome | The package resulting from the coiling of looped domains in a mitotic chromosome, which forms chromatids with widths of 700-nm. |
| Heterochromatin | The interphase chromatin that can be seen as irregular clumps using a light microscope. |
| Euchromatin | The interphase chromatin that is less compacted and more dispersed. |
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