Review Questions on Growth, Control of Growth, Antibiotics and DNA & Genetics - Assignment Example

MB 12 – Review Questions on Growth, Control of Growth, Antibiotics Anti-microbial agents help in the prevention and treatment of diseases caused by microbes. The use of antibiotics and immunization procedures against infectious diseases has increased the average life span of humans by nearly 20 years. Chemical disinfectants help in killing pathogenic microbes. 2. The use of the antimicrobials has been a short-term solution because it has led to antimicrobial resistance. Simultaneously, antimicrobials need to be frequently improved as new strains of microbes make its way into human lives. 3. Antibacterial soaps and detergents are unnecessary since regular soaps and detergents help reduce the risk from bacteria. It may infact be dangerous to use antimicrobial soaps and detergents because the chemicals used in them can accumulate in the environment and even promote potentially dangerous resistant germs. 4. Bacterial cell walls contain a peptidoglycan layer that is essential for its survival in hypotonic environments. Penicillin drug interferes with the peptidoglycan molecules and weakens the bacterial cell wall. Another drug isoniazid, used in the treatment of tuberculosis and other mycobacterial infections, is known to inhibit the formation of very long chain fatty acids such as those found in the cell walls of mycobacteria. 5. The permeability of bacterial plasma membrane can be targeted for disturbance. Antibiotics like Polymyxin B increases the permeability of bacterial plasma membrane and causes membrane disruption. 6. Antibiotic chloramphenicol, a product isolated originally from Streptomyces, acts as an inhibitor of protein synthesis in a bacterial cell. 7. Endospores can be destroyed by sterilization, autoclaving and using chemical disinfectants like iodine. 8. Unlike gram positives, gram negatives have a greater resistance to certain antimicrobial chemicals because a major component of their outer membrane is lipopolysaccharide (LPS). The LPS produces a negative charge and repels hydrophobic compounds including certain drugs and disinfectants that would otherwise kill the cell. 9. Alexander Fleming left a culture plate smeared with Staphylococcus bacteria on his lab bench and went on a holiday. When he returned, he noticed a clear halo surrounding the yellow-green growth of a mold that had accidentally contaminated the plate. He deduced that the mold (Penicillium notatum) must have released a substance that inhibited the growth of the bacteria. 10. Bacteria evolve resistance to antimicrobial agents through mutation in the bacterial DNA and acquisition of plasmids from other organisms. 11. Incineration, autoclaving, pasteurization and hot air oven kills all microorganisms. Boiling kills everything except some endospores. Refrigeration at low temperatures slows the rate of growth of microbes. In case of freezing, most organisms grow very little or not at all at 00. 12. High concentration of oxygen increases the formation of free radicals, which can react with metals to form superoxides that are toxic to cells. Most facultative and aerobic organisms have an enzyme called superoxide dismutase that converts the superoxide anion into ground-state oxygen thus ridding the cell of destructive superoxide anions. 13. Oxidative damage occurs as a result of oxidation within our bodies in which free radicals produced during normal cell processes bind to and attack fats, carbohydrates, proteins, enzymes and DNA. Oxidative damage increases with aging and may lead to death and dysfunction of cells. Some chemical and physical methods of causing oxidative damage include cigarette smoking, exposure to toxins such as mercury, severe infection with shock and heavy exercise. 14. The preparation of beef jerky involves cooking the beef at 160°F followed by the dehydration process. This process ensures that any bacteria present will be destroyed. Black raspberries contain phytochemicals like ellagitannins that are known to selectively inhibit the growth of human pathogenic bacteria. Hence it acts as a natural antimicrobial agent. 15. Normal microbiota in the rumen of a cow are destroyed when pH changes. The cow may respond by developing acidosis and founder or die. pH changes may promote growth of new and often pathogenic bacteria. In such cases antibiotics need to be administered to slow the infections which may also lead to the bacteria developing resistance. MB 12 – Review Questions on DNA & Genetics 1. Genome is the entire set of genes in an organism. It cannot give the instructions for how to make something like the DNA. Therefore genomes are considered list of ingredients. 2. During DNA replication, the lagging strand is synthesized in fragments known as Okazaki fragments while the leading strand is synthesized in a continuous manner. Hence the lagging strand is synthesized more slowly than the leading strand. DNA replication begins when the double helix partially unwinds and the enzyme DNA polymerase moves into position where synthesis will begin. The sequence of bases on each separated strand serves as a template to guide the insertion of complementary set of bases on the strand being synthesized. On completion, two DNA molecules identical to each other and the parent molecule are formed 3. Chromosomes are super-coiled to take up less space within the cell. 4. If a gene is expressed, the gene’s DNA sequence is converted into the functional proteins of the cell. The process involves transcription of the gene to yield an RNA molecule (primary transcript). This RNA molecule is processed to remove the introns and form the mRNA (mature transcript) which is then translated into a sequence of amino acids that defines the protein. 5. Gene expression is influenced by the environmental factors like exposure to pesticides, industrial chemicals, diet and smoking habits. Those genes that express themselves regardless of environmental conditions are called constitutive genes. These genes probably subserve the essential constituents of an organism and are hence not regulated. 6. Genes coding for anabolic enzymes are usually repressible because they regulate enzymes that produce a needed product within the cell. Repression occurs in response to an excess of end product. 7. Genes coding for catabolic enzymes are usually inducible. If this is not the case, the production of catabolic enzymes can get out of control, as they are involved in breaking up organic compounds. Presence of the substrate initiates induction. 8. Activator is a DNA-binding protein that regulates one or more genes by increasing the rate of transcription. An inducer is a molecule that starts gene expression. It functions by disabling repressor proteins. 9. The operon has four parts: a. Repressor Gene that produces a protein which fits in the operator to turn operon off b. Promoter to which RNA polymerase attaches to begin transcription of the genes, c. Operator to which the active repressor fits to block RNA polymerase and turn off transcription and d. Structural Genes with code for enzymes to digest lactose. 10. arg operon lac operon a. “normal state” repressible inducible b. status of repressor in normal state repressed expressed c. repressor is activated by . . . corepressor lactose d. repressor is inactivated by . . . arginine inducer e. enzymes coded by structural genes are anabolic 11. Absence of lactose prevents RNA polymerase from transcribing the lac operon’s genes and hence turns the operon OFF. The presence of lactose turns the operon ON. When lactose and glucose are both present, the lac operon will not be transcribed. 12. Mutations can lead to extra base pairs being added or removed from the DNA resulting in the production of useless proteins. Mutations can also lead to the production of altered amino acids in the protein product affecting its function. 13. Mutations can lead to death or cause slower growth (sickness). Mutations can also change the amino acid sequence of a protein affecting its activity. It may also change the binding site of RNA polymerase, repressor or some other protein, thereby affecting the amount of a protein. 14. Mutations can be silent when the genetic code is redundant. E.g. CUC and CUA and UUG all code for leucine. Mutations in non-coding regions can also have little or no effect. 15. There are 5 major types of mutations. They include point mutation, missense mutation, nonsense mutation, frameshift mutation and silent mutation. 16. Mutagens include X-rays, UV rays, pesticides, nitrosamines and benzpyrene. A cell can reverse an existing mutation by undergoing reverse mutation. Frameshift mutations sometimes have “second site reversions”, where a second frameshift downstream from the first frameshift reverses the effect. 17. Mutations can make a cell more likely to survive in a particular environment. E.g., mutations in the ribosome often cause slower growth, which is a sign of “sickness”, but it may also allow the cell to resist macrolide antibiotics. 18. Greater the genetic diversity within a population, greater the chance that some individuals that possess the ability to survive and reproduce under the new conditions will flourish. Works Cited Madigan, Michael T. & John M. Martinko. Brock Biology of Microorganisms. 11th ed. ISBN: 0-13-144329-1. Read More