Chapter 8: Microbial Genetics DUE 24TH APRIL 2024

Chapter 8: Microbial Genetics DUE 24TH APRIL 2024 1. Define genetics, genome, chromosome, gene ,genetic code, genotype, phenotype, and genomics - CORRECT ANSWER-genetics-the study of what genes are, how they carry info, how info is expressed, and how genes are replicated genome-the entire genetic makeup of an organism including both its genes and noncoding sequences that link these chromosome-naked, circular piece of DNA containing approx. genes gene-a segment of DNA that encodes a functional product, usually a protein genetic code-the set of rules that determines how a nucleotide sequence is converted into the amino acid sequence of a protein genotype-an organism's genetic makeup, the info that codes for all particular characteristics of that organism; represents potential properties, but not the properties themselves phenotype-actual, expressed properties, such as the organism's ability to perform a particular chemical reaction; manifestation of genotype genomics-the sequencing and molecular characterization of genomes 2. Describe how DNA serves as genetic information. - CORRECT ANSWER-the structure of DNA helps explain two primary features of biological info storage. -first, the linear sequence of bases provides the actual info -genetic info is encoded by the sequence of bases along the strand of DNA, in much the same way as our written language uses linear sequence of letters to form words and sequences 3. Describe the process of DNA replication. - CORRECT ANSWER-1. the double helix of the parental DNA separates as weak hydrogen bonds between the nucleotides on opposite strands break in response to the action of replication enzymes 2. hydrogen bonds form between new complementary nucleotides and each strand of the parental template to form new base pairs 3. enzymes catalyze the formation of sugar-phosphate bonds between sequential nucleotides on each resulting daughter strand 4. Describe protein synthesis, including transcription, RNA processing, and translation. - CORRECT ANSWER-In the process of *transcription*, genetic info in DNA is copied, or transcribed, into a complementary base sequence of RNA. The cell then uses the info encoded in this RNA to synthesize specific proteins thru the process of *translation*. Compare protein synthesis in eukaryotes and prokaryotes. - CORRECT ANSWERDefine operon. - CORRECT ANSWER-genes that are involved in the same biochemical pathway, are usually organized together Explain the regulation of gene expression in bacteria by induction, repression, and catabolite repression. - CORRECT ANSWER--Constitutive genes are expressed at a fixed rate -Other genes are expressed only as needed Repression controls the synthesis of one or several (repressible) enzymes. It is the regulatory mechanism that inhibits gene expression and decreases the synthesis of enzymes. When cells are exposed to a particular end product, the synthesis of enzymes related to that product decreases. Repression is mediated by regulatory proteins called repressors, which block the ability of RNA polymerase to initiate transcription from the repressed genes. The process that turns on the transcription of a gene or genes is called induction. In the presence of certain chemicals (inducers), cells will synthesize more enzymes (induction). Transcription of structural genes for catabolic enzymes (such as B-galactosidase) is induced by the absence of glucose. It is important to note that the presence of glucose inhibits metabolism of alternative carbon sources by catabolic repression (the "glucose effect"). This is due to the fact that when glucose is available the level of cAMP in the cell is low, and consequently CRP is not bound. Define mutagen. Describe the effect of mutagens on the mutation rate. - CORRECT ANSWER-Mutagen is an agent in the environment that brings about mutation. If a mutagen is present, it will usually increase the spontaneous rate of mutation, which is approximately 1 in 106 replicated genes, by a factor of 10-1000 times. This is a 1 to 3 order of magnitude increase, meaning a mutation rate of 10-6 becomes 10-5 or possibly 10-3. Describe two ways mutations can be repaired. - CORRECT ANSWER--enzymes that cut out and replace the damaged portion of DNA ex: in UV radiation damage -base repair by enzymes ex: photoreactivation enzymes that repair thymine dimers in the presence of visible light Identify the purpose of and outline the procedure for the Ames test. - CORRECT ANSWER-purpose: access chemicals for their ability to cause mutations 1. two cultures are prepared of salmonella bacteria that have lost the ability to synthesize histidine (histidine-dependent) 2. the suspected mutagen is added to the experimental sample only; rate liver extract (an activator) is added to both samples 3. each sample is poured onto a plate of medium lacking histidine. the plates are then incubated at 37 degrees Celcius for two days. only bacteria whose histidine-dependent phenotype has mutated back (reverted) to histidine-synthesizing will grow into colonies 4. the number of colonies on the experimental and control plates are compared. the control plate may show a few spontaneous histidine-synthesizing revertants. the test plates will show an increase in the number of histidine-synthesizing revertants if the test chemical is indeed a mutagen and potential carcinogen. the higher the concentration of mutagen used, the more revertant colonies will result Differentiate horizontal and vertical gene transfer. - CORRECT ANSWER-vertical gene transfer- occurs during reproduction between generations of cells; genes are passed from an organism to its offspring. horizontal gene transfer- occurs between cells of the same generation; donor cell gives a portion of its DNA to a recipient cell. Compare the mechanisms of genetic recombination in bacteria. - CORRECT ANSWERVERTICAL GENE TRANSFER-occurs during reproduction between generations of cells HORIZONTAL GENE TRANSFER-the transfer of genes between cells of the same generation TRANSFORMATION- genes are transferred from one bacterium to another as "naked" DNA in solution CONJUGATION- genetic material is transferred fro one bacterium to another; requires direct cell-to-cell contact; cells must be of the opposite mating type (F- and F+, Sex pili) TRANSDUCTION-bacterial DNA is transferred from a door cell to a recipient cell inside a virus that infects bacteria called a bacteriophage. Describe the functions of plasmids and transposons. - CORRECT ANSWER-Plasmids: Conjugative plasmid: carries the genes for sex pili and transfer of the plasmid Dissimilation plasmid: encode enzymes for catabolism of unusual compounds R factors: encode antibiotic resistance Transposons: segments of DNA that can move fro one region of DNA to another; contain insertion sequences for cutting and resealing DNA (transposase); complex transposons carry other genes