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FSU MCB 2004 - Lecture 11- Chapter 8: Microbial Genetics

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Lecture 11- Chapter 8: Microbial Genetics• Define genetics, genome, chromosome, genetic code, genotype, phenotype, genomicso Genetics: the science of heredity; it includes the study of what genes are, how they carry information, how information is expressed, and how genes are replicated and passed to subsequent generations of cells or passed between organisms and how the expression of their information within an organism determines the particular characteristics of that organism.o Genome: the genetic information in a cello Chromosome: structures containing DNA that physically carry hereditary informationo Gene: a segment of DNA that encodes a functional product, usually a protein ( it is repeating units of nucleotides).o Genetic Code: the set of rules that determines how a nucleotide sequence is converted into the amino acid sequence of a proteino Genotype: genetic makeup, the information that codes for all particular characteristics of the organism; represents potential properties.o Phenotype: actual, expressed properties, such as the organism’s ability to perform a particular chemical reaction. In bacteria, either enzymatic or structuralo Genomics: the molecular study of genomes• Describe how DNA serves as genetic information:o DNA stores genetic information. The way the proteins match together tell what the cell/creature will look like by the way and order in which they are put together• Describe mRNA, rRNA, tRNAo mRNA: messenger RNA translates DNAs genetic code; goes through the ribosome.o tRNA: transfer RNA, bond with amino acids at the ribosome.o rRNA: ribosomal RNA, forms an integral part of ribosome’s, the cellular machinery for protein synthesis; makes polypeptides that assemble amino acids that make up proteins.• Describe DNA replication, RNA transcription, and protein translationDNA replication: one “parental” strand is made into two “daughter” strands1. The double helix of the pariental DNA seperates as weak hydrogen bonds between the nucleotides on opposite strands break in response to the action of replication enzymes2. Hydrogen bonds form between new complementary nucleotides and each strand of the parental template to form new base pairs3. Enzymes catalyze the formation of sugar-phosphate bonds between sequential nucleotides on each resulting daughter strandRNA transcription: the synthesis of a complementary strand of RNA from a DNA template (essentially, DNA is copied to RNA)1. RNA polymerase binds to the promoter, and DNA unwinds at the beginning of a gene.2. RNA is synthesized by complementary base pairing of free nucleotides with the nucleotide bases on the template strand of DNA.3. The site of synthesis moves along DNA; DNA that has been transcribed rewinds.4. Transcription reaches the terminator.5. RNA and RNA polymerase are released and the DNA helix re-forms.Protein Translation: Decodes the “language” of nucleic acids and converting that information into the “language” of proteins.1. Components needed to begin translation come together. (the two ribosomal subunits, a tRNA with the anticodon UAC, and the mRNA molecule to be translated)2. On the assembled ribosome, a tRNA carrying the first amino acid is paired with the start codon (AUG) on the mRNA. A tRNA carrying the second amino acid approaches.3. The second codon of the mRNA pairs with a tRNA carrying the second amino acid at the active site. The first amino acid joins the second by a peptide bond. This attaches the polpeptide to the tRNA at the P site.4. The ribosome moves along the mRNA until the second tRNA is in the P site, the next codon to be translated is brought into the A site. The first tRNA now occupies the E site.5. The second amino acid joins to the third by another peptide bond, and the first tRNA is released from the E site.6. The ribosome continues to move along the mRNA, and new amino acids are added to the polypeptide.7. When the ribosome reaches a stop codon, the polypeptide is released.8. Finally, the last tRNA is released, and the ribosome comes apart. The released polypeptide forms a new protein.• Explain the regulation of gene expression in bacteria by induction, repressionRepression: it’s a regulatory mechanism that inhibits gene expression and decreases the synthesis of enzymes; it’s a response to the overabundance of metabolic pathway and causes a decrease in the rate of synthesis of the enzymes that form the product; its mediated by repressors; default is onInduction: the process that turns on the transcription of a gene or genes; its regulated by a gene called inducer; default is off• Classify mutations by type, and describe how mutations are perverted and repaired• Base substitution: (point mutation) a single base at one point in the DNA sequence is replaced with a different baseo Missense mutation: change in one base, results in a change in the amino acid i.e. sickle cell anemiao Nonsense mutation: when the base substitution results in a nonsense codon (stop codon) being created in the middle of an mRNA moliculeFrameshift mutation: Insertion or deletion of one or more nucleotide pairs.i.e. Huntington’s diseaseRepaired: o Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone.o Nucleotide excision repairs mutationso UV radiation causes thymine dimers and light repair separates thymine dimers• Define mutagenAgents in the environment, such as certain chemicals and radiation, that directly or indirectly bring about mutations• Describe the purpose of and outline the procedure for the Ames testThe Ames test is based on the observation that exposure of a mutagant bacteria to mutagenic substances may cause new mutations to reverse the effect of the original mutation (called reversion)The test uses bacteria to find carcinogens (things that cause cancer in humans). Most mutogenic things are carginogenic.1. Two cultures are prepared.2. The suspected mutagen is added to the experimental sample only.3. Each sample is poured onto a plate of medium lacking a needed medium.4. The numbers of colonies on the experimental and control plates are compared. The control plate may show a few spontaneous revertants. The test plate should show a lot if the chemical is a mutagent.Positive selection: finding a mutant celli.e. placing normally penicillin sensitive plate and whichever grows is a mutation• Differentiate between horizontal and vertical gene


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