Microbiology Exam 2 CHAPTER 8 Microbial Genetics I Structure and Function of the Genetic Material Genetics is the science of heredity including the study of what genes are how they carry information how they are replicated and passed to subsequent generations of cells and how the expression of their information within an organism determines the particular characteristics of that organism Genome genetic information in a cell Chromosome structures containing DNA that physically carry hereditary information genes Genes segments of DNA that code for functional products DNA double helix each strand having a string of alternating sugar and phosphate groups and a nitrogenous base attached to each sugar Base pairs are held together by hydrogen bonds AT CG The linear sequence of the basis provides the actual information The complementary structure allows for the precise duplication of DNA during cell division Genetic code set of rules that determine how a nucleotide sequence is converted to the amino acid sequence of a protein A Genotype and Phenotype a Genotype genetic makeup information that codes for all the particular characteristics of the organism Represents the potential properties b Phenotype actual expressed properties such as the organism s ability to perform a particular chemical reaction This is the manifestation of genotype In molecular terms it s an organism s collection of proteins B DNA and Chromosomes bacteria typically have a single circular chromosome consisting of a single circular molecule of DNA with associated proteins The chromosome is looped and folded attaching to the plasma membrane Open reading frames are regions of DNA that are likely to encode a protein These are base sequences between start and stop codons a Genomics sequencing and molecular characterization of genomes C Flow of genetic information DNA replication allows for the flow of genetic information from one generation to the next DNA of a cell replicates before cell division allowing offspring cell to receive an identical chromosome The genetic information contained in DNA is transcribed into mRNA and then translated into protein D DNA Replication a One parent double stranded DNA is converted into two identical daughter molecules One strand acts as a template for the production of the other strands When replication begins the supercoiling is relaxed by topoisomerase and the two strands are unwound by helicase and separated from each other Free nucleotides in the cytoplasm are matched up to the exposed bases of the single stranded parental DNA and once aligned the newly added nucleotides are joined to the growing DNA strand by DNA polymerase The parental DNA is unwound further to allow the addition of the next nucleotides The point of replication occurs at the replication fork Because the new double stranded DNA molecule contains one original strand and one new strand this is a semiconservative replication process The proofreading of DNA polymerase accounts for the high accuracy of replication E RNA and Protein Synthesis b The end with the hydroxyl attached to the 3 carbon is called the 3 end of the DNA strand the end having a phosphate attached to the 5 carbon is called the 5 carbon end The 5 3 direction of one strand runs counter to the 5 3 direction of the other strand DNA polymerases an add new nucleotides to the 3 end only so as the replication fork moves along the parental DNA the two new strands grow in different directions c The energy needed for replication is provided for by the nucleotides Two phosphate groups are removed to add the nucleotide to a growing strand of DNA this hydrolysis is exergonic and provides energy to make the new bonds in the DNA strand d Some bacteria DNA replication goes bidirectionally around the chromosome Two replication forks move in opposite directions meeting eventually when the replication is completed The loops are then separated by topoisomerase a Transcription genetic information in DNA is copied into a complementary base sequence of RNA Transcription begins when RNA polymerase binds to the DNA at the promoter site RNA is synthesized in the 5 3 direction and continues until RNA polymerase reaches a site on the DNA called the terminator i Messenger RNA mRNA carries the coded information for making specific proteins from DNA to ribosomes where proteins are synthesized Acts as an intermediate between the permanent storage forms DNA and translation b Translation protein synthesis which involves decoding the language of nucleic acids and converting that information into the language of proteins i Codons language of mRNA in the form of groups of three nucleotides each coding for a particular amino acid Determines the sequence of amino acids that will be in the protein being synthesized 1 Degeneracy of the code most amino acids are signaled by several alternative codons Allows for a certain amount of change or mutation in the DNA without affecting the protein ultimately produced 2 Sense codons 61 64 total codons that code for the amino acids a AUG start codon methionine and formylmethionine 3 Nonsense codons 3 64 total codons referred to as stop codons that signal the end of the protein molecule s synthesis a UAA UAG UGA ii Transfer RNA tRNA site of translation of codons to their corresponding amino acids 1 Anticodon sequence of three bases that is complementary to a codon present in each tRNA molecule allowing for each molecule to base pair with its associated codon The ribosomes direct the order of binding of tRNAs to condons and to assemble the amino acids brought there into a chain ultimately producing a protein iii The ribosome comes apart into its two subunits and the mRNA and newly synthesized polypeptide chain are released The tRNAs mRNA and ribosome are then available to be used again There are usually a number of ribosomes attached to a single mRNA all at various stages of 1 protein synthesis In prokaryotes translation can begin even before transcription is complete and the entire mRNA molecule is even made In eukaryotes transcription takes place in the nucleus and the mRNA must be completely synthesized before translation can begin Eukaryotic genes contain exons the regions of DNA expressed and introns the intervening regions of DNA that don t encode protein Particles called snRNPs remove the introns and splice the exons together II Regulation of Bacterial Gene Expression A Repression and Induction mechanisms that regulate the transcription of mRNA and
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