Class Note for MIC 205A at UA
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Date Created: 02/06/15
Why do we need to know about microbial genetics Mlcroblal Genetlcs I Genetics is the basis of expression of certain traits DNA Repl39camquot and the central e g Ertam metabuh pathways m mmrubes ur mug Dogma Eye cutur m humans I If metabolism is the basis of life and genes encode enzymes THEN microbial genetics is the basis ofthe basis of life I Like in metabolism many drugs used to treat infections interfere with microbial DNA replication or protein synthesis I DNA forms the basis of many new diagnostic tests for bacterial and viral infections Definitions DNA and chromosomes I Genetics The science of heredity how traits I Bacterial are passed from generation to generation ch romosome I Genome A cells genetic information usually I Lengm onhe DNA E coli I Chromosomes Stmctures that contain DNA chromosome I Genes segments of DNA generally that code 17 mm for functional products Length ofthe I Genotype the genes of an organism potential E colicell 2 pm Prope ieS DNA is I Phenotype actual expressed properties supercoiled phenotype is the manifestation of genotype topoisomerase I The flow of genetlc Informatlon DNA has dlrectlonallty 0 I Polymer of nucleotides sugar deoxyribose phosphate and nitrogenous bases adenine A guanine G thymine T cytosine C I quotBackbonequot is deoxyribose phosphate I Start at the Carbon 5 ofthe rst sugar Poo539339PO539339PO 539 339 OH I This is referred to as the 53 direction 5 mamn DNA is 9 double stranded I My say I Strands held together by hydrogen bonds between AT and C G I Strands are directional complementary and antiparallel DNA replication H H anm 3 pm I One parental double quot v stranded DNA molecule to m 34 n n rawIn two Identical daughter 1 Lia Mm molecules semi quotat 2111 conservative u mowwow u HOW vmwmnm Z I Mogul 7 zn am I DNA unwinds and strands 7 quot rmquot I are separatedreplication Ii1 fork I Free nucleotides are matched to exposed bases I DNA polymerase joins nucleotides I New and original strands rewind Dill vmm mm M mm a hm mm mm Addition of nucleotides I DNA polymerase only adds m nucleotides to 91310 0 LEOquot the 3 end of quot DMOQ 9v Era P DNA 0 quoto a a quot o I owe GEEC7 I Synthesis on o 0 g 0 requires energy 1 exquot quotClo T 31400 gained from 39 a Equot If 0 o o hydrolysis of 1 phosphate bonds Events at the replication fork 3 1 Helicase separates ynthesis ofthe leading strand the doublestranded roceeds continuousl 5 to 3 molecule iscontinuous also 5 to 3 2 Primase Okazaki fragments Synthesizes an R I primerfragment 3 DNA polymerase III adds nucleotides onto the 339 end ofthe 39agment 5 DNA ligase seals the gaps between adjacent fragments 4 DNA polymerase I replaces the RNA primerwith deoxynucleotides Summary of events at the replication fork I DNA is unwound and replication fork forms I Leading strand is synthesized continuously I Lagging strand is synthesized in small segments 1000bpOkazaki fragments I DNA synthesis is primed by RNA primers I RNA primers and replaced by DNA I DNA fragments are joined together Some Enzymes Involved in DNA Replication and Their Functions Enzyme Function Helium Unripping the DNA hclix Primasc Synthesiing on RNA prirncr DNA pnlymcrmc Ill Adding hast m the new DNA chitin proul39rctkling lhc Chitin for mixmkcx Removing primer closing gtps repairing lllilllillt lt Lignm Final himlingofn s in DNA durng ynlltcsix and repair Supercoiling DNA polymerase l Uymsc topoisomerase Replication of bacterial DNA u I Bidirectional replication two replication forks I Following replication I Each origin binds to opposite poles of the cells I Each daughter cell receives one DNA molecule Transcription I An RNA copy of the DNA encoding a gene or genes is made I RNA is like DNA except the sugar ribose not deoxyribose and uses uracil U instead of T I Three types of RNA I mRNA messenger contains the information from DNA to make protein by translation I tRNA transfer acts as a translator between the sequence of the mRNA and the sequence of the protein I rRNA ribosomal structural part of the ribosome Transcription Dlvenlon oi lranscllplmn WWW nanscnm I Proceeds in the 5 a 3 direction I U in the RNA pairs with A in the DNA The Central Dogma I Information in DNA is transcribed into RNA I Information in RNA is translated into proteins Transcription initiation I Begins when RNA polymerase binds to the promoter sequence I A copy of the coding DNA strand is made using the other strand as a template RNA Polymelase Temulah strand Termulle semi nal Transcription termination mm to w x mummuuu I DNA rewinds as RNA transcript leaves I Transcription proceeds until a terminator is reached I Signals the RNA polymerase to detach from the DNA Eucaryotic mRNA One ofseveral big differences The presence of introns sequences that are noncoding located within coding regions exons omeNA mo 3 What purpose an inlrons serve Translation I mRNA is translated in codons 3 nucleotides L I Each codon speci es an amino acid in the protein I The genetic code is degenerate that is more than one codon codes for one amino acid Translation occurs on ribosomes I Translation occurs on ribosomes I The ribosome recognizes the mRNA through a ribosome binding site on the mRNA I Starts AUG and stops UAA UAG UGA I tRNAs are used to translate codons into amino acid sequence l The rst codon AUG is recognized by the tRNA carrying formyl methionine This tRNA moves to the P site and the second tRNA moves into the A site a An enzyme catalyzes the formation of a peptide bond between amino acids 1 and 2 on RNA 2 l The emptthNA 1 is released rom via the E site The mRNA moves along one codon so that RNA 2 moves from the A site to the P site The third tRNA then enters the A site using its anticodon to recognize the codon I A peptide bond is formed between the growing peptide chain and amino acids 3 on RNA 3 I The empty tRNA 2 leaves the ribosome through the E site tRNA 3 with the peptide attached moves the P site Codon 4 on the mRNA moves into the A site and is recognized by the anticodon on RNA 4 l Amino acid 4 is added to the eptide chain on tRNA he process is repeated for each new amino acid added until a sto codon moves into t e A site I When a stop codon enters the A site 5i nals an Enz rnetu cleave the ul 2 tidefrum thgfinaltRNAy p W p Cumpunents are then released fur anuther ruund uf translatiun The protein assembly line I Bacterial cells can translate mRNA molecules into proteins as they are being transcribed I Allows rapid response of protein production in response to changing conditions Antibiotics that interfere with transcription or translation I Rifamycins bind to bacterial transcriptase and mRNA synthesis is inhibited I Erythromycin and Azithromycin bind to the bacterial ribosome blocking mRNA attachment I Tetracycline binds to the bacterial ribosome blocking mRNA elongation
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