DNA Replication & Transcription in Bacteria PDF

Other features of plasmids In several pathogenic bacteria, virulence factors (e.g., ability to attach or produce toxins) are encoded by plasmid genes. Bacteriocins can be encoded on plasmids. proteins that inhibit or kill closely related species or different strains of the same speci...

Other features of plasmids In several pathogenic bacteria, virulence factors (e.g., ability to attach or produce toxins) are encoded by plasmid genes. Bacteriocins can be encoded on plasmids. proteins that inhibit or kill closely related species or different strains of the same species Rhizobia require plasmid-encode functions to fix nitrogen. Metabolism (e.g., hydrocarbon degradation) Important for conjugation (horizontal gene transfer) III. Copying the Genetic Blueprint: DNA Replication Note the bidirectional DNA synthesis  Figure 4.11 DNA replication is semiconservative. (Figure 4.11) Each of the two resulting double helices has one parental (template) strand and one new strand. Precursor of each nucleotide is a deoxynucleoside 5′-triphosphate (dNTP). Replication ALWAYS proceeds from the 5′ end to the 3′ end.  DNA polymerases catalyze polymerization of deoxynucleotides. Five different DNA polymerases (DNA Pol I-V) in E. coli DNA Pol III is primary enzyme replicating chromosomal DNA; DNA Pol I, plays a lesser role. Other DNA polymerases repair damage. Table 4.2  DNA synthesis begins at the origin of replication in prokaryotes. DNA polymerases require a primer: a short stretch of RNA. (Figure 4.12) Primer made from RNA by primase. Figure 4.12  Replication fork: zone of unwound DNA where replication occurs (Figure 4.13) DNA helicase unwinds the DNA. Figure 4.13  Extension of DNA (Figure 4.14) occurs continuously on the leading strand 5' to 3' discontinuously on the lagging strand—no 3'-OH Okazaki fragments Figure 4.14  Connecting DNA fragments on the lagging strand DNA synthesis on lagging strand continues until it reaches previously synthesized DNA. (Figure 4.15) DNA polymerase I removes the RNA primer and replaces it with DNA. DNA ligase seals nicks in the DNA.  Bidirectional Replication DNA synthesis is bidirectional for the circular chromosome two replication forks moving in opposite directions (Figure 4.16) DNA Pol III adds 1,000 nucleotides per second.  Replisome and Proofreading Replisome: complex of multiple proteins involved in replication. The replisome consists of two copies of DNA polymerase III and DNA gyrase, plus helicase and primase (together forming the primosome), and many copies of single-strand DNA-binding protein.  DNA replication is extremely accurate. Proofreading helps to ensure high fidelity. Mutation (changes in DNA sequence) rates in cells are 10–8 to 10–11 errors per base inserted. DNA Pol I and Pol III can detect mismatch through incorrect hydrogen bonding and remove with 3'→5' exonuclease. Proofreading occurs in prokaryotes, eukaryotes, and viral DNA replication systems. IV. RNA Synthesis: Transcription in Bacteria Central dogma Replication: DNA is duplicated by DNA polymerase. Transcription: Information from DNA is transferred to RNA by RNA polymerase. mRNA (messenger RNA): encodes polypeptides (proteins) Translation: Information in RNA is used to build polypeptides. tRNA (transfer RNA): convert mRNA to amino acid sequence of protein rRNA (ribosomal RNA): catalytic and structural ribosome components  Characteristics of mRNA transcription Eukaryotes Each gene is transcribed individually into a single mRNA. Replication and transcription occur in nucleus. RNAs must be exported outside nucleus for translation. Prokaryotes Multiple genes may be transcribed in one mRNA. Coupled transcription and translation occur (Figure 4.7), producing proteins at maximal rate.