Chapter 7 Microbial Genetics

PowerPoint® Lecture Slides for MICROBIOLOGY ROBERT W. BAUMAN Chapter 7 Microbial Genetics

• Genetics • Study of what genes are • how they carry information • how information is expressed • how genes are replicated

• Gene = Segment of DNA that encodes a functional product • usually a ______

• Genome All of the genetic material in a cell • Genomics Molecular study of genomes • ______Genes of an organism • Phenotype Expression of the genes

Horizontal Transfer

Vertical/ Linear Transmission

Central Dogma

Figure 7.1 Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings The Structure of Genomes • Prokaryotic • Eukaryotic • Genome in two structures • Genome in two structures • Chromosomes • Nuclear DNA • ______• Extranuclear DNA • ______Chromosome • Several Linear Chromosomes • Located in the Nucleoid • Located in Membrane bound ______

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Plasmids • Small, circular molecules of DNA • ______replicating • Carry information required for their own replication, and often for one or more cellular traits • Not essential for normal bacterial metabolism, growth, or reproduction • Can confer ______advantages • Many types of plasmids • Fertility factors, Resistance factors, Bacteriocin factors • Virulence plasmids, Cryptic plasmids

• Polymer of nucleotides: adenine, thymine, cytosine, guanine • Double helix associated with ______• "Backbone" is deoxyribose- phosphate • Strands held together by ______bonds between AT and CG • Strands are antiparallel

Semi-Conservative Replication

Nucleotides are added by what enzyme? They are always added to the 3’ end.

• DNA is copied by DNA polymerase • In the ______direction • Initiated by an RNA primer • ______strand synthesized continuously • Lagging strand synthesized discontinuously • Okazaki fragments • RNA primers are ______and Okazaki fragments joined by a DNA polymerase and DNA ligase

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.6 DNA Replication • An anabolic polymerization process that requires monomers and energy • Triphosphate deoxyribonucleotides serve both functions • Key to replication is complementary structure of the two strands • Replication is semiconservative – new strands composed of one original strand and one daughter strand

Figure 7.5a Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Initial Processes in DNA Replication • DNA polymerase binds to each strand and adds nucleotides to hydroxyl group at 3’ end of nucleic acid • Replicates DNA only 5’ to 3’ • Because strands are antiparallel, new strands synthesized differently • Leading strand synthesized continuously • Lagging strand synthesized discontinuously

Figure 7.5c Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Other Characteristics of DNA Replication • Bidirectional • DNA is ______; methylation plays role in variety of processes • Control of genetic expression • Initiation of DNA replication • Protection against viral infection • Repair of DNA

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings DNA Replication • DNA Polymerase • Editing function • ______bases are pulled out and replaced • Race between finishing replication and ______• 1/1,000,000 bases may be incorrect • Mutations from DNA replication = spontaneous mutations

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings DNA Replication • Prokaryotes • Eukaryotes • 1 circular chromosome • Multiple linear Chromosomes • ______ori site • ______ori sites • Smaller genome • Much larger genome • 1-2 polymerase • Multiple polymerases • ______DNA

Semi-conservative Bidirectional

• DNA replication is semiconservative

Theta model

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.7 Prokaryotic - Rolling Circle Replication • Plasmid DNA replication • Small, circular, autonomously replicating DNA • Nick in the DNA backbone of one strand • Ensures both cells get a copy of the plasmid • More than 1 copy of DNA can be made with ______.

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Transfer of Genetic Information • Transcription – information in DNA is copied as RNA nucleotide sequences • Translation – polypeptides synthesized from RNA nucleotide sequences • Central dogma of genetics • DNA transcribed to RNA • RNA translated to form polypeptides • DNA RNA Protein

• DNA is transcribed to make RNA pre-mRNA tRNA rRNA

mRNA • Transcription begins when RNA polymerase binds to the ______sequence • Transcription proceeds in the 5  3 direction • Transcription stops when it reaches the ______sequence

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Events in Transcription • Three types of RNA transcribed from DNA • mRNA • rRNA • tRNA • Where occurs • Nucleoid of prokaryotes • Nucleus, mitochondria, and chloroplasts of eukaryotes • Three steps • Initiation • ______• Termination Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Initiation of Transcript

Figure 7.8 Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings RNA Polymerase Versus DNA Polymerase • RNA polymerase does not require helicase • RNA polymerase slower than DNA polymerase • Uracil incorporated instead of thymine • RNA polymerase lacks proofreading function (more errors)

Figure 7.13 Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Stages of Translation • Three stages • Initiation • ______• Termination • All stages require additional protein factors • Initiation and elongation require energy (GTP)

Figure 7.16 Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Termination • Release factors somehow recognize stop codons and modify ribosome to activate ribozymes which sever polypeptide from final tRNA • Ribosome dissociates into subunits

Are transcription and translation simultaneous?

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.11 Control of Transcription • ______of genes are expressed at all times • Other genes are regulated so they are only transcribed and translated when ______• Allows cell to conserve energy • Regulation of protein synthesis • Typically halt transcription • Can stop translation directly

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Can cells control gene expression? • Control at various levels • DNA • Transcriptional level of control = no mRNA • mRNA • Translational level of control = ______• Protein • Post-translational level of control = protein activated when needed