Microbial Geneticsrms.rsccd.edu/faculty/KathyTakahashi/Bio229/ExamIIPosted/MicGenA.pdf•Eukaryotic...

PowerPoint® Lecture Slides for

ROBERT W. BAUMAN

MICROBIOLOGY

Chapter 7

Microbial Genetics

Terminology

• 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 ___________

Terminology

• Genome All of the genetic material in a cell

• Genomics Molecular study of genomes

• _________ Genes of an organism

• Phenotype Expression of the genes

Flow of Genetic Information

Figure 8.2

Central Dogma

Horizontal Transfer

Vertical/

Linear Transmission

The Structure of Nucleic Acids

The Structure of Genomes

• Prokaryotic

• Genome in two structures

• Chromosomes

• ___________

• _______ Chromosome

• Located in the Nucleoid

• Eukaryotic

• Genome in two structures

• Nuclear DNA

• Extranuclear DNA

• Several Linear Chromosomes

• Located in Membrane bound ________

• 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

Plasmids

Figure 8.29

E. coli

Figure 8.1a

Eukaryotic Chromosomal Packaging

• 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

Figure 8.4

Figure 8.3

Semi-Conservative Replication

Adding a Nucleotide

Figure 8.5

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

DNA Replication

Figure 8.6

• 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

DNA Replication

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

Initial Processes in DNA Replication

Synthesis of the Leading Strand

Synthesis of the Lagging Strand

• 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

Other Characteristics of DNA Replication

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

DNA Replication

• Prokaryotes

• 1 circular chromosome

• ______ ori site

• Smaller genome

• 1-2 polymerase

• _________ DNA

• Eukaryotes

• Multiple linear Chromosomes

• __________ ori sites

• Much larger genome

• Multiple polymerases

Semi-conservative

Bidirectional

• DNA replication is semiconservative

Prokaryotic DNA Replication

Figure 8.7

Theta model

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 _______________.

• 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

Transfer of Genetic Information

• DNA is transcribed to make RNA

pre-mRNA tRNA rRNA

• Transcription begins when RNA polymerase binds to the __________ sequence

• Transcription proceeds in the 5 3 direction

• Transcription stops when it reaches the ___________ sequence

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

Events in Transcription

Initiation of Transcript

Elongation of the RNA Transcript

• RNA polymerase does not require helicase

• RNA polymerase slower than DNA polymerase

• Uracil incorporated instead of thymine

• RNA polymerase lacks proofreading function (more errors)

RNA Polymerase Versus DNA Polymerase

Termination of Transcript

Genetic Code

N-formylmethione

Prokaryotic mRNA

Eukaryotic mRNA

Ribosomes and rRNA

• Three stages

• Initiation

• ____________

• Termination

• All stages require additional protein factors

• Initiation and elongation require energy (GTP)

Stages of Translation

Initiation

Elongation

Polyribosome

• Release factors somehow recognize stop codons and modify ribosome to activate ribozymes which sever polypeptide from final tRNA

• Ribosome dissociates into subunits

Termination

Translation

Figure 8.11

Are transcription and

translation

simultaneous?

• ______ 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

Control of Transcription

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

Microbial Geneticsrms.rsccd.edu/faculty/KathyTakahashi/Bio229/ExamIIPosted/MicGenA.pdf•Eukaryotic...

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