Microbial Genetics Flashcards
What did Charles Darwin draw to explain how lifeforms might diverge?
Darwin drew a tree of life in his notebooks, likening it to a coral with hidden and dead branches.
What did Darwin’s tree of life represent?
The trunk represented evolution from an ancestor, and the branches ended in variants representing extant lifeforms and dead ends.
How were evolutionary relationships historically classified?
According to observable characteristics and reproductive strategies, resulting in a phylogenetic tree with man at the top.
What was the limitation of historical evolutionary classification?
It was limited because many microorganisms do not share the same features and reproductive strategies as other organisms.
Who proposed an alternative classification system in 1977?
Karl Woese.
What molecule did Karl Woese propose for measuring phylogenetic relationships?
Ribosomal RNA (rRNA).
What are the four requirements for the molecule Karl Woese sought?
Broadly distributed, a component of all self-replicating organisms, readily isolated, and sequence changes slowly over time.
What does a bacterial genome contain?
All the genetic information in a cell, including plasmids, transposons, phages, and the chromosome.
How do bacteria reproduce?
By binary fission, where the cell elongates, duplicates the chromosome, and forms new daughter cells.
What is DNA replication?
The process of copying the mother cell’s chromosome into two versions during bacterial reproduction.
What can errors in DNA replication lead to?
Mutations that may alter the polypeptide sequence of the encoded protein.
How can mutations within the 16S rRNA gene be used?
To measure the difference between organisms that have diverged from a common ancestor.
What is horizontal gene transfer?
The process by which bacteria acquire new genes, contributing to genetic diversity beyond mutation.
What are the three main mechanisms of horizontal gene transfer?
Conjugation, transduction, and transformation.
What are plasmids?
Extra-chromosomal pieces of DNA often transferred by conjugation.
What are bacteriophages?
Bacterial viruses that may integrate their genome into the host cell chromosome or lyse the host cell.
What is transformation in bacteria?
The process by which bacterial cells take up DNA from the environment when they are in a competent state.
What are transposons?
DNA elements that can move within a genome or between genomes, sometimes carrying antibiotic resistance genes.
What are E. coli pathotypes?
Different groups of E. coli that cause various types of intestinal diseases.
What characterizes extra-intestinal pathogenic E. coli such as APEC?
Carriage of a large conjugative virulence plasmid causing respiratory disease in birds.
What was significant about the 2011 E. coli outbreak in Germany
It was caused by a novel, virulent E. coli O104
, a hybrid of EHEC and EAEC pathotypes.
What can accumulation of mutations result in for bacteria?
Loss or gain of function, with new gene acquisition expanding the host cell’s functions.
What are constitutive genes?
Genes that are continuously expressed in bacteria.
What are operons?
Groupings of structural genes under a single promoter, regulated and not constitutively expressed.
How can operons be regulated?
By activators, repressors, or inducers.
What is the trp operon an example of?
A repressor operon controlled by the metabolic product Trp.
What is the lactose operon an example of?
An inducible operon where the repressor is inactivated by lactose, allowing gene expression.
How is virulence gene expression in V. cholerae regulated?
By environmental signals like bicarbonate levels, with ToxT activating virulence genes CT and TCP.
How is Shiga toxin expression in EHEC regulated?
By the lytic cycle induction of a prophage embedded in the bacterial chromosome, amplifying stx gene copy numbers.
