Microbial Genetics

Question 1

What did Charles Darwin draw to explain how lifeforms might diverge?

Answer 1

Darwin drew a tree of life in his notebooks, likening it to a coral with hidden and dead branches.

Question 2

What did Darwin’s tree of life represent?

Answer 2

The trunk represented evolution from an ancestor, and the branches ended in variants representing extant lifeforms and dead ends.

Question 3

How were evolutionary relationships historically classified?

Answer 3

According to observable characteristics and reproductive strategies, resulting in a phylogenetic tree with man at the top.

Question 4

What was the limitation of historical evolutionary classification?

Answer 4

It was limited because many microorganisms do not share the same features and reproductive strategies as other organisms.

Question 5

Who proposed an alternative classification system in 1977?

Answer 5

Karl Woese.

Question 6

What molecule did Karl Woese propose for measuring phylogenetic relationships?

Answer 6

Ribosomal RNA (rRNA).

Question 7

What are the four requirements for the molecule Karl Woese sought?

Answer 7

Broadly distributed, a component of all self-replicating organisms, readily isolated, and sequence changes slowly over time.

Question 8

What does a bacterial genome contain?

Answer 8

All the genetic information in a cell, including plasmids, transposons, phages, and the chromosome.

Question 9

How do bacteria reproduce?

Answer 9

By binary fission, where the cell elongates, duplicates the chromosome, and forms new daughter cells.

Question 10

What is DNA replication?

Answer 10

The process of copying the mother cell’s chromosome into two versions during bacterial reproduction.

Question 11

What can errors in DNA replication lead to?

Answer 11

Mutations that may alter the polypeptide sequence of the encoded protein.

Question 12

How can mutations within the 16S rRNA gene be used?

Answer 12

To measure the difference between organisms that have diverged from a common ancestor.

Question 13

What is horizontal gene transfer?

Answer 13

The process by which bacteria acquire new genes, contributing to genetic diversity beyond mutation.

Question 14

What are the three main mechanisms of horizontal gene transfer?

Answer 14

Conjugation, transduction, and transformation.

Question 15

What are plasmids?

Answer 15

Extra-chromosomal pieces of DNA often transferred by conjugation.

Question 16

What are bacteriophages?

Answer 16

Bacterial viruses that may integrate their genome into the host cell chromosome or lyse the host cell.

Question 17

What is transformation in bacteria?

Answer 17

The process by which bacterial cells take up DNA from the environment when they are in a competent state.

Question 18

What are transposons?

Answer 18

DNA elements that can move within a genome or between genomes, sometimes carrying antibiotic resistance genes.

Question 19

What are E. coli pathotypes?

Answer 19

Different groups of E. coli that cause various types of intestinal diseases.

Question 20

What characterizes extra-intestinal pathogenic E. coli such as APEC?

Answer 20

Carriage of a large conjugative virulence plasmid causing respiratory disease in birds.

Question 21

What was significant about the 2011 E. coli outbreak in Germany

Answer 21

It was caused by a novel, virulent E. coli O104

, a hybrid of EHEC and EAEC pathotypes.

Question 22

What can accumulation of mutations result in for bacteria?

Answer 22

Loss or gain of function, with new gene acquisition expanding the host cell’s functions.

Question 23

What are constitutive genes?

Answer 23

Genes that are continuously expressed in bacteria.

Question 24

What are operons?

Answer 24

Groupings of structural genes under a single promoter, regulated and not constitutively expressed.

Question 25

How can operons be regulated?

Answer 25

By activators, repressors, or inducers.

Question 26

What is the trp operon an example of?

Answer 26

A repressor operon controlled by the metabolic product Trp.

Question 27

What is the lactose operon an example of?

Answer 27

An inducible operon where the repressor is inactivated by lactose, allowing gene expression.

Question 28

How is virulence gene expression in V. cholerae regulated?

Answer 28

By environmental signals like bicarbonate levels, with ToxT activating virulence genes CT and TCP.

Question 29

How is Shiga toxin expression in EHEC regulated?

Answer 29

By the lytic cycle induction of a prophage embedded in the bacterial chromosome, amplifying stx gene copy numbers.