Chapter 2: The bacteria

Question 1

What are the differences between the cell walls of Gram-positive and Gram-negative bacteria?

Answer 1

Gram-positive bacteria have a thick peptidoglycan layer external to the cell membrane with lipoteichoic acids traversing the cell wall and anchored in the cell membrane.
Gram-negative bacteria have a thin peptidoglycan layer overlaid by an outer membrane, anchored to lipoproteins molecules in the peptidoglycan layer. The principal molecules of the outer membrane are LPS and lipoprotein.

Question 2

Describe the structure of peptidoglycan. Where is it found?

Answer 2

unique macromolecule composed of glycan chains (alternating N-acetyl glucosamine and N-acetyl muramic acid) cross linked with short peptide fragments; provides a strong but flexible framework. Found in cell walls of most bacteria.

Question 3

Where are teichoic acid and lipoteichoic acid found and what are their functions?

Answer 3

Found in the Gram positive cell wall.
Functions:
-cell wall maintenance
-enlargement during cell division
-acidic charge on cell surface

Question 4

Why can lysozyme lyse through Gram negative bacteria more easily than through Gram positive bacteria?

Answer 4

the thinner peptidoglycan layer in Gram negative bacteria, compared to that of Gram positive bacteria, makes Gram negative bacteria more sensitive to lysis

Question 5

What is the pupose of staining with Gram’s iodine after staining with cresyl violet?

Answer 5

The iodine complexes with cresyl violet, and the larger molecules become trapped and more apparent in the microscope

Question 6

What happens to Gram negative cells during the de-staining step in Gram staining?

Answer 6

During destaining with alcohol, the cresyl violet-iodine complex comes off Gram negative cells because it is not held tightly enough by the thin peptidyglocan layer in the cell wall.

Question 7

What is the purpose of staining with safranin during Gram staining?

Answer 7

Stains Gram-negative bacteria pink after de-staining with alcohol.

Question 8

What characteristics does the lipopolysaccharide layer confer on Gram negative bacteria?

Answer 8

Confers antigenic properties (‘O antigens’ from carbohydrate chains) and toxic properties (‘endotoxin’ from lipid A component)

Question 9

Describe the growing conditions of obligate aerobes.

Answer 9

Grow in the presence of O2, do not grow in absence of O2. Contain O2-detoxifying enzymes.

Question 10

Describe the growing conditions of microaerophiles.

Answer 10

Grow in low O2 conditions (require ~5% O2 when atmospheric O2 is 20-21%). Do not grow in absence of O2. Some O2-detox enzymes absent; reduced enzyme concentration.

Question 11

Describe the growing conditions of obligate anaerobes.

Answer 11

Do not grow in presence of O2. Grow in absence of O2. O2-detoxifying enzymes absent.

Question 12

Describe the growing conditions of facultative anaerobes.

Answer 12

Grow in presence of O2, grow in absence of O2, O2-detoxifying enzymes present.

Question 13

How many ATP are produced from aerobic respiration of one glucose molecule?

Answer 13

38 ATP

Question 14

How many ATP are produced from anaerobic respiration of one molecule of glucose?

Answer 14

34 ATP

Question 15

How many molecules of ATP are produced from fermentation of glucose after being converted to pyruvate?

Answer 15

2 ATP

Question 16

Name three oxygen detoxifying enzymes.

Answer 16

superoxide dismutase, catalase, peroxidase

Question 17

Under what conditions is the bacterial growth curve measured?

Answer 17

Bacteria are placed in a controlled environment in a flask, and no new nutrients are added while their growth is measured

Question 18

What is an operon? What is the benefit of encoding genes this way?

Answer 18

Organization of DNA in which a promoter and terminator may flank multiple structural genes, resulting in polycistronic mRNA encoding more than one protein. Operons provide a way of ensuring that protein subunits that make up particular enzyme complexes or are required for a specific biological process are synthesized simultaneously and in the correct stoichiometry.

Question 19

What is a regulon?

Answer 19

Group of genes and operons that are controlled by the same regulator protein (activator or repressor)

Question 20

What happens to the lac operon when lactose is present and glucose is absent? What two proteins control it?

Answer 20

In the presence of lactose as the sole carbon source for growth, the lac operon is switched on. Transcription is controlled by the lactose repressor protein (LacI, negative regulation), and by the catabolite activator protein (CAP, positive regulation)

Question 21

What is two-component regulation of bacterial virulence genes?

Answer 21

A signal transduction process that allows cellular functions to react in response to a changing environment. An appropriate environmental stimulus results in autophosphorylation of the sensor protein, which, by a phosphotransfer reaction, activates the response protein that affects gene regulation.

Question 22

What is the role of quorum sensing bacteria?

Answer 22

Produce autoinducer signaling compounds which, in sufficient concentration, bind to receptors that activate transcription of specific response genes (e.g. for biofilm production, etc.)

Question 23

What is the significance of endospore?

Answer 23

They are formed when bacteria cells are unable to grow. The presence of dipicolinic acid and high calcium content are thought to confer the endospore’s extreme resistance to heat and chemicals. They can remain viable in a dormant state for many years, re-converting rapidly when conditions improve. They are abundant in soils.

Question 24

How doe bacteriophages differ from other viruses in term of what enter the host host cells?

Answer 24

Bacteriophages release only DNA into cells, whereas the whole virus enter host cells.

Question 25

Describe transposons and their integration process.

Answer 25

They are jumping genes that can move from one DNA site to another; they inactivate the recipient gene into which they insert. Transposons often contain genes which confer resistance to antibiotics. The integration process occurs by site-specific recombination between circular cassettes and their recipient integron, which is directed by an integrase gene (intI) with promoter P(int) and and an associated attachment site (attI)

Question 26

How can transformation occur in bacteria, and how clinically relevant is it?

Answer 26

Most bacteria are not naturally competent to be transformed by DNA, but competence can be induced artificially by treating cells with certain bivalent cations (e.g. Ca2+) and then subjecting them to heat shock at 42C or by electric shock treatment (electroporation). Since DNA is unprotected and vulnerable by environmental extremes, it is the least clinically relevant, least likely for transfer within a patient.

Question 27

Describe transduction

Answer 27

transfer of genetic material by infection with a bacteriophage

Question 28

Describe conjugation

Answer 28

a type of bacterial ‘mating’ in which DNA is transferred from one bacterium to another

Question 29

Summarize who genome sequence analysis

Answer 29

library preparation with copies of extracted genome -> copies of overlapping reads sequenced from library -> reads assembled to reproduce original genome sequence or reads mapped to related reference genome-> bioinformatics: comparison of SNPs; gene-by-gene comparison of genes in the ‘core’ genome