What functions to anchor peptidoglycan to the cytoplasmic membrane in Gram positive bacteria, but not Gram negative ones?
a) Teichoic acid
b) Lipoteichoic acid
c) flagellin
d) phospholipid
What functions to anchor peptidoglycan to the cytoplasmic membrane in Gram positive bacteria, but not Gram negative ones?
a) Teichoic acid
b) Lipoteichoic acid
c) flagellin
d) phospholipid
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A 47 year old female patient presents herself to you with symptoms of pneumonia. All indications are that the patient is suffering from an infection of Streptococcus pneumoniae, a Gram-positive bacterium. Since the patient is not allergic to penicillin, you prescribe a dose of amoxicillin, a semi-synthetic penicillin. This drug works by blocking the peptide cross-links, between the muramic acid subunits, of peptidoglycan chains. This leads to a destabilization of the bacterial cell, leading to its rupture.
However, after the patient finished her course of amoxicillin, no improvement in symptoms were reported. Perplexed, you decide to culture and examine the bacteria infecting her lungs. The test you order is a Gram stain test, which comes back as Gram-negative. You feel like a failure as a health care provider due to your misdiagnosis of this bacterium.
The same day, you put the patient on an aminoglycoside class antibiotic. This antibiotic is Gram-negative specific and works by shutting down ribosomes. You are dismayed and confused when this treatment also fails.
To get a full read on the disease, you have a barcoding DNA test done on the causative bacterium. The test comes back and it clearly shows that the bacterium is within the group of Gram-positive bacteria. With the results of this test, you come up with the theory that the patient is infected with a strain of Drug Resistant Streptococcus pneumoniae (DRSP), resistant to amoxicillin. You decide to treat the DRSP by administering intravenous vancomycin, which is indicated for the treatment of serious, life-threatening infections by Gram-positive bacteria. This treatment also fails.
In the end, you figure out that you were wrong about everything, and that there was a simple solution to the treatment of the patient.
Now knowing that the patient was infected with Mycoplasma pneumoniae, what is the likely explanation for the false Gram-negative test?
Before you answer this question you may want to know how Gram staining works. Briefly, the Gram stain is a differential stain meaning that you are using two dyes that stain different structures. Based on the structural differences of the bacteria, the dyes will interact differently with them, producing different results (colors). The Gram stain (Crystal Violet together with Gram's iodine) stains thick layers of peptidoglycan purple and thin layers of peptidoglycan very, very lightly purple. The second stain (or counterstain) is safranin. Safranin is a dye which interacts with and binds to lipid bilayers. Yes, safranin also stains the cytoplasmic membrane of Gram-positive bacteria, but the deep purple color of the Gram stain makes it impossible to see.
A. | The Gram stain was able to penetrate the cell making it turn pink | |
B. | The counterstain stained the cytoplasmic membrane, making it look like a Gram-negative bacterium | |
C. | The counterstain stained the mycolic acid in the cellular envelope, thus making it look like a Gram-negative bacterium | |
D. | The Gram stain lightly stained the present peptidoglycan (making it look pink rather than red). |
QUESTION 1
Which of the following statements about the bacterial cytoplasmic membrane is false?
a. | It resists attachment of the bacterial chromosome to its inner surface. | |
b. | It contains a protein complex that drives ATP synthesis. | |
c. | It is asymmetric. | |
d. | It consists of relatively equal amounts of phospholipids and proteins. |
1 points
QUESTION 2
Which of the following statements regarding Mycobacteria is false?
a. | The genome has relatively low Guanine (G) and Cytosine (C) content. | |
b. | The cytoplasmic membrane is surrounded by a polymer (peptidoglycan) consisting of alternating N-Acetylglucosamine (NAG) and N-Acetylmuramic (NAM) acid units. | |
c. | It infects approximately one-third of the global human population. | |
d. | It has a Gram-positive cell wall with an additional waxy lipid layer of mycolic acid. |
1 points
QUESTION 3
Which of the following outer membrane porins enables Mycobacteria to adapt to acidic and intracellular environments, and shows homology to outer membrane porin A?
a. | OmpATb. | |
b. | OmpA. | |
c. | MspA. | |
d. | Lipid A. |
1 points
QUESTION 4
Based on your understanding of bacterial membranes, which of the following is not likely to be found in an E. coli outer membrane?
a. | Membrane-anchored enzymes. | |
b. | Mycolic acid. | |
c. | Lipopolysaccharide. | |
d. | Porin channels. |
1 points
QUESTION 5
Based on the conclusions of this paper, which of the following statements would the author most likely disagree with?
a. | Some archaeon do not contain all of the genes essential for life. | |
b. | The membrane structures of prokaryotes show far greater diversity than those of eukaryotes. | |
c. | As demonstrated in this definitive report, scientists have a great understanding of the majority of basic functions and evolution of bacterial membranes. | |
d. | The outer membrane (and its associated components) of archaea, Gram-negative bacteria, and Gram-positive bacteria likely evolved independently of one another. |
1 points
QUESTION 6
Which of the following is not true for Gram-negative, acid-fast, and archaeal membranes?
a. | They modify their lipid content in response to environmental changes. | |
b. | They have co-evolved the same outer membrane composition and structure. | |
c. | They all have a cytoplasmic membrane. | |
d. | Membrane transport proteins regulate nutrient uptake and waste removal. |
1 points
QUESTION 7
Compared to Mycobacteria, Gram-negative bacterium contain:
a. | More mycolic acid. | |
b. | Pores of increased length. | |
c. | Less peptidoglycan. | |
d. | 50-fold-lower numbers of porins. |
1 points
QUESTION 8
Archaea are found to survive in strongly acidic lakes compared to bacteria and Eukaryotes. Which of the following supports this claim according to the study?
a. | The presence of L-glycerol ether linked lipids in Archaea membranes. | |
b. | The presence of D-glycerol ether linked lipids in Archaea membranes. | |
c. | The presence of L-glycerol ester linked peptidoglycans in Archaea membranes. | |
d. | The presence of L-glycerol ester linked lipids in Archaea membranes. |
1 points
QUESTION 9
Based on your understanding of the symbiotic relationship between Nanoarchaeum equitans and Ignicoccus, which of the following below is not true?
a. | The membrane lipids of N. equitans are synthesized by Ignoccocus. | |
b. | In exchange for membrane lipids, N. equitans provide Ignicoccus with many essential cytoplasmic enzymes. | |
c. | N. equitans lack enzymes capable of catalyzing lipid biosynthesis. | |
d. | Intraperiplasmic vesicles produced by Ignicoccus allow for lipid transfer to N. equitans. |
1 points
QUESTION 10
What is the role of hydrogen bonds in bacteria, as mentioned in the article?
a. | They mediate transmembrane electron flow. | |
b. | They mediate lipid biosynthesis. | |
c. | They help to stabilize the cytoplasmic membrane. | |
d. | They are responsible for the selective permeability of the cytoplasmic membrane. |