MIMM 211 Lecture Notes - Lecture 6: Gram-Negative Bacteria, Peptidoglycan, Gram-Positive Bacteria

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chocolatecod197

3 Oct 2016

School

McGill University

Department

Microbiology & Immunology

Course

MIMM 211

Professor

Benoit Cousineau

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Document Summary

Gram- (3layers: cytoplasmic membrane (inner or plasma membrane, cell wall (peptidoglycan, outer membrane. Gram+ (2 layers: cytoplasmic membrane, cell wall. Thicker cell wall to keep up with harsh environment since no outer membrane. Periplasm is where a lot of enzymes are: it"s a space between cell wall and plasma membrane. Functions: contains the cytoplasm, regulates what comes in and what goes out using specific transporters. Contains proteins (50% dry weight: transmembrane proteins. Stuck on either side of the membrane. Proteins float and are a mobile unit. Gram and gram + both have cytoplasmic membranes. Contains a: r group, phosphate group, glycerol, fatty acids. The hydrophobic interactions are together while hydrophilic heads are towards water. Charged polar heads: hydrophilic, negatiovely charged phosphate groups. Hydrophobic long lipid tails or fatty acids( non polar: insoluble in water and tend to interact with each other. Phospholipids align to have hydrophilic towards water. Fluidity of phospholipid bilayers rigidity required for stability.

Related Questions

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.

HELP WITH BIO MULTI CHOICE QUESTIONS:

QUESTION 2

Which of the following structures discussed in class is NOT found on all bacteria?
Flagella
Capsid
Fimbria
Plasma membrane

QUESTION 3
You are presented with a strain of bacteria that is resistant to the antibiotic penicillin. What steps would you take to confirm that you have a resistant bacterium?
Perform a Gram stain to determine pink stained Gram-positive bacteria.
Perform a Gram stain to determine purple stained Gram-positive bacteria.
Perform a Gram stain to determine pink stained Gram-negative bacteria.
Perform a Gram stain to determine purple stained Gram-negative bacteria.

QUESTION 4
With respect to bacterial growth into a fresh culture tube containing nutrient broth, at which phase do organisms undergo binary fission the most rapidly?
Lag phase
Stationary
Exponential
death

QUESTION 5
How would antibiotic resistance be passed from one bacterium to another bacterium?
Through the flagella via a plasmid.
Through the sex pilus via chromosomal DNA.
Through the sex pilus via a plasmid.
Through the flagella via chromosomal DNA.

QUESTION 6
When an F plasmid integrates into the host chromosome, the strain is referred to as

Hfr.
F'.
F-.
F+.

QUESTION 7
If you remove the peptidoglycan layer from a Gram-positive cell, it would still stain purple with a Gram stain (T/F).
True
False

QUESTION 8
During infection with a bacteriophage, bacterial DNA is packaged into a capsid and will:

be integrated into the genome of a new bacterium upon ligation.
be integrated into the genome of a new virion upon recombination.
be integrated into the genome of a new bacterium upon recombination.
be integrated into the genome of a new virion upon liagation.

QUESTION 9
Which of the following statements best describes most bacteria?
They are generally harmful.
They are limited to living in a few habitats.
They are very common in the environment.
They are responsible for the âcommon cold.â

QUESTION 10
Prokaryotes lack some parts found in eukaryotic cells, including which item?
a nuclear membrane
DNA
one or more chromosomes
a plasma membrane
all of the above

QUESTION 11
With respect to gram negative bacteria, what is the order of the bacterial cell structure from outside to inside?
Thin peptidoglycan layer, plasma membrane

thick peptidoglycan layer, plasma membrane

outer membrane, thick peptidoglycan layer, plasma membrane

outer membrane, thin peptidoglycan layer, plasma membrane

QUESTION 12
In transformation, a piece of DNA from a dead host can be taken up by living host

True
False

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).

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MIMM 211 Lecture Notes - Lecture 6: Gram-Negative Bacteria, Peptidoglycan, Gram-Positive Bacteria

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