Chapter 3 Exam Material (pt3)

Peptidoglycans are composed of sugars and _____. lipids amino acids nucleic acids teichoic acids

amino acids Amino acids combine to form the peptide portion of the peptidoglycan.

Peptidoglycan is a polymer of millions of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) sugars based on glucose molecules linked together in long chains cross-braced with four amino acids that link individual polymer chains together in a chain-link fence pattern. Layers of cross-braced NAG and NAM sheets are stacked vertically and held together by proteins with lipid anchors attached to the cell's cytoplasmic membrane to form a scaffold of sugars and proteins that is able to hold the bacterial cell's shape, even in response to extreme osmotic pressures. How would you expect a microbiology student to be able to describe the composition of peptidoglycan? What is the composition of the peptidoglycan layers found in the cell wall of bacteria? Pick the answer that lists the composition of the bacterial cell wall. amino acids, NAG, and NAM NAG and NAM proteins and sugars short amino acid chains, NAG, NAM, and some lipid proteins

short amino acid chains, NAG, NAM, and some lipid proteins

One chain of alternating NAGs and NAMs is connected to another chain via _____. tetrapeptides enzymes teichoic acids lipids

tetrapeptides Tetrapeptides are composed of four amino acids and make up the "peptido" portion of peptidoglycan.

The peptidoglycan cell wall of bacteria is most analogous to _____. a chain-link fence a rain coat an impenetrable brick wall a sugary candy shell

a chain-link fence The peptidoglycan cell wall is meshlike, allowing for easy passage of ions, amino acids, and nutrients and maintaining structural integrity.

The region between the outer and inner membranes of a Gram-negative bacterial cell is known as the __________, and it is the location of enzymes that assemble peptidoglycan. lipopolysaccharide layer intramembranous space cytoplasm periplasmic space

periplasmic space The periplasmic space is an area surrounding the bacterial cytoplasmic membrane.

One of the main differences between a Gram-positive and a Gram-negative bacterial cell wall is that the peptidoglycan portion of a Gram-positive cell wall is _____ as compared to a Gram-negative cell wall. more lipid rich composed of a greater percentage of NAGs than NAMs thicker positively charged

thicker The peptidoglycan layer of Gram-positive bacteria is much thicker than that of Gram-negative bacteria.

The peptidoglycan cell wall and the one or two membranes present also impart a three-dimensional shape to the bacterial cell. The overall shape and arrangement of bacteria are genetically determined, so that each genus of bacteria has a characteristic shape (round, rod, spiral, etc.) and arrangements of the growing cell population (individual cells, chains of cells, or clustered cells). Bin 1 - Image of a single round bacterium. Bin 2 - Image of a single rodishaped bacterium. Bin 3 - Image of a cluster of round bacteria. Bin 4 - Image of a string of rodishaped bacteria. Bin 5 - Image of a vibrio (commaishaped) bacterium. Bin 6 - Image of a corkscrewishaped spirochete bacterium.

1. cocci 2. bacilli 3. staphylococci 4. streptobacilli 5. vibrio 6. spirochete

A cell wall is a requirement for all living bacteria. True or False.

False

At this point in writing your tutorial, you have to find a way to get across to the students the importance of a cell wall to a bacterium. How do you convey that the bacterial cell will be at the mercy of its environment? The cell wall will need to act as a support mechanism to neutralize the inflow or outflow of water that would alter the shape of the cell. The cell cannot search out for a better place in the environment that has more available water; or if there is water that it has a high enough solute concentration that the cell will not gain water. Because that's the problem for a bacterial cell, it cannot control the tonicity due to solute concentrations in the surrounding water. Water will flow in or out depending on solute concentrations and the only thing a bacterial cell can do to keep from collapsing due to water loss or rupturing due to too much water coming in is to have a strong cell wall that will hold its shape regardless of the osmotic pressures. The rigidity of the cell wall will maintain a set shape regardless of water flow. The proteins and lipids that anchor the cytoplasmic membrane to the cell wall will tether the membrane to the peptidoglycan layer so that when environmental conditions result in the loss of water from the cell, the membrane will not collapse in on itself. Similarly, changes in environmental conditions that would result in the inflow of water would expand the volume of the cell to the limits of the cell wall and no more. The composition of the cell wall allows for the expansion and contraction of the cell wall in response to the gain or loss of water from the cell. True or False.

False

With the description of the different cell walls, membranes, and associated proteins set in the students' minds, you now need to introduce them to the idea that the cell wall can also act as a foundation to build things upon. Bacterial appendages require a strong foundation that will offer the support needed to move and function in a dynamic world. For example, flagella are long, whiplike protein structures that are used by many Gram-positive and Gram-negative bacteria for locomotion. In order to function effectively, a flagellum must be firmly anchored to the cell wall. How will you be able to get across the idea that the peptidoglycan cell wall is strong enough to support such a mechanism? With a protein rod that passes through the cell wall and protein rings used to anchor it in the membranes, these basal bodies are the rudimentary biological motors that use ATP power to spin the hook and the flagella attached to it. Bacterial flagella have a biological motor that spins within the cell wall and is powered by ATP. This allows the flagella to spin in a whiplike motion to propel the bacterium. True of False.

False The biological motor that spins the flagella for bacterial propulsion is powered by the electron imbalance across the membrane that generates a gradient that the cell can harness for energy via proton motive force.

The thickness of this sugar-protein scaffold of peptidoglycan can be used to separate most bacteria into two groups. In your tutorial, you want to illustrate to the students that the thickness of the peptidoglycan layer can be used by microbiologists to differentiate many bacteria by only using an easy staining method that all microbiologists will have to master. This staining procedure, known as the Gram stain, is based on the retention of dyes within the cell wall for a positive result or the rinsing away of the dyes and leakage of the membrane for a negative result. A thicker cell wall will allow for retention of dye crystals that will give the bacterial cell a blue-purple color (positive result), but the thinner cell walls will not allow for the retention of these crystals during rinsing, which will mean that these cells will then be colorless unless another dye that does not require interaction with the cell wall to maintain its retention is used (negative result). In addition to differences in cell wall thickness, Gram-positive and Gram-negative bacteria also differ in the proteins and lipids associated with their cell walls, as well as the composition of their cell membranes. Gram-positive walls are composed of an underlying cytoplasmic membrane, with the thick peptidoglycan layer on the outside offering support. Proteins anchor the membrane and the cell wall together to provide support and structure between the two. Gram-negative staining walls have a different layout. You try to explain in your tutorial that even though these bacteria stain "negative" they do have a thin layer of peptidoglycan sandwiched in between two lipid bilayer membranes. Place each attribute into the bin of the bacterial group it belongs to, based on whether the bacterium is a Gram-positive or a Gram-negative cell.

Gram-positive bacterial cell wall: thick layer of peptidoglycan teichoic acids single lipid bilayer membrane Gram-negative bacterial cell wall: thin layer of peptidoglycan lipopolysaccharides periplasmic space dual lipid bilayer membrane With the written review materials and the quiz questions, you try to impart to the students the idea that the peptidoglycan layer composing a cell wall is found in both Gram-positive and Gram-negative bacteria, that the terms positive and negative refer to the retention of a stain and not the presence or absence of a peptidoglycan cell wall.

A patient is infected with Gram-negative bacteria and is experiencing only mild symptoms. When the patient is given an antibiotic causing lysis of the bacterial cells, he suddenly experiences an increase in inflammation and fever, as well as the formation of blood clots. What explanation best describes what happened? Any part of the bacterial cell wall released during lysis is seen as foreign and thereby elicits a severe immune response by the body's immune system. The antibiotic is toxic and is affecting the patient adversely. The lysis of the cells releases NAG and NAM from the cell wall. The lysis of the cells releases lipid A from the lipopolysaccharide layer.

The lysis of the cells releases lipid A from the lipopolysaccharide layer. Lipid A is known to cause inflammation, fever, and blood clots.

What role do the teichoic acids play within the cell wall of Gram-positive bacteria? They serve as pores allowing the passage of ions, nutrients, and amino acids into the cell. They serve as adhesins, allowing bacteria to bind to one another. They serve to stabilize the cell wall and hold it in place. They act as crossbridges, holding the peptides and sugar molecules together.

They serve to stabilize the cell wall and hold it in place. Some of the teichoic acids are anchored to lipids within the cytoplasmic membrane and are thus called lipoteichoic acids.

Within the peptidoglycan layer, the crossbridges that connect the chains of alternating sugar molecules extend between _____. two glucose molecules an N-acetylmuramic acid and an N-acetylglucosamine two N-acetylmuramic acid molecules two N-acetylglucosamine molecules

two N-acetylmuramic acid molecules The crossbridges link NAM molecules to one another and provide the structural integrity of the peptidoglycan layer.