(a) Name the polysaccharide that makes up the bacterial cell wall. (b) Bacterial

Question

(a) Name the polysaccharide that makes up the bacterial cell wall.

(b) Bacterial cell walls are classified as Gram-negative or Gram-positive according to the response for the Gram stain. What structural characteristic is responsible for this outcome? (answer should be brief – three or four sentences! Alternatively, you can draw clear, labeled diagrams to point out the differences)

(c) What is the most common storage polysaccharide in plants?

(d) In what two chemical forms does (c) exist? (names only)

(e) Name the type of glycosidic linkage in each form in (c). Point out the MAJOR difference between the two forms. (You can draw a figure to show the differences using a diagram or, give a clear description without the diagram).

Explanation / Answer

1)The major structural component of the cell wall is peptidoglycan, which is a complex molecule composed of alternating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) cross-linked by short peptides. What results is a flat, crosshatch pattern that is very strong and rigid, yet open enough for movement of particles.

2) Gram-positive bacteria have a thick mesh-like cell wall which is made up of peptidoglycan (50-90% of cell wall), which stains purple.  

Gram-negative bacteria have a thinner layer of peptidoglycan (10% of the cell wall) and lose the crystal violet-iodine complex during decolorization with the alcohol rinse, but retain the counter stain Safranin, thus appearing reddish or pink.

3) starch.

4) starch is composed of two different molecules, amylose and amylopectin

5) alpha 1-4linkage,

Amylose is a helical polymer made of -D-glucose units, bound to each other through (14) glycosidic bonds.

This polysaccharide is one of the two components of starch, making up approximately 20-30% of the structure. The other component is amylopectin, which makes up 70–80% of the structure..

Amylopectin /æmlopktn/ is a soluble[1][2] polysaccharide and highly branched polymer of glucose found in plants. It is one of the two components of starch, the other being amylose.

Glucose units are linked in a linear way with (14) glycosidic bonds. Branching takes place with (16) bonds occurring every 24 to 30 glucose units, resulting in a soluble molecule that can be quickly degraded as it has many end points onto which enzymes can attach. In contrast, amylose contains very few (16) bonds, or even none at all. This causes amylose to be hydrolyzed more slowly, but have higher density and be insoluble.

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