Exam 1: Topic 2

Question 1

What is the S-layer?
a)Where is it found in a prokaryotic cell?
b)What biomolecule is the S-layer made of?
c)How might this help in protecting the cell’s internal environment against changes in external pH?
d)How might the S-layer help resist phagocytosis?
e)Do all prokaryotic cells make an S-layer?

Answer 1

○ The S-layer (surface layer).
○ In bacteria it is found outside of the cell wall; in some archae the s-layer serves as the cell wall.
○ It is made of structural proteins and glyco proteins.
○ The S layer serves as a buffer for extreme pH
○ Resists phagocytosis by creating a physical barrier on the cell surface, preventing phagocytes from easily attaching to and engulfing the bacteria
○ Not all prokaryotic cells produce an s-layer.

Question 2

What are the two forms of glycocalyx? How do they differ? How are they similar?
a)Where is the glycocalyx found in the cell?
b)What is glycocalyx made of?
c)What are the advantages of having a slime layer or capsule?
d)Briefly discuss why capable cells are not always encapsulated.

Answer 2

○ Two forms of glycocalyx are slime layer and capsule.
○ Similar due to its composition of carbohydrate-gelatinous material.
○ Differ because slime layer has a loose arrangement and easy to remove (composed of glycoproteins, glycolipids, or polysaccharides), while capsule has tight arrangement and is difficult to remove (composed of proteins or polysaccharides).
○ Glycoxalyx is found outside of the cell wall.
○ Having a slime layer or capsule increases the cells pathogenicity (ability to cause disease) because the capsule makes it more difficult for phagocytic cells to engulf and kill the bacteria; while slime layer acts as a protective barrier and prevents dessication, protect cells from predation, and hinder the actions of antibiotics and disinfectants.
Not all cells consist of this, because these are specialized structures with specialized functions that not all cells require.

Question 3

What is the survival advantage of sporulation? Which two genera readily form spores?

Answer 3

1. Bacillus
2. Clostridiu.
   - ○ The survival advantage is to protect the bacterial genome in a dormant state when environmental conditions are not favorable. This allows bacterial cells to survive long periods without food or water, as well as exposure to chemicals, extreme temperatures, and even radiation.
   Some species have been shown to persist for 1000 years! When conditions become favorable again, the endospore undergoes germination reentering a vegetative state where the cell can once again be metabolically active undergoes normal activity, including growth and cell division.

Question 4

Contrast between the term endospore and vegetative cell.

Answer 4

○ Vegetative cells:
1. Sensitive to extreme temperature and radiation.
2. Gram positive
3. Normal water content and enzymatic activity.
4. Capable of active growth and metabolism.
○ Endospores:
1. Resistant to extreme temperature and pH.
2. Do not absorb gram stain–only absorb special endospore stain.
3. Dehydrated; no metabolic activity.
Dormant; no growth or metabolism.