Question

*Bacterial cell walls are made of peptidoglycan that:

a. consist of linear polysaccharides that are cross linked by simple sugars to form a ‘mesh like’ structure that maintains cell integrity

b. consist of linear polysaccharides that are cross linked by short polypeptide chains to form a ‘mesh like’ structure that maintains cell integrity

c. consist of linear polysaccharides that are cross linked by short polypeptide chains to form a ‘mesh like’ structure that promotes the diffusion of nutrients into cells

d. None of the above

*Lipopolysaccharides (LPS) are found in:

a. Gram-positive bacteria

b. Gram-negative bacteria

c. all Bacteria

d. Archaea

e. Eukaryotes

*There are similarities and differences between Gram-negative and Gram-positive bacteria. Which of the following is not true?

a. The cell wall of Gram-negative cells is composed of only one or two layers of peptidoglycan whereas the cell walls of Grampositive bacteria have many peptidoglycan layers

b. Only Gram-positive bacterial cells have a periplasm

c. The cell membranes of both Gram-negative and Gram-positive bacteria are lipid bilayers

d. There is a second membrane (called the outer membrane) just outside the cell wall of Gram-negative bacteria, but this is absent from Gram-positive bacteria

*The cell membranes of Bacteria

a. serve as a barrier that separates the cell contents from the environment

b. prevent cells from bursting due to osmotic pressure

c. can be stained to distinguished Gram positive from Gram negative bacteria

d. prevents the entry of organic compounds into cells.  

e. all of the above

Answer 1

Bacterial cell walls are made of peptidoglycan that consist of linear polysaccharides that are cross linked by short polypeptide chains to form a ‘mesh like’ structure that maintains cell integrity.

Peptidoglycan is made up of heteropolymer chains of alternating NAG (N-acetyl glucosamine) and NAM (N-acetyl muramic acid)connected by glycosidic bond. The tetrapeptide sidechains present in NAM are connected by peptide interbridge that forms the mesh like structure.

Lipopolysaccharides (LPS) are found in Gram-negative bacteria

In addition to peptidoglycan cell wall, the gram-negative bacterium contain an additional membrane, the outer membrane which constitutes lipopolysaccharides, lipoproteins, proteins and phospholipids. The lipid and polysaccharides are linked in the outer membrane to form a lipopolysaccharide.

There are similarities and differences between Gram-negative and Gram-positive bacteria. Which of the following is not true? Only Gram-positive bacterial cells have a periplasm

The periplasm is found in gram-negative bacteria and is the space in between the cytoplasmic and outer membranes. Since gram-positive bacteria do not posses an outer membrane, it is absent in them.

The cell membranes of Bacteria serve as a barrier that separates the cell contents from the environment

Bacterial cell wall is stained to distinguish between gram positive and gram negative bacteria.It is the cell wall that maintains the osmotolerance and prevents the entry of organic compounds into cells. The role of cell membrane also called as the plasma membrane or cytoplasmic membrane is to separate the cell contents from the environment.