Question

A) What physical-chemical properties of a lipid bilayer allow it to be an effective semipermeable barrier towards ions in solution?

B) Would it be as effective a barrier towards hydrophobic molecules?

C). Describe the basic structure of a:

• proteoglycan

• proteoglycan aggregate

• peptidoglycan

Answer 1

A) lipid bilayer of cell membrane is an effective barrier that keeps larger essential metabolites (sugars, amino acids, phosphorylated intermediates, etc.) from diffusing out of the cell because of the chemical and structural nature of the bilayer. It has a hydrophobic core, hence, only small molecules and lipid-soluble molecules can pass through the lipid bilayer.   

b) No it would not be effective barrier towards hydrophobic and small molecules.

c) Proteoglycans are heavily glycosylated proteins. Its basic unit consists of a "core protein" with one or more covalently attached glycosaminoglycan.

Proteoglycan aggregate is  composed of aggrecan, hyaluronan and link protein. It is a structural component of the extracellular matrix of the cartilage.

Peptidoglycan forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell walls made from a polymer consisting of sugars and amino acids.