Question

A protein you are studying is believed to have a beta barrel secondary structure that consists of several duplicate hydrophobic amino acid sequence repeats. Describe the cell structure you anticipate finding this protein in based on these characteristics

Answer 1

Answer: Beta barrel secondary structure that consists of several duplicate amino acid sequence repeats is likely to be found in outer membranes of chloroplast,mitochondria and Gram negative bacteria.

    The membranes have a typical structure of lipid bilayer in which the polar heads or the hydrophilic ends are facing outside and the non-polar tails or hydrophobic ends are in between. The membrane is selectively permeable allowing only certain solutes to pass through with the help of proteins which are spread over the entire membrane.

The beta barrel structure is a characteristic of porins the transmembrane proteins.The hydrophobic residues are oriented inside and the hydrophilic residues form the outer structure of the barrel

The porins as against the other membrane proteins are large,made up of beta sheets and they allow the passage of molecules by passive diffusion also.

Structurally they are made up of 16-18 beta strands antiparallel and cylindrically arranged and hence they are known as beta barrels. In these the nonpolar ends face outward and the polar sides are inside forming the aqueous channels. Most porins are non selective for water soluble molecules.