2. From studies of chemistry, we know that in a straight chain hydrocarbon, such

Question

2. From studies of chemistry, we know that in a straight chain hydrocarbon, such as a fatty acid, each methylene group lengthens the chain by about 0.13 nm. From studies of protein structure, we know that one turn of an -helix takes 3.6 amino acid residues and lengthens the axis of the helix by about 0.56 nm. Using this information, answer the following questions: (Answer parts a-c to one decimal place in units of nm, e.g. 9.0 nm.)

a. (1 pt) Using this information, how thick is the non-polar core of the bilayer containing the GLUT1 transporter (i.e. what is the length of each helix)?

b. (1 pt) How many fatty acid methylene groups would be needed to span this distance? (Round to closest whole number.)

c. (1 pt) Since fatty acids in membrane lipids always have an even number of carbons in their chains, what chain lengths might be common in this membrane? (Write the number of carbons. More than one number may be correct.)

d. (2 pts) Most membrane lipids have 16 or 18 carbons, how can the length of these fatty acids be accommodated in the membrane?

Explanation / Answer

a. In GLUT 1, there is a 12 membrane spanning alpha helices, each helix contains 20 amino acids. For 3.6 amino acids, the length of the alpha-helix turn is 0.56 nm, on that basis for 20 amino acids its length would be 3.11 nm. So, for 12 helices, 240 amino acids and 37.33 nm length (GLUT 1). The thickness of non-polar core of the bilayer consists of GLUT1 is occupied by 6-helilces, so that 0.56 (w) x 3.11 (h) x 6 = 10.45 nm.

b. Each helix length is 3.11 nm in the transmembrane so that, 24 methylene groups of the fatty acid chain would need to span this distance. If you are asking in regard of thickness, it would need 80 methylene groups (for 10 nm thickness).

C. it seems that 16 carbon chains would be more common as per the above number of methylene groups (16 x 5) and 8 carbon chains.

d. 2.08 (16C) to 2.34 (18C) nm in length respectively

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