What characteristic would the R groups of amino acids have if they are located within the interior of biological membranes?

Question

A.  The R groups would be able to form ionic bonds.
B.  The R groups would be polar.
C.  The R groups would hydrophobic.
D.  The R groups would be hydrophilic.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

Gather Content
· What do you know about proteins in membranes? How does it relate to the question?

Consider Possibilities  
· What other information is related to the question? Which information is most useful?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  The R groups would hydrophobic.

Clarify Question
· What is the key concept addressed by the question?
        o The question asks about the nature of amino acids in a membrane.
· What type of thinking is required?
        o You are being asked to apply your knowledge of the properties of amino acid side chains to predict which would be found in a membrane.
· What key words does the question contain and what do they mean?
        o R groups – these are the side chains of amino acids.  These can be polar or non-polar.
        o Interior of biological membranes – this is a hydrophobic, non-polar environment.

Gather Content
· What do you know about proteins in membranes? How does it relate to the question?
        o Membranes contain lipids and are hydrophobic, non-polar environments.  Amino acids with side chains that are non-polar or hydrophobic will be more soluble in this environment.

Consider Possibilities  
· What other information is related to the question? Which information is most useful?
        o R groups that are hydrophilic, polar or able to form ionic bonds will all be soluble in water. These will not be soluble in a lipid membrane.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o R groups that are hydrophobic are repelled by water and will be the most soluble in the membrane.  Because of this, proteins that span membranes contain long stretches of hydrophobic or non-polar amino acids.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to apply the properties of different amino acid R groups to predict which would be present in a biological membrane. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you have trouble recalling that a biological membrane contains lipids and is thus hydrophobic and non-polar?  Did you understand that non-polar amino acid R groups would be more soluble in a lipid membrane?  Did you realize that the other options were all R groups that would be soluble in water and not in a membrane?