username3417448
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Describe how the primary structure of leptin enables it to be soluble in water.
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Jpw1097
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(Original post by Bioroj)
Describe how the primary structure of leptin enables it to be soluble in water.
This is essentially asking how does structure of a protein relate to function. They could ask the same thing for any protein, but they have chosen leptin in this case. So the primary structure is the linear sequence of amino acids in the polypeptide chain. This sequence of amino acids determines the secondary structure of the polypeptide. Secondary structure is the folding of local segments of a polypeptide due to hydrogen bonds between the amino and carboxyl groups of nearby amino acids - the most common secondary structures are alpha helices and beta pleated sheets. The primary structure also determines the tertiary structure of the polypeptide chain - that is, the overall 3D geometrical conformation (i.e. shape) of the polypeptide. Tertiary structure is determined by interactions between R groups of amino acids - these interactions include hydrogen bonds, disulphide bonds, ionic bonds and Van der Waals forces. For leptin to be soluble in water (or any water-soluble protein for that matter), amino acids with hydrophilic R groups are on the outside of the protein whereas amino acids with hydrophobic R groups are on the inside of the protein. The hydrophilic R groups are what allows the protein to be soluble in water.
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macpatgh-Sheldon
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(Original post by Jpw1097)
This is essentially asking how does structure of a protein relate to function. They could ask the same thing for any protein, but they have chosen leptin in this case. So the primary structure is the linear sequence of amino acids in the polypeptide chain. This sequence of amino acids determines the secondary structure of the polypeptide. Secondary structure is the folding of local segments of a polypeptide due to hydrogen bonds between the amino and carboxyl groups of nearby amino acids - the most common secondary structures are alpha helices and beta pleated sheets. The primary structure also determines the tertiary structure of the polypeptide chain - that is, the overall 3D geometrical conformation (i.e. shape) of the polypeptide. Tertiary structure is determined by interactions between R groups of amino acids - these interactions include hydrogen bonds, disulphide bonds, ionic bonds and Van der Waals forces. For leptin to be soluble in water (or any water-soluble protein for that matter), amino acids with hydrophilic R groups are on the outside of the protein whereas amino acids with hydrophobic R groups are on the inside of the protein. The hydrophilic R groups are what allows the protein to be soluble in water.
Jpw1097
Brilliant answer young man - you would make an excellent A level biology tutor to help your student budget - - although as a medical student you will not get the time to do that - you have shown OP how to work out what exactly the examiner is testing the student's knowledge of!

One point I thought of in addition - the point about R groups - will the tertiary structure not also depend on the actual R groups? i.e. those a.a.-s with longer or more branched R groups [larger amino acids e.g. citrulline] and those with extra -COOH groups e.g. aspartic acid OR -NH2 groups e.g. histidine, will produce more e.g. hydrogen bonds?
M
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Jpw1097
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(Original post by macpatgh-Sheldon)
Jpw1097
Brilliant answer young man - you would make an excellent A level biology tutor to help your student budget - - although as a medical student you will not get the time to do that - you have shown OP how to work out what exactly the examiner is testing the student's knowledge of!

One point I thought of in addition - the point about R groups - will the tertiary structure not also depend on the actual R groups? i.e. those a.a.-s with longer or more branched R groups [larger amino acids e.g. citrulline] and those with extra -COOH groups e.g. aspartic acid OR -NH2 groups e.g. histidine, will produce more e.g. hydrogen bonds?
M
Thank you very much! I could definitely do with some help with my student budget - as you say, time is a bit tricky.

You’re absolutely right. The tertiary structure will depend on the specific amino acids involved - as you’ve mentioned, some R groups will form multiple bonds depending on the number of carboxyl or amino or other groups.
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