Question

1. what is the relationship between polarity and hydrophobicity, in general?
2. for each of the following biological molecules, indicate whether the molecule is primarily hydrophobic or hydrophilic. for each molecule, justify why you indicated it was hydrophilic or hydrophobic.

a.
b.
c.
d.

Explanation:

1. Polar molecules have an uneven distribution of charge, while non - polar molecules have an even distribution. Hydrophobicity is related to non - polarity. In general, polar molecules are hydrophilic (water - loving) and non - polar molecules are hydrophobic (water - fearing) because water is a polar molecule and like dissolves like.

11.
a. This is a sugar molecule (a monosaccharide). It has multiple hydroxyl (-OH) groups. Hydroxyl groups are polar and can form hydrogen bonds with water. So, it is hydrophilic.
b. This is an amino - acid (serine). It has a carboxyl group (-COOH), an amino group (-NH2) and a hydroxyl - containing side chain. These functional groups are polar and can interact with water through hydrogen bonding and ion - dipole interactions. So, it is hydrophilic.
c. This is a nucleotide (adenosine tri - phosphate, ATP). It has phosphate groups which are highly polar and negatively charged, and a ribose sugar with hydroxyl groups and a nitrogenous base. These polar components allow it to interact with water, so it is hydrophilic.
d. This is a fatty acid. It has a long non - polar hydrocarbon chain and a polar carboxyl group at one end. However, the long hydrocarbon chain dominates the properties, and overall it is hydrophobic as the non - polar part does not interact well with water.

Answer:

1. In general, polar molecules are hydrophilic and non - polar molecules are hydrophobic.

11.
a. Hydrophilic; due to multiple polar hydroxyl groups.
b. Hydrophilic; due to polar carboxyl, amino and hydroxyl - containing side chain.
c. Hydrophilic; due to polar phosphate groups, hydroxyl groups in sugar and polar base.
d. Hydrophobic; due to long non - polar hydrocarbon chain.