The Hydrophobic Effect: Why Water and Oil Don't Mix
All lipids are at least partially hydrophobic.
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Transcript
Have you ever seen oil floating in a glass of water? Oil is a lipid and all lipids are at least partially hydrophobic. This means they are not attracted to water. Let’s look at the chemical structure of a lipid and a water molecule to understand the hydrophobic effect.
Water is made up of two hydrogen atoms and one oxygen atom. The arrangement of these atoms makes water polar: one side of the molecule (the hydrogen side) has a small positive charge while the other side (the oxygen side) has a small negative charge.
And what about lipids? Let’s look at a triglyceride, one type of lipid. It is made up of a glycerol molecule and three fatty acids. Both the glycerol and the fatty acids are negatively charged. This means the charge of the molecule is evenly distributed, making it nonpolar. When a polar substance interacts with another polar substance the positively charged parts of one are attracted to the negatively charged parts of the other and vice versa. This is why polar substances dissolve in water. Water molecules surround and detach the negative and positive parts of the other molecule from each other.
But when water comes into contact with a triglyceride, such as oil, the water molecules cannot surround and detach the fatty acids from the glycerol. The lipid molecule is not attracted to the water molecule. In fact, lipid molecules will clump together to stay away from water. It is the hydrophobic effect that keeps oil and water separated. The hydrophobic nature of lipids has many biological consequences, including protein folding and the movement of materials across cell membranes.
And what about lipids? Let’s look at a triglyceride, one type of lipid. It is made up of a glycerol molecule and three fatty acids. Both the glycerol and the fatty acids are negatively charged. This means the charge of the molecule is evenly distributed, making it nonpolar. When a polar substance interacts with another polar substance the positively charged parts of one are attracted to the negatively charged parts of the other and vice versa. This is why polar substances dissolve in water. Water molecules surround and detach the negative and positive parts of the other molecule from each other.
But when water comes into contact with a triglyceride, such as oil, the water molecules cannot surround and detach the fatty acids from the glycerol. The lipid molecule is not attracted to the water molecule. In fact, lipid molecules will clump together to stay away from water. It is the hydrophobic effect that keeps oil and water separated. The hydrophobic nature of lipids has many biological consequences, including protein folding and the movement of materials across cell membranes.