Quick 10Q: Lipids*

Which of the following element(s) are found in lipids?

• carbon/hydrogen

• oxygen

• phosphorus

• nitrogen

• sulfur

Which of the following is not a lipid?

• steroid

• fat

• lipase

• phospholipid

Answer explanation

Lipase is an enzyme which is a protein. You know it is an enzyme based on the ending (-ase).

Which of the following describes the difference between a phospholipid and a fat?

• Phospholipids are polar and fats are nonpolar.

• Phospholipids are nonpolar and fats are polar.

• Phospholipids have one more fatty acid than fats.

• Phospholipids have one less fatty acid than fats.

Answer explanation

Recall: Phospholipids are 2 fatty acids and 1 phosphate group while Fats are 3 fatty acids.

Phospholipids are amphipathic. Which of the following describes how that term applies to phospholipids?

• The phosphate group is nonpolar and the fatty acids are polar.

• The phosphate group is polar and the fatty acids are nonpolar.

• The phosphate group can amplify signal transduction by phosphorylating signaling molecules.

• The fatty acids can amplify signal transduction by phosphorylating signaling molecules.

Answer explanation

Recall: Phosphate is a charged group, so it will be polar. Fatty acids are long hydrocarbons, so they will be nonpolar. This allows the phospholipid to have a polar and nonpolar region (amphipathic).

Steroids are a type of hormone. Polar materials require a transport protein while nonpolar materials can pass easily through the plasma membrane. Which of the following describes how steroid hormones enter the cell?

• Steroids are polar so they pass easily through the plasma membrane.

• Steroids are nonpolar so they pass easily through the plasma membrane.

• Steroids are polar so they require a transport protein to pass through the plasma membrane.

• Steroids are nonpolar so they require a transport protein to pass through the plasma membrane.

Answer explanation

Steroids are composed of four fused rings. These rings are hydrocarbons (hydrogen and carbon based) so they are nonpolar. The prompt even tells you that nonpolar passes easily through the membrane.

Which of the following describes the difference between saturated and unsaturated fatty acids?

• Saturated fatty acids are more polar than unsaturated fatty acids.

• Unsaturated fatty acids are polar than saturated fatty acids.

• Saturated fatty acids have more double bonds than unsaturated fatty acids.

• Unsaturated fatty acids have more double bonds than saturated fatty acids.

Answer explanation

Saturated fatty acids involve all single bonds so each carbon is completely "saturated" with hydrogens. Unsaturated fatty acids involve at least 1 double bond so the carbons are not completely saturated.

Lipids are polymers.

• True

• False

Answer explanation

Polymers have repeating structures (monomers). Lipids do not have a repeated structure/not composed on monomers.

Which of the following describes the function of cholesterol (a steroid) in the plasma membrane?

• Cholesterol is a polar compound that aids in transport of polar substance across the membrane.

• Cholesterol acts as a receptor molecule to bind to signaling molecules in the signal transduction pathway.

• Cholesterol provide energy for active transport across the plasma membrane.

• Cholesterol binds to the fatty acid tails to maintain fluidity of the membrane.

Answer explanation

The cholesterol binds to the saturated fatty acids to inhibit solidification of the membrane. It binds to the unsaturated fatty acids to inhibit increased spacing in the membrane,

Which of the following describes the process to add a fatty acid to the glycerol in a triglyceride?

• This is a dehydration reaction leading to water lost.

• This is a hydrolysis reaction leading to water lost.

• This is a dehydration reaction leading to water used.

• This is a hydrolysis reaction leading to water used.

Answer explanation

The hydroxyl group on the glycerol binds with the hydrogen from the carboxyl group on the fatty acid. This makes water and is considered a dehydration reaction.

Which of the following describes why lipids are hydrophobic?

• Lipids are composed mostly of hydrocarbons which is nonpolar.

• Lipids have hydrogen bonds that repel the hydrogen bonds in water.

• Lipids have more neutrons on their atoms making the compound neutral.

• Lipids are gaseous materials that do not dissolve in water.