Storage Lipids and Structural Lipids

Question 1

What are the primary functions of lipids in biological systems?

Answer 1

Lipids serve as structural components in membranes (phospholipids), energy storage and oxidation molecules (triglycerides), and carrier molecules for hydrophobic signaling (steroids).

Question 2

Define a lipid and describe its solubility properties.

Answer 2

A lipid is a small, water-insoluble biomolecule. It is more soluble in non-polar solvents, allowing it to form membranes and interact with hydrophobic molecules.

Question 3

What are the main types of lipids, and which type is primarily responsible for energy storage?

Answer 3

The main types of lipids include fatty acids, triglycerides, phospholipids, and steroids. Fatty acids, particularly in the form of triglycerides, are the primary lipids involved in energy storage.

Question 4

Describe the basic structure of a fatty acid and its amphipathic nature.

Answer 4

A fatty acid consists of a hydrophobic hydrocarbon tail and a hydrophilic carboxyl group. This amphipathic nature allows fatty acids to interact with both polar and non-polar environments.

Question 5

How are the carbon atoms in fatty acids labeled for naming conventions? (ex. FA with 18 carbons and 2 double bonds)

Answer 5

The carboxyl carbon is labeled as C1, with the carbon next to it designated as the “alpha” carbon. The fatty acid name also includes chain length and the number of double bonds (e.g., 18:2 for a fatty acid with 18 carbons and 2 double bonds).

Question 6

How do you indicate the position of a double bond in fatty acids?

Answer 6

The position of each double bond is indicated by a superscript next to the delta symbol (Δ), representing the first carbon in each double bond. For example, Δ9 denotes a double bond starting at the ninth carbon.

Question 7

What is the general chain length of most naturally occurring fatty acids, and why?

Answer 7

Most naturally occurring fatty acids are 12-24 carbons long and have an even number of carbons. This is due to their synthesis from 2-carbon units added sequentially.

Question 8

Describe the differences between saturated and unsaturated fatty acids, including examples.

Answer 8

Saturated fatty acids have no double bonds (e.g., lauric acid), while unsaturated fatty acids contain one or more double bonds (e.g., palmitoleic acid). Unsaturated fatty acids are less rigid and more fluid than saturated ones.

Question 9

In unsaturated fatty acids, where are double bonds commonly located, and what configuration do they typically have?

Answer 9

Double bonds are commonly located at Δ9, Δ12, or Δ15 and almost always have a cis configuration. This placement and configuration contribute to the molecule’s flexibility and fluidity.

Question 10

What is the significance of even carbon numbers in fatty acids?

Answer 10

Even carbon numbers in fatty acids result from the two-carbon additions during biosynthesis, making it common for fatty acids to have 12-24 carbons in their chains.

Question 11

Why are double bonds in natural fatty acids almost never conjugated?

Answer 11

Natural fatty acids rarely have conjugated double bonds because their biosynthetic pathways introduce double bonds in non-conjugated patterns, usually separated by a -CH2- group.

Question 12

How does the structure of cis double bonds in unsaturated fatty acids affect membrane fluidity?

Answer 12

Cis double bonds introduce kinks in the hydrocarbon chain, preventing tight packing of fatty acids and increasing membrane fluidity, which is essential for cellular functions.

Question 13

How do the length and degree of unsaturation of the hydrocarbon chain affect the physical properties of fatty acids?

Answer 13

The length and degree of unsaturation in fatty acids determine their melting point and physical state at room temperature; saturated fatty acids are solid, while unsaturated fatty acids are liquid at room temperature due to differences in molecular packing

Question 14

Why do saturated fatty acids have higher melting points than unsaturated fatty acids?

Answer 14

Saturated fatty acids have higher melting points because their acyl chains pack tightly, allowing for stronger van der Waals interactions. Their stable, extended conformation facilitates this tight packing, unlike unsaturated fatty acids, which have kinks due to cis double bonds.

Question 15

How do cis double bonds in unsaturated fatty acids influence their physical state?

Answer 15

is double bonds create kinks in the hydrocarbon chain of unsaturated fatty acids, preventing tight packing and reducing intermolecular forces. This results in a lower melting point, making them liquid at room temperature.

Question 16

What is the biological significance of combining saturated and unsaturated fatty acids in lipid bilayers?

Answer 16

The combination of saturated and unsaturated fatty acids in lipid bilayers helps maintain optimal membrane fluidity, which is essential for proper membrane function and cellular processes.

Question 17

What are omega fatty acids, and why are they essential?

Answer 17

Omega fatty acids, such as omega-3 and omega-6, are essential because they serve as precursors to eicosanoids, important signaling molecules. They cannot be synthesized by the body and must be obtained through diet.

Question 18

How is the naming convention for omega fatty acids different from other fatty acids?

Answer 18

Omega fatty acids are named based on the location of the first double bond from the methyl (omega) end of the carbon chain. For example, omega-3 fatty acids have their first double bond three carbons from the end.

Question 19

What are triacylglycerides (TAGs), and how are they structured?

Answer 19

TAGs are the simplest lipids constructed from three fatty acids esterified to a glycerol backbone. This ester linkage creates a hydrophobic molecule used primarily for energy storage.

Question 20

Why are TAGs considered an efficient form of energy storage?

Answer 20

TAGs are more energy-dense than carbohydrates because their carbon atoms are more reduced. They are also hydrophobic, allowing them to be stored without water, which conserves space and avoids osmotic disruption in cells.

Question 21

How do TAGs contribute to insulation in certain animals?

Answer 21

In warm-blooded polar animals, TAGs are stored in adipose tissue under the skin, providing insulation against cold temperatures. Blubber in marine animals is a key example.

Question 22

What are the primary advantages of storing energy as TAGs compared to glycogen?

Answer 22

TAGs are highly energy-dense, hydrophobic, and unhydrated, allowing for dense storage without added water weight. They provide long-term energy storage, unlike glycogen, which is limited to short-term storage.

Question 23

How does the lack of hydration in TAGs benefit energy storage?

Answer 23

Unlike carbohydrates, TAGs do not require hydration, saving space and weight in cells. This enables large quantities of TAGs to be stored efficiently as energy reserves in lipid droplets.

Question 24

Why is energy from TAGs higher in kJ/mol compared to carbohydrates?

Answer 24

TAGs contain more reduced carbon atoms than carbohydrates, allowing more energy to be released upon oxidation, resulting in a higher energy yield per mole.

Question 25

How does the fatty acid composition of olive oil, butter, and beef fat affect their physical states?

Answer 25

Olive oil, with a high proportion of unsaturated fatty acids, is liquid at room temperature. Butter, with more saturated fats, is a soft solid, while beef fat, rich in saturated fatty acids, is a hard solid.