Lipids: Structure, Types, Amphipathic Nature, and Vesicle Formation

A set of practice flashcards covering the definition of lipids, hydrophobicity, saturation, major lipid types (fats, steroids, phospholipids), amphipathic nature, bilayer and vesicle formation, and spontaneous vesicle stability.

What defines lipids as a biomolecule class?

Lipids are defined by their water insolubility and hydrophobic character, with few or no polar/charged groups; they are not defined by subunit structures like proteins or nucleic acids.

Why are lipids hydrophobic?

Because they are dominated by nonpolar C-C and C-H bonds, which are not attracted to water and interact mainly with each other via hydrophobic interactions.

What shape do hydrocarbon tails of lipids typically have and how can they bend?

They are long hydrocarbon chains; tails can be straight or bent due to double bonds (unsaturation).

Saturated vs unsaturated hydrocarbon chains.

Saturated: no double bonds; unsaturated: one or more double bonds; saturated chains pack more tightly in membranes.

Name the three major lipid types discussed.

Fats (triacylglycerols), Steroids, and Phospholipids.

Structure of fats.

Fats consist of three fatty acids attached to a glycerol backbone; fatty acids have hydrocarbon chains and a carboxyl group (-COOH).

What is a fatty acid carboxyl group?

The carboxyl group is -COOH (carbonyl C=O and hydroxyl OH).

What is a triglyceride?

A fat with three fatty acids attached to a glycerol backbone (via ester bonds).

Glycerol in fats.

A 3-carbon backbone that attaches to three fatty acids to form fats.

Structure of a fatty acid.

A hydrocarbon chain with a terminal carboxyl group (-COOH).

Steroids' core structure.

Four fused carbon rings; vary by attached R-groups; cholesterol is a common example.

Cholesterol.

The most abundant steroid in the body; has an -OH group and a hydrocarbon tail.

Phospholipid structure.

Two long hydrocarbon tails and a polar head containing a phosphate group and a polar group; head is hydrophilic; tails are hydrophobic.

What makes each phospholipid class distinct?

Different polar head groups and tails that vary in length and degree of saturation.

Amphipathic.

Molecules with both hydrophilic and hydrophobic regions (e.g., phospholipids).

Literal meaning of amphipathic.

Dual sympathy.

Vesicle formation from phospholipids.

When phospholipids are placed in water and agitated, vesicles form with a bilayer enclosing an aqueous interior.

What is a bilayer?

Two-layer arrangement of phospholipids with hydrophobic tails inward and heads facing water on both sides.

Why is vesicle formation spontaneous?

It occurs without energy input, driven by hydrophobic tail interactions and hydrogen bonding between heads and water.

What stabilizes lipid bilayers?

Hydrophobic interactions among tails and hydrogen bonding between water and the hydrophilic heads.

Where is water located relative to a bilayer or vesicle?

Water is on both sides of the bilayer (outside and inside the vesicle lumen), while the hydrophobic core excludes water.

What does the cartoon rendering of phospholipids emphasize?

The hydrophilic head and hydrophobic tail to illustrate bilayer orientation.

What does the polar head of phospholipids typically contain?

A phosphate group and a polar group with charges or partial charges.

What is the role of unsaturation in lipid packing?

Double bonds introduce kinks that reduce tight packing, affecting membrane fluidity and stability.