MCAT lipid structures and membranes cheat sheet

Phospholipid structure

Consists of glycerol, two fatty acids, and a phosphate group. Amphipathic properties allow formation of bilayers.

Triglycerides function

Energy storage; composed of glycerol and three fatty acids. Efficient for long-term energy.

Saturated vs. Unsaturated fats

Saturated: no double bonds; solid at room temperature. Unsaturated: one or more double bonds; liquid at room temperature.

Cholesterol role

Maintains membrane fluidity and stability. Precursor for steroid hormones.

True or False: Waxes are highly hydrophilic.

False. Waxes are hydrophobic, providing waterproofing and protection.

Glycolipids definition

Lipids with carbohydrate groups. Function in cell recognition and signaling.

Steroid structure

Four fused carbon rings. Examples: cholesterol, testosterone, estrogen.

Fill in the blank: Fatty acids can be ____ or ____.

Saturated or Unsaturated.

Role of sphingolipids

Structural components of membranes; involved in signaling and recognition.

Phospholipid bilayer properties

Fluid mosaic model; dynamic and selectively permeable.

Function of lipoproteins

Transport lipids in the bloodstream; examples include LDL and HDL.

Differences between phospholipids and triglycerides

Phospholipids: two fatty acids, amphipathic. Triglycerides: three fatty acids, hydrophobic.

Omega-3 fatty acids

Type of unsaturated fats; beneficial for heart health. Found in fish oils.

Role of eicosanoids

Signaling molecules derived from fatty acids; involved in inflammation and immunity.

Cis vs. Trans fats

Cis: hydrogens on same side; healthier. Trans: hydrogens on opposite sides; associated with health risks.

Lipid bilayer formation cause

Hydrophobic interactions; hydrophilic heads face outward, tails inward.

Phospholipid structure

Composed of a glycerol backbone, two fatty acid tails, and a phosphate group.

Function of cholesterol in membranes

Increases membrane fluidity and stability; helps prevent phase transitions.

True or False: All membrane proteins are peripheral.

False: Some are integral, spanning the membrane.

Compare integral vs peripheral proteins.

Integral: embedded in the membrane; Peripheral: loosely attached to the surface.

Fill in the blank: Phospholipids arrange in a ________ bilayer.

lipid

Role of glycoproteins in membranes

Cell recognition, signaling, and adhesion through carbohydrate chains.

What are sphingolipids?

A class of lipids containing a sphingosine backbone; important in signaling.

Fluid mosaic model components

Phospholipids, proteins, cholesterol, and carbohydrates.

Cause → Effect: Cholesterol removal from membranes.

Decreased fluidity and increased rigidity.

What are lipid rafts?

Microdomains in membranes rich in cholesterol and sphingolipids; involved in signaling.

Phospholipid bilayer permeability

Permeable to small uncharged molecules; impermeable to ions and large polar molecules.

Role of membrane proteins

Transport, enzymatic activity, signal transduction, and cell recognition.

True or False: All proteins in membranes are functional.

True: Each protein has a specific role in cellular function.

What are fatty acids?

Long hydrocarbon chains; can be saturated (no double bonds) or unsaturated (with double bonds).

Composition of lipid membranes

Approximately 50% lipids and 50% proteins by weight.

Function of carbohydrates in membranes

Cell-cell communication and recognition; attached to proteins or lipids.

Fluid mosaic model → definition

The fluid mosaic model describes membranes as a fluid combination of lipids and proteins, allowing lateral movement within the layer.

True or False: Cholesterol increases membrane fluidity.

False. Cholesterol stabilizes membranes, increasing rigidity at high temperatures and preventing solidification at low temperatures.

Membrane permeability depends on:

Size, polarity, and charge of molecules. Small nonpolar molecules pass easily; large or charged molecules require transport proteins.

Function of phospholipids in membranes

Form bilayers due to hydrophilic heads and hydrophobic tails, creating a semi-permeable barrier.

Question: What increases membrane fluidity at high temperatures?

Unsaturated fatty acids increase fluidity due to kinks that prevent tight packing.

Fill in the blank: Membranes are _________ permeable.

selectively

Comparison: Saturated vs Unsaturated fatty acids

Saturated: no double bonds, solid at room temperature. Unsaturated: one or more double bonds, liquid at room temperature.

Fluidity increases with:

- Higher temperatures - Shorter fatty acid chains - More unsaturated fatty acids

Role of membrane proteins

Transport, signal transduction, enzymatic activity, intercellular joining, and cell-cell recognition.

What is the significance of membrane fluidity?

Maintains functionality of proteins, flexibility for cell movement, and facilitates cell signaling.

True or False: All molecules passively diffuse through membranes.

False. Only small nonpolar molecules diffuse; larger or charged particles need specific transport mechanisms.

Peripheral vs Integral proteins

Peripheral: loosely attached, often for signaling. Integral: embedded, typically involved in transport or acting as receptors.

Cause → Effect: High temperature effect on membrane

Causes increased fluidity, potentially leading to loss of membrane integrity.

Question: How do temperature changes affect membranes?

Higher temperatures increase fluidity; lower temperatures decrease fluidity, potentially leading to rigid, less functional membranes.

Transport types across membranes

- Passive transport: diffusion, facilitated diffusion - Active transport: requires energy

What maintains membrane structure?

The balance of lipid composition, cholesterol content, and protein interactions.

Phospholipase C role in signaling?

Hydrolyzes PIP2 into IP3 and DAG, activating signaling pathways.

True or False: Steroids are involved in rapid signaling.

False. Steroids typically act slowly by altering gene expression.

What do eicosanoids derive from?

Arachidonic acid; involved in inflammation and signaling.

Fill in the blank: DAG activates ___________.

Protein kinase C (PKC), involved in various signaling pathways.

Compare GPCRs and RTKs in signaling.

GPCRs activate via G-proteins; RTKs activate via autophosphorylation.

What is the function of sphingolipids in membranes?

Cell signaling, recognition, and structural integrity.

Cause → Effect: Increased cAMP levels result in?

Activation of protein kinases, affecting various cellular responses.

Role of phosphatidylinositol in signaling?

Serves as a minor phospholipid; precursor for second messengers.

Name a key second messenger derived from lipids.

Inositol trisphosphate (IP3), releases calcium from ER.

What is the effect of leukotrienes?

Mediators of inflammation, bronchoconstriction, and immune responses.

True or False: Cholesterol is a signaling molecule.

True. Cholesterol is involved in membrane fluidity and signaling.

Function of ceramides in signaling?

Involved in apoptosis, differentiation, and stress responses.

What initiates the arachidonic acid cascade?

Phospholipase A2 releases arachidonic acid from membrane phospholipids.

Fill in the blank: Nitric oxide is a __________ signaling molecule.

Gaseous; diffuses across membranes to activate guanylate cyclase.

Role of prostaglandins in the body?

Involved in pain, fever, and inflammatory responses.

What is the general structure of a steroid?

Four fused carbon rings with various functional groups.