Lipids, Membranes, and Metabolism Lecture Review

Comprehensive vocabulary flashcards covering lipid classification, membrane structure/function, thermodynamics of metabolism, transport energetics, glycolysis, and glycogen metabolism based on the provided lecture notes.

Lipids

Biological compounds that are insoluble in water (hydrophobic) but soluble in organic solvents such as chloroform and methanol.

Saturated Fatty Acids

Carboxylic acids with hydrocarbon chains containing no double bonds between carbons in the chain.

Unsaturated Fatty Acids

Carboxylic acids with hydrocarbon chains containing one or more double bonds between carbons in the alkyl chain.

Essential Nutrients (Omega Fatty Acids)

Polyunsaturated fatty acids like $\omega-3$ and $\omega-6$ that humans need but cannot synthesize and must obtain from their diet.

Trans Fatty Acids

Lipids formed by partial hydrogenation of unsaturated fatty acids to increase shelf life; they have higher melting points and can pack more regularly than cis-isomers.

Triacylglycerols

The primary storage form of lipids (body fat) consisting of a glycerol backbone esterified to three fatty acids.

Lipases

Enzymes that catalyze the hydrolysis of stored triacylglycerols, releasing free fatty acids.

Waxes

Esters of long-chain saturated and unsaturated fatty acids with long-chain alcohols, characterized by high melting points and water-repellent properties.

Glycerophospholipids

Primary constituents of cell membranes consisting of an L-glycerol-3-phosphate backbone, two fatty acids, and a polar head group.

Sphingolipids

Membrane lipids with a sphingosine backbone where a fatty acid is joined via an amide linkage and a polar head group is attached by a phosphodiester or glycosidic linkage.

Glycosphingolipids

Lipids in the outer cell membrane that determine blood groups based on the type of sugars located on their head groups.

Sterols

Structural lipids in eukaryotic membranes containing a steroid nucleus of four fused rings and a polar hydroxyl group at the $C-3$ position.

Eicosanoids

Paracrine hormones derived from arachidonate $20:4(\Delta^{5,8,11,14})$ that include prostaglandins, thromboxanes, and leukotrienes.

NSAIDs

Nonsteroidal anti-inflammatory drugs like aspirin and ibuprofen that reduce prostaglandin and thromboxane formation by inhibiting cyclooxygenase (COX1/COX2) enzymes.

Amphipathic

A molecule possessing both a hydrophobic (nonpolar) and a hydrophilic (polar) region.

Micelles

Structures formed in aqueous solution by amphipathic molecules with a larger polar head than tail, sequestering hydrophobic groups in the center.

Flip-Flop (Spontaneous Transverse Diffusion)

The rare movement of an individual lipid from one leaflet of a bilayer to another, which is slow because the charged head group must pass through the hydrophobic core.

Lipid Rafts

Membrane microdomains containing clusters of sphingolipids with long tails and cholesterol that are more ordered (less fluid) than the surrounding bilayer.

Fluid Mosaic Model

Proposed by Singer and Nicholson in 1972, this model describes lipids as a viscous two-dimensional solvent into which proteins are inserted.

Integral Membrane Proteins

Proteins firmly associated with the membrane that can only be extracted using detergents to coat their hydrophobic domains.

Peripheral Membrane Proteins

Proteins weakly associated with the membrane through ionic interactions or hydrogen bonds, removable by high salt or changes in pH.

Hydropathy Index

A scale used to predict transmembrane regions of proteins, where high positive values indicate hydrophobic segments.

Free-energy change for transport of a neutral solute (\Delta G_t)

$\Delta G_t = RT \ln \left(\frac{C_2}{C_1}\right)$, where $C_1$ is the starting concentration and $C_2$ is the destination concentration.

Faraday Constant (F)

$96,500\,JV^{-1}mol^{-1}$.

Ion Channels

Gated membrane proteins that allow ions to diffuse at very high rates ($10^7$ to $10^8$ ions/s) and are not saturable at physiological concentrations.

Primary Active Transport

A process where solute movement against an electrochemical gradient is directly driven by the energy released from ATP hydrolysis.

Secondary Active Transport

A process where a solute is moved against its electrochemical gradient using the energy provided by another ion moving down its pre-established gradient.

P-type ATPases

Cation transporters, like the $Na^+/K^+$ ATPase or SERCA pump, that are reversibly phosphorylated by ATP during the transport cycle.

Catabolism

The metabolic phase involving the degradation of organic compounds to obtain energy.

Anabolism

The metabolic phase involving the biosynthesis of compounds using energy carriers and precursors.

Steady State

A condition in living systems where the concentrations of products and reactants remain constant, but not at their equilibrium concentrations.

Biochemical Standard Free Energy Change (\Delta G^{\circ'})

The free energy change at standard state defined for biological systems at aqueous solution (water value 1) and pH 7.

Mass Action Ratio (Q)

The ratio of product concentrations to reactant concentrations at any given instantaneous state of a system out of equilibrium.

Thermodynamic Coupling

The strategy by which living organisms drive endergonic (unfavorable) reactions by pairing them with exergonic (favorable) reactions, making their combined $\Delta G$ additive.

Oxidoreductases

Enzymes that catalyze the transfer of electrons, such as dehydrogenases, oxidases, and reductases.

Kinases

A subclass of transferases that catalyze phosphoryl group transfers from ATP to a substrate.

Ligases

Enzymes that catalyze the formation of $C-C$, $C-S$, $C-O$, or $C-N$ bonds by condensation reactions coupled to ATP cleavage.

NAD+/NADH

Universal water-soluble electron carriers where NAD+ is typically used in oxidation reactions and NADPH is used in reduction reactions.

Standard Reduction Potential (E^{\circ'})

A measure of the affinity of a particular redox pair for electrons; a more positive value indicates a higher affinity to gain electrons.

Nernst Equation

$E_{rxn} = E_{rxn}^{\circ'} - \frac{RT}{nF} \ln(Q)$, used to determine the reduction potential of a reaction under non-standard conditions.

Feedback Inhibition

A regulatory mechanism where a pathway intermediate acts as an allosteric modulator to inhibit an enzyme earlier in the same pathway.

Glycolysis

The sequence of ten enzyme-catalyzed reactions that converts glucose into pyruvate, yielding a net gain of 2 ATP and 2 NADH.

Phosphofructokinase-1 (PFK-1)

The enzyme for the first committed step of glycolysis, catalyzing the phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate.

Substrate-Level Phosphorylation

The synthesis of ATP from ADP by the direct transfer of a high-energy phosphate group from its substrate, as seen in steps 7 and 10 of glycolysis.

Mutases

Enzymes that catalyze the apparent migration of functional groups within a single molecule.

Fermentation

The anaerobic process that regenerates NAD+ for further glycolysis by reducing pyruvate to products like lactate or ethanol.

Cori Cycle

The metabolic pathway in which lactate produced by active muscle is transported to the liver and converted back into glucose.

Gluconeogenesis

The anabolic pathway that generates glucose from non-carbohydrate precursors such as pyruvate, lactate, or glucogenic amino acids.

Fructose 2,6-bisphosphate (F-2,6-BP)

A key regulator that allosterically activates PFK-1 (glycolysis) and inhibits FBPase-1 (gluconeogenesis).

Pentose Phosphate Pathway (PPP)

A pathway utilized to generate NADPH for biosyntheses and Ribose 5-phosphate for nucleotide synthesis from glucose 6-phosphate.

Glycogen Phosphorylase

The enzyme that degrades glycogen by catalyzing the phosphorolysis of $\alpha(1\rightarrow 4)$ glycosidic bonds at nonreducing ends.

Glycogenin

A protein that acts as both the primer and the catalyst for initial glycogen synthesis by attaching glucose units to its own Tyr residue.