Comprehensive Lipid and Carbohydrate Metabolism Review for Biochemistry

What are the six major lipid categories?

Fatty acids, triacylglycerols, glycerophospholipids, sphingolipids, glycolipids, sterols.

How does Δ‑nomenclature number carbons?

From the carboxyl carbon; double bonds listed as Δx,y.

How does ω‑nomenclature number carbons?

From the methyl (ω) end; first double bond = ω‑x.

What are the essential fatty acids?

Linoleic acid (18:2 Δ9,12) and α‑linolenic acid (18:3 Δ9,12,15).

What are the building blocks of triacylglycerols?

Glycerol + 3 fatty acids.

What is the difference between a fat and an oil?

Fat = solid; oil = liquid at room temperature.

Why are TAGs efficient energy storage molecules?

Highly reduced, hydrophobic, stored without water, energy‑dense.

How does chain length affect melting temperature (Tm)?

Longer chain → higher Tm.

How does saturation affect Tm?

More saturated → higher Tm.

How do cis double bonds affect Tm?

Lower Tm by disrupting packing.

What are the four major classes of membrane lipids?

Glycerophospholipids, sphingolipids, glycolipids, sterols.

What are the building blocks of glycerophospholipids?

Glycerol + 2 FA + phosphate + head group.

What are the building blocks of sphingolipids?

Sphingosine + FA + head group.

What drives membrane bilayer formation?

The hydrophobic effect.

How does cholesterol affect membrane fluidity?

High T: decreases fluidity; Low T: prevents solidification.

How do you recognize cholesterol structurally?

Four fused rings + OH at C3 + hydrocarbon tail.

What hormones derive from cholesterol?

Cortisol, aldosterone, estrogen, progesterone, testosterone.

Which vitamin derives from cholesterol?

Vitamin D.

Which vitamins are lipid‑soluble?

A, D, E, K.

What are the functions of lipid‑soluble vitamins?

A: vision D: Ca²⁺ homeostasis E: antioxidant K: blood clotting

Where does glycolysis occur?

Cytosol.

Where does gluconeogenesis occur?

Liver (cytosol, mitochondria, ER).

Where does lactic fermentation occur?

Cytosol of muscle and RBCs.

Net equation of aerobic glycolysis?

Glucose → 2 pyruvate + 2 ATP + 2 NADH.

Net equation of anaerobic glycolysis?

Glucose → 2 lactate + 2 ATP.

Net equation of gluconeogenesis?

2 pyruvate → glucose (requires 4 ATP + 2 GTP + 2 NADH)

What is lactic acid fermentation?

Pyruvate → lactate to regenerate NAD⁺.

Why is fermentation important?

Allows glycolysis to continue without oxygen.

What does a kinase do?

Transfers phosphate.

What does a phosphatase do?

Removes phosphate via hydrolysis.

What does a dehydrogenase do?

Catalyzes redox reactions.

What does an isomerase do?

Rearranges atoms within a molecule.

What does a mutase do?

Moves a functional group to a new position.

What does aldolase do?

Cleaves C-C bonds (aldol cleavage).

What does enolase do?

Dehydrates 2‑PG → PEP.

Mechanism of phosphohexose isomerase?

Aldose ↔ ketose via enediol intermediate.

Mechanism of aldolase?

Forms Schiff base; cleaves F1,6BP → GAP + DHAP.

Mechanism of GAPDH?

Thioester intermediate → 1,3‑BPG + NADH.

What activates PFK‑1?

AMP, ADP, F2,6BP.

What inhibits PFK‑1?

ATP, citrate.

What inhibits F1,6‑bisphosphatase?

AMP, F2,6BP.

Why is glycolysis unidirectional?

Contains irreversible steps with large negative ΔG.

Why is gluconeogenesis unidirectional?

Uses different enzymes + ATP/GTP to overcome irreversible steps.

Why does reaction 6 (GAPDH) not require ATP?

Oxidation drives formation of a high‑energy thioester; actual ΔG < 0 in cells.

How is pyruvate converted to acetyl‑CoA?

By PDH complex.

What cofactors does PDH require?

TPP, lipoamide, CoA, FAD, NAD⁺.

What are the products of one TCA turn?

3 NADH, 1 FADH₂, 1 GTP, 2 CO₂.

What are the two stages of TCA?

Oxidative decarboxylation and Regeneration of OAA

Key regulatory enzymes of TCA?

Citrate synthase, isocitrate dehydrogenase, α‑KG dehydrogenase.

Why does TCA stop without oxygen?

NADH accumulates → no NAD⁺ → dehydrogenases stop.

What is the function of the ETC?

Transfer electrons → pump protons → create PMF.

What does Complex I do?

Accepts NADH electrons; pumps protons.

What does Complex II do?

Accepts FADH₂ electrons; does NOT pump protons.

What does Complex III do?

Transfers electrons to cytochrome c; pumps protons.

What does Complex IV do?

Reduces O₂ → H₂O; pumps protons.

How are protons pumped across the membrane?

Electron transfer drives conformational changes that move H⁺ to the intermembrane space.

How many ATP per NADH?

~2.5-3.

How many ATP per FADH₂?

~1.5-2.

Why does NADH yield more ATP than FADH₂?

NADH enters at Complex I → more proton pumping.

What are the three conformations of ATP synthase?

O (open), L (loose), T (tight).

How does ATP synthase make ATP?

Proton flow rotates γ‑subunit → β‑subunits cycle O → L → T → ATP release.