Biochemistry Lecture – Lipid Metabolism, Membrane Transport & Diabetes

Vocabulary flashcards covering lipid transport, signaling pathways, diabetes, and related biochemical enzymes and transporters from the lecture notes.

Ketone bodies

Water-soluble molecules made in the liver from acetyl-CoA that lower blood pH and are converted back to acetyl-CoA for energy.

Cerebrosides

Glycosphingolipids that contain a single sugar residue attached to a ceramide backbone.

Gaucher disease

Lysosomal storage disorder caused by deficiency of glucocerebrosidase leading to glucocerebroside accumulation.

GLUT2

Low-affinity, bidirectional glucose transporter that functions without ATP or insulin, found in liver, pancreas, kidney, and intestine.

SGLT1

Sodium-glucose symporter that uses the Na⁺ gradient to actively transport glucose into intestinal and renal cells.

GLUT4

Insulin-dependent glucose transporter in muscle and adipose tissue that is translocated to the plasma membrane by insulin.

Chylomicron remnants

Particles left after triglyceride removal from chylomicrons; taken up by the liver via Apo-E recognition.

Intermediate-density lipoprotein (IDL)

VLDL remnant taken up by the liver through Apo-E–mediated binding.

Apo-E

Apolipoprotein on chylomicron remnants and IDL that mediates hepatic uptake.

Apo-CII

Apolipoprotein that activates lipoprotein lipase (LPL) to hydrolyze triglycerides in chylomicrons and VLDL.

Lipoprotein lipase (LPL)

Capillary enzyme activated by Apo-CII that releases free fatty acids from triglyceride-rich lipoproteins.

Apo-B100

Apolipoprotein required for LDL binding to LDL receptors on cells.

Apo-A1

Major apolipoprotein of HDL; activates LCAT for cholesterol esterification.

Farxiga (dapagliflozin)

SGLT2 inhibitor for T2DM that increases urinary glucose loss and risk for dehydration and hyperosmolar hyperglycemic state.

Adenylyl cyclase (AC)

Enzyme that converts ATP to cAMP; inhibited by Gαᵢ proteins.

Gαᵢ protein

G-protein α-subunit that decreases cAMP by inhibiting adenylyl cyclase.

Type 1 diabetes mellitus (T1DM)

Autoimmune destruction of pancreatic β-cells leading to absolute insulin deficiency; treated with insulin and exercise.

Emergency glucagon

Hormone administered to raise blood glucose rapidly during severe hypoglycemia.

Acetyl-CoA carboxylase (ACC)

Rate-limiting enzyme of fatty-acid synthesis converting acetyl-CoA to malonyl-CoA; activated by citrate/insulin and inhibited by palmitate/AMPK.

Palmitate

End-product of fatty-acid synthase; feedback inhibitor of ACC.

AMP-activated protein kinase (AMPK)

Energy-sensing kinase that phosphorylates and inhibits ACC, blocking fatty-acid synthesis.

Mixed micelles

Aggregates of bile salts and lipid digestion products formed in the small intestine to aid absorption.

cAMP

Second messenger that activates protein kinase A (PKA).

Diabetes insipidus

Disorder of water balance involving vasopressin signaling, unrelated to blood glucose metabolism.

Fatty-acid synthesis rate-limiting step

Conversion of acetyl-CoA to malonyl-CoA by ACC.

GTPase-activating protein (GAP)

Protein that accelerates GTP hydrolysis on Gα; loss of this activity keeps G-protein signaling active.

Gαq protein

G-protein α-subunit that activates phospholipase C (PLC).

Phospholipase C (PLC)

Enzyme that cleaves PIP₂ into DAG and IP₃ upon Gαq activation.

Symport

Transporter moving two different molecules in the same direction, e.g., SGLT1.

Uniport

Transporter moving one molecule at a time across a membrane.

Antiport

Transporter exchanging two molecules in opposite directions.

Permease

General term for a membrane transporter protein.

Very-low-density lipoprotein (VLDL)

Particle made in liver that delivers endogenous triglycerides to peripheral tissues.

Chylomicron

Intestinal lipoprotein that transports dietary triglycerides to tissues.

High-density lipoprotein (HDL)

Lipoprotein that collects cholesterol from tissues and returns it to the liver.

Low-density lipoprotein (LDL)

Derived from VLDL; delivers cholesterol to peripheral tissues and elevates cardiovascular risk when high.

Ketogenesis

Process stimulated in liver during insulin deficiency (e.g., missed insulin in T1DM) producing ketone bodies.

Gastric lipase

Enzyme in the stomach that begins dietary triglyceride digestion.

Lingual lipase

Enzyme secreted by salivary glands that hydrolyzes triglycerides in the stomach.

Arachidonic acid

Polyunsaturated fatty acid released by PLA₂; precursor to eicosanoids.

Thromboxane A₂ (TXA₂)

Platelet aggregating and vasoconstricting eicosanoid produced from arachidonic acid via COX-1.

Cyclooxygenase-1 (COX-1)

Constitutive enzyme converting arachidonic acid to prostaglandins and thromboxanes; inhibition leads to gastric and platelet effects and vasodilation

Exercise

Lifestyle intervention that increases tissue sensitivity to insulin.

HMG-CoA reductase

Rate-limiting enzyme of cholesterol synthesis; target of statins.

Perilipin

Adipocyte lipid-droplet protein; dephosphorylated during high insulin to promote fat storage, phosphorylated when insulin is low to release fatty acids.

5-Lipoxygenase (5-LOX)

Enzyme converting arachidonic acid to leukotrienes.

Triacylglycerol

Storage form of fatty acids consisting of glycerol esterified to three fatty acids.

Cholesterol

Sterol synthesized via the HMG-CoA reductase pathway; component of membranes and precursor of bile acids.

Prostaglandins

Eicosanoids produced via COX enzymes involved in inflammation and pain signaling.

ABC transporter

ATP-binding cassette pump that exports small molecules (e.g., drugs) out of cells.

P-class pump

Primary active transporter that moves ions such as H⁺, Na⁺, or K⁺ across membranes.

V-class pump

ATP-driven proton pump that acidifies intracellular compartments or extracellular space.

Aspirin (acetylsalicylate)

NSAID that irreversibly inhibits COX enzymes; analgesic effect mainly due to COX-2 inhibition.

Saturated fat

Fatty acid with no double bonds; typically solid at room temperature.

Unsaturated fat

Fatty acid containing one or more double bonds that create bends; usually liquid at room temperature.

Isocitrate dehydrogenase

TCA cycle enzyme; reduced activity lowers citrate levels.

ATP citrate lyase

Cytosolic enzyme converting citrate to oxaloacetate and acetyl-CoA for fatty-acid synthesis.

Acyl-CoA synthetase

Enzyme that activates free fatty acids by esterifying them to CoA.

Carnitine palmitoyltransferase I (CPT-I)

Outer-mitochondrial membrane enzyme that converts acyl-CoA to acyl-carnitine; inhibited by malonyl-CoA.

Carnitine-acylcarnitine translocase

Transporter that shuttles acyl-carnitine into and free carnitine out of the mitochondrial matrix.

Carnitine palmitoyltransferase II (CPT-II)

Inner-mitochondrial membrane enzyme that regenerates acyl-CoA from acyl-carnitine.

Malonyl-CoA

Intermediate in fatty-acid synthesis that inhibits CPT-I, preventing β-oxidation.

Glucocerebroside vs. Ganglioside

Glucocerebrosides contain one sugar; gangliosides possess multiple sugar residues including sialic acid.

HDL vs. LDL in CVD

High HDL lowers cardiovascular risk; high LDL elevates risk.

IP₃ (inositol-1,4,5-trisphosphate)

Second messenger from PLC that opens ER Ca²⁺ channels.

Diacylglycerol (DAG)

Second messenger from PLC that directly activates protein kinase C (PKC).

Protein kinase C (PKC)

Serine/threonine kinase activated by DAG and Ca²⁺ involved in many signaling pathways.

Cholera toxin

Bacterial exotoxin that locks Gαs in GTP-bound state, causing persistent cAMP production.

Pertussis toxin

Bacterial exotoxin that inhibits Gαi, preventing AC inhibition and increasing cAMP.

Type 2 diabetes mellitus (T2DM)

Adult-onset disease characterized by insulin resistance; managed with lifestyle changes, metformin, other drugs, and sometimes insulin.