Lipid and Protein Metabolism Lecture Review

Comprehensive vocabulary flashcards covering lipid digestion, lipoprotein transport, fatty acid synthesis and oxidation, ketone metabolism, alcohol metabolism, and protein biochemistry and turnover.

Essential Fatty Acids

Fatty acids that must be supplied by the diet, specifically a-linoleic acid and linoleic acid.

Glycerol

The triacylglycerol component that can be used directly as an energy source in tissues other than adipose.

Lipases

Enzymes that break down triacylglycerols and release free fatty acids from adipose tissue during oxidation.

Albumin

A nonspecific transport protein synthesized in the liver that constitutes $55\%$ of plasma proteins, binds free fatty acids, calcium, zinc, and vitamin B6, and maintains plasma osmotic pressure.

Cholesterol Esters

The storage form of cholesterol inside cells, formed when a fatty acid binds to the hydroxyl group of a cholesterol molecule.

Endogenous Synthesis

The production of molecules inside the body's own cells, such as the approximately $700\,\text{mg}$ of cholesterol synthesized internally from acetyl-CoA.

Secondary Bile Acids

Bile acids formed when intestinal bacteria act upon primary bile acids.

Upper Jejunum

The most active site of lipid digestion where most triacylglycerides are digested following emulsification by bile acids.

Enterocytes

Intestinal cells into which micellar lipid products diffuse and resynthesize triacylglycerides, phospholipids, and cholesterol esters.

Chylomicrons

Lipoprotein particles assembled in the intestinal mucosa that enter the lymphatic system to transport exogenous (dietary) triacylglycerols to muscle and adipose tissue and dietary cholesterol to the liver.

Lipoprotein

A lipid-protein complex responsible for transporting hydrophobic lipids through aqueous body fluids.

Apolipoproteins

Protein constituents of lipoproteins that maintain particle structural stability, act as enzyme cofactors, and serve as receptor recognition ligands.

Lipoprotein Lipase

An enzyme located in adipose tissue and muscle that removes fatty acids from circulating chylomicrons.

High-Density Lipoprotein (HDL)

An endogenous lipoprotein whose main component is protein, recognized for having anti-atherogenic, anti-inflammatory, and antioxidant properties.

Trans Unsaturated Fatty Acids

Dietary fats considered highly atherogenic because they elevate serum LDL while simultaneously lowering HDL.

Omega-3 Polyunsaturated Fatty Acids (n-3 PUFAs)

Hypocholesterolemic dietary lipids that reduce platelet aggregation by inhibiting thromboxane production and lower proinflammatory leukotrienes and serum triacylglycerols.

Statins

Fungal HMG-CoA reductase inhibitors that lower plasma cholesterol by increasing cellular uptake of LDL particles.

Nicotinic Acid

A pharmacological agent that lowers plasma VLDLs and LDLs by inhibiting hepatic VLDL secretion and free fatty acid mobilization from adipose tissue.

Orlistat

A weight-loss drug that acts by inhibiting pancreatic lipase activity in the gastrointestinal tract.

Acetyl-CoA Carboxylase (ACC)

The rate-limiting enzyme in fatty acid synthesis that is allosterically activated by citrate and inhibited by palmitoyl-CoA and other long-chain fatty acids.

Carnitine Palmitoyl Transferase I

A mitochondrial enzyme target inhibited by malonyl-CoA to suppress fatty acid oxidation during active fatty acid synthesis.

Hormone-Sensitive Lipase

An adipose tissue lipolytic enzyme stimulated by epinephrine and glucagon and inhibited by insulin.

Insulin

A potent anabolic hormone that stimulates cellular uptake of glucose, amino acids, and fatty acids, enhances synthetic enzyme pathways, and antagonizes lipolysis.

Ketosis

A metabolic state characterized by an accumulation of excessive ketone bodies in the bloodstream resulting from accelerated fat catabolism.

Ketoacidosis

A severe disruption of acid-base balance caused by the accumulation of acidic ketone bodies ($\text{pH } 3.5$), commonly triggered in type 1 diabetes by impaired cellular glucose supply and uncontrolled fatty acid oxidation.

Alcohol Dehydrogenase (ADH)

A primary hepatic cytosolic pathway that oxidizes ethanol into acetaldehyde.

Acetaldehyde Dehydrogenase (AcDH)

A mitochondrial enzyme pathway that oxidizes toxic acetaldehyde into acetate.

Alpha 1-Antitrypsin

An $\alpha_1$-globulin blood protease inhibitor that neutralizes elastase to protect lung elastic tissue.

Ceruloplasmin

An $\alpha_2$-globulin transport protein that binds and carries approximately $95\%$ of all copper in the body.

Haptoglobin

An $\alpha_2$-globulin plasma protein whose primary role is to bind free hemoglobin in the blood.

Immunoglobulin G (IgG)

The most abundant antibody class ($70\%$ of all circulating immunoglobulins), which responds to repeated antigen exposures and crosses the placenta to provide passive fetal protection.

Immunoglobulin M (IgM)

The structurally largest immunoglobulin class and the first antibody produced in response to a newly encountered antigen.

Primary Protein Structure

The linear sequence of amino acids linked together by covalent peptide bonds in a polypeptide chain.

Secondary Protein Structure

Local conformational folding driven by hydrogen bonding between carbonyl oxygens and amide hydrogens, forming structures such as $\alpha$-helices and $\beta$-pleated sheets.

Tertiary Protein Structure

The overall three-dimensional conformation of a single polypeptide chain stabilized by noncovalent interactions between amino acid side chains.

Quaternary Protein Structure

The spatial arrangement and noncovalent association of multiple polypeptide chains forming an oligomeric protein complex.

Indispensable Amino Acids

The $8$ to $10$ amino acids—including lysine, threonine, and histidine—that human cells cannot synthesize and must obtain from dietary sources.

Secretin

A gastrointestinal hormone triggered by acidic duodenal chyme that stimulates pancreatic secretion of alkaline juice to neutralize acidity.

Cholecystokinin (CCK)

A hormone released by the duodenum in response to chyme that initiates pancreatic zymogen release, enabling enteropeptidase and trypsin activation cascades.

Hartnup Disease

An inherited defect in neutral amino acid transport systems that manifests with pellagra-like symptoms due to cellular depletion of tryptophan.

Cystinuria

The most common genetic defect of amino acid transport, caused by a deficient dibasic amino acid carrier leading to urinary cystine accumulation and kidney stone formation.

Glutathione

A nonprotein nitrogen-containing tripeptide synthesized from cysteine, glycine, and glutamate.

Transamination

The enzymatic transfer of an amino group to an acceptor keto acid to generate glutamate, serving as the first step of amino acid catabolism and requiring vitamin B6.

Ammoniagenic Organ

A physiological classification of the kidney reflecting its ability to deaminate glutamine to produce ammonia ($\text{NH}_3$), which buffers protons to form ammonium ($\text{NH}_4^+$).

Glutaminase

A renal enzyme whose activity increases during metabolic acidosis to liberate ammonia from glutamine for proton excretion in urine.

Protein Turnover

The continuous breakdown and resynthesis of bodily proteins, turning over approximately $1\text{--}2\%$ ($30\text{--}40\,\text{g}$) of total protein mass daily.

Positive Nitrogen Balance

A state in which dietary nitrogen consumption exceeds excretion, typical during growth, pregnancy, lactation, and recovery from metabolic stress.

Negative Nitrogen Balance

A state where total nitrogen excretion exceeds intake, seen in dietary protein deficiency, lack of essential amino acids, starvation, sepsis, trauma, and uncontrolled diabetes.

Marasmus

A severe form of protein-calorie malnutrition characterized by progressive tissue wasting and emaciation due to gross dietary deficiency in calories and protein.

Kwashiorkor

A pediatric nutritional deficiency disease linked to low-protein diets such as maize, primarily driven by a deficiency of the essential amino acid tryptophan.