Nutrition: Metabolism, Proteins, and Lipids

Comprehensive vocabulary flashcards covering energy metabolism, protein digestion and genetics, and lipid structures and transport from Chapters 6, 7, and 8.

Anabolism

Metabolic pathways that build larger, complex molecules from smaller ones; these are uphill reactions that require energy input.

Catabolism

Metabolic pathways that break down larger molecules into smaller units; these downhill reactions release usable and heat energy.

Adenosine Triphosphate (ATP)

A high-energy phosphate compound functioning as the body's primary energy currency; the human body operates at approximately $25\%$ efficiency when converting food energy into cellular work.

Glycolysis

An anaerobic metabolic pathway occurring in the cytosol that converts $1\text{ glucose}$ molecule into $2\text{ pyruvate}$ molecules, producing a net yield of $2\text{ ATP}$.

Pyruvate Dehydrogenase Reaction

An aerobic mitochondrial reaction that converts pyruvate to acetyl CoA; it requires the B-vitamins thiamin, riboflavin, niacin, and pantothenic acid as coenzymes.

Lactate

A compound produced by muscle cells from pyruvate during anaerobic metabolism when oxygen is absent; its accumulation is linked to muscle pain and fatigue.

Cori Cycle

The metabolic process in which the liver removes lactate from the bloodstream, converts it back into glucose via gluconeogenesis, and releases it into circulation.

Citric Acid (TCA) Cycle

An aerobic mitochondrial pathway that metabolizes acetyl CoA to generate electron carriers, supporting a complete ATP yield of up to $38\text{ ATP}$ alongside oxidative phosphorylation.

Beta-Oxidation

The mitochondrial catabolic pathway where enzymes cleave two-carbon segments from fatty acid chains to produce acetyl CoA, alongside $\text{FADH}_2$ and $\text{NADH}$.

Deamination

The removal of an amino group ($\text{NH}_2$) from an amino acid; in the deamination of alanine, pyridoxal phosphate (PLP) serves as a cofactor to produce pyruvate and ammonia for the urea cycle.

Transamination

The transfer of an amino group from an amino acid to a carbon skeleton; for example, alanine transaminates with $\alpha$-ketoglutarate via the enzyme alanine aminotransferase (ALT) and cofactor PLP to form pyruvate and glutamate.

Ketosis

A metabolic state wherein ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone) are produced from excess acetyl CoA as an alternative, non-preferred energy source for the brain and central nervous system, lowering blood pH.

Essential Amino Acids

Nine amino acids that the body cannot synthesize or make in sufficient quantities to meet physiological needs: threonine, valine, tryptophan, isoleucine, leucine, lysine, phenylalanine, methionine, and histidine.

Conditionally Essential Amino Acid

A non-essential amino acid that becomes indispensable under specific clinical circumstances or diseases, such as kidney or liver disease.

Peptide Bond

A strong covalent bond formed between the carboxylic acid group of one amino acid and the amine group of another, releasing water during formation.

Pepsin

A gastric enzyme activated in the presence of hydrochloric acid ($\text{HCl}$) that initiates the chemical breakdown of dietary proteins by cleaving peptide bonds.

Blood Urea Nitrogen (BUN)

A blood biomarker measuring the nitrogen content of circulating urea, produced by the liver after amino acid deamination.

Urine Urea Nitrogen (UUN)

A clinical biomarker measured in urine that reflects the kidneys' excretion of urea and serves as a direct indicator of dietary protein intake.

Recommended Dietary Allowance (RDA) for Protein

The standard adult baseline recommendation of $0.8\,\text{g}$ of protein per kilogram of body weight ($\text{g/kgbw}$) daily.

Dietary Guidelines for Americans (DGA) Protein Serving Goals (2025–2030)

Dietary guideline recommending a protein intake range of $1.2\text{--}1.6\,\text{g/kgbw}$ per day to support lean tissue and satiety.

Food Allergy

An inappropriate immune and inflammatory response to one or more harmless proteins (allergens) in a food, which can present with hives, eczema, wheezing, gastrointestinal distress, or anaphylaxis.

Anaphylaxis

A severe, life-threatening systemic allergic response involving acute airway constriction and cardiovascular collapse, managed emergently with epinephrine.

Celiac Disease

An autoimmune disorder affecting roughly $2\text{ million}$ U.S. adults in which gluten ingestion causes immune-mediated damage to the intestinal mucosa and microvilli, diagnosed via antibody testing and intestinal biopsy.

Nutrigenetics

The scientific discipline studying how an individual's specific genetic variations influence their physiological responses to nutrients and dietary patterns.

Nutrigenomics

The study of how dietary nutrients and bioactive components affect the expression of a person's genome.

Food Insecurity

The condition of being unable to consistently access enough nutritious food necessary for an active, healthy life; reported in $2022$ to affect over $44\text{ million}$ Americans.

Triglyceride

The primary chemical form of lipids in foods and the body ($95\%$ of dietary fat), composed of a glycerol backbone esterified to three fatty acids.

Saturated Fatty Acid (SFA)

A fatty acid whose hydrocarbon chain contains no double bonds between carbon atoms; generally solid at room temperature and associated with an increased risk of heart disease when consumed in excess.

Monounsaturated Fatty Acid (MUFA)

A fatty acid containing exactly one carbon-carbon double bond along its hydrocarbon chain; typically liquid at room temperature and associated with reduced cardiovascular risk.

Polyunsaturated Fatty Acid (PUFA)

A fatty acid possessing two or more carbon-carbon double bonds, categorized into families such as omega-3 and omega-6 fatty acids.

Omega-3 Fatty Acids

A class of polyunsaturated fatty acids found in fish, flaxseed, walnuts, and breast milk that reduce inflammation and help decrease risks of heart disease, depression, and arthritis while aiding infant brain development.

Hateful 8 Seed Oils

A colloquial term for eight omega-6-rich refined oils—canola, corn, cottonseed, grapeseed, soybean, sunflower, safflower, and peanut oil—frequently found in ultra-processed foods.

Trans Fatty Acids

Fatty acids characterized by trans carbon-carbon double bond configurations, primarily generated via industrial partial hydrogenation of vegetable oils, which adversely affect cardiovascular health.

Phospholipids

Amphipathic lipids structured with a glycerol backbone, two fatty acids, and a phosphorus-containing group; essential as structural constituents of cellular membranes and food emulsifiers.

Cholesterol

A sterol lipid found exclusively in animal-derived foods and endogenously synthesized in the liver ($\frac{2}{3}$ of total); serves as a vital structural component of brain and nerve cell membranes and a precursor to bile, vitamin D, and steroid hormones.

Micelle

A water-soluble spherical lipid aggregation created by bile salts and digestion products (monoglycerides and fatty acids) that delivers digested fats to the brush border of intestinal absorptive cells.

Chylomicron

A lipoprotein assembled inside intestinal absorptive cells that packages reassembled triglycerides and cholesterol with a protein and phospholipid coat for lymphatic and circulatory transport.

Low-Density Lipoprotein (LDL)

A lipoprotein rich in cholesterol that carries lipids from the liver to peripheral tissues like muscle and adipose; clinically desirable levels are $< 100\,\text{mg/dL}$.

High-Density Lipoprotein (HDL)

A protein-dense lipoprotein that scavenges cholesterol from peripheral tissues and vascular walls, returning it to the liver for catabolism and elimination; desirable levels are $> 50\,\text{mg/dL}$ for females and $> 40\,\text{mg/dL}$ for males.

Acceptable Macronutrient Distribution Range (AMDR) for Lipids

The dietary intake recommendation that total fat provide $20\text{--}35\%$ of daily caloric intake, with saturated fat kept below $10\%$ of total calories.