Nutrition and Metabolism Study Guide: Proteins, Energy Metabolism, and Weight Management

Comprehensive vocabulary flashcards covering the structure and metabolism of proteins, aerobic and anaerobic cellular energy extraction, and the principles of energy balance, body composition, and weight regulation.

Amino Acid

A building block of protein containing a central carbon, an amino group with nitrogen, an acid group, a hydrogen atom, and a variable side chain (R group).

Peptide Bond

The chemical bond that links amino acids together to form a polypeptide chain.

Polypeptide

A chain of amino acids joined together by peptide bonds.

Primary Protein Structure

The linear sequence of amino acids in a polypeptide chain.

Secondary Protein Structure

Local folding patterns within a polypeptide, such as coils and sheets.

Tertiary Protein Structure

The overall three-dimensional shape of a single polypeptide chain.

Quaternary Protein Structure

The spatial arrangement and interaction of multiple polypeptide chains in a functional protein.

Denaturation

The disruption of a protein's normal folded structure caused by factors such as heat or changes in pH, without breaking peptide bonds.

Essential Amino Acid

An amino acid that the body cannot synthesize in sufficient quantities to meet its needs and therefore must be obtained from the diet.

Nonessential Amino Acid

An amino acid that the body can ordinarily synthesize in adequate amounts using carbon skeletons and nitrogen sources.

Conditionally Essential Amino Acid

An amino acid normally synthesized by the body whose production can become insufficient under certain physiological conditions.

Pepsin

A gastric protease activated from pepsinogen in an acidic environment that begins the enzymatic digestion of proteins by breaking peptide bonds.

Protein Turnover

The continuous cellular process of breaking down and rebuilding body proteins.

Deamination

The removal of an amino group from an amino acid, yielding a nitrogen waste portion and a carbon skeleton.

Urea

A nitrogen-containing waste product synthesized by the liver from toxic ammonia and excreted from the blood by the kidneys in urine.

Complete Protein

A dietary protein source that supplies all essential amino acids in adequate proportions to meet biological requirements.

Limiting Amino Acid

The specific essential amino acid that is in the shortest supply relative to human physiological needs.

Protein Complementation

The practice of combining food sources whose differing amino acid profiles compensate for each other's limitations (e.g., combining lysine-limited grains with methionine-limited legumes).

Catabolism

Metabolic reactions that break down larger molecules into smaller units and release energy.

Anabolism

Energy-requiring metabolic reactions that build complex molecules from simpler precursors.

ATP

Adenosine triphosphate; the primary molecule that captures and transfers usable chemical energy to power cellular work.

Reduced Coenzymes

Molecules such as $\text{NADH}$ and $\text{FADH}_2$ that accept and carry high-energy electrons to the electron transport chain.

Glycolysis

A cytosolic anaerobic pathway that breaks down one six-carbon glucose molecule into two three-carbon pyruvate molecules, producing a net yield of $2\,\text{ATP}$ and $\text{NADH}$.

Acetyl CoA

A two-carbon acetyl unit coupled to coenzyme A that acts as a central metabolic junction where carbohydrates, fats, and some amino acids enter the TCA cycle.

TCA Cycle

A mitochondrial matrix pathway (also called the citric acid or Krebs cycle) that oxidizes acetyl groups to $\text{CO}_2$, yielding reduced coenzymes and approximately $2\,\text{ATP}$ equivalents per glucose.

Electron Transport Chain

A series of electron carriers located on the inner mitochondrial membrane that use electron energy to pump hydrogen ions and establish an electrochemical gradient for ATP synthesis.

Oxidative Phosphorylation

The metabolic pathway where ATP synthase uses the hydrogen-ion gradient formed by the electron transport chain to produce the majority of cellular aerobic ATP.

Lactate

The product formed from pyruvate during anaerobic glycolysis in the cytosol, which regenerates $\text{NAD}^+$ to keep glycolysis functioning.

Gluconeogenesis

The synthesis of new glucose molecules from noncarbohydrate precursors, such as glucogenic amino acids, glycerol, and lactate, primarily in the liver.

Ketogenesis

The metabolic production of ketone bodies by the liver from fat-derived acetyl CoA during periods of carbohydrate shortage or prolonged fasting.

Ketosis

An adaptation characterized by an elevated concentration and increased availability of ketone bodies in the blood.

Ketoacidosis

A pathological state marked by an extreme, uncontrolled accumulation of ketone-associated acids that significantly lowers blood pH.

Energy Balance

The relationship wherein total caloric intake equals total caloric expenditure over time, resulting in stable body energy stores.

Positive Energy Balance

A metabolic state where energy intake exceeds energy expenditure over time, leading to increased stored energy and weight gain.

Negative Energy Balance

A metabolic state where energy expenditure exceeds energy intake over time, requiring the body to mobilize stored energy reserves.

Basal Metabolism

The energy expended to sustain basic life-support processes under resting, basal conditions, including circulation, breathing, and organ maintenance.

Thermic Effect of Food

The energy required to digest, absorb, transport, and metabolize ingested nutrients from food.

Body Composition

The relative proportions of different tissues comprising total body weight, particularly fat mass and fat-free mass.

Body Mass Index (BMI)

A standardized screening ratio of weight to height calculated as $\text{BMI} = \frac{\text{weight in kilograms}}{(\text{height in meters})^2}$ or $\text{BMI} = \frac{703 \times \text{weight in pounds}}{(\text{height in inches})^2}$.

Set Point Theory

A physiological hypothesis suggesting that biological regulatory feedback actively alters appetite and energy expenditure to defend a specific body weight or fat level.

Leptin

A hormone produced primarily by adipose cells that communicates stored energy availability to the brain and generally acts to suppress appetite.

Leptin Resistance

A condition characterized by a diminished cellular or brain responsiveness to circulating leptin signals.