Lipids, Proteins, and Energy Homeostasis

Comprehensive vocabulary flashcards covering lipid classifications and metabolism, protein structure and digestion, energy homeostasis, appetite regulation, and body composition based on lecture notes.

Saturated vs. Unsaturated Fats

Saturated fats possess carbon octets that are completely full of hydrogen with only single bonds, whereas unsaturated fats have one or more carbon-carbon double bonds along the hydrocarbon chain.

Triglycerides

The most common type of lipid in the body, consisting of a glycerol backbone chemically bonded to three fatty acids; found in butter, oils, and other dietary fats.

Phospholipids

Lipids that make up the cell membrane bilayer, consisting of a hydrophilic head linked to two hydrophobic fatty acid chains.

Sterols

Ring-shaped lipids that play essential roles in cell structure, physiological function, and interacting with phospholipids and proteins embedded within the cell membrane.

Amphipathic (Emulsifier)

A property of a molecule that possesses both polar (hydrophilic) and nonpolar (hydrophobic) regions within its chemical structure.

Membrane Fluidity

The viscosity and flexibility of the lipid bilayer in a cell membrane, which prevents phospholipids from clumping together and keeps them from spreading apart.

Monounsaturated vs. Polyunsaturated Fat

A monounsaturated fat contains exactly one double bond in its carbon backbone, while a polyunsaturated fat contains two or more double bonds.

Trans Fat

Man-made unsaturated fats that double the risk of heart disease compared to saturated fats, cause weight gain even on equal caloric intake, and increase insulin resistance and risk of type 2 diabetes.

Essential Fatty Acids

Fatty acids including omega-3 and omega-6 that cannot be synthesized by the human body and must be acquired through the diet.

Anti-Inflammatory Signaling

A physiological mechanism that acts as a signal to turn off inflammation, initiates tissue repair and regeneration, and stimulates macrophages to clear dead cells from injured sites.

Omega-3 Fatty Acids

Essential fatty acids that improve hormone functions, act as anti-inflammatory agents, maintain healthy endothelial tissues, lower blood pressure, and help prevent arterial hardening.

Omega-6 Fatty Acids

Essential fatty acids that drive inflammatory responses, amplify allergic reactions, increase blood clotting, constrict blood vessels, and support reproductive function, skin, hair, and bone health.

Eicosanoids

Lipid signaling molecules released after injury that mediate inflammation, pain, heat, redness, swelling, fever, and allergy responses.

Cholecystokinin (CCK)

A hormone released by cells in the upper small intestine in response to fats that stimulates the liver/gallbladder to release bile and the pancreas to secrete pancreatic lipase, while also signaling satiety.

Micelles

Small emulsified fat droplets formed by bile salts that allow digestive lipases to break triglycerides down into free fatty acids and monoglycerides for absorption.

Enterocytes

The specialized absorptive epithelial cells that line the inner wall of the small intestine.

Chylomicrons

Lipoprotein particles synthesized in enterocytes that carry absorbed lipids into the lacteals of the lymphatic system, traveling to the bloodstream via the left subclavian vein.

Lipoprotein Lipase

An enzyme located along blood vessels that breaks down triglycerides inside circulating chylomicrons into free fatty acids and glycerol for uptake by body cells.

Amphoteric

The chemical property of blood proteins that allows them to maintain pH balance by functioning as either a proton acceptor or proton donor.

Albumin and Globulin

Major blood proteins responsible for maintaining fluid balance by keeping water within the vascular system against outward blood pressure created by heartbeats.

Amino Acid Structure

The standard molecular structure composed of a central carbon backbone, a hydrogen atom, an amino group, a carboxyl group, and a variable side chain ($R$-group).

Amino Acid Side Chain ($R$-Group)

The variable group on an amino acid that determines the protein's overall shape, chemical properties, and function; can be polar, nonpolar, charged, aromatic, or sulfur-containing.

Protein Structure Levels

The structural hierarchy of proteins: primary (amino acid sequence), secondary (alpha helices and pleated sheets via backbone hydrogen bonding), tertiary (3D conformation from side-chain interactions), and quaternary (assembly of multiple peptide chains).

Sickle Cell Anemia

A genetic condition caused by an incorrect substitution of a single amino acid in a polypeptide chain, altering side-chain interactions and resulting in abnormal red blood cell shapes.

Pepsin

An enzyme found in gastric juices of the stomach that hydrolyzes peptide bonds to break down proteins after they have been denatured by hydrochloric acid ($\text{HCl}$).

Trypsin

A pancreatic digestive enzyme secreted into the small intestine that breaks down peptide bonds and activates other protein-digesting enzymes from the intestinal lining.

Amino Acid Pool

The collection of circulating free amino acids available in the body used to synthesize new proteins, repair tissues, or be converted into energy.

Gluconeogenesis

The metabolic pathway through which the body synthesizes glucose and ATP from non-carbohydrate carbon substrates, such as deaminated amino acids, when carbohydrate stores are depleted.

Deamination

The biochemical removal of an amine group from an amino acid, allowing nitrogen to be excreted as urea while the remaining carbon skeleton is converted into energy.

Limiting Amino Acid

The essential amino acid present in the lowest concentration relative to nutritional requirements, which slows or completely stops protein synthesis when depleted.

Complementary Proteins

Two or more incomplete dietary protein sources combined together to supply all essential amino acids missing from individual components.

Branched-Chain Amino Acids (BCAAs)

A group of essential amino acids consisting of leucine, isoleucine, and valine that are metabolized directly in skeletal muscle rather than the liver, accounting for approximately $35\%$ of essential amino acids in muscle protein.

Macronutrient Distribution Ranges

The recommended dietary intake ranges expressed as percentages of total calories: carbohydrates ($45\text{--}65\%$), protein ($10\text{--}35\%$), and fat ($20\text{--}35\%$).

Catabolism

The metabolic phase consisting of chemical pathways that break down larger molecules into smaller units, resulting in the release of energy.

Anabolism

The phase of metabolism that utilizes cellular energy and building blocks to synthesize larger biological molecules, such as glycogen and triglycerides.

Cellular Energy Flow (ATP)

The physiological pathway converting chemical energy from carbohydrates, fats, and proteins into ATP (the body's energy currency) to drive cellular metabolism, releasing heat and producing chemical waste ($\text{CO}_2$ and $\text{H}_2\text{O}$).

Total Daily Energy Expenditure (TDEE)

The total amount of energy expended by an individual across a 24-hour day, comprising BMR, EAT, NEAT, and TEF.

Basal Metabolic Rate (BMR)

The rate of energy expenditure needed to maintain involuntary vital life processes at complete rest, including respiration and circulation.

Non-Exercise Activity Thermogenesis (NEAT)

The caloric energy expended during all spontaneous physical movements outside of planned athletic exercise, such as fidgeting, walking, and yard work.

Thermic Effect of Food (TEF)

The caloric cost of digesting, absorbing, and assimilating nutrients, accounting for approximately $10\%$ of daily expenditure (fats: $0\text{--}5\%$, carbs: $5\text{--}10\%$, proteins: $20\text{--}30\%$).

Human Body Composition

The anatomical distribution of body mass; reference males average $45\%$ muscle, $3\%$ essential fat, $12\%$ non-essential fat, and $15\%$ bone, while reference females average $36\%$ muscle, $12\%$ essential fat, $15\%$ non-essential fat, and $12\%$ bone.

Appestat

The hunger control center located in the hypothalamus that senses blood-borne hormonal and nutrient signals, increasing appetite when blood glucose falls and suppressing it when glucose is plentiful.

Ghrelin

An appetite-stimulating hormone produced in the stomach that promotes hunger sensations, triggers fat storage, stimulates growth hormone release, and accelerates gastrointestinal motility.

Leptin

A hormone secreted by adipose tissue that provides long-term regulation of energy balance, signaling satiety and suppressing appetite over time.

Neuropeptide Y (NPY)

A potent central nervous system neurotransmitter that stimulates appetite and carbohydrate cravings, which becomes activated when circulating leptin levels drop.

Lipogenesis

The metabolic process of synthesizing and storing fatty acids as triglycerides within adipocytes for future energy demands.

Lipolysis

The biochemical catabolism and breakdown of stored triglycerides into free fatty acids and glycerol to yield metabolic energy.

Hypertrophy vs. Hyperplasia

Hypertrophy refers to an increase in the individual size of existing cells, whereas hyperplasia denotes an increase in the total number of cells.

Body Mass Index (BMI)

A mathematical screening ratio based on weight relative to height that provides an estimate of body size without distinguishing between fat mass and lean mass.

Diet Breaks

A structured, intentional pause from an ongoing caloric deficit maintained for a predetermined timeframe to manage appetite and help prevent metabolic slowing.