Human Body Structure, Transport, and Energy Metabolism

Vocabulary flashcards covering body organization, fluid compartments, cellular organelles, protein synthesis, transport processes, and energy metabolism pathways.

Total Body Water

The total volume of fluid in the body, accounting for $60\%$ of body weight and divided into intracellular and extracellular compartments.

Intracellular Fluid

The fluid compartment contained within cells, comprising $\frac{2}{3}$ of total body water.

Extracellular Fluid

The fluid compartment outside cells, comprising $\frac{1}{3}$ of total body water, subdivided into plasma ($20\%$) and interstitial fluid ($80\%$).

Homeostasis

The maintenance of a relatively constant internal environment within the body through negative and positive feedback mechanisms.

Cholesterol

The most common steroid molecule in the body, found in high amounts in the plasma membrane and acting as the precursor for all other steroids.

Peroxisomes

Cytoplasmic organelles that degrade cellular biomolecules and toxins, generating $H_2O_2$ and subsequently breaking it down using the enzyme catalase ($2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2$).

Lysosomes

Sac-like organelles in the cytoplasm containing digestive enzymes to break down cellular debris from old internal organelles or external endocytosis.

Tight Junctions

Cellular adhesions located between epithelial cells that form a tight barrier and define the paracellular pathway.

Desmosomes

Cell-to-cell junctional structures found in tissues subject to mechanical stress, providing structural strength to prevent cell tearing.

Gap Junctions

Intercellular channels composed of connexons (made of $6$ connexin proteins) that allow direct movement of small molecules and ions between adjacent cells.

Transcription

The process of synthesizing messenger RNA (mRNA) from a DNA template in the nucleus.

Translation

The cytosolic process of synthesizing a polypeptide chain from an mRNA nucleotide sequence.

Semiconservative Replication

The mode of DNA duplication in which each produced double-stranded DNA molecule contains one original parent strand and one newly synthesized strand.

Substrate-Level Phosphorylation

The formation of ATP by the direct transfer of a phosphate group from a phosphorylated intermediate substrate to ADP via an enzyme.

Oxidative Phosphorylation

The aerobic synthesis of ATP driven by electron transport and hydrogen proton pumping across the inner mitochondrial membrane.

Glycolysis

The cytosolic pathway that splits glucose into $2\text{ pyruvate}$ (aerobic) or $2\text{ lactate}$ (anaerobic), yielding a net $2\text{ ATP}$ and $2\text{ NADH} + \text{H}^+$.

Linking Step

The reaction catalyzed by pyruvate dehydrogenase that converts pyruvate from glycolysis into acetyl CoA to enter the Krebs cycle.

Krebs Cycle

A cyclic mitochondrial pathway that oxidizes acetyl CoA to produce $3\text{ NADH} + \text{H}^+$, $1\text{ FADH}_2$, $1\text{ ATP}$, and $2\text{ CO}_2$ per acetyl CoA molecule.

Electron Transport Chain

A series of protein complexes in the inner mitochondrial membrane that transfer electrons to create a hydrogen gradient used to drive ATP synthesis.

Glycogenolysis

The enzymatic breakdown of stored glycogen into glucose units.

Gluconeogenesis

The metabolic pathway that synthesizes new glucose from non-carbohydrate precursors such as lactate, glycerol, and amino acids.

Lipolysis

The breakdown of stored triglycerides into one glycerol molecule and three free fatty acids.

Beta Oxidation

The process of fatty acid catabolism that sequentially cleaves long carbon chains into $2\text{-carbon}$ acetyl CoA units.

Proteolysis

The metabolic breakdown of proteins into individual constituent amino acids.

Phosphofructokinase

The key rate-limiting enzyme of glycolysis regulated by cellular $\text{ATP/ADP}$ energy levels.

Citrate Synthase

The mitochondrial enzyme that initiates the Krebs cycle by combining acetyl CoA with oxaloacetic acid to form citric acid.

ATP Synthase

The inner mitochondrial membrane enzyme that uses energy from hydrogen ions moving down their gradient to synthesize ATP from ADP and inorganic phosphate.

ATP/Creatine Phosphate System

An immediate energy pathway used at the onset of exercise or short high-intensity bursts ($6\text{--}8\,\text{seconds}$) to rapidly re-phosphorylate ADP to ATP.

Phagocytosis

A form of endocytosis in which a cell engulfs and breaks down large unwanted particles or debris using lysosomes.

Pinocytosis

A form of endocytosis in which a cell engulfs extracellular fluid containing dissolved particles for cellular utilization.

Proteotoxic Stress

Damage to cellular function caused by heat-induced protein denaturation, occurring at approximately $40\,^\circ\text{C}$ in rodent cells and $41\text{--}42\,^\circ\text{C}$ in human cells.