Biological Catalysts and Hormonal Regulation

A set of vocabulary flashcards covering the mechanism of enzyme catalysis and the classification and regulation of hormones.

Enzymes

Proteins that act as catalysts to increase the rate of virtually all chemical reactions within cells by providing a template for reactants.

Active sites

Clefts or grooves on the surface of an enzyme, usually composed of amino acids from the tertiary structure, where substrates bind via noncovalent interactions.

Lock-and-key model

The simplest model of enzyme-substrate interaction where the substrate fits precisely into the active site.

Induced fit

A process in which the configurations of both the enzyme and substrate are modified upon binding to bring the substrate closer to the transition state.

Transition state

A high-energy state of reactants that enzymes stabilize to lower the required energy of activation for a reaction.

Prosthetic groups

Small molecules, such as heme in hemoglobin or metal ions like zinc and iron, that are bound to proteins and play critical functional roles.

Coenzymes

Low-molecular-weight organic molecules, often related to vitamins, that work with enzymes to enhance reaction rates and are recycled rather than irreversibly altered.

Nicotinamide adenine dinucleotide ($NAD^+$)

A coenzyme that functions as an electron carrier in oxidation-reduction reactions by accepting $H^+$ and two $e^-$ to form $NADH$.

Vitamins

Organic compounds that contribute to the structure of coenzymes; they are necessary in human diets because humans cannot synthesize them.

Hormones

Chemicals released into body fluids, usually blood, that carry signals to target cells to elicit a specific response.

Endocrine system

The collective group of cells, tissues, and organs, such as the adrenal and thyroid glands, that secrete hormones to maintain homeostasis.

Lipid-derived hormones

Hormones mostly derived from cholesterol, such as steroid hormones, which are insoluble in water and can diffuse across plasma membranes.

Steroid hormones

A primary class of lipid hormones in humans that are usually ketones or alcohols, including testosterone and estradiol.

Amino acid-derived hormones

Relatively small molecules derived from tyrosine or tryptophan, such as epinephrine, norepinephrine, and melatonin, with names typically ending in "-ine."

Peptide hormones

Hormones consisting of polypeptide chains, ranging from short chains like oxytocin to large glycoproteins like follicle-stimulating hormone.

Negative feedback

The primary mechanism for hormone regulation where a stimulus triggers a release, and once the substance reaches a certain level, it signals to stop further release.

Humoral stimuli

The control of hormone release in response to changes in extracellular fluids or ion concentrations, such as blood glucose levels triggering insulin.

Hormonal stimuli

The release of a hormone in response to another hormone, such as the hypothalamus stimulating the anterior pituitary gland.

Neural stimuli

A mechanism where the nervous system directly stimulates endocrine glands, such as the sympathetic nervous system triggering the adrenal medulla to release epinephrine.

Cortisol

A steroid hormone released by the adrenal glands that has a half-life of $60$ to $90$ minutes.

Epinephrine

An amino acid-derived hormone triggered by neural stimuli that has a half-life of approximately $1$ minute and regulates the fight-or-flight response.

Thyroxine

An amino acid-derived hormone produced by the thyroid gland to regulate metabolic rates.

Homeostasis

The maintenance of stable internal conditions within the body through the coordinated actions of the endocrine and nervous systems.