Protetin test A

Enzymatic activity

The protein function most directly described by "catalyze reactions"

Ferritin

The primary intracellular iron-storage protein in humans

R group (side chain)

The variable part of an amino acid that determines its identity

Dehydration synthesis (condensation)

The chemical process that links monomers together while releasing water

Carboxyl; amino

A peptide bond forms when the of one amino acid reacts with the of another, releasing water

Dipeptide

A chain of 2 amino acids

Primary structure

The linear sequence of amino acids in a polypeptide

Secondary structure

The folding of a polypeptide into alpha-helices and beta-pleated sheets, stabilized by backbone hydrogen bonds (C=O and N-H)

40-70%

The fraction of cell dry weight that proteins contribute

Enzymes

Used to break peptide bonds and separate individual amino acids in a protein

Hydrophobic interactions

The interaction most responsible for creating "water-free pockets" in folded proteins

Salt bridge

An attraction between oppositely charged side chains in tertiary protein structure

Thiol (-SH) groups on cysteine residues

The functional group involved in forming disulfide bridges

Quaternary structure

The overall shape formed by 2+ folded polypeptide subunits assembling together

Hemoglobin (HbA)

A tetramer with two alpha and two beta subunits that transports oxygen in the blood

Actin and myosin

The pair of proteins most directly associated with muscle contraction

ATP

The molecule that provides energy to power actin-myosin cycling

Protein

A folded, functional polypeptide chain (or chains) — distinguished from a simple polypeptide

Denaturation

The disruption of secondary, tertiary, and quaternary protein structure while leaving primary structure intact

Neutral pH (near physiological)

The condition that is NOT typically considered a protein denaturing agent

Heat denaturation

Disrupts noncovalent interactions stabilizing higher-order protein structure

Mechanical agitation

Denatures proteins by disrupting weak interactions and promoting unfolding/foaming (e.g., beating egg whites)

Detergents

Denature proteins by inserting into hydrophobic regions and disrupting hydrophobic packing

~70% alcohol

A better disinfectant than 95% alcohol because it penetrates cells better and denatures internal proteins more effectively

Limiting amino acid

The essential amino acid present in the smallest amount relative to need in a food

Essential amino acids

Amino acids that must be obtained in the diet because humans cannot synthesize enough of them

8,000

The number of distinct tripeptides possible from 20 standard amino acids (20³), assuming order matters and repetition is allowed

Single amino acid substitution

Can disrupt protein function by altering folding and changing the protein's 3D shape and active/binding sites

Secondary structure

Involves alpha-helices and beta-sheets stabilized mainly by backbone hydrogen bonds

Native state

The naturally folded, functional 3D conformation of a protein under physiological conditions

Albumin

The protein associated with maintaining osmotic concentration of the blood

Enzyme

A protein that catalyzes biochemical reactions as a biological catalyst

Sodium-potassium pump

A membrane transport protein

Chaperones (chaperonins)

Proteins that help newly made polypeptides fold correctly

Heat shock proteins (HSPs)

Stress-induced molecular chaperones that help prevent protein aggregation and refold proteins

Embryogenesis (developmental patterning)

The life stage explicitly linked to the importance of the Notch transmembrane receptor pathway

Hemoglobin

An example of a transport protein — carries oxygen in the blood

Amylase → starch

The most accurate enzyme-substrate pairing as a digestion example

Homeostasis

Helps prevent denaturation that would reduce protein function, explaining why proteins must operate within limited temperature and pH ranges

Prions

Associated with transmissible spongiform encephalopathies (e.g., "mad cow disease") — an example of protein misfolding disease

Fibrous protein

A protein (e.g., collagen, keratin) most likely to function as a structural component

Peptide bond

A covalent bond formed by dehydration synthesis between the carboxyl group of one amino acid and the amino group of another

Aquaporins

The protein explicitly connected to water transport through membranes

C-terminus

The end of a polypeptide where new amino acids are generally added during synthesis

Tertiary structure

The precise 3D folding driven by R-group interactions (hydrophobic, ionic, H-bonds, disulfide bridges)

Denaturation

Loss of functional 3D structure (usually secondary/tertiary/quaternary) without breaking primary peptide bonds

Urea + high-speed spinning (shear)

The method used in the Ted-Ed "How to Un-cook an Egg" talk to refold denatured egg proteins

Shear stress from velocity gradient

The physical reason rapid spinning helps refold denatured egg-white proteins — repeatedly stretches and relaxes proteins, encouraging native shape

Collagen converting to gelatin

The process that makes "low-and-slow" barbecue cuts tender over long cook times

Gases binding myoglobin (nitric oxide/carbon monoxide)

The explanation for the "smoke ring" seen in barbecue meat