Protein and Enzyme Lecture Practice Flashcards

A set of vocabulary flashcards covering amino acid classifications, protein structural levels, functional properties in food science, and key industrial enzymes.

Primary Structure

The linear assembly and precise sequence of $\alpha$-amino acids in a peptide chain.

Secondary Structure

Structural types like the $\alpha$-helix and $\beta$-sheet, held together by hydrogen bonding between amido-hydrogen and carbonyl groups.

Tertiary Structure

The full folding of a primary sequence into a compact 'globular' 3D structure via intramolecular forces like dispersion forces, hydrogen bonds, ionic bridges, and covalent disulfide bridges.

Quaternary Structure

A macro structure formed when a number of polypeptide subunits come together via intermolecular forces, such as in Hemoglobin.

Acidic Amino Acids

Amino acids that include Aspartic acid and Glutamic acid, both containing an extra $-COOH$ group.

Basic Amino Acids

Amino acids containing nitrogen-rich side chains, categorized as Histidine, Arginine, and Lysine.

Branched-Chain Amino Acids (BCAAs)

A group of non-polar amino acids consisting of Valine, Leucine, and Isoleucine.

Aromatic Amino Acids

Amino acids containing a ring structure, specifically Phenylalanine, Tyrosine, and Tryptophan.

Cysteine

A special amino acid that contains a thiol ($-SH$) group and is capable of forming disulfide bonds.

Proline

The only cyclic amino acid whose side chain loops back to bond with the amino group, making it a secondary amine.

Glycine

The smallest amino acid.

Tryptophan

The largest amino acid.

Iso-electric point (pI)

The specific $pH$ at which a protein's net charge is exactly zero, resulting in minimum solubility.

Denaturation

The process where a protein's ordered structure is chemically or physically altered, leading to decreased solubility and loss of biological activity.

Viscosity

The resistance to flow, which is a critical physical functionality for food consistency in products like yogurt or milkshakes.

Gelation

The transformation of a viscous fluid into a viscoelastic 3D network, often induced by heating or cooling.

Proteases

A class of enzymes that hydrolyze peptide bonds in proteins to form smaller peptides and amino acids, including examples like Pepsin, Trypsin, and Papain.

Rennet

An enzyme used in cheese manufacturing that specifically cleaves the $Phe_{105}-Met_{106}$ peptide linkage of $\kappa$-casein.

Amylases

Enzymes that hydrolyze polysaccharides (starch) into smaller units like maltose, dextrin, and glucose.

Pectinases

Enzymes that hydrolyze galacturonic acid linkages in plant cell walls, used for fruit ripening and juice clarification.

Lipases

Enzymes that reversibly hydrolyze ester bonds in triglycerides to form free fatty acids and glycerol.

Polyphenol Oxidase (PPO)

An enzyme that catalyzes the oxidation of phenolic compounds into quinones, causing enzymatic browning in fruits and vegetables.

Immobilized Enzymes

Enzymes attached to a solid matrix (like alginate beads) to allow for reuse and to avoid the need for thermal inactivation in the final food product.

Casein

The milk protein fraction (approx. $80\%$) that forms spherical micelle structures stabilized by colloidal calcium phosphate.

Whey Proteins

The milk protein fraction (approx. $20\%$) consisting of dissolved globular proteins like $\beta$-lactoglobulin and $\alpha$-lactalbumin.

Gluten

A water-insoluble matrix in wheat flour composed of Gliadin and Glutenin, providing viscoelasticity to bread dough.

Gliadin

A component of gluten that is extractable by ethanol and contains secondary structures such as $\beta$-spirals.

Gelatin

A protein-derived gelling agent produced by the thermal extraction of collagen from animal bones and connective tissues.

how well a substance can dissolve in a liquid (usually water)

At the isoelectric point (pI), solvation is lowest.

This means:

• The protein has no overall charge.

• Protein molecules stick to each other instead of water.

• They don't dissolve well, so solubility is lowest.