INTRODUCTION to PROTEINS

A collection of vocabulary flashcards covering the key terms and concepts from the protein lecture notes.

Protein

A naturally occurring polymer of amino acids linked by peptide bonds; the most abundant organic molecules in living systems; the term derives from the Greek proteios meaning holding the first place.

Amino acid

Organic compounds containing an amino group (-NH2) and a carboxyl group (-COOH) attached to an α-carbon; more than 300 exist, but 20 are standard.

Monomer

A single unit that can join with others to form polymers.

Polymer

A large molecule made up of repeating monomer units; proteins are polymers of amino acids.

Peptide bond

Bond formed between amino acids through a condensation reaction between the carboxyl group of one amino acid and the amino group of another.

Structural protein

Proteins that provide strength and structure to cells, tissues, and organs (e.g., elastin, collagen).

Enzyme

Proteins that catalyze biochemical reactions in the body.

Transport protein

Proteins responsible for the transport of metabolites; also involved in respiration.

Regulatory protein

Proteins that regulate metabolic pathways (e.g., insulin).

Defence protein

Proteins that protect the body from infection and other toxins (antibodies/immunoglobulins).

Muscle protein

Proteins required for mechanical work (contractile proteins).

pH regulation by proteins

Proteins regulate the pH of various body fluids, as well as osmotic pressure and electrolyte balance.

Nucleoprotein

Conjugated protein formed by histone combined with RNA or DNA.

Chromoprotein

Conjugated protein containing a colored prosthetic group (e.g., heme, riboflavin).

Phosphoprotein

Conjugated protein that includes a phosphate group (e.g., milk casein).

Glycoprotein

Conjugated protein containing carbohydrate moieties (amino sugars, sulfates, sugar acids).

Lipoprotein

Conjugated protein consisting of proteins bound to lipids; found in brain and membranes.

Metalloprotein

Conjugated protein with metal ions (e.g., Fe, Co, Zn) attached.

Simple protein

Proteins composed only of amino acids, with no non-protein prosthetic group.

Conjugated protein

Proteins that contain non-protein prosthetic groups (e.g., glycoproteins, lipoproteins, nucleoproteins, metalloproteins, phosphoproteins).

Derived protein

Denatured or degraded products of simple or conjugated proteins.

Coagulated protein

Denatured proteins formed by heat, acids, or alkalies.

Protean (proteins)

First hydrolysis products of proteins produced by enzymes or acids.

Metaprotein

Second-stage products of protein hydrolysis obtained under stronger acids.

Primary structure

The linear sequence of amino acids in a protein, forming its backbone.

Secondary structure

Spatial arrangement of the polypeptide chain via twisting/folding; includes α-helix and β-sheet.

α-helix

A common spiral secondary structure stabilized by hydrogen bonds.

β-sheet

Secondary structure formed by hydrogen bonds between neighboring segments; can be parallel or antiparallel.

Tertiary structure

Three-dimensional arrangement of a protein; hydrophobic interior and hydrophilic exterior.

Quaternary structure

Assembly of two or more polypeptide chains (subunits) into a functional complex; e.g., hemoglobin.

Oligomer

Two or more polypeptide chains held together in a protein.

Monomer

A single peptide chain; building block of polymers.

Haemoglobin

A protein with four polypeptide chains (two α and two β) and heme groups; example of a quaternary protein.

Globular protein

Globular, water-soluble proteins with roughly spherical shapes (e.g., albumins, globulins).

Fibrous protein

Fiber-like, insoluble proteins (e.g., collagen, elastin, keratins).

Histone

Basic proteins associated with DNA; typically nucleoprotein components.

Lectin

Carbohydrate-binding proteins involved in cell–cell interactions; example is agglutinin.

Simple protein

Proteins consisting only of amino acids without prosthetic groups.

Glycoprotein

Conjugated protein with carbohydrate groups; example of attached sugars.

Amino acid

Amino acids are categorized by structure, polarity, and essentiality, and form the building blocks of proteins.

Amino acid (essential vs. nonessential)

Essential amino acids cannot be synthesized by the body and must be obtained from the diet; nonessential amino acids can be synthesized by the body.

Aliphatic amino acid

Non-aromatic amino acids with aliphatic side chains (e.g., alanine, glycine, valine, leucine, isoleucine).

Aromatic amino acid

Amino acids containing an aromatic ring (phenylalanine, tyrosine, tryptophan).

Hydroxyl-containing amino acid

Amino acids with hydroxyl groups (serine, threonine).

Sulfur-containing amino acid

Amino acids containing sulfur (cysteine, methionine).

Acidic amino acid

Amino acids with acidic side chains (glutamic acid, aspartic acid).

Basic amino acid

Amino acids with basic side chains (histidine, lysine, arginine).

Imino acid

Proline; an imino acid with a secondary amine.

Nonpolar (hydrophobic) amino acid

Amino acids with nonpolar R groups; lack charge (e.g., alanine, valine, leucine).

Polar (hydrophilic) amino acid

Amino acids with polar or charged R groups (e.g., glycine, serine, cysteine).

Essential amino acid

Amino acids that cannot be synthesized by the body and must be obtained from the diet (e.g., valine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, histidine in children, arginine).

Nonessential amino acid

Amino acids synthesized by the body and not required from the diet (e.g., glycine, alanine, serine, cysteine, aspartate, glutamate, glutamine, tyrosine, proline).

Denaturation

Unfolding of a protein due to heat or chemicals; loss of biological activity.

Biuret test

A test for proteins using copper sulfate in alkaline solution; violet color indicates presence of peptide bonds.

TCA precipitation

Precipitation of proteins after addition of trichloroacetic acid.

Xanthoproteic reaction

Nitration of aromatic amino acids giving yellow color; turns orange with alkali.

Millon's test

Proteins react with mercuric sulfate in the presence of nitrite and sulfuric acid to yield a red color.

Kwashiorkor

Severe protein malnutrition in children (1–4 years); edema, skin changes, enlarged liver; causes include poor maternal health and poor diet; cure with protein-rich foods.

Marasmus

Severe undernutrition in infants under 1 year; wasting; treat with protein-rich diet.

Nutritional edema

Swelling due to protein deficiency; can occur with prolonged protein deprivation.