Proteins and Amino Acids Lecture: Chapter 16

Flashcards covering the classification, structure, and function of proteins and amino acids, including enzyme kinetics and inhibition.

Proteins

Polymers made from $20$ different amino acids that form structural components, act as enzymes, and transport substances like oxygen in the blood.

$\alpha$-carbon

The central carbon atom of an amino acid bonded to a hydrogen atom, an ammonium group ($-NH_3^+$), a carboxylate group ($-COO^-$), and an R group.

Nonpolar Amino Acids

Amino acids classified as hydrophobic with hydrocarbon side chains where the R group is H, alkyl, or aromatic.

Polar Amino Acids

Amino acids classified as hydrophilic with R groups containing a hydroxyl ($-OH$), a thiol ($-SH$), or an amide.

Acidic Amino Acids

Amino acids where the R group is a carboxylate group ($-COO^-$).

Basic Amino Acids

Amino acids where the R group is an amine, which ionizes to form an ammonium ion.

Zwitterion

A molecule or ion, such as an amino acid, that possesses separate positively and negatively charged groups.

Isoelectric Point

The specific pH at which an amino acid or molecule carries no net electrical charge and is electrically neutral.

Peptide Bond

An amide bond formed when the $-COO^-$ group of one amino acid reacts with the $-NH_3^+$ group of the next amino acid.

N-terminus

The side of a peptide chain that contains the exposed ammonium group ($-NH_3^+$).

C-terminus

The side of a peptide chain that contains the exposed carboxylate group ($-COO^-$).

Essential Amino Acids

The $9$ amino acids that cannot be synthesized by the body and must be obtained through the diet.

Complete Proteins

Food sources like eggs, milk, meat, and fish that contain all of the essential amino acids.

Primary Structure

The specific sequence of amino acids in a protein held together by peptide bonds.

Alpha Helix ($\alpha$ helix)

A secondary protein structure shaped like a spiral staircase, held together by hydrogen bonds between the oxygen of $C=O$ groups and the hydrogen of $N-H$ groups.

Beta-Pleated Sheet ($\beta$-pleated sheet)

A secondary protein structure where hydrogen bonds between carbonyl oxygen atoms and amide hydrogen atoms bend the polypeptide chain into a sheet.

Triple Helix

A secondary structure consisting of three polypeptide chains woven together like a rope, typical of collagen found in connective tissue.

Tertiary Structure

The overall three-dimensional shape of a protein caused by interactions and cross-links between the R groups of the amino acid chain.

Salt Bridges

Ionic bonds that occur between the ionized R groups of basic and acidic amino acids, helping stabilize tertiary structure.

Disulfide Bonds

Covalent $-S-S-$ bonds formed between the $-SH$ groups of cysteine amino acids in a protein chain.

Quaternary Structure

The combination of two or more protein units, such as the four polypeptide subunits found in hemoglobin.

Sickle-Cell Anemia

A condition where the sixth amino acid in the $\beta$-chain of hemoglobin, glutamic acid, is replaced by valine, causing red blood cells to take a crescent shape.

Denaturation

The disruption of secondary, tertiary, or quaternary structures by agents like heat, acids, bases, or agitation, causing a loss of biological activity.

Enzymes

Proteins that act as biological catalysts by lowering the energy of activation for chemical reactions in the body.

Active Site

A specific region on an enzyme that fits the shape of a substrate and catalyzes its reaction.

Induced-Fit Model

A model of enzyme action where the flexible enzyme structure adjusts its shape specifically to bind the substrate for optimal catalysis.

Isoenzymes

Different forms of an enzyme, such as the $5$ forms of lactate dehydrogenase ($LDH$), that catalyze the same reaction in different tissues.

Optimum Temperature

The temperature at which an enzyme is most active, which is usually $37^ ext{o} ext{C}$ in humans.

Competitive Inhibitor

An inhibitor with a structure similar to the substrate that competes for the active site; its effect is reversed by increasing substrate concentration.

Noncompetitive Inhibitor

An inhibitor that binds to an enzyme away from the active site, altering the enzyme's shape and preventing substrate binding.

Irreversible Inhibitor

A molecule that forms a permanent covalent bond with an amino acid side chain, causing the enzyme to lose all catalytic activity.