Chapter 16: Amino Acids, Proteins, and Enzymes

Structural Protein

Structural Protein

It provides structural components.

Contractile Protein

It makes muscle moves.

Transport Proteins

They carry essential substances throughout the body

Storage Proteins

They store nutrients.

Hormone Proteins

They regulate body metabolism and the nervous system.

Enzyme Proteins

They catalyze biochemical reactions in the cells.

Protection Proteins

They recognize and destroy protein substances.

Amino Acids

These are the molecular building blocks of proteins.

Isoelectric Point

The pH at which an amino acid exists in an ionized form with an overall net charge of zero.

Nonpolar amino acids

These acids have hydrogen, alkyl, or aromatic R groups, which make them hydrophobic.

Polar amino acids

These acids have R groups that interact with water, which makes them hydrophilic.

acidic amino acid

The R group of a polar ______ contains a carboxylate group

basic amino acid

The R group of a polar _____ contains an amino group, which ionizes to give an ammonium ion.

isoelectric point (pI)

An amino acid with positive and negative charges and thus an overall neutral charge forms only at a certain pH called the _____.

5.1 to 6.3. L

The pI values for nonpolar and polar neutral amino acids are from pH _______.

pH 3

The pI values of the acidic amino acids are around ____, and the carboxylic acid group in the R groups is not ionized.

pH 7.6 - 10.8

The pI values of basic amino acids are typically higher than physiological pH values, ranging from ____.

Peptide Bond

An amide bond forms when the —COO- group of one amino acid reacts with the —NH3+ group of the next amino acid.

peptide

The linking of two or more amino acids by peptide bonds forms a _____.

Dipeptide

Two amino acids form this.

Tripeptide

Three amino acids form this.

Tetrapeptide

Four amino acids form this.

Pentapeptide

A chain of five amino acids form this.

Polypeptide

A chain of multiple amino acids.

Primary Structure of Protein

The particular sequence of amino acids is held together by peptide bonds.

insulin

The first protein to have its primary structure determined was ____, which was accomplished by Frederick Sanger in 1953.

Frederick Sanger

The first protein to have its primary structure determined was insulin, which was accomplished by __________ in 1953.

secondary structure of a protein

This structure describes the type of structure that forms when amino acids form hydrogen bonds within a polypeptide or between polypeptide chains.

alpha helix

In an _____, hydrogen bonds form between the oxygen of the C=O groups and the hydrogen of N—H groups of the amide bonds in the next turn of the ɑ helix.

beta-pleated sheet

In a _____, hydrogen bonds form between the oxygen atoms in the carbonyl groups in one section of the polypeptide chain and the hydrogen atoms in the N—H groups of the amide bonds in a nearby section of the polypeptide chain.

Collagen

It makes up as much as one-third of all proteins in vertebrates. It is found in connective tissue, blood vessels, skin, tendons, ligaments, the cornea of the eye, and cartilage.

triple helix

The strong structure of collagen is a result of three polypeptides woven together like a braid to form a _____.

Tertiary Structure of Protein

The folding of the secondary structure of a protein into a compact structure that is stabilized by the interactions of R groups.

Hydrophobic interactions

These are interactions between two nonpolar amino acids that have nonpolar R groups.

Hydrophilic interactions

These are attractions between the external aqueous environment and the R groups of polar amino acids that are pulled to the outer surface of globular proteins where they form hydrogen bonds with water.

Salt bridges

These are ionic bonds between ionized R groups of basic and acidic amino acids.

Hydrogen bonds

These form between the H of a polar R group and the O or N of another amino acid.

Disulfide bonds

These are covalent bonds that form between the —SH groups of cysteines in a polypeptide chain.

Quaternary Structure of Protein

A protein structure in which two or more protein subunits form an active protein

Hemoglobin

A globular protein that transports oxygen in the blood, consists of four polypeptide chains.

141

two 𝛼-chains of hemoglobin has ______ amino acids.

146

two 𝜷-chains of hemoglobin has ______ amino acids.

Myoglobin

A single polypeptide chain with a molar mass of 17 000, has about one-fourth the molar mass of hemoglobin.

Globular Proteins

Group of proteins that have e compact, spherical shapes because sections of the polypeptide chain fold over on top of each other due to the various interactions between R groups.

Fibroid Proteins

These are proteins that consist of long, thin, fiber-like shapes. They are typically involved in the structure of cells and tissues.

𝛼-keratins

These are the proteins that makeup hair, wool, skin, and nails. In hair, three helices coil together like a braid to form a fibril.

𝜷-keratins

These are the type of proteins found in the feathers of birds and scales of reptiles.

Denaturation of Proteins

• It occurs when there is a change that disrupts the interactions that stabilize the secondary, tertiary, or quaternary structure.

• It also occurs by adding certain organic compounds or heavy metal ions or by mechanical agitation.

Enzymes

These are biological catalysts that are needed for most chemical reactions that take place in the body.

Catalyst

It increases the reaction rate by changing the way a reaction takes place but is itself not changed at the end of the reaction.

uncatalyzed reaction

An _____ in a cell may take place eventually, but not at a rate fast enough for survival.

Substrates

The molecule that reacts in the active site in an enzyme-catalyzed reaction.

Active site

A pocket in a part of the tertiary enzyme structure that binds substrate and catalyzes a reaction.

Enzyme–Substrate Complex

It is formed when there’s a combination of an enzyme and a substrate within the active site that provides an alternative pathway with lower activation energy.

Lock-And-Key Model

• It described the active site as having a rigid, nonflexible shape.

• According to this theory, the shape of the active site was analogous to a lock, and its substrate was the key that specifically fit that lock.

Induced-Fit Model

• In the dynamic model of enzyme action, the flexibility of the active site allows it to adapt to the shape of the substrate.

• At the same time, the shape of the substrate may be modified to better fit the geometry of the active site.

Oxidoreductases

These are for oxidation–reduction reactions.

Oxidases

_____ oxidize a substance.

Reductases

____ reduce a substance.

Dehydrogenases

_____ remove 2H atoms to form a double bond.

Transferases

Transfer a group between two compounds.

Transaminases

____ transfer amino groups.

Kinases

____ transfer phosphate groups.

Hydrolases

For hydrolysis reactions.

Proteases

They hydrolyze peptide bonds in proteins.

Lipases

They hydrolyze ester bonds in lipids.

Carbohydrases

They hydrolyze glycosidic bonds in carbohydrates.

Phosphatases

They hydrolyze phosphodiester bonds.

Nucleases

They hydrolyze nucleic acids.

Lyases

Add or remove groups involving a double bond without hydrolysis.

Isomerases

Rearrange atoms in a molecule to form an isomer

Carboxylases

_____ add CO2.

Deaminases

_____ remove NH3.

Isomerases

These convert cis to trans isomers or trans to cis isomers.

Epimerases

These convert D to L stereoisomers or L to D.

Ligases

Form bonds between molecules using ATP energy.

Synthetases

These combine two molecules.

activity

The ____ of an enzyme describes how fast an enzyme catalyzes the reaction that converts a substrate to a product.

optimum temperature

Enzymes are most active at _______, which is 37 °C, or body temperature, for most enzymes.

optimum pH

Enzymes are most active at their ____, the pH that maintains the proper tertiary structure of the protein.

Inhibitors

Kinds of molecules that cause enzymes to lose catalytic activity.

reversible inhibitor

An enzyme with a _____ can regain enzymatic activity.

irreversible inhibitor

An enzyme attached to an ____ loses enzymatic activity permanently.

Competitive Inhibitor

It has a chemical structure and polarity that is similar to that of the substrate.

Noncompetitive Inhibitor

It does not resemble the substrate and does not compete for the active site. It binds to a site on the enzyme that is not the active site.

Irreversible Inhibition

a molecule causes an enzyme to lose all enzymatic activity. Most irreversible inhibitors are toxic substances that destroy enzymes.

Irreversible Inhibition

It forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from binding to the active site or prevents catalytic activity.