Chapter 20- Enzymes and Vitamins

Enzyme

Biological catalysts that

• increase rate of reaction

• Not changed in the process

• Lowers the AE of the reaction

Enzymes increase the rate of reaction by

Reducing the AE

Carbonic Anhydrase

Catalyzes the reverse reaction, converting bicarbonate and H+ to CO2 and H2O

Substrates

The reactant consumed during a catalytic reaction. Enzymes binds a small group of reacting molecules called…

Active Site

Tertiary structure, where one or more small groups of substrates bind to create a chemical reaction.

Active site interacting with functional groups of the substrate to form…

Hydrogen Bonds, salt bridges, and hydrophobic interactions.

Absolute Enzyme

• Catalyzes ONE type of reaction for ONE substrate.

Example of absolute enzyme

Urease: catalyzes only the hydrolysis of urea.

Group Enzyme

Catalyzes ONE type of reaction for SIMILAR substrates.

Example of group enzyme

Hexokinase: adds a phosphate group to hexoses

Linkage Enzyme

Catalyzes ONE type of reaction for a SPECIFIC type of bond

Enzyme-Substrate (ES) complex

• combination of enzyme and substrate

• Provides an alternative pathway for the reaction with lower AE

Enzyme-Product (EP) Complex

When amino acid R groups catalyze the reaction and forms…

Lock-and-key model

Rigid substrate binding to a rigid enzyme, much like a key fitting into a lock

Induced-fit model

A more dynamic model of enzyme action, states that the active site is flexible enough to adapt to the shape of the substrate.

Oxidoreductases

Catalyze oxidation-reduction reactions

Transferases

Catalyze the transfer of a functional group between TWO compounds

Hydrolases

Catalyze hydrolysis (add H2O) reactions that split a compound into TWO products

Lysases

Catalyze the addition or removal of a group without hydrolysis

Isomerases

Catalyze the rearrangement (isomerization) of atoms within a substrate

Ligases

Catalyze the joining of two substrates, using ATP energy

Aminase

Adds NH3

Synthetase

Combines two molecules to make a new compound

Dehydrogenase

Removes two H atoms to form a double bond

Factors affecting enzyme activity

• temperature (optimum @ 37C)

• pH (optimum @ 7.4)

• Enzyme concentration

• Substrate concentration

Allosteric Enzymes

Changes the shape of the enzyme, which causes a change in the shape of the active site.

• positive: allows the substrate to bind more effectively

• Negative: prevent the proper binding of the substrate, which decreases the rate of the catalyzed reaction.

Zymogens

Inactive enzyme precursors that require a biochemical change to become active enzymes. They are synthesized and stored in an inactive form to prevent undesired activity, and activation occurs typically through the cleavage of specific peptide bonds

• digestive enzymes, protein hormones such as insulin

Phosphorylation

The process of adding a phosphate group (PO4) to a molecule, typically a protein, which can change the protein's function and activity. This modification is crucial in regulating enzyme activity, signaling pathways, and energy transfer in cells.

Covalent Modification

Enzyme activity is modified by covalent bonds to a group on the polypeptide chain that are formed or broken. IS REVERSIBLE !!

• ex: phosphorylase kinase

Isoenzymes

Different forms of an enzyme that catalyze the same reaction but differ in structure, kinetic properties, and regulatory mechanisms. They allow for variation in enzyme activity in different tissues or under different physiological conditions.

Reverse Inhibitors

• cause a loss of enzyme activity that can be restored.

• Act different ways but does not form covalent bonds with the enzyme

Competitive Inhibtors

• competes with the substrate for the active site

• Has its effect REVERSED by increasing substrate concentration

• Similar chemical structure and polarity similar to the substrate

• Ex: antimetabolites

Noncompetitive Inhibitors

• does not compete for the active site

• Distorts the shape of the enzyme, which prevents the binding of the substrate at the active site. CANNOT be reversed by adding more substrate

• Different structure from substrate

Irreversible inhibition

Enzyme activity is destroyed when

• the inhibitor covalently bonds with R groups of an amino acid that may be near the active site

• The inhibitor changes the shape of the enzyme, which prevents the substrate from entering the active site

Coenzyme

A cofactor (such as metal ions, required for some enzymes can become active) that is a small organic molecule such as a vitamin.

Vitamins

Organic molecules that are essential for normal health and growth, obtained from diet.

Thiamine, B1

• water soluble

• Found in: liver, yeast, whole grain bread, cereals, and milk

• Necessary to avoid: beriberi, fatigue, poor appetite, and weight loss

Riboflavin, B2

• water soluble

• Found in liver, beef, chicken, eggs, green leafy vegetables, dairy foods, peanuts, and whole grains

• Necessary to avoid: dermatitis, dry skin, red, sore tongue, and cataracts

Niacin, B3

• water soluble

• Found in brewer’s yeast, chicken, beef, fish, liver, brown rice, and whole grains

• Necessary to avoid: pellagra, dermatitis, muscle fatigue, loss of appetite, diarrhea, and mouth sores

Pantothenic Acid, B5

• water soluble

• Found in: salmon, beef, liver, eggs, brewer’s yeast, whole grains, and fresh vegetables

• Necessary to avoid: fatigue, retarded growth, muscle cramps, and anemia

Pyridoxine, B6

• water soluble

• Found in meat, liver, fish, nuts, whole grains, and spinach

• Necessary to avoid: dermatitis, fatigue, anemia, and retarded growth

Folic Acid, B9

• water soluble

• Found in green leafy vegetables, beans, meat, seafood, yeast, asparagus, and whole grains enriched with folic acid

• Necessary to avoid: Abnormal red blood cells, anemia, intestinal tract disturbances, loss of hair, growth impairment, and depression

Cobalamin, B12

• water soluble

• Found in liver, beef, kidney, chicken, fish, and milk products

• Necessary to avoid: pernicious anemia, malformed red blood cells, and nerve damage

Ascorbic Acid, C

• water soluble

• Found in blueberries, citrus fruits, strawberries, cantaloupe, tomatoes, peppers, broccoli, cabbage, and spinach

• Necessary to avoid: scurvy, bleeding gums, weakened connective tissues, slow-healing wounds, and anemia

Biotin, H

• water soluble

• Found in liver, yeast, nuts, and eggs

• Necessary to avoid: dermatitis, loss of hair, fatigue, anemia, and depression

Water-Soluble Vitamins

• soluble in aqueous solutions and cannot be stored in the body

• Are cofactors for many enzymes

• Are excreted in urine each day

• Are easily destroyed by heat, oxygen, and UV light

Retinol, Vitamin A

• Fat soluble

• Antioxidant

• Is needed for retinol (vision) and synthesis of RNA

• Necessary to avoid: night blindness, immune system repression and slowed growth

Cholecalciferol, Vitamin D

• fat soluble

• Is synthesized in skin exposed to sunlight

• Regulates the absorption of phosphorus and calcium during bone growth

• Necessary to avoid: weakened bones

Tocopherol, Vitamin E

• fat soluble

• Antioxidant in cells

• Found in whole grains and vegetables

• Necessary to avoid: hemolysis and anemia

Menaquinone, Vitamin K

• fat soluble

• Needed for the synthesis of zymogens for blood clotting

• Necessary to avoid: prolonged bleeding time and bruising