Lesson 10 Enzymes

noncompetitive inhibitor

-bind to another part of an enzyme (not the active site), causing an enzyme to change shape and making the active site less effective -heavy metal poisoning: binds to enzyme and alters function by altering 3D shape -ex: toxins, poisons, pesticides, and antibiotics

competitive inhibitors

-binds to the active site of an enzyme, competing with the substrate -ex: sarin nerve gas (covalently binds to R group of the amino acid serine at the active site of acetylcholinesterase-allows muscles to relax) & methanol (converted to formaldehyde by alcohol dehydrogenase, damages tissue / ingest methanol->intravenous infusion of ethanol to compete with methanol)

importance of enzyme activity regulation

-chemical chaos without tight regulation in cells' metabolic pathways -cell does this by switching on or off the genes that encode specific enzymes or by regulating the activity of enzymes (isolate in organelles)

how enzymes lower the Ea barrier

-enzymes catalyze reactions by lowering the Ea barrier -enzymes do not affect the change in free energy (∆G); instead, they hasten reactions that would occur eventually -more energy=less stable -breakdown into something more stable and release energy

activation energy barrier

-every chemical reaction between molecules involves bond breaking and bond forming -the initial energy needed to start a chemical reaction is called the free energy of activation, or activation energy (Ea) -activation energy often supplied in the form of heat from the surroundings

cooperativity

-form of allosteric regulation that can amplify enzyme activity -binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits -binding of active site stabilizes the shape of the other active sites on this quaternary structure -ex: oxygen binding to hemoglobin causes increased affinity of hemoglobin for O2 and O2 binding in remaining sites (hemoglobin has 4 O2 binding sites)

allosteric regulation

-may either inhibit or stimulate an enzyme's activity -occurs when a regulatory molecule binds to a protein at one site and affects the protein's function at another site -most allosterically regulated enzymes are made from polypeptide subunits -each enzyme has active and inactive forms: 1) the binding of an activator stabilizes the active form of the enzyme 2) the binding of an inhibitor stabilizes the inactive form of the enzyme -ex: enzymes in catabolic pathways inhibited by ATP, stimulated by ADP -don't confuse the active form of an allosteric enzyme with the active site of an enzyme -allosteric regulators: attractive drug candidates for enzyme regulation (inhibition of proteolytic enzymes called caspases may help management of inappropriate inflammatory responses

cofactors

-nonprotein enzyme helpers, required for proper active site function -may be: 1) inorganic- (like metal in ionic form) zinc, copper, iron, etc 2) organic- (coenzyme) vitamins, vitamin derivatives

ways the active site can lower an Ea barrier

-orienting substrates correctly -straining substrate bonds -providing a favorable microenvironment -covalently bonding to the substrate -usually a substrate interacts with the active site through hydrogen or ionic bonds

effects of local conditions on enzyme activity

-speed of enzyme activity influenced by: 1) substrate concentration-maximum substrate concentration saturates enzyme's active site 2) concentration of enzyme -an enzyme's activity can be affected by: 1) general environmental factors like temp and pH (affect 3D shape of the enzyme proteins) / optimal temp for most human enzymes=35-40 degrees C & most pH 6-8 2) chemicals that specifically influence the enzyme (cofactors)

enzymes

-speed up metabolic reactions by lowering energy barriers -an enzyme is a catalytic protein -hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme-catalyzed reaction

specific localization of enzymes within a cell

-structures within the cell help bring order to metabolic pathways -some enzymes act as structural components of membranes -in eukaryotic cells, some enzymes reside in specific organelles -ex: enzymes for cellular respiration are located in mitochondria

feedback inhibition

-the end product of a metabolic pathway shuts down the pathway -prevents a cell from wasting chemical resources by synthesizing more product than is needed -isoleucine production regulated by feedback inhibition to the allosteric enzyme called threonine deaminase

substrate specificity of enzymes

-the reactant an enzyme acts on is the enzyme's substrate -the enzyme binds to its substrate, forming an enzyme-substrate complex -the active site is the region on the enzyme where the substrate binds -induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction -specific enzymes will work on specific substrates (maltase catalyzes the conversion of maltose to glucose subunits & lactase catalyzes the conversion of lactose to glucose and galactose subunits) -R groups of amino acids in active site binds specific enzymes