Cell Biology: Enzymes Lesson 1 – Enzyme Theory and Function ( Inquiry into Life pg )

Today’s Objectives  Analyze the roles of enzymes in biochemical reactions, including:  Explain the terms: metabolism, enzyme, substrate, coenzyme, activation energy  Use graphs to identify the role of enzymes in lowering the activation energy of a biochemical reaction  Explain models of enzymatic action (eg. Induced fit)  Differentiate between the roles of enzymes and coenzymes in biochemical reactions  Identify the role of vitamins as coenzymes  Identify the thyroid as the source gland for thyroxin, and relate the function of thyroxin to metabolism

Definitions  Metabolism:  A term which refers to all the chemical reactions of a cell  Enzyme:  A protein catalyst (speeds up a certain reaction) (not used up)  Apoenzyme:  Protein portion of an enzyme  Its shape accounts for an enzyme’s ability to run only a single type of reaction  Coenzyme:  Non-protein portion of an enzyme  Can donate or accept atoms to or from a reaction  Our body often cannot make coenzymes, so we need them in our diet  Example: vitamins

Definitions  Holoenzyme:  Enzyme that requires a coenzyme to function  Enzyme + coenzyme = holoenzyme

Definitions  Substrate:  A reactant (raw material) in an enzyme-controlled reaction  Activation Energy:  Many reactions will not occur unless energy is added to start them off  This input energy is called activation energy or energy of activation (Ea)  Example: a piece of woods needs an input of energy to start it burning

Enzyme Function  Enzymes bring the substrate close enough together so that the reaction can occur without as much activation energy

Enzyme Theory  Lock and Key Theory of Enzyme Action:  1) In order for a reaction to occur, the reactants (substrates) must be brought close together  2) The substrates bond to the active site on the enzyme, and are brought close together. Sometimes the active site changes shape to bring the substrates together (this is also called the induced fit model  3) The reaction occurs and the product(s) are released. The enzyme goes back to its normal tertiary configuration (shape)

Lock and Key Theory

Review of Lock and Key  According to this analogy, an enzyme acts like a key by combining with a specific substrate and “unlocking” the substrate for further activity in the cell  The key (enzyme) must have the correct shape to fit the lock (substrate)  After the lock has been opened (reaction takes place), the key (enzyme) is freed and unchanged so that it may be used repeatedly in the same manner  The portion of the enzyme that is involved in the reaction is called the active site

Review of Lock and Key

Metabolic Pathway (pg. 106)  Metabolic reactions often require more than one step to produce the final product  This is called a metabolic pathway  A series of reactions will take place, where the products of the first reaction become the substrate for the second reaction, and so on ABCDABCD  A = Beginning substrate  B,C = intermediate products/reactants  D = final product  Each step requires a specific enzyme

Role of Coenzymes  Coenzymes are the non-protein portion of an enzyme  Can participate in a reaction by accepting or contributing atoms to the reaction

Significance of Vitamins  Many coenzymes are vitamins  Our bodies cannot make many of those that we require, we must get them in our diet  Vitamins are vital for efficient metabolism  We only need small quantities because as part of enzymes, they can be used over and over again

Thyroxin  Thyroxin is a protein hormone that is secreted into the blood by cells of the thyroid gland  The thyroid gland, located in the neck, accumulates iodine in order to produce thyroxin  Thyroxin attaches to receptor sites on the surfaces of our body cells where it governs the rate that cells consume oxygen, thus having an overall impact on the body’s metabolism

Thyroxin  Thyroxin does not have a target organ; it stimulates most of the cells of the body to metabolize at a faster rate  The number of respiratory enzymes increases, as does oxygen intake  Thyroxin helps regulate growth and development  Thyroglobulin is the storage form of thyroxin  Iodine is required for thyroglobulin to be made  If no iodine, no thyroxin