Cell Biology:Enzymes

Lesson 1 – Enzyme Theory and Function(Inquiry into Life pg. 106-109)

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

Animation 1 Animation 2

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

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 ABCD A = Beginning substrate B,C = intermediate products/reactants D = final product Each step requires a specific enzyme

Pathway Animation 1 Pathway Animation 2

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