Learning Outcomes

B11- analyse the roles of enzymes

in biochemical reactions•explain the following 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 (e.g., induced fit)

What do you know about enzymes?

• Definition?

• Function?

• Some examples in the body?

• Type of molecule?

• Where are they made?

Thinking Question…..

What are some chemical reactions that occur in the human body

• To break down substances?

• To synthesize substances?

Metabolic Pathways

• Cellular metabolism consists of many different chemical reactions

• Reactions result in synthesis or breakdown of substances

• Most reactions occur in several steps (metabolic pathways)

• Each reaction is catalyzed by a different enzyme

A B C DE1 E2 E3

ENZYMES

• Are usually proteins

• Each have a specific shape

• Are specific for one reaction

• Act as organic catalysts

• Are not used up in the reaction

SUBSTRATES

• Are the reactants in enzyme-catalyzed reactions

• May be broken down (ex. hydrolysis), or combine with other substrates (synthesis)

• Are used up in the reaction to produce products

What are some examples of substrates…

• Of digestive enzymes?

• Of the enzyme DNA polymerase?

• Of enzymes in the mitochondria?

• Of hydrolytic enzymes in the lysosomes?

Examples of enzymes

• Polymerases - catalyze polymerization reactions

• Catalase - breaks down hydrogen peroxide (H2O2)

• Digestive enzymes - amylase, lipase, lactase, etc.

(names usually end in “ase”)

Enzyme activity

• All chemical reactions have a specific energy of activation, needed to get the reaction started

• Enzymes lower the energy of activation of a chemical reaction, allowing the reaction to take place with a lower input of energy (at body temperature)

Fig. 6.5

• Enzymes are specific for a particular substrate due to their shape

Lock and key model

• The active site of an enzyme binds to the substrate like a lock-and-key

• An enzyme - substrate complex is formed

Induced fit model

• Sometimes the active site of an enzyme may change shape to fit the substrate

Fig. 6.7

• The reaction occurs while the substrate is attached to the enzyme• After the reaction is complete, the products are released• The enzyme is now free to combine with another molecule of

substrate

TA p113

Fig. 6.6