8.1: Metabolism

Definition Metabolism is the term used to describe the sum of all the chemical reactions occurring within living cells. All metabolic reactions include: A series of reactions forming the metabolic pathway – this is called a chain of reactions Sometimes metabolic pathways for a cycle rather than a straight chain What metabolic reaction do you know? Plant or animal? Respiration  meal worm lab.

Investigating respiration in mealworms (larvae of the beetle Tenebrio molitor)

Enzymes & activation energy Enzymes lower the activation energy of a reaction. Reactants in this case include a substrate binding to the active site of an enzyme, before being converted into products.

Enzyme inhibition Inhibitors prevent or hinder the action of an enzyme. There are two categories of enzyme inhibition: Competitive inhibition Non-competitive inhibition

Competitive inhibition Molecule that actively competes for the active site. Decreases rate of reaction. e.g. sulphanilamide a drug used to kill bacteria during infection. Folic acid essential as a co-enzyme for bacteria. Produced by enzyme action on para-aminobenzoic acid (PABA). Sulphanilamide competes with PABA and blocks enzyme. Bacteria do not have folic acid, bacteria die. Molecules other than substrates can affect the active site. The are inhibiting the action of the enzyme.

Non-Competitive inhibition Molecule interacting with enzyme resulting in a change of the active site. e.g. metallic ions (Mg) Can be reversible or non-reversible depending on the nature of the inhibitor Site the inhibitor binds to is called allosteric site (inhibitors also referred to as allosteric inhibitors). By binding the the allosteric site, the inhibitor causes the active site to change shape. The allosteric site can be anywhere on the enzyme. Does not have to be on the active site. There are examples of allosteric interactions activating enzymes, as well as the examples of inhibition.

End-Product inhibition End product inhibition is used to regulate the production of a given molecule. The initial substrate is a molecule that is altered in three steps by enzymes 1,2 and 3. The end product will combine with enzyme 1 to stop the reaction. Important process – cell only makes what it needs. Not wasting resources. Each stage of the process is catalysed by a specific enzyme. Once a specific quantity of the end product has been made the production line shuts down.

SKILL: Distinguish different types of inhibition from graphs Sketch graph, fig. 7 on pg. 376. Write a statement describing what is shown from this graph.

DBQ pg. 379 *rate = difference/time e.g. 4 degrees (19.4 – 18.8)/60 = 0.1