7.6 Enzymes

Metabolic Pathways• Metabolic pathways are specific sequences of

enzyme-catalyzed reactions that often occur in chains or cycles

Glycolysis Calvin Cycle

Remember…

All living things MUST1. Grow2. Reproduce3. Respond to stimuli4. Maintain Homeostasis5. Nutrition6. METABOLISM – sum of all chemical reactions inside

the living organismEx: respiration, photosynthesis, digestion

Anabolism – the building of larger organic molecules (condensation reactions)

Catabolism –the breakdown of organic molecules (hydrolysis reactions)

Review Slide

The Induced-Fit Model

• The Induced-Fit Model is a more accurate portrayal of enzyme-substrate relationship– Substrate does not fit perfectly into enzyme until it binds

to active site– Once it binds the active site shape chages slightly, which

weakens the bonds within substrate– Weakened bonds lowers activation energy and allows

reaction to happen faster/easier

Activation Energy

Activation Energy is the energy necessary to break bonds and/or make new bonds

Enzymes lower AE by weakening the bonds in the reactants and allow reaction to take place easier/faster

Competitive Inhibition

• Competitive inhibition is when a molecule that is structurally similar to a substrate binds with the needed enzyme; the result is fewer reactions between the “true” substrate and enzyme; affects can be reduced by adding more substrate

• Ex: malonate can block succinate from binding with dehydrogenase during Kreb’s cycle

Non-Competitive Inhibition

• Non-competitive inhibition is when an inhibitor binds with the enzyme but not at the active site (instead at the allosteric site), however the result can be a change in the shape of the active site

• Ex: metal ions like Silver and Mercury bind to sulfur parts of R groups on amino acids which inhibits disulfide bonds and changes shape of proteins

Allosteric site

End-Product Inhibition• With assembly line metabolic reactions (metabolic

pathways) cells have developed a way to regulate enzyme activity so resources and energy are not wasted– When end products are abundant, the metabolic

pathway is shut down by inhibiting the action of the 1st enzyme

– Usually, inhibition is achieved when final product binds to 1st enzyme at allosteric site

– Then, when more product is needed, the 1st enzyme will be reactivated with removal of product at allosteric site