C.1.1 Enzymes & Metabolism

Based on the 3rd edition biology textbook written by C.J. Clegg, Andrew Davis, Christopher Talbot

enzyme

mainly proteins (some are RNA) that function as biological catalysts

catalyst

a substance that speeds up the rate of a chemical reaction

Effective in small amounts and remain unchanged at the end of the reaction

metabolism

the total sum of reactions that occur throughout the body within each cell that provide the body with energy

= anabolism + catabolism

anabolism

the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions

ex: synthesis of proteins from amino acids, synthesis of polysaccharides from simple sugars, photosynthesis

catabolism

the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers

ex: hydrolysis of macromolecules into monomers in digestion, oxidation of substrates in respiration

substrate

the starting substance (reactant) in a reaction catalysed by an enzyme. It is the molecule that the enzyme reacts with

product

what the substrate is converted to in a reaction catalysed by an enzyme

active site

region of an enzyme molecule where the substrate molecule binds and catalysis occurs

enzyme-substrate (ES) complex

a temporary structure formed when a substrate binds to the active site of an enzyme

induced-fit

the binding of the substrate to the enzyme causes a change in the shape of the enzyme and the substrate, resulting in the proper alignment of the catalytic groups on its surface, which enables catalysis to take place

immobilized enzyme

an enzyme attached to an inert, insoluble material, enabling recovery, reuse and improved enzyme stability

activation energy

energy required by a substrate molecule before it can undergo a chemical change

extracellular enzyme

secreted by a cell that functions outside the cell

ex: chemical digestion in the gut

intermolecular enzymes

functions within the cell in which it was produced

endotherms

warm-blooded

ectotherms

cold-blooded

coupled reaction

when an exergonic reaction fuels an endergonic reaction

done in adenosine triphosphate (ATP)

metabolic pathway

sequence of enzyme-catalyzed biochemical reactions in cells and tissues

metabolism

consists of series of reactions in which the product of one reaction is an intermediate of the next

linear metabolic pathway

a series of enzyme-catalyzed reactions that run in one direction, from reactant to product

ex: glycolysis

cyclical metabolic pathway

a circular series of enzyme-catalyzed reactions where there is no end to the series

one reaction leads to the next and eventually back to the starting point

ex: Krebs cycle (photosynthesis), Calvin cycle

enzyme inhibitor

a substance that slows or blocks enzyme action

competitive inhibitor

a substance that binds to the active site of an enzyme, competing with the other substance

non-competitive inhibitor (allosteric regulators)

a substance that does not bind to the active site but to another part of the enzyme (allosteric). It changes the shape of the enzyme

end-product inhibition

when the product of the last reaction in a metabolic pathway inhibits the enzyme that catalyzes the first reaction of the pathway

ex: pathway that converts threonine to isoleucine: isoleucine acts as a non-competitive inhibitor

mechanism-based inhibition

a process that occurs when unreactive molecules are transformed into an active form through catalytic reactions

these active forms inhibit the enzyme, typically through a covalent modification of the active site

it is an irreversible form of enzyme inhibition

ex: penicillin and DD-transpeptidase