Enzymes HL

C1.1.11 Intracellular amd extracellular eznyme-catalysed reaction

  • glycolysis and the Krebs cycle as intracellular examples

  • chemical digestion in the gut as an extracellular example

Intracellular enzyme activity:

  • Free floating ribosomes in the cytoplasm

Extracellualr enzyme activity:

  • ribosomes attached to rough edoplasmic reticulum

  • Proteins are sent to golgi apparatus for processing

  • The golgi packages enzymes in secretory vesicles which releases enzymes via ezocytosis

C1.1.12 Generation of heat energy by the reactions of metabolism

  • mammals, birds and some other animals depend on this heat production to maintain constant body temeprature

Endotherms: ( warm blooded )

  • animals which maintain constant body temo

  • depend o the release of heat from metabolism to maintain a constant body temp

  • idea that heat generation is inevitablebecause metabolic reactions are not 100% efficient in energy transfer.

C1.1.13 cyclical and lindear pathways in metabolims

  • use glycolisis, the Krebs cycle and the Calvin cycle as examples

Metabolism: is the sum total of all chemical reactions in an organism

  • each reaction or stage catalysed by a specific enzyme

  • the product of the 1st enzyme controlled reaction becomes the substrate for thee next

  • maybe a chain or cycle of reaction

C1.1.14

C1.1.15 competetive inhibitions as a consequence of an inhibitor binding reversibly to an active site

Competetive inhibitors

  • statin is the example of competetive inhibitors

  • Inhibitors is similar in structure substrate

  • Its important to understand this graph

How statin reduces cholesterol levels in humans after statin enters liver cells:

  • A metabloc pathway of reactions produces cholesterol in the liver

  • If no satin - the enzyme HMG-CoA reductase converts HMg-CoA to mevalonic acid

  • Mevalonic acid is converted to cholesterol through a series of enzyme-catalysed reactions.

  • Statin are competetive inhibitors of HMG-CoA reductase

  • If there is less mevalonic acid produced, there will also be less cholesterol produced

Non - competetive inhibitors

  • Does not bind to active site

  • its called the ‘ ALLOSTERIC SITE “

  • binding causes a change in the 3-D shape of the active site

  • e.g. cyanide inhibits cytochrome oxidase ( preventing the transfer of electrons in repsiration )

  • Are different in structure and chemistry to the substrate

  • Binding of the inhibitor to the allosteric site is reversible

Similarites of competetive vs non-competetive:

  • Both classes of inhibitors bind to the enzyme

  • Both slow down or stop enzyme activity

Differences

C1.1.16 regulation of metabolic pathways ny feedback inhibition

EXAMAMPLE OF END - PRODUCT INHIBITION BETWEEN THREONINE AND ISOLEUCINE

C1.1.17 Mechanisms-based inhibition as a consequence of chemical changes to the active site caused by the irreversible binding of an inhibitor

  • mechanism - based inhibitors are competetive inhibitors which permanently convalent;y bond to the active site of an enzyme

  • penicillin is a mechanisms-based inhibitor that binds to transpeptidases, which are enzymes that are involved in constructing the peptidoglycan cell walls of bacteria

  • penicillin prevents bacteria from building cell wallks, as ot orreversibly inhibits transpeptidase. Bacterial cells without cell wals undergo lysis and die.