Enzymes and Metabolic Pathways

Flashcards covering enzymes, metabolic pathways, enzyme inhibition and regulation, and heat generation in metabolism.

Intracellular Enzyme-Catalyzed Reactions

Reactions catalyzed by enzymes that occur inside cells.

Extracellular Enzyme-Catalyzed Reactions

Reactions catalyzed by enzymes that occur outside cells.

Glycolysis and the Krebs Cycle

An intracellular example of enzyme-catalyzed reactions.

Chemical digestion in the gut

An extracellular example of enzyme-catalyzed reactions.

Heat Generation

An inevitable byproduct of metabolic reactions due to inefficient energy transfer; mammals and birds use this for maintaining constant body temperature.

Cyclical Pathways

Metabolic pathways that form a cycle where the end product of one reaction starts the rest of the pathway.

Linear Pathways

Metabolic pathways that involve a linear chain of reactions.

Allosteric Site

A site on an enzyme where specific substances can bind, causing conformational changes that alter the active site and prevent catalysis.

Competitive Inhibition

A type of enzyme inhibition where an inhibitor binds reversibly to the active site, preventing substrate binding; statins are an example.

Feedback Inhibition

Regulation of metabolic pathways where the end product acts as an inhibitor; the isoleucine pathway is an example.

Mechanism-Based Inhibition

A type of enzyme inhibition where an inhibitor binds irreversibly to the active site, causing chemical changes; penicillin is an example.

Intracellular enzyme features

Enzymes produced by free ribosomes in the cell for use inside organelles (e.g., mitochondria, nucleus), cytoplasm or bound to membranes where intracellular reactions are catalyzed.

Extracellular enzyme features

Enzymes synthesized by the rER which are released from glands or specialized cells into the interior of an organ catalyzing the breakdown of larger macromolecules into monomers.

Enzyme Inhibitors

Chemical substances that reduce or prevent enzymatic reactions by blocking the enzyme.

Competitive Inhibitor

Inhibitor that can bind with the same active site as the substrate. This binding is reversible.

Non-Competitive Inhibitor

The inhibitor binds to a different site from the active site (allosteric site), changing the conformation in the active site of the enzyme. This binding is reversible.

Heavy Metals

Metals such as lead, mercury, arsenic or copper that bind irreversibly to the active site of the enzyme by forming strong covalent bonds

Cyanide

A poison which prevents ATP production via aerobic respiration, leading to eventual death. It non-competitively binds to an allosteric site on cytochrome oxidase.

Sarin

A nerve gas used in biological warfare that works as a non-competitive irreversible inhibitor of the enzyme acetylcholinesterase.

ACE inhibitors

Inhibit the action of the enzyme ACE helping to control high blood pressure.

Statins

Medicines that work by competitive enzyme inhibition to treat cardiovascular disease caused by cholesterol.

Transpeptidase

An enzyme that bacteria use to catalyze the formation of peptidoglycan cross-links in its cell wall. Penicillin binds to this bacterial enzyme, inducing a permanent change

Penicillin

Penicillium produces a chemical known as this and it is a mechanism-based inhibitor that binds to the active site of transpeptidase in the cell walls of bacteria.

Competitive Inhibition and Substrate Concentration

At high concentrations, the substrate out-competes the inhibitory molecules for the active site. The rate of reaction therefore increases and reaches the same maximum as without the inhibitor.

Non-Competitive Inhibition

The presence of this always significantly reduces the rate of reaction – the maximum enzyme activity will not be reached. This is because the binding of the inhibitor to the allosteric site causes a deformation of the active site, which prevents the binding of any more substrate.

Allosteric enzymes

End product inhibition usually includes these with an active site and an allosteric site.

Isoleucine

If in high enough quantities, this binds to the allosteric binding site on the enzyme threonine deaminase, preventing further binding of threonine to the active site.

Heat energy

Metabolic reactions often result in the release of this because the products of a reaction usually have less energy than the reactions

Heat generation in Birds and Mammals

Birds and mammals show adaptations to heat generation to raise their basal metabolic rate above the external temperature or huddle together in groups to take advantage of the metabolic heat released by their neighbours.

Brown fat cells

These cells in adipose tissue contains more mitochondria than white fat cells or any other body tissue. More energy can be generated through uncoupled respiration (without the production of ATP)