C1.1 Enzymes & Metabolism HL Flashcards
Enzyme-catalysed reactions can be _____ or _____
intracellular or extracellular
give examples of intracellular reactions
glycolysis & Kreb’s cycle → in respiration
give examples of extracelluar reactions
chemical digestion outside of cells in the lumen of the small intestine
are metabolic reactions 100% efficient with enzymes, why?
no
heat will be generated and lost
e.g. while maintaining a constant body temperature
define metabolic pathways. also state and explain
Metabolic pathways are chains or cycles of enzyme-catalysed reactions
- The product of one reactant is a reactant in the next
Initial substrate → intermediates → end-product
give an example of a linear metabolic reaction
glycolysis in respiration
give examples of enzyme-catalysed, cyclical metabolic pathways
the Kreb cycle in (cell) respiration
the Calvin cycle in photosynthesis
what is competitive enzyme inhibition
inhibitor fits the active site and prevents the substrate from entering
give an example of competitive enzyme inhibition and explain how it works
- Statin (stops someone from making too much cholesterol)
- used to treat high blood cholesterol (contributes to heart disease)
- binds to active site of enzyme HMG-CoA reductase
- [this enzyme] catalyses one of the reactions in the metabolic pathway used to synthesise cholesterol in liver cells
- rate-limiting step in the pathway
- if statins lower the rate → less cholesterol produced by the body
what is allosteric site?
other site (somewhere other than the active site on the enzyme)
what is non-competitive enzyme inhibition?
inhibitor fits into an allosteric site causing a conformational change in the active site → the substrate cannot attach to react
- no longer fits the substrate
give an example of non-competitive enzyme inhibition
Isoleucine
- as concentration of isoleucine builds up → binds to allosteric site of the first enzyme in the chain (threonine deaminase)
explain end product inhibition (using isoleucine as an example)
- after sufficient isoleucine is produced it blocks the enzyme from producing it → if too much end product is made
- if have enough end product → stop production = negative feedback
- end product bind to allosteric site
- how to restart? → use up end product → get rid of inhibition
is inhibition reversible?
mostly reversible
explain end product inhibition
inhibited enzyme has an allosteric site to which the end product binds
- binding changes shape of active site → prevent catalysis for as long as the end product remains bound
- the enzyme that is inhibited has an allosteric site to which the end product binds
- this binding changes the shape of the active site, preventing catalysis for as long as the end product remains bound
- if too much end-product is made, it will increasingly inhibit the first enzyme in the pathway
- effectively switches off the whole pathway and prevents synthesis of more end product
- if there is too little of the end product → minimal inhibition of the first enzyme
- the metabolic pathway will be open to produce more of the end product
explain competitive inhibition in a general sense
- blocks the active site, preventing the substrate from entering
- the higher the concentration of inhibitor, the slower the rate of reaction
- even with competitive inhibition, the same maximum rate of reaction will be achieved if more substrate is added - bc we have not changed the number of enzymes available
what does the graph of competitive enzyme inhibition look like?
same maximum rate of reaction
also same start point?
explain non-competitive enzyme inhibition in a general sense
non-competitive inhibitors bind to an allosteric site on the enzyme
the active site is altered and the substrate cannot attach and react
what does the graph of non-competitive enzyme inhibition look like?
not the same maximum rate of reaction
as the concentration of non-competitive enzyme inhibition increase, what happens to the rate of reaction and why?
rate of reaction decrease
bc there are fewer function(al)? active sites available for reaction
the max rate of reaction is reduced - with fewer functional active sites, the enzyme has reduced ability to process the substrates, even if substrate concentration is increased
explain mechanical-based inhibition
irreversible binding of an inhibitor (mechanical based inhibition) can cause chemical changes to the active site via covalent bond
give an example of mechanical-based inhibition
penicillin
if cell wall of bacteria weakened (lysis occurs easily)
explain the example of mechanical-based inhibition
- cells walls of bacteria prevent them from bursting when low external solute concentrations cause water to enter by osmosis and hydrostatic pressures inside the cell become very high
- enzyme: transpeptidase
- very important in the process of cell wall formation → cross-links strands of carbohydrate into one huge peptidoglycan molecule that forms the entire cell wall
- when bacteria grow: one enzyme breaks these links, allowing the wall to expand
- transpeptidase then remakes the links
- saprotrophic bacteria and fungi compete for food because they both secrete enzymes for extracellular digestions of carbon compounds in dead matter and then absorb the products of digestion
- The fungus Penicillium notatum produces penicillin
- binds to the active site of transpeptidase in the cell walls of bacteria and prevents the substrate of the enzyme from binding
- Penicillin forms a permanent covalent bond with a particular amino acid in the active site, binding irreversibly with the enzyme
- the enzyme that breaks cross-links in the bacterial cell wall continues working but the transpeptidase enzyme cannot work to reform these links
- the cell wall is weakened and the bacteria are killed by bursting (lysis)
- penicillium can then monopolize the food source
- the fungus only does this when food supplies are limited, because resources are needed for the synthesis and secretion of penicillium
is mechanical-based inhibition competitive or non-competitive?
competitive
bc it binds to the active site
