Enzymes the story so far
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Enzymes – the story so far. Enzymes are biological catalysts Speed up reactions Lower the energy needed to make reactions proceed Enzymes react with substrates - very specific Substrates have a structure complimentary to the active site of the enzyme (‘lock & key’)

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Enzymes – the story so far

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Enzymes the story so far

Enzymes – the story so far

  • Enzymes are biological catalysts

  • Speed up reactions

  • Lower the energy needed to make reactions proceed

  • Enzymes react with substrates - very specific

  • Substrates have a structure complimentary to the active site of the enzyme (‘lock & key’)

  • Reaction complete = enzyme is unchanged

  • Can help ‘build-up’ or ‘breakdown’ reactions


Enzymes ctd

Enzymes ctd.

  • Can be intracellular or extracellular

  • All made of protein, most globular

  • Amino acid sequence, and bonding between them, determines active site shape

All have an active site


Factors affecting enzymes

Factors affecting enzymes

  • Temperature:

  • Increasing temp makes atoms vibrate

  • above 40oC, vibrations break chemical bonds holding enzyme together

  • Structure unravels, active site is lost

  • = denatured

  • pH:

  • All enzymes have an optimum pH

  • Mostly close to neutral (5-9)

  • exceptions

  • - pepsin (2-3)

  • - alkaline phosphatase/phosphorylase (10)


Factors affecting enzymes1

Factors affecting enzymes

  • Enzyme concentration:

  • - enzyme-substrate reaction is very brief

  • - enzyme then moves on to the next substrate molecule

  • Turnover Number:

  • - no. of substrate molecules which an enzyme acts on in a given time

  • range: 100-4000 per second

  • Increased enzyme conc. = increased reaction rate

  • This will increase at a steady rate as long as there is substrate present


Factors affecting enzymes2

Factors Affecting Enzymes

  • Substrate Concentration:

  • Increasing substrate conc. will increase reaction rate

  • - more substrates binding with active sites

  • After a certain point all the active sites will be filled

  • Therefore increasing substrate conc. will no longer have an effect


Inhibitors

Inhibitors

  • Competitive:

  • - compete directly for enzyme’s active site

  • - have a structure very similar to that of the substrate

  • - active site gets blocked

  • - reaction rate goes down as more sites get blocked by inhibitor

  • - increasing substrate conc. can return reaction rate to normal


Inhibitors1

Inhibitors

  • Non-Competitive:

  • - Don’t combine with active site

  • - Attach to another region on the enzyme

  • - This results in the active site structure being altered indirectly

  • e.g cyanide, heavy metals

  • - increasing substrate conc. will not return reaction rate to normal


Activation of enzymes

Activation of Enzymes

  • Co-Factor:

  • A non-protein substance which helps to activate an enzyme

  • e.g. Zn, Fe, Cu, Mg

  • Often helps the substrate to fit the active site

  • Some are known as Co-Enzymes

  • These are mostly made of vitamins

  • e.g. Vitamin B - transfers Hydrogen during aerobic respiration


Other enzymes

Other Enzymes

  • Many digestive enzymes start off inactive

  • In the gut they’re activated by enzyme activators

  • e.g. trypsin & chymotrypsin in the pancreas

  • - both protein digesting enzymes

  • - if permanently active, could digest the pancreas itself

  • InactiveActivatorActive enzyme

  • trypsinogen+ enterokinase trypsin

  • Chymotrypsinogen + trypsin chymotrypsin + trypsin


Inborn errors of metabolism

Inborn Errors of Metabolism

(PKU)

  • Metabolism - sum of all the chemical reactions in the body

  • Products of one reaction often go into another reaction

  • All reactions controlled by enzymes

  • If a genetic fault occurs, the enzymes are not produced correctly

  • Intermediate metabolites accumulate and cause disorders

  • e.g. albinism, PKU


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