36. Enzyme action

Question 1

what does enzyme shape effect?

Answer 1

• determines function
• determined by AA sequence
  – and bonding between AAs
• active site shape determines type of substrate and reaction
• protein enzymes
  – active site get properties from AAs
  – set of AA in active site, position in 3D space give active site specified size/shape and chemical behavior
• active site uniquely suited to bind particular substrate
  – and help chemical reaction

Question 2

how does enzyme action work?

Answer 2

• enzyme changes shape as substrate enters active site (fit more precise)
  – held together by weak forces (van der waals, hydrogen bonds)
• E+S (k-1)<–>(k1) [E-S] –>(k2) E+P
  – E=enzyme
  – S=substrate
  – [E-S] enzyme-substrate complex
  – P=product
  – k1=rate forward rxn
  – k-1=rate reverse rxn
  – k2=rate product formation

Question 3

what are the models of enzyme action?

Answer 3

• lock and key
  – only correct shaped substrate it active site
• induced model
  – active site changes shape to fit substrate

Question 4

what is the lock and key model?

Answer 4

• each enzyme has receptor sites
  – allow specific substrates to enter and create chemical exn product
• molecular structure of substrate correspond to size and shape of receptor site
  – in order to produce desired chemical response
• enzyme locates appropriate substrate
  – substrate enter receptor site
  – chemical rxn occurs

Question 5

what is the induced fit model?

Answer 5

• matching between enzymes acitve site and substrate
• enzyme changes shape when binds to substrate
  – tighter fit

Question 6

what happens when an enzyme binds to its substrate?

Answer 6

• lowers Ea
  – quicker rxn
• depends on eznyme
  – speed up rxns (2 substrates together in right orientation)
  – create environment inside active site thats favourable
  – bends substrate molecules to facilitate bond-breaking
  – take part of chemical rxn (active site residues temporary covalent bonds)
• all return to original state at end of rxn

Question 7

what is enzyme promiscuity?

Answer 7

• different types of enzymes have different degree of specificity
• some accept only particular substrate
  – not catalyse rxn closely related
• range of target molecules
  – type of bond
  – or chemical group

Question 8

how does the environment affect enzyme function?

Answer 8

• very sensitive to envrionmental change
• Temperature
  – general higher rates at high T
  – but can affect chemical bonds in active site and less suited to bind substrates or denaturation
• pH
• ion concentrations

Question 9

what affect does temperature have?

Answer 9

• very low
  – inactive/damaged
  – substrate move slowly
  – slow reaciton
• optimum
  – faster movement
  –more contact
  – faster reaction
  – depends on enzyme type/origin
• very high
  – atoms vibrate vigorously and break bonds
  – shape changes (active site no longer functional)
  – denaturation

Question 10

what si the effec tof pH?

Answer 10

• AA residues
  – acidic/basic properties for catalysis
• pH changes effect residues
  – hard for substrate bind
• best work at specific pH range
  – and T range
• extreme pH make enzymes denature

Question 11

what is the effect of ion conentrations?

Answer 11

• presence/absence of specific ions impact enzyme activity
  – some require specific ions
• high concentration
  – affect charge of R-groups of AAs in proteins and enzymes
  – changes shape and activity