Enzymes Flashcards
Factors affecting rate of enzyme controlled reactions
Substrate / enzyme concentration, pH, temperature, presence of inhibitors / _ activators
Explain induced fit model
Substrate collides with active site, binds to it activesite changes shape to fit substrate better ( both active site and substrate change shape to bring their reactive groups together which puts strain and pressure on bonds within substrate, weakening them, lowering activation energy ESC form + then so do EPCs and active site return to normal shape and product released
Explain relationship between rate of reaction and increasing temperature
① Initially ROR increases exponentially as temp increases to optimum because increase in kinetic energy = increase in successful collisions = more escs form and active site of enzyme will change shape as
molecules vibrate more so that it becomes better fit
② optimum temp → highest ROR because active site of enzyme is perfectly complementary to substrate so highest number of successful collisions and production is at max rate
③ ROR reduces rapidly until no more because when temp >optimum then vibrations in molecules are so great that breaks hydrogen bonds holding different parts of protein together altering specific shape of active site so no longer complementary to substrate + progresses as temp ↑
Example of induced fit
Lysozyme
Explain relationship between ROR and pH
At optimum pH, ROR is highest because charges of active site and substrate and shapes are complementary so attracted to each other and shape of active site and substrate are complementary
As pH moves away from optimum, ROR declines because 3D shape of enzyme and therefore its active site is distorted by breaking of hydrogen and ionic bonds so active site and substrate no longer complementary
and charges between enzyme and active site changed due to free H plus and hydroxide ions so-enzyme and substrate repel each other so fewer successful collisions. The r groups of the amino acids of the enzyme on the surface of the active site (?) are what are affected by the free ions ( if active site has you many h plus ions, could repel each others ) the OH ions change charges on the active site making the enzyme inactive
Define ph
Measure of h+ ions concentration
What happens if enzyme becomes more acidic
H plus ions bond to the negative charges on active site making them positive so no longer complementary to substrate + repels it
What is an immobilised enzyme
Enzyme stabilised in an inert material improving the enzyme’s stability by widening the optimum pH / temp range
Ways to immobilise an enzyme
Alginate beads, gel membrane, meshwork of in ent material, stuck to polyethene..
Effect of immobilising enzymes
Stabilises enzyme and widens its optimum range and stable at higher temps because reduces ability of polypeptide chain to move so pH and temp have less effect on enzymes 3D structure and therefore its function.
What is a catalyst
Biological molecule which can speed up rate of reaction without being used up or changing products by providing alternate reaction path with lower activation energy so reactions can occur at low temperature
What is activation energy
Minimum amount of Extra energy required to enable reaction to start
Why is tertiary structure of enzyme essential to its function
. Tertiary structure and bonding in it determines shape of active site which is only complementary to specific substrate so change in active site shape means that enzyme cannot catalyse reaction since enzymes are proteins
What does enzyme actually do when it breaks apart a substrate
Hydrolysis with breaking of… Bond
Explain lock and key model
Shape and charge of active site of enzyme is specific and complementary to substrate so they fit perfectly together like key in lock and bind together and enzyme substrate complex formed and products released and active site never changes shape
Why is induced fit model preferred over lock and key
Enzymes aren’t rigid structures and enzyme - substrate complex changes shape slightly and ensures tighter bonding in active site
What happens to enzymes when temp is too high
Enzymes denature because hydrogen bonds in tertiary structure break so shape of active site changes so enzyme no longer functions
What are 2 characteristics of enzymes
Reusable and shape of active site remains unchanged
Difference between intracellular and extra cellular enzymes
Intracellular = inside cell
Extracellular = outside cell
Explain effect of substrate concentration on ROR.
ROR increases steadily linear / exponentially as substrate concentration increases because more successful collisions so more enzyme substrate complexes form + more product made → ROR plateaus even as substrate concentration increases because every enzyme working at maximum rate and maximum tum over number so active site is continually filled and increasing substrate concentration has no effect → enzyme conc has become limiting factor
Explain effect of enzyme concentration on ROR when substrate is in excess
As enzyme conc increases, ROR increases linearly because more active sites available so more successful collisions between active site and substrate so more enzyme - substrate complexes form so more product each minute → continues as long as substrate in excess
Purpose of buffer
Maintain pH otherwise pH for adequate controls could affect rate of reaction, denature enzymes or to help keep pH at optimum for max ROR
Explain non- competitive inhibitor
Don’t compete for active site with substrate → instead binds to allosteric site distorting tertiary shape of enzyme to active site shape change so substrate no longer complementary and can’t fit so enzyme-substrate complexes can’t form so ROR decreases and maximum rate of enzyme activity is reduced → binding is usually irreversible if it bonds permanently but ones involved in control of metabolic pathway are reversible
Effect of substrate conc on level of inhibition by non competitive inhibitor
No effect because substrate no longer fits → isn’t complementary
