Chapter 4- Enzymes Flashcards
Why is enzyme described as extracellular?
-works outside cells
What should you keep constant when changing conc. of substrate?
- pH
- temp
- enzyme conc.
- vol of solution
- conc. of cofactors
explain the graph that is linear and then plateaus
Increasing substrate conc. against rate of product formation
- linear part means more successful collisions with active site at inc. starch conc. thus, more ESC at increasing starch conc. so more product formation in given time.
- plateau means all active sites occupied as enzyme working at Vmax. So further inc. in starch conc has no affect on rate. Enzyme conc. now limiting factor.
Why is it important to keep pH constant?
- so H and ionic bonds unaffected
- so tertiary structure unaltered
- so enzyme doesn’t denature
- so substrate complementary to active site
-so results are valid as rate of reaction will vary if pH changes and to ensure only 1 independent variable changed
Explain why enzyme x is bale to break down both a and b (diagram)
- have similar 3D shape
- e.g. of similarity
- both are complementary to active site
Suggest why DEG contaminated (harmful) wines with higher ethanol conc (not harmful) may result in less DEG poisoning than contaminated wines with lower ethanol conc.
- ethanol competes with DEG
- when at higher conc. ethanol more likely to bind to active site and thus less toxic product formed
why the lock-and-key and induced-fit explanations are termed models?
Simple representations of the process
why most scientists now accept the induced-fit model rather than the lock-and-key model?
-it has now been found that the enzyme changes shape during the reaction
Rate of product formation was slower at 1c when catalysed with enzyme from non Antarctic fish than Antarctic fish. Why?
Not at optimism temperature so fewer collisions between active site and substrate
how a more flexible structure might help enzyme work faster at lower temperatures?
- easier for substrate to bind to active site
- more bonds can form
- easier for active site to change shape
how the structure of the enzymes may differ in Antarctic and non-Antarctic fish?
- diff amino acid sequence in primary structure
- diff quaternary structure as polypeptide will fold differently
how the DNA of the Antarctic and non-Antarctic fish might differ?
- diff base sequence
- diff ratio of bases
why the loss of enzymes might be undesirable
Enzyme could have future application
Explain the term biological catalysts
-speed up metabolic reactions
One problem with using celery as source of catalase in investigation and how to minimise problem?
- diff samples have diff conc of catalase
- extract source for whole experiment from same plant
How to check reliability of data?
- repeat experiment
- identify anomalous results
- calculate mean
- calculate SD
- compare results with book values
How Cl- ions increase the rate of reaction?
- acts as a cofactor
- Cl- binds to enzyme
- ESC forms more quickly
Explain the effect of increasing the conc. of substrate on the rate of reaction
- more substrate molecules enter the active site
- more ESC formed
- at high conc all active sites occupied
- reaches Vmax
- at high substrate conc. the enzyme conc. is the limiting factor
Explain why x acts as a competitive inhibitor to y
- both have similar shape
- both are complementary to active site of enzyme
- give E.g. of similarity
Explain the effect of increasing the substrate concentration in the presence of an inhibitor
- inhibitor competes for active site
- occupies active site reversibly
- thus, fewer active sites available for substrate
- at higher conc of substrate the substrate can outcompete the inhibitor and reduce the chance of inhibitor binding to active site
-describe how an enzyme breaks down a substrate
- substrate complementary to active site
- substrate binds to active site
- in an induced fit
- forms ESC
- straining of bonds in substrate
- forms EPC
- products leave active site
How would you draw a line on a graph to show the action of a competitive inhibitor?
- below substrate line
- doesn’t peak or plateau
- x acts as a competitive inhibitor of y
What can you conclude about the structure of x
- similar shape to substrate
- complementary to active site
This enzyme action can break down elastin.
Use the example of elastin breakdown to explain the induced-fit hypothesis of enzyme action
- elastin is substrate
- substrate binds to active site
- enzyme changes shape to get tighter fit between active site and substrate
- more bonds form between active site and enzyme
- forms ESC
- straining of bonds in substrate
- activation energy reduced
why different enzymes are involved in each stage?
- enzymes are specific
- substrates are different shapes
- active site and substrate are complementary
- substrate binds to active site
- forms ESC
Explain why the activity of the enzyme falls to 0 at pH 7
- pH much higher than optimum
- hydrogen and ionic bonds break
- active site shape altered
- enzyme denatured
- substrate no longer fits active site
What is meant by ‘catalyst’
-a substrate that speeds up a reaction without being used up in the reaction
What is meant by activation energy and how does the presence of an enzyme affect it?
- Ea is the minimum amount of energy needed to start a reaction
- enzymes lower the Ea
Enzymes are globular proteins. What does this mean in terms of quaternary structure?
Multiple polypeptide chains coiled together to make a compact structure
Why is the tertiary structure of an enzyme essential to its function?
- tertiary structure determines specific shape of active site
- active site is only complementary to specific substrate
- any change in shape will mean the enzyme cannot catalyse that reaction
How does the maltase enzyme interact with maltose?
- maltose is a complementary shape to the active site of maltase
- ESC formed
- reaction occurs, breaking the glycosidic bond between disaccharide
- 2 glucose monosaccharides are released
What is the ‘lock and key’ model of enzyme action?
- substrate fits into the active site of enzyme in same way that key fits into lock
- they are exactly complementary shapes
Why ‘induced fit’ model considered to be better theory than ‘lock and key’ model?
- enzymes are not rigid structures
- ESC changes shape slightly
- ensures tighter binding in active site
Which enzyme inhibitor would be more likely to have temporary affects and why?
- competitive inhibitor
- has similar shape to substrate
- occupies active site and prevents substrate from binding
- no reaction can take place until inhibitor becomes dislodged
Name the 2 types of competitive inhibitors?
- competitive
- non - competitive
How does increasing the enzyme concentration increase the rate of reaction?
- the more enzymes present the more active sites available and thus more likely a successful collision will occur
- forming an ESC
- thus, increasing the rate of reaction
What is meant by denature?
- change in conditions will cause bonds to break in the structure of the enzyme, changing its shape
- thus, can no longer function
Explain the graph for how temperature affects the rate of reaction
- as the temp increases, the rate of reaction increases
- at certain point, the temp causes the enzyme to denature
Explain the graph for how pH affects the rate of reaction
- each enzyme works at an optimum pH
- any pH either side of this will reduce the rate of reaction before denaturing the enzyme completely
Cyanide is a non-competitive inhibitor that interferes with Cytochrome C Oxidase in mitochondria of cells I’m final stages of cellular respiration.
Explain how exposure to cyanide is lethal
- cyanide binds to separate allosteric site on cytochrome C oxidase enzyme
- causes permanent changes to shape of active site
- enzyme can no longer function
- cells cannot respire, no energy synthesised
What are Inactive precursor enzymes?
Some enzymes are synthesised in an inactive precursor form and need to be activated E.G.another enzyme removes part of enzyme
What is temperature coefficient (Q 10)?
Effect of 10°C rise in temperature on the rate of reaction
How would calculated reaction differ from inial reaction?
- initial likely to be greater
- bc higher conc. of substrate molecules at start
- more chance of entering AS
Explain competitive inhibition?
- similar shape to substate
- complemenatry to active site
- prevents substrate binding to site temporarily
How could you tell from a graph that it is competitive inhibiton?
-at high substrate conc. rate approaches Vmax in absence of inhibitor
Why enzyme activity low at pH 4?
- H bonds disrupted
- ionic bonds disrupted
- tertairy structure altered
- substrate no longer complementary to active site
- enzyme denatured
Biological catalyst?
Speed up metabolic reactions
Problems with samples of liquidised celery as a source of catalase and how to minimise problem?
- diff samples have diff conc. of catalase
- source the extract for whole experiment from a single source
What type of enzymes will be the ones that digest food in the small intestine?
Extracellular
Why proteins required in large amounts but vitamins and minerals are not?
-proteins are not stored in body but vitamins are minerals are
