Topic 3 Flashcards
Enzymes
Biological catalysts that speeds up the rate of reactions without being used up or changed
What types of proteins are enzymes
Globular
Intracellular protein
Enzymes are produced and function inside the cell
Extracellular protein
Enzymes are secreted by cells and catalyze reactions outside the cell
Denaturation
Change in conditions leading to change in shape of enzyme, resulting in loss of function and no desired reaction occurring
5 factors that affects rates of reactions
pH, temperature, substrate concentration, enzyme concentration, inhibitor concentration (Competitive and non-competitive)
Examples of intracellular enzymes
DNA polymerase, DNA helicase, catalase
Extracellular examples
Digestion enzymes - proteases, amylase, maltase, lipase
How temperature affects enzyme [4]
1) As kinetic energy increases, collisions increase
2) Rates of reaction increases up to optimum temperature
3) Beyond optimum, bonds in enzymes starts to break changing the shape of active site
4) This cannot be reversed and the enzyme is denatured.
How do enzymes increase rates of reaction?
By lowering the activation energy of the reaction they catalyse
Intracellular enzyme vs extracellular enzyme
Intracellular, enzyme is produced and functions inside the cell
Extracellular, enzyme is produced and secreted to function outside the cell
Describe lock and key model [4]
1) Active site and substrate have complementary shapes before binding
2) The enzyme binds with substrate to form an enzyme-substrate complex
3) Products released from the active site and enzyme can be reused
4) Only 1 substrate can fit each active site
Describe induced fit theory [3]
1) enzyme is molded around substrate as it enters to become complementary to form an enzyme-substrate complex
2) Bonds form between oppositely charged groups on substrate and R groups to induce a better fit
3) This puts a strain on the substrate molecule so reaction occur more easily
How enzyme concentration affect activity of enzyme [3]
1) Rate of reaction increases as enzyme concentration increases as there are more active sits for substrate to bind to
2) This will plateau out as eventually there will be more active sites than substrate
3) substrate concentration becomes a limiting factor
How does substrate concentration affect activities of enzymes [2]
1) As concentration of substrate increases, rates of reaction increase because more enzyme-substrates are formed.
2) This will plateau out because enzyme concentration will become the limiting factor
How does pH affect activities of enzymes [4]
1) As pH move away from the enzyme’s optimum, rate of reaction decreases
2) the PH is a measure of hydrogen ions. Each enzyme has an optimum pH
3) The wrong PH changes the charges on amino acids which makes up the active site
4) This breaks the bonds and enzyme becomes denatured
How does concentration of inhibitors (comp and non-comp) affect activities of enzymes [4]
Competitive reversible inhibitors
As concentration increase, rates of reaction decrease as active sits are temporarily blocked by inhibitors so substrate cannot bind
Non competitive reversible inhibitors
As concentration increases, rates of reaction decreases as shape of enzyme (Not active site) is altered by the inhibitors
Catalase activities & practical [4]
1) Catalyzes the breakdown of hydrogen peroxide
2) Products; Oxygen and water
3) Measure the rate of oxygen produced over time
4) Plot graph of time vs volume of oxygen produced
Amylase activities & practical [8]
1) Catalyzes the breakdown of starch
2) Products: Maltose
3) Amylase is added to starch samples
4) Samples taken at time intervals
5) Use iodine to test for starch
6) Measure the absorbance in a colorimeter
7) Darker the colour the higher the starch concentration hence higher absorbance
8) Plot graph of time vs absorbance
Types of inhibition [4]
1) Competitive
2) Non-competitive
3) Feedback
4) Reversible
Competitive inhibition [3]
1) Inhibitor molecule binds to the active site of an enzyme
2) Stops substrates from binding to it
3) Can be reversed by increasing the substrate concentration as inhibitor is diluted
Non-competitive inhibition [2]
1) Inhibitor doesn’t bind to the active site but binds to a different part of the enzyme (allosteric site). which changes shape of an enzyme
2) Decreases rate of reaction as substrate cannot bind to the enzyme
Feedback inhibition [2]
1) End products binds to enzyme at the start of reaction
2) Stops the pathway until the concentration of the end products decreases
Reversible inhibition
Can be comp or non-comp
Once they are removed from enzyme, inhibition stops and it works again
Michaelis-Menten equation
Vo= Initial velocity (Moles/time)
S= Substrate concentration (molar0
Vmax= maximum velocity
Km= Substrate concentration at half Vmax
Immobilising enzymes [4]
1) When enzymes are in solution they can only be used once as its difficult and time consuming to separate them from the product
2) Therefore they are immobilised by attaching them to an insoluble inert material (Calcium alginate)
3) Forms a gel capsule around them to hold them in place during reaction
4) This process enables enzymes to be reused as they can be easily separated from the products
State two precautions you would take when preparing a standard homogenate of liver tissue
1) Same weight of liver
2) Same species
investigate the effect of temperature on the activity of catalase [4]
1) Select a range of temperature for water bath (0-70)
2) Same standard homogenate of liver in each case
3) Measure volume of oxygen produced over 1 minute
4) repeat experiment at each temperature and calculate mean
What does chloride ions do for amylase activity [3]
1) Chloride ion is amylase’s allosteric activator
2) They bind to enzyme to change its molecular shape
3) So active site can bind with substrate
effect of pH on the rate of an enzyme controlled reaction [4]
1) Enzymes have optimum pH
2) As pH increase or decrease, shape of active site will be changed
3) Less binding, less substrate-enzyme complex can form
4) Rates of reaction decreases
Define competitive inhibitor
1) Substrate that is structurally similar to normal substrate
2) competes for active site of enzyme
Comp vs non-comp inhibitors [2]
1) Comp are structurally similar to normal enzyme
2) Non comp binds on allosteric site, comp binds on active site
Define biological catalyst
1) Facilitate biological reactions
2) Speeds up rates of reaction and it isn’t used up after reaction
Catabolic reactions
Breaks down complex molecules into smaller products
Anabolic reactions
Builds more complex molecules from smaller substrates
Using a colorimeter [2]
1) Colorimeter can be calibrated
2) different starch conc can be used to plot a calibration graph
Explain how the level of protein structure enable enzyme specificity [3]
1) Sequence of amino acids
2) Hydrogen bonding in the secondary structure determine formation of alpha helices and beta pleated sheets
3) tertiary structure of proteins determines shape of active site
Why is buffer solution important
High or low pH doesn’t really affect the solution
Maintain pH of the solution
Immobilised enzyme [3]
1) Enzyme is bound to insoluble material
2) Enzyme is held in place during reaction
3) Whole cells with specific enzyme can also be immobilised
3 advantages of using immobilised enzyme
1) No enzyme in the product therefore product is not contaminated
2) Immobilised enzyme can be reused multiple times which is efficient and economical
3) Greater tolerance of pH and temperature as it makes the enzyme more stable
2 examples of reactions that uses immobilised enzymes
1) Making lactose-free milk using lactase
2) Making ethanol using yeast
The optimum pH of an intracellular enzyme is not necessarily identical with the pH of the intracellular surroundings suggest reasons [2]
1) There is more than one type of enzyme working within the cell which can have different optimum pH
2) Some enzymes have to work slower so pH is tolerable for other enzymes
Plot out the graph of
Non-inhibitor
comp inhibitor
non-comp inhibitor
against substrate concentration and explain their different position
