Topic 1A- Biological Molecules (Enzyme Action) Flashcards
What type of biological molecules are enzymes
Proteins
What is a metabolic reaction
A biochemical reaction that takes place in living organisms in order to keep them alive
What does intracellular and extracellular mean
Intracellular - within cells
Extracellular - outside cells
What part of an enzymes structure causes it to be highly specific
Their Tertiary structure
How do enzymes catalyse reactions
They offer an alternate reaction pathway with a lower activation energy by stressing or forming bonds
What is the definition of activation energy
The minimum amount of energy required to start a reaction
What is formed when a substrate binds to an enzymes active site
An enzyme - substrate complex
Explain how enzymes join or break apart the substrate
Join- If two substrate molecules need to be joined, being attached to the enzymes active site holds them close together, reducing any repulsion between the molecules so they can bond more easily
Break apart - If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate so the substrate molecule breaks up more easily
Outline the lock and key model
This works exactly like a lock and key work- the substrate must be the exact same shape as the enzymes active site to form an enzyme substrate complex
What model was made after the lock and key model
The induced fit model
Outline the induced fit
The active site can change shape slightly when bonding to the substrate to enable a complete fit, so they only need to be a similar shape (complimentary) to form an enzyme substrate complex
Explain why changing the primary structure of an enzyme will denature it
The primary structure is the number and sequence of amino acids in the polypeptide chain, and this defines the order and type of the R groups.
The bonds formed in the tertiary structure (e.g alpha helixes and beta pleated sheets) are dependent on the amino acid R groups- if the primary structure changes, the R groups will change and therefore the tertiary structure will change and the active site will also change shape.
This means the enzyme is no longer complimentary to the substrate, so can’t carry out it’s function anymore
Give three things that you can change to change the shape of the active site
1) temperature
2) pH
3) Add a non - competitive inhibitor
Explain how mutations can change the shape of an enzymes active site
The primary structure (amino acid sequence) of a protein is determined by a gene. If a mutation occurs in that gene, it could change the tertiary structure of the enzyme produced, therefore changing the structure and shape of the active site
Outline and Explain how increasing the temperature changes an enzymes activity
As the temperature increases, the enzyme’s molecules gain kinetic energy, causing them to vibrate more. This increases the frequency of the collisions between the enzyme and substrate particles, as well as increasing the energy at which they collide (increasing the chance of successful collisions occurring). This means that more enzyme substrate complexes are formed, so more substrate is turned into product and the rate of reaction increases.
However, if the temperature gets too high, the enzymes particles gain enough energy to break the bonds holding the enzyme in shape. The active site changes shape and the enzyme and substrate no longer fit together. At this point, the enzyme is denatured, meaning no enzyme substrate complexes are formed and no product is formed. The rate of reaction decreased until all of the enzymes are denatured and the reaction stops.
Explain how pH effects enzyme activity
All enzymes have an optimum pH value at which their rate of reaction is the highest. Above and below the optimum pH, the H+ and OH- ions found in acids and alkalis can mess up the ionic bonds and hydrogen bonds that hold the enzyme’s tertiary structure in place. This makes the active site change shape, so no enzyme substrate complexes can form and the enzyme is denatured. The rate of reaction decreases rapidly as the pH moves away from the optimum until all enzymes are denatured, so the reaction stops.
Explain how enzymes concentration effects the rate of reaction
1) As the enzyme molecule concentration increases, the more likely a substrate is to collide with one and form an enzyme substrate complex increases, increasing the rate of reaction.
2) however, if the amount of substrate is limited, there becomes a point when there’s more than enough enzyme molecules to form enzyme substrate complexes with all the available substrate, so adding no enzymes has no further effect as there is no more product to collide with.
Explain how substrate concentration effects the Rate of reaction
1) As the substrate concentration increases, the rate of reaction increases as there is more substrate molecules so a collision between substrate and enzyme is more likely and so more active sites will be used to form enzyme substrate complexes.
However, this stops increasing the rate of reaction when the saturation point is reached/ the enzyme concentration becomes the limiting factor (all active sites are filled, so adding more substrate has no effect as the surplus substrate has no active sites to bind to).
What are the two types of Inhibitors
Competitive inhibitors
Non competitive inhibitors
Outline how competitive inhibitors work
1) They have a similar shape to that of the substrate molecules, meaning they are a similar shape to the active site.
2) they compete with the substrate to bind to that of the active site, but no reaction takes place. Instead, they block the active site so no substrate molecules can fit in it until they leave the active site.
3) how much the enzyme is inhibited depends on the relative concentrations of the inhibitor and the substrate
4) if theres a high concentration of the inhibitor, it’ll take up nearly all of the active sites and hardly any substrates will bind to enzymes, meaning less enzyme substrate complexes formed and a lower rate of reaction. However, all of the substrate eventually becomes product.
5) if there’s a higher concentration of substrate, the substrates chances of getting to an active site and forming an enzyme substrate complex increases, so the rate of reaction increases.
Outline how non-competitive inhibitors work
1) they bind to an allosteric site on the enzyme (a site that’s not the active site).
2) This causes the enzymes tertiary structure to change shape and therefore the active site to change shape. The enzyme is now permanently denatured so the substrate molecules are no longer complimentary and can no longer bind to it. This means no more enzyme substrate complexes can be formed
3) Increasing the concentration of substrate won’t make any difference to the rate of reaction - enzyme activity will be inhibited permanently.
What are the two ways you can measure rate of reaction
1) measure how fast the product of the reaction is made
2) measure how fast the substrate is broken down
Outline the steps of how you could measure how temperature effects catalase activity and find the average rate of reaction
(Using the enzyme catalase which catalyzes the breakdown of hydrogen peroxide into water and oxygen)
1) set up 4 boiling tubes, all containing the same volume and concentration of hydrogen peroxide. To keep the pH constant, add equal volumes of a suitable buffer solution to each tube.
2) Put each boiling tube in a water bath set to a different temperature (10°C, 20°C, 30°C and 40°C), along with another tube containing catalase. Leave them for 5 minutes.
3) set up the apparatus as shown in textbook on page 14. Use a pipette to add the same volume and concentration of catalase to each boiling tube. Quickly attach the bung and delivery tube to each one.
4) Record how much oxygen is produced in the first minute of the reaction, using a stopwatch to measure the time.
5) repeat steps 1-4 three times, and use the results to find an average volume of oxygen produced.
6) calculate the average rate of reaction at each temperature by dividing the volume of oxygen produced by the time taken. The units will be in cm³s^-1. Plot the results on a graph with temperature on the x axis and rate of reaction on the y axis.
Give the steps of how you can measure the effect of concentration of amylase on rate of reaction with starch.
1) using a pipette, add a drop of iodine in potassium iodide into each well on a spotting tile.
2) add a known concentration of amylase and starch into a test tube together and start a timer.
3) every 30 seconds, use a dropping pipette to add a drop of this mixture into one of the wells containing the iodide solution.
4) keep doing this until the iodide solution stops turning blue-black (this means there’s no starch left).
5) repeat steps 1-4 with different concentrations of amylase
6) repeat steps 1-5 two more times and find the mean time for each concentration.
7) work out rate of reaction
