Enzymes Flashcards
All 26 cards in this deck
What is the active site of an enzyme?
The part of the enzyme that the substrate binds to. Its shape is complementary to the substrate.
Catalase breaks hydrogen peroxide down into water and oxygen. Which of these is the substrate, and which are the products?
Hydrogen peroxide is the substrate; water and oxygen are the products.
What is meant by enzyme specificity?
Each enzyme catalyses only one reaction, because only a substrate with a shape complementary to its active site can fit and bind.
What happens to an enzyme's active site when the enzyme is denatured?
The active site changes shape, so it is no longer complementary to the substrate — the substrate cannot bind and no enzyme-substrate complexes form.
What happens to the rate of an enzyme-controlled reaction as temperature increases up to the optimum?
The rate increases: molecules have more kinetic energy, so there are more collisions with the active site and more enzyme-substrate complexes form.
What is meant by the optimum pH of an enzyme?
The pH at which the enzyme has its fastest rate of reaction.
e.g. pepsin pH 2, trypsin pH 8What happens to the rate of an enzyme-controlled reaction as substrate concentration is increased?
The rate increases (more collisions with active sites, more enzyme-substrate complexes), then plateaus when all active sites are occupied and the enzyme becomes the limiting factor.
True or false? Boiling an enzyme kills it.
False. Enzymes are not alive — at high temperature the enzyme is denatured and the active site changes shape.
What are the steps to investigate the effect of pH on amylase activity?
e.g. using starch solution, amylase and iodine- Mix starch solution, amylase and a pH buffer solution in a test tube.
- Every 30 seconds, put a drop on a spotting tile and add iodine solution.
- Record the time for the iodine to stay orange-brown (all starch digested); repeat at different pH values.
What colour is iodine solution when starch is present, and when it is not?
Blue-black when starch is present; orange-brown when no starch is present.
Give three variables that must be controlled when investigating the effect of pH on amylase activity.
Temperature; volume and concentration of amylase; volume and concentration of starch. (Also the size of the test tube.)
Give two improvements that would help find an enzyme's optimum pH more precisely.
Use smaller intervals of pH around the optimum; repeat each pH and calculate a mean. (Also use a water bath to control temperature.)
What is the equation for the rate of an enzyme reaction from the time taken?
rate = 1 ÷ time (units: s⁻¹, i.e. per second)
What is the equation for the rate of an enzyme reaction from the amount of product formed?
rate = amount of product formed ÷ time (e.g. g per minute)
What is a biological catalyst?
A substance (an enzyme) that speeds up the rate of a reaction in a living organism without being used up itself.
What are proteins broken down into by a protease?
Amino acids.
What is starch broken down into by amylase (a carbohydrase)?
Sugars (such as maltose) — the bonds between the glucose units in the starch polymer are broken.
What are lipids broken down into by lipase?
Fatty acids and glycerol — the fatty acids make the mixture more acidic, lowering its pH.
True or false? Enzymes only break large molecules down; they are not needed to build large molecules.
False. Enzymes also catalyse synthesis reactions, joining small molecules to make carbohydrates, proteins and lipids.
In an investigation, one tube contains starch solution with distilled water instead of amylase. Give one reason this tube is included.
It is a control — to check that starch does not break down into sugars without amylase.
True or false? Cooling an enzyme to 0°C denatures it.
False. Low temperature slows enzyme activity (fewer collisions with the active site) but does not change the shape of the active site, so activity returns when it is warmed.
In an enzyme investigation, what is an anomalous result?
A repeat result that does not fit the pattern of the other repeats.
e.g. one curdling time of 45 s when the other repeats at that temperature are 20 s and 22 sWhat should you do with an anomalous result when working out the mean time for an enzyme reaction?
Leave it out, and calculate the mean from the remaining repeats only.
What is the 'lock and key' model of enzyme action?
A model of how enzymes work: the active site has a shape that only the matching substrate fits, just as only the right key fits a lock.
Why does the rate of an enzyme-controlled reaction fall above the optimum temperature?
The high temperature breaks bonds that hold the enzyme in shape. The active site changes shape and the substrate can no longer bind, so the enzyme is denatured.
Which enzyme joins glucose molecules together to make glycogen?
Glycogen synthase. Glycogen is a store of energy in animals.