enzymes Flashcards
what kind of proteins are enzymes?
globular proteins (tertiary structure)
what is metabolism?
all enzyme controlled reactions in the body
what is anabolism?
synthesis of complex molecules
what is catabolism?
the reactions that break down more complex molecules into separate products
what are metabolic pathways?
a series of reactions where the product of one enzyme is the substrate of another
what is an example of an anabolic reaction?
protein synthesis and photosynthesis
what is an example of a catabolic reaction?
digestion and respiration
what are the two enzyme-substrate formation theories?
lock and key theory and induced fit theory
what is the lock and key theory?
the substrate has a complementary shape to the enzyme’s active site
what is the induced fit theory?
the enzymes active site is altered by the binding substrate molecule - active site changes to bind with the substrate
what do enzymes do as biological catalysts?
they lower the activation energy needed to start a reaction- chemical reactions speed up
what is activation energy?
the minimum energy required that must be put in a chemical system for a reaction to occur
what 5 things impact enzyme action?
pH, temperature, enzyme conc., substrate conc., presence of inhibitors
what are the two types of inhibitors for enzymes?
competitive and non-competitive inhibitors
what are competitive inhibitors?
a molecule that has a similar shape to the substrate and so it also has a complementary shape to the active site - prevents ES complex forming but binding site will eventually become free again
what are non competitive inhibitors?
these bind to an allosteric site on the enzyme. this changes the shape of the enzyme, preventing substrate molecules from forming an ES complex
what happens to the rate of reaction when the substrate concentration increases?
ROR also increases since there is a greater chance of a successful collision resulting in more ES complexes forming. when all enzyme active sites are occupied, a plateau is reached - max ROR
what happens to the rate of reaction when the temperature increases?
both substrate and enzyme gain kinetic energy, so move faster which increases chance of successful collisions. ROR reaches optimum - above this, H bonds break in the tertiary structure due to increased vibrations and enzyme denatures
how does the pH level effect the enzyme’s ROR?
when the pH increases/decreases either side of the optimum, the rate of reaction decreases
what will happen to the substrate if too many H+ or OH- ions are present?
the substrate can be repelled from the active-site, preventing it from binding
what are the use of buffers in enzyme experiments?
ensures that pH is controlled ideally at its optimum, so that it is not limiting the rate of reaction
what is a pH buffer for enzymes?
a solution that can resist changes in pH by neutralising acid/alkalis that are added to the solution.
what is an immobilised enzyme?
enzymes that are fixed to an inert matrix - does not mix with substrate in solution
how are immobilised enzymes achieved?
entrapment (held inside a gel) or micro-encapsulation (trapped inside a micro-capsule)
what are 4 advantages to immobilising enzymes?
- enzyme can be recovered + reused
- product is not contaminated by enzyme
- more stable at higher temps.
- catalyse reactions in a wider range of pH
what is a disadvantage of immobilising enzymes?
enzyme may bind with a lower substrate affinity
what happens when enzymes are in an inert substance?
reduces ability of polypeptide chain to move, so changes in temperature and pH have less of an effect on the enzyme shape
what is an example of an industrial use of immobilised enzymes?
immobilising lactase to produce lactose-free milk
how is lactose-free milk produced?
lactase is immobilised in alginate gel beads. milk is passed over the beads and lactase digests the lactose into glucose and galactose. the milk is not contaminated by the enzyme and the beads can be reused
what are some examples of immobilised enzymes used in medicine?
biosensors (glucose oxidase) and analytical reagents
what are the steps in using a biosensor?
An enzyme electrode is placed on a blood sample. The glucose diffuses up into the immobilised enzyme layer, where O2 is taken up. The rate of O2 uptake is proportional to glucose conc. Glucose conc. is displayed on a digital display
How do biosensors work?
work on the principle that enzymes are specific and able to select one type of molecule from a mixture even in very low conc. electrode probe detects changes in substrate or product ect.
