1.4.2 - How enzymes work Flashcards
what is activation energy?
the energy needed for a reaction to get started
(in other words, the energy the reacting molecules must have in order to break the chemical bonds that hold them together)
what is a substrate?
the molecule or molecules on which an enzyme acts
what is the lock-and-key hypothesis?
model that explains enzyme action by an active site in the protein structure that has a very specific shape
- enzyme and substrate fit together to form a complex
- (as a key fits a lock)
what is the active site?
area of an enzyme that has a specific shape into which the substrate of a reaction fits
- it is this that gives the enzyme its specificity
how can the activation energy be lowered?
- by the formation of the enzyme/substrate complex
- active site affects the bonds in the substrate –> making them easier to break
- the reacting substances are brought closer together, making it easier for the bonds to form between them
what is the induced-fit hypothesis?
a modified version of the lock-and-key hypothesis for enzyme action
- where the active site is considered to have a more flexible shape
- however, it still has a distinctive shape and arrangement
explain the induced-fit hypothesis.
- once the substrate enters the active site, the shape of that site is modified around it to form the active complex
- once the products have left the complex, the enzyme reverts to its inactive, relaxed form
- until another substrate molecule binds
how could you investigate the effect of an enzyme?
- measure the rate of reaction with and without the enzyme
- scientists use this and it has shown that enzymes generally increase reaction rates by factors from 10^8 to 10^26
- (why only tiny amounts of enzymes are needed)
what is the initial rate of reaction?
the measure taken to compare the rates of enzyme controlled reactions under different conditions
- used to investigate the way a factor affects the rate of reaction
- this area is the maximum reaction rate for an enzyme under particular conditions
what happens if the 3D shape of the enzyme is affected?
- it will affect its ability to do its job
- therefore, the 3D nature of enzymes is important to the way it works
- a change in shape of the enzyme changes the shape of the active site as well –> enzyme can no longer function
what is the molecular activity of an enzyme? (or turnover number)
the number of substrate molecules transformed per minute by a single enzyme molecule
name the factors that affect enzyme controlled reactions?
- the concentration of enzymes
- the concentration of substrate (if the enzymes become saturated then only an increase in enzymes will speed up the rate of reaction - an increase in substrate concentration won’t do anything as there are only so many active sites available)
- the temperature ( number of successful collisions increases at higher temperatures)
- pH (affects the shape of proteins)
what is the temperature coefficient?
Q10
the measure of the effect of temperature on the rate of reaction
Q10 = rate of reaction at (x + 10)°C / rate of reaction at x °C
at what temperature do enzymes start to denature?
40°C
- most proteins will start to lose their tertiary and quaternary structure
- shape of active site changes –> lose their ability to catalyse reactions
what do enzymes that denature at higher temperatures posses compared to other enzymes?
- temperature - resistant proteins
- they contain a very high density of hydrogen bonds and disulfide bonds
- these hold the enzyme together even at high temperatures
