Module 2.1.4 Enzymes Flashcards
What are enzymes?
Globular proteins that have a specifically shaped active site formed in the tertiary structure
What is a biological catalyst?
A molecule that speeds metabolic reactions without being used up/changed
What types of reaction can enzymes catalyse?
Cellular level (e.g. respiration)
The whole organism
How does an enzyme affect an organism?
Can affect structures & functions
Are enzymes intracellular or extracellular?
Can be both
What is an intracellular enzyme?
An enzyme that works inside cells
What is an example of an intracellular enzyme & its function?
Catalase -> catalyses the breakdown of hydrogen peroxide into water & O2 as if it accumulates, it can become toxic
What is an extracellular enzyme?
An enzyme that works outside cells
What are some examples of extracellular enzymes & their functions?
Amylase -> found in saliva & secreted from the salivary glands, catalyses the hydrolysis of starch into maltose
Trypsin -> produced in the pancreas, found in the small intestine & catalyses the hydrolysis of peptide bonds in proteins
How do enzymes speed up rate of reaction?
They lower the activation energy to speed it up
What is the activation energy?
The minimum amount of energy required to start a reaction
How do enzymes reduce activation energy?
Via the formation of enzyme-substrate complexes
What is an enzyme-substrate complex?
When the substrate fits into the active site putting a strain on their bonds (which are needed to break down) & repulsion is reduced between substrates which need joining allowing bonds to break/form more easily
What is the active site?
A cleft/depression specifically shaped by the tertiary structure
What are the 2 mechanism models of enzyme activity?
The lock & key fit model
The induced fit model
What is the lock & key model?
A model of enzyme activity suggests that a substrate fits into the specifically shaped active site due to its complimentary shape allowing an exact fit
What is the induced fit model of enzyme activity?
A newer model of the lock & key model suggesting the active site changes shape slightly to fit the substrate more closely but the substrate must be near to being exactly complementary
What are the similarities between the 2 models?
The substrate fits into the active site to form an enzyme substrate complex, reaction occurs & chemically changes the substrate to form an enzyme product complex, then the products are released
What are the 4 factors affecting enzyme activity?
Temperature
PH
Enzyme concentration
Substrate concentration
How does temperature affect enzyme activity?
As temperature increases, so does the kinetic energy of the molecules. This increases the rate of successful enzyme-substrate collisions and therefore the rate of reaction. Once temperature goes above optimum, the rate of reaction decreases as the molecules vibrate too much and break the bonds holding the enzymes tertiary structure in place. This causes the active site to change shape & therefore denatures the enzyme
How does PH affect enzyme activity?
Above & below the optimum pH of the enzymes, H+ & OH- ions in acids & alkalis disrupt the ionic & hydrogen bonds holding the tertiary structure in place. This causes the active site to change shape & therefore denatures the enzyme
What is the temperature coefficient?
Q10 -> how much the rate of reaction changes when the temperature is raised by 10 degrees
Q10 + R2(rate at higher temp)/R1 (rate at lower temp)
How does enzyme concentration have an effect on enzyme activity?
As the concentration increases, the amount of molecules present in the reaction increases. This causes more successful enzyme-substrate collisions which increases the rate of reaction.
What happens when there is limited substrate & the enzyme concentration is further increases?
There will be no further effect as it will be unused
How does substrate concentration have an effect on enzyme activity?
As concentration increases, so does the number of molecules present in the reaction. This increases the likelihood of sucessful enzyme-substrate collisions & therefore the rate of reaction
What happens if there is limited enzyme concentration & an increasing substrate concentration?
There will be no further effect as the enzyme will reach saturation point which, if left unchanged with decrease the rate of reaction as the substrate is used up
What is the saturation point?
The point that all the active sites are occupied
What is a cofactor?
A non-proteins substance bound to some enzymes which helps the enzyme & substrate bind together but doesnt directly participants in the reaction (remains unchanged)
Inorganic molecules/ions
What is an example of a cofactor in an enzyme?
Cl- in amylase
What is a coenzyme?
Organic cofactors which participate in the reaction & are changed by it, allowing them to act as carriers of different chemical groups between different enzymes being continually recycled during this process
What is an example of a coenzyme?
Vitamins
What are prosthetic groups?
A cofactor that is tightly bound to the enzyme
What is an example of a prosthetic group?
Heme -> haemoglobin
What are the 4 different types of inhibitors?
Competitive
Non-competitive
Reversible
Irreversible
What are the characteristics of competitive inhibitors?
Similarly shaped to the substrate
Compete with the substrate to bind to the active site, blocking it so no enzyme-substrate complex can form so there is no reaction
If substrate concentration is greater than the inhibitor concentration, rate of reaction with increase until all non-inhibited enzymes are saturated
What are the characteristics of non-competitive inhibitors?
- Different shape to the substrate
- Doesn’t compete with the substrate & instead binds to the allosteric site on the enzyme, which causes a reaction & the active site to change shape so the substrate can no longer fit & an enzyme-substrate complex cannot form
- Increasing the substrate concentration wont effect the reaction rate as the substrate is no longer complementary to the active site
What are the characteristics of reversible inhibitors?
Removed easily
Held by weak hydrogen/ionic bonds
What are the characteristics of irreversible inhibitors?
Cannot be removed easily
Held by strong covalent bonds
What are some examples of enzymes inhibitors as metabolic poisons?
Cyanide -> inhibits cytochrome C oxidase
Malonate -> inhibits succinate dehydrogenase
Arsenic -> inhibits pyruvate
All involved in respiration reactions, when inhibited cells cannot respire = death
What are some examples of enzyme inhibitors as asmedicinal drugs?
Antiviral drugs -> reverse transcriptase inhibitors (inhibits reverse transciptase) -> virus cannot replicate
Antibiotics -> penicillin -> inhibits transpeptidase -> prevents proteins synthesis in the bacterial cell walls which weakens the cells well so it will burst due to osmotic pressure not
being regulated
What are inactive precursors?
Molecules that are unable to function which prevent them causing damage to cells
What is an example of inactive precursors?
Some protease enzymes -> synthesised as an inactive precursor to stop them damaging proteins in the cells they are made
Can an inactive precursors turn back into an enzyme?
Yes as when the inhibiting part of the precursor is removed the enzyme becomes active again
What is a metabolic pathway?
A series of connected metabolic reactions in which the product of the first reaction takes part in the second reaction and so on with each reaction being catalysed by a different enzyme
What is production inhibition?
When an enzyme is inhibited by the product of the reaction it catalyses which is reversible
What is end product inhibition?
When the final product in a metabolic pathway inhibits an enzyme catalysing a reaction from earlier on in the pathway
What is positive about end product inhibition?
It is a good way of controlling the amount of end product produced as it is reversible (when the level of product falls the level of inhibition will fall and the enzyme can function again to produce more product)
