module 2 - 2.1.4 enzymes Flashcards
what are enzymes?
biological catalysts
how does the enzyme molecule bind to the active site?
collisions between enzyme and substrate
what happens to the product molecules?
diffuse away from the active site
what is the most important function of proteins?
catalysis
what happens in the absence of catalysis?
reactions in biological systems would happen far too slowly to provide products at a good pace for metabolising organisms
where do catalysts serve their function?
living organisms called enzymes
what type of proteins are enzymes?
globular proteins
what can enzymes increase the rate of reaction up by a factor of?
10^20 over uncatalysed reactions
in an enzyme-catalysed reaction, what does the enzyme bind to?
substrate to form a complex
what does the lock and key model propose?
the substrate binds to the active site which fits exactly
what are some characteristics of enzymes?
- they are proteins of high molecular weight
- they are biological catalysts
- sensitive to temperatures, pH and concentration
- generally specific in reactions they catalyse
what happens at the active site?
chemical reactions take place
what happens if the temperature is not controlled?
if temp is too low, chemical reactions happen and a slower rate, is temp is too high, it can cause the enzyme to denature and therefore not fit with the substrate
what does it mean when enzymes are of a ‘high molecular weight’?
contain lots of amino acids
what is the induced fit model?
model that takes into account the fact that proteins (enzymes) have some three-dimensional flexibility
what happens to the enzyme in the induced fit model?
binding of the substrate induced the enzyme to change shape and form an exact fit
according to the induced fit model, when can reactions take place?
after the induced fit has occurred
why are enzymes catalysts?
they lower the activation energy needed to drive a reaction
what do substrates need to overcome before they convert to products?
an energy barrier
what happens in relation to molecular collisions at low temperatures?
- molecules are constantly in motion and colliding with one another
- the speed of motion and number of collisions is affected by temperature (slower - less energy)
what happens in relation to molecular collisions at high temperatures?
- more enzyme-substrate complexes
- more product molecules are formed at higher temperatures
what temperature is the maximum rate of reaction reached?
between 37°C to 40°C
this is called the optimum temperature
what happens when the temperature increases beyond the optimum?
- the bonds that stabalise the enzyme’s secondary and tertiary structure are broken
- enzyme loses shape (denatures) and can no longer bind to the active site
why is the optimum temperature (37°C to 40°C) not true for all enzymes?
- some bacteria are extremophiles/ thermophiles that are thermostable and so can survive in high temperatures
- optimum temp is 80°C
what is an example of a thermophile/ extremophile?
bacteria that live in hot geysers
which bonds stay together when an enzyme has denatured?
the peptide bonds
what is Q10?
the reaction rates doubles for every 10°C rise in temperature
when does Q10 occur?
in the temperature range from 4°C to 40°C
what does Q10 equal when it doubles every 10°C?
Q10 = 2
what happens to the product when there is low substrate concentration?
low product concentration per unit time
what happens to the product when there is an increased substrate concentration?
more product formed, increased reaction rate
how is the acidity of a solution measured?
measured by the concentration of hydrogen ions (H+) and is expressed in terms of pH
what are the specific conditions that an enzyme can work in?
- particular range of pH
- each enzyme has its own optimum pH where the rate of reaction is maximum
what do the effects of pH on the rate of enzyme controlled reactions display characteristically on a graph?
bell shaped curves
what can a change in pH affect?
can affect the ionic and hydrogen bonds that make the specific tertiary structure of enzymes
what do extremes of pH result in?
- breaks the hydrogen and ionic bonds
- denatures the enzyme
what does pH stand for?
potential hydrogen (ions)
what happens to the hydrogen concentration if an acid is added to pure water?
hydrogen ion concentration increases
what happens to the hydrogen if a base is added to pure water?
- hydrogen ion concentration decreases
- hydroxyl ion concentration increases
what does an acidic solution contain within the solution?
H+ ions and one OH- ion
what does an alkaline solution contain within the solution?
OH- ions and one H+ ion
what happens if there is further increase in substrate concentration?
- maximum product formation
- maximum rate of reaction
what happens if there is excess substrate concentration? what is the limiting factor?
- no further increase in product formation
- maximum reaction rate maintained
- enzyme concentration is a limiting factor
what happens when a reaction reaches V Max.?
- no further increase in reaction rate
- all active sites of the enzymes are occupied
what does it mean if the rate of reaction is directly proportional to the enzyme concentration?
as enzyme concentration increases, rate of reaction increases
what does the presence of a reversible inhibitor do to the rate of enzyme controlled reactions?
inhibitor molecules decrease in the rate of enzyme reactions by reversible combinations
what is a competitive inhibitor?
when a molecule competes with the normal substrate active site though random collisions (can be reversible)
where do reversible inhibitors attach to on the enzyme?
attaches to the enzyme at a position away from the active site
what happens once the inhibitor has attached to the enzyme away from the active site?
- the substrate molecule can still bond to the active site
- substrate cannot be converted into product as inhibitor changes shape of active site preventing induced fit
what is the effect of competitive inhibitors on enzyme action?
low substrate concentration makes the inhibitor compete successfully for the active site
- reduced rate (less substrate molecules converted to products)
what happens to the inhibitor when substrate concentration is low?
low substrate concentration makes the inhibitor compete successfully for the active site
- reduced rate (less substrate molecules converted to products)
what is the effect of competitive inhibitors on enzyme action?
to overcome when high concentration of substrate molecules compete successfully for the active sites of enzymes
how can the effect of competitive inhibitors be overcome?
- by very high concentrations
- high temperatures cause the inhibitor to be out-competed
what is a non competitive inhibitor?
- the inhibitor works elsewhere
- substrate molecules not converted when inhibitor molecules are bound to the enzyme
what happens at high substrate concentration with non-competitive inhibitors?
all active sites are occupied
what happens to substrate molecules bound to enzymes with attached inhibitors?
- they are not converted into products
- maximum reaction rates are never achieved
when are substrate molecules converted into product?
when there is no inhibitor attached to enzyme
what are metabolic pathways?
sequences of chemical reactions each controlled by a specific enzyme
when is it wasteful for a sequence of chemical reactions to continue?
when the end product in being produced at a rate too much for the requirements
what are hydrolases?
an enzyme that catalyses hydrolysis reactions
what is maltOse?
a disaccharide consisting of 2 alpha-glucose molecules joined by 1-4 glycosidic bond
what is maltAse?
a hydrolase enzyme that catalyses the hydrolysis of maltose into 2 glucose molecules
what are transferases?
enzymes that catalyse reactions that transfer atoms from one molecule to another
during cellular respiration, which group is transferred from ATP to glucose?
a phosphate group
what are oxidoreductases?
enzymes that catalyse reactions involving oxidation and reduction
what is oxidation?
- addition of oxygen
- removal of hydrogen atoms
- removal of electrons
what is reduction?
- removal of oxygen
- addition of hydrogen atoms
- addition of electrons
what are cofactors?
non-protein chemical compounds
what are cofactors required for?
- ‘helper molecule’
- required for enzyme activity as catalyst
what are holoenzymes?
an active enzyme with non protein component (cofactor)
what are apoenzymes?
an inactive enzyme without its non protein component (no cofactor)
what is a coenzyme?
small organic molecule that binds with specific enzymes, helping to catalyse a reaction
what are the main enzymes used in respiration?
- NAD
- CoA
- FAD
what are prosthetic groups?
- non protein group combined with a protein
- tightly bound, specific non polypeptide unit used for biological functions of some proteins
what is the catalase formula?
2H20 –(catalase)-> 2H2O +O2
