enzymes Flashcards
what are enzymes
- biological catalysts
- globular proteins
- interact with substrate molecules
- causing them to react at much faster rates
what are anabolic reactions
- ‘building up’
- needed for growth
- catalysed by enzymes
what are catabolic reactions
- ‘breaking down’
- in metabolic pathways which release energy
- catalysed by enzymes
what is metabolism
- the sum of all different reactions and reaction pathways happening in a cell/organism
- can only happen with enzymes
what is the Vmax
- enzymes can only increase the rates of reaction up to a certain point called the Vmax
- Vmax is the maximum rate of an enzyme-catalysed reaction
what is the specificity of an enzyme
each enzyme catalyses one biochemical reaction, of which there are thousands in any given cell
what is activation energy
- the energy needed to be supplied in order for a reaction to start
- enzymes can reduce the activation energy because they help molecules collide successfully
Lock and key hypothesis
- only a specific substrate will fit in the active site of an enzyme
- an enzyme-substrate complex is formed when the substrate binds to the active site
- the R groups in the active site will interact with the substrate, forming temporary bonds
- these put a strain on the bonds within the substrate
- the substrates react and products are formed in an enzyme-product complex
- the products are released
- the enzyme is unchanged and able to be reused
what is the active site of an enzyme
an area within the tertiary structure which has a shape that is complementary to the shape of a specific substrate molecule
the induced fit hypothesis
- the active site of the enzyme changes slightly as the substrate enters
- the initial interaction between the enzyme and the substrate is relatively weak
- these interactions rapidly induce changes in the enzyme’s tertiary structure that strengthen binding
- this puts a strain on the substrate molecule
- this weakens bonds in the substrate. lowering the activation energy
what are intracellular enzymes- give an example
- enzymes that act within cells
- catalase breaks down hydrogen peroxide (toxic byproduct of metabolic pathways) to oxygen and water
what are extracellular enzymes
- enzymes that are released from cells to break down large nutrient molecules into smaller molecules (digestion)
- these smaller molecules can now be absorbed by the cell
- e.g. amylase, trypsin
digestion of starch
- starch polymers are partially broken down into maltose (disaccharide) by amylase
- amylse is produced in the salivary glands and pancreas
- maltose is broken down into glucose(monosaccharide) by maltase
- maltase is present in the small intestine
- glucose is small enough to be absorbed by cells and the bloodstream
digestion of proteins
- trypsin is a protease
- proteases are a type of enzymes that catalyse digestion of proteins into smaller peptides
- peptides are broken down further into amino acids by other proteases
- trypsin is produced in the pancreas and released with pancreatic juice to the small intestine where it acts on proteins
- amino acids produced are absorbed by cells and bloodstream
what factors affect enzymes
- temperature
- pH
what is the temperature coefficient Q10
- a measure of how much the rate of reaction increases with a 10C rise in temperature
- for enzyme controlled reactions it usually doubles with a 10C temperature increase
why does increasing temperature increase rate of reaction of enzyme-controlled reactions
- increased K.E. of particles
- particles move faster
- more frequent successful collisions between substrate and enzyme
why do enzymes denature
- at higher temperatures, the bonds holding the protein together vibrate more
- vibrations icnrease until the bonds strain and then break
- change in tertiary structure of the protein
- enzyme has changed shape
- the active site has changed shape and is no longer complementary to the substrate
- substrate can no longer fit into the active site so enzyme will no longer function as a catalyst
- enzyme is denatured
what is the optimum temperature
- the temperature a which the enzyme has the highest rate of activity
- most enzymes in the human body have optimums of around 40C
where are thermophilic bacteria found
hot springs
where are psychrophilic orgnisms found
cold areas such as antarctic and arctic regions
what are enzymes adapted to the cold like
- more flexible structures, particularly the active site
- making them less stable
- smaller temperature changes will denature them
what are thermophiles
- organisms adapted to living in very hot environments like hot springs
- enzymes are more stable due to increased number of bonds (hydrogen, disulfide in tertiary s.)
- shape of these enzymes and active sites are more resistant to change as temperature increases
what does a change in PH refer to
- a change in the hydrogen ion concentration
- low pH- more hydrogen ions
- high pH- less hydrogen ions
what is the optimum pH
the certain hydrogen ion concentration at which the active site will be in the right shape
what is renaturation
when the pH returns to the optimum pH, the protein will resume its normal shape and catalyse the reaction again
why does the shape of the enzyme change as the pH changes
- the more H+ ions, the less the R-groups are able to interact with each other
- this leads to bonds breaking and enzyme shape changing
- this is because H+ ions interact with polar/charged R-groups
- the degree of this interaction is changed when pH changes
what can enzymes be activated by
cofactors
what can enzymes be inactivated by
inhibitors
what are inhibitors
molecules that prevent enzymes from carrying out their normal function of catalysis
what is competitive inhibition
- molecule with similar shape to substrate can fit into the active site
- substrate is blocked from the active site
- enzyme is prevented from catalysis
- enzyme cannot carry out its function so it is inhibited
- reduced number of enzyme-substrate complexes so reduced rate of reaction
do competitive inhibitors bind temporarily?
- they only bind temporarily to the active site
- their effect is reversible
- with the exception of aspirin
effect of competitive inhibitors on rate of reaction
- reduced rate of reaction for a given concentration of a substrate
- does not change the Vmax of the enzyme it inhibits
- if substrate concentration is increased enough, the Vmax can still be reached
example of competitive inhibition
- statins are competitive inhibitors of an enzyme used in the synthesis of cholesterol
- aspirin irreversibly inhibits the active site of COX enzymes, preventing synthesis of chemicals which produce pain
non-competitive inhibition
- inhibitor binds to enzyme at allosteric site
- causes change in the tertiary structure of the enzyme so active site changes shape
- active site no longer complementary to substrate and unable to bind to it
- enzyme cannot carry out its function so it is inhibited
effect of non-competitive inhibition on rate of reaction
- increasing concentration of enzyme or substrate will not overcome inhibitor
- increasing concentration of inhibitor will decrease rate of reaction as more active sites become unavailable
what is end-product inhibition
- enzyme inhibition that occurs when the product of a reaction acts as an inhibitor for the enzyme that produces it
- negative feedback
- non-competitive reversible inhibition
what is a cofactor
- non-protein component needed by the enzyme to carry out its function as a biological catalyst
- inorganic
- obtained via the diet as minerals
what is a coenzyme
- non-protein component needed by the enzyme to carry out its function as a biological catalyst
- organic
- obtained from the diet as vitamins
what cofactor does amylase contain
chloride ion necessary for formation of a correctly shaped active site
what does vitamin B3 synthesise
- NAD- a coenzyme responsible for transfer of hydrogen atoms between molecules in respiration
- NADP- photosynthesis
what does vitamin B5 make
- coenzyme A which is essential for breakdown of fatty acids and carbohydrates in respiration
what are prosthetic groups
- required by enzymes to carry out their catalytic function
- they are tightly bound to form a permanent feature of the protein
- e.g. carbonic anhydrase contains Zn2+ ions . It is an enzyme for metabolism of CO2
what are inactive precursor enzymes
- enzymes that are produced in an inactive form
- particularly those that cause damage within the cells producing them or to tissues when they are released, or enzymes that need to be controlled and only activated in certain conditions
how can precursor enzymes be activated
- they need to undergo a change in shape (tertiary) to be activated
- can be achieved by the addition of a cofactor
what is an apoenzyme
a precursor enzyme before its cofactor is added
what is a holoenzyme
a precursor enzyme after its cofactor is added and the enzyme is activated
what are zymogens or proenzymes
when a change in conditions (pH or temp) results in a change of tertiary structure and activates a precursor enzyme
what happens when pepsinogen is released into the stomach
- pepsinogen is inactive
- it digests proteins
- the acid pH transforms it into the active enzyme pepsin
- this protects body tissues against the digestive action of pepsin
