enzymes Flashcards
define enzyme
biological catalysts that interact with a substrate to facilitate chemical reactions
what type of protein usually makes up an enzyme?
globular proteins
define substrate
chemical reactants that enzymes bind to
define product
substance formed from a chemical reaction
explain why enzymes are necessary for life
- most important metabolic reactions are slow
- would need to happen at very high temp + pressures to be fast enough to match demand
- these conditions would damage cell components + impossible to reach in living cells
- enzymes speed up metabolic reactions w/o needing harsh environmental conditions
define an anabolic reaction
metabolic reactions that construct molecules from smaller units
- require energy
define a catabolic reaction
metabolic reactions that break molecules down into smaller units
- release energy
define digestion
process where large biomolecules are hydrolysed into smaller constituent molecules so can be absorbed across cell membranes
define metabolism
sum of all of the different reactions and reaction pathways happening in a cell or an organism
define intracellular enzyme + example
enzymes that act within cells
- eg. catalase
define extracellular enzyme + example
enzymes that act outside of cells (released from cells to act outside them)
- eg. amylase, trypsin
state the substrates and products of amylase, trypsin and catalase
- amylase (starch –> maltose)
- trypsin (protein –> peptide)
- catalase (hydrogen peroxide –> H2O + O2)
explain the role of extracellular enzymes in general
digest nutrients into smaller molecules so that they can be absorbed and used by cells
summarise the digestion of starch as an example of the role of extracellular enzymes.
- starch polymers partially broken down into maltose (disaccharide) using amylase (released in saliva, produced by salivary glands and pancreas)
- maltose is broken down into glucose (monosaccharide that can be absorbed by cells) using maltase (present in small intestine)
summarise the digestion of proteins as an example of the role of extracellular enzymes.
- proteins digested into smaller peptides using trypsin (produced in pancreas and released into small intestine)
- peptides further broken down into aa by other proteases
- aa are absorbed by cell lining of digestive system, then absorbed into bloodstream
define active site
area of an enzyme with a shape complementary to a specific substrate so enzyme can bind to a substrate with specificity
define specificity
term that describes how each enzyme catalyses one biochemical reaction
explain why an enzyme only catalyses one type of reaction.
- different enzymes have differently shaped active sites
- each active site is complementary to a specific substrate shape
- so each enzyme will only be able to catalyse a specific substrate + only one type of reaction
state the sequence of events in an enzyme-controlled reaction.
- molecules move and randomly collide
- when substrate binds to specific enzyme, it forms enzyme-substrate complex
- substrates react and products are formed in enzyme-product complex
- products are released, leaving enzyme unchanged and able to catalyse more
describe the lock and key hypothesis
- idea of a specific key fitting into a specific lock
- active site shape is exactly complementary to the shape of the substrate
- enzyme does not change shape
describe the induced-fit hypothesis
- enzyme changes shape slightly as the substrate enters
- weak interactions between substrate and enzyme induce change in tertiary structure that strengthen bind, putting strain on substrate molecule
- bonds weaken in the substrate, lowering the activation energy
define activation energy
energy required to initiate a reaction.
suggest how R-groups of amino acids are involved in catalysing reactions.
- R-groups interact with substrate, forming temporary bonds
- the bonds put strain on bonds within substrate which helps lower the activation energy
state what the presence of an enzyme does to the activation energy for the reaction and explain why this increases the rate of reaction.
- enzymes lower activation energy
- so lowers minimum amount of energy required in particles for them to react
- higher proportion of particles are able to react = more reactions happen during a given time interval = higher rate
