C1.1 Enzymes Flashcards
Enzyme
Globular protein that alters the rate of a reaction without taking part in it.
Induced Fit
binding of substrate induces a conformational change in the substrate and the active site. Both adjust their shape to provide an optimal fit.
Intracellular enzyme
- enzymes that are produced in certain cells and remains to react in the cell
- could exist in cytoplasm (in organelles) or in nucleus
free ribosomes to nucleus/mitochondria/lysosomes
Extracellular enzyme
Enzyme produced by a cell but then transported out of the cell for action outside of cell
ER ribosomes to golgi to vesicles to outside cell
Factors affecting rate of reaction
1) Temperature
2) catalyst (+its concentration)
3) concentration of reactants
4) position of functional groups
5) pressure
6) presence of inhibitor
key terms
V max - maximum rate [decided by substrate conc, high sub conc means enzyme active sites fully occupied leading to plateau in reaction rate]
optimum rate - steady rate based on environment (pH, temp, enzyme conc)
graph terms
proportional increase
plateau
Steps
1) Substrate binds to active site of enzyme because of structural and chemical specificity
2) While the substrates are bound to the active site (ES complex or intermediate stage or transition state), bonds in the substrate are stressed or weakened causing it to change into different chemical substances (products)
3) The products separate from the active site, leaving it vacant for substrates to bind again.
Substrate specific
Over 3 dimensional structue and the enzymes amino acid sequence in the active site is specific to the substrate. This ensures that the active site binds to the substrate molecules, holds on to it and lowers the activation energy for the reaction.
3 factors affect substrate-active site collisions
1) molecular motion of both enzyme and substrate causes random collisions between molecules. Reaction occurs in aqueous solution (ensures constant motion of molecules)
2) correct alignment and angle affects success rate of collision
3) speed of movement (affected by size of molecules) substrates are usually smaller than enzymes so their motion is faster.
Denaturation
High temperature causes denaturation as the extra energy leads to increased vibration, breaking intramolecular bonds within the protein (peptide, disulfide bridge) - irreversible
Changes in pH lead to high or lower concentration of hydrogen ions in the solution - as a consequence hydrogen bonds within the enzyme are broken - disrupts R-group stability - reversible
Rate of enzyme
k1/t or k2/t
k2/t usually taken
instantaneous rate of reaction (because rate isn’t linear) - tangent and then change in product over change in time
Cyclic and Linear pathway
- most chemical changes don’t happen in one big step but many small steps
- most metabolic pathways involve a linear chain of reactions
- some metabolic pathways form a cycle (the end product of one reaction starts the rest of the pathway)
Enzyme inhibition
some chemical substance reduce or even prevent enzymatic reactions to happen by blocking the enzyme
These chemical substances are called inhibitors (or enzyme inhibitors)
Non-competitive inhibition and allosteric sites
- active site shape is changed by non-competitive inhibitor in allosteric site
- substrate and inhibitor are no chemically similar
- the inhibitor binds to a different site (anwhere but active site of the enzyme)
- the enzyme is denatured
- reversible
- allosteric inhibitors are a class of non competitive inhibitors where the inhibitor binds to a specific allosteric site, causing changes to enzyme or active site
- substrate may still be able to bind to the active site, but reaction may not take place or only at a slow rate.
Competitive inhibitor
- similar to substrate
- mimic subtrate, competes with substrate to bind to active site
- can be reversed with a higher substrate concentration
- active site + enzyme is intact
competitive vs non competitive
competitive:
- competes for active site
- reversible
- substrate binding decreases so ES complex decreases
- increasing sub conc reverses effect of inhibitor
- v max not affected
- initial ROR and velocity decrease
non competitive:
- active site changed by non comp inhibitor in allosteric site
- reversible
- substrate bind decreases, ES complex drastically reduces
- even if s conc increases, can’t reverse effect
- v max drastic decrease
- initial ROR decrease + intial velocity decrease
Heavy metal poisoning
- irreversible non comp
- metals such as lead, mercury, arsenic, or copper bind irreversibly bind to the active site of the enzyme by forming strong covalent bonds
- occurs at amino acids with sulfur-containing R-groups
- active site changes configuration (further substrate binding can not occur)
Cyanide
- poison which prevents ATP production via aerobic respiration (leads to eventual death)
- Non comp - binds to allosteric site on cytochrome oxidase
- cytochrome is a carrier molecule that forms part of the ETC
- without functioning enzyme, electrons can not be passed on to the final acceptor (oxygen)
- this blocks the respiration pathway, resulting in suffocation and death, it’s too quick of a process to be reversed
Sarin (nerve gas)
- used in biological warfare
- non comp, irreversible
- inhibitor of acetylcholinesterase (responsible for reuptake of acetlycholine and regulation of excitatory nerve impulse)
- if acetylcholine doesn’t under go reuptake, it will always be in an excited state. THe nerve endings will continually be active, leading to nerve damage and death
ACE inhibitors
- competitive
- angiotensin is a substance produced by enzyme ACE
- induces vasoconstriction or blood vessel contraction
- binds to receptors in walls of artieries, inducing constriction of blood vessels leading to increase in blood pressure
- people suffering from high blood pressure can be treated with ACE inhibitors that reduces synthesis of angotensin
Statins
- competitive inhibitors
- statins are medicine
- bind to enzymes used to synthesize cholesterol in liver cells
- treat cardiovascular disease
Penicillin
- binds to enzyme transpeptidase
- enzyme is responsible for synthesis of bacterial cell wall by forming cross-links
- competitive but irreversible
- forms covalent bond with acctive site, permanently damaging it
Feedback inhibition
- enzyme pathways can be controlled by product concentration (end product inhibition)
- end product inhibition involves allosteric enzymes with active and allosteric site
