L3- Enzymes Flashcards
enzymes are
biological catalysts that increase the rate of reaction by lowering the activation energy - reduces amount of energy for transition state
activations tate
minimum energy substrate must have to allow reaction
transition sttae
high energy intermediate that lies between substrate and product
what can affect the rate fo reaction
1) temperature 2) concentration 3) enzymes
temp
increases number of molecules with activation energy
conc
increases chance of molecular collisions
enzymes are
highly specific- only work on one substrate
enzymes do not affect
reaction equilibrium- will not make an unfavourable reaction favourable
enzymes remain
unchanged after the reaction
enzymes may require
cofactors
active sites at the place where
substrate bind and where chemical reactions occur
where are active sites found
occupy small parts of the enzyme - like crevices (exclude water which disrupts reactions)
most enzymes are less than ……. amino acids
1000
active site have how many amino acids
fews
enzymes act as a scaffold to
create the active site (make sure it has the right shape)
active site formed by
amino acids from different parts of the primary sequences e.g. alpha helixes and beta sheets
two theories of substrate enzyme binding
1) lock and key 2) induced fit
lock and key
substrate has a complementary shape to active site
induced fit
substrate can induce changes in the conformation- only form complementary shape after substrate binding
how are substrate bound to enzymes
multiple weak bonds NON-COVALENT - van der waals -electrostatic - hydrostatic
Covalent bonds are usually
permanent
enzymes hold substrate in the right
configuration for the reaction to occur
enzyme kinetics
- to start the concentration of substrate is high - when the enzyme is added conversion of the substrate to product begins - overtime the tibial rate of reaction V0 will decrease due to the concentration of the substrate being reduced and the enzyme having less substrate to convert to product (why graph plateaus
V0
initial rate of reaction
diff enzyme have different optimum
pHs and temperatures
graph which shows how as concentration increases velocity.
- what shape will it be
Michaelis menton graph
Regtangular hyperbola due to a maximal velocity being reached
Vmax
maximal rate at which all enzyme active sites are saturated with substrate
Km
substrate concentration that gives half maximal velocity
significance of Km
Km values give a measure of the affinity of an enzyme for tis susbtrate
a low Km
high affinity for susbtrate
a high Km
low affinity for susbtrate
hexokinase has a
very low Km - high affinity for glucose (always active compared to glucokinase which only comes active when glucose levels peak after feeding)
glucokinase has a
high Km - low affinity for its substrate
rate of enzyme catalysed reaction is
proportional to the conc of enzyme e.g. double the amount of enzyme, double the rare
Michaelis menton equations
lineweaver burk plot
M-M equation can be rearranged to give a linear plot
- allows for easy estimation of Km and Vmax from linear plot
Enzyme inhibitors
slow down or prevent an enxyme reaction
enzymes inhibitors can bind both ….
reversibly and irreversibly
and
non competitively and competitively
irreversible enzyme inhibitors
Bind very tightly
i.Covalent bonds form
E.g. nerve gases such as sarin
reversible enzyme inhibitors
Non-covalent
Freely dissociate
- Competitive-binds active site
- Non-competitive-binds to another site on the enzyme
non competitive inhibtors bind to
alternative sites and decrease the turnover number of the enzyme
- lowers Vmax
- Km = unaffected
The graph:
- Vmax- where the lines cross the Y axis is differe
- Km: where the line touches the X axis stays the same
competitive inhibitors
resembles rthe substrate and bidns tot he active site, reduucing the proportion of enzyme meolcuels bound to the enzyme
E.g. Tamiflu used to treat influenza virus, has a very similar structure to neuraminidase- prevents binding
- no affect on Vmax (adding enough susbtrate will always overcome effect fo the inhibitor)
- Km will increase- inhibitors competes witht he substrate for AS
Lines are at different points on the X axis but both cross the Y axis at the same point
drugs can itneract with enzymes to
inhibit the action of enzymes
michaelis menton equation shows that
rate of an enzymes catalysed reaction is related to the conc of substrate
