Lecture 4 Flashcards
isoelectric point
the pH at which the protein has no net charge and does not move in electric field (positive charges = negative charges)
enzyme function
accelerate specific reactions
what is the fastest enzyme?
carbonic anhydrase
are all enzymes proteins?
yes, but exception of catalytic RNAs
what happens if there is an absence of enzymes?
chemical reactions in the body would occur too slowly to sustain life
- reactions would also occur at temperatures that are incompatible with life
why are enzymes necessary for life?
they maintain precise control of all reactions at normal physiological temperatures
catabolic pathways
breaking down foodstuffs into smaller molecules for energy or building blocks for other materials
anabolic (biosynthetic) pathways
use energy from catabolic pathways to synthesize components
how do enzymes speed up chemical reactions?
lowering the energy barrier
second law of thermodynamics
any isolated system, the degree of disorder can only increase
-systems have tendency to become more disordered
entropy
measure of disorder
spontaneous reaction
no energy is required for reaction to happen
do cells violate the second law of thermodynamics?
appear to violate second law, but cells take energy in from environment, and generate order themselves
- energy is released as heat into environment (entropy increases)
first law of thermodynamics
energy can be converted rom one form to another but it cannot be created or destroyed
how does the first law of thermodynamics apply to cells?
cells convert energy in chemical bonds of food into the random thermal motion of molecules
free energy
loss of free energy (loss of energy) can be harnessed to do work or drive chemical reactions
what direction does chemical reactions take?
direction that leads to loss of free energy (going downhill –> energetically favorable)
activation energy
a boost over an energy barrier, which leaves reaction more stable state
transition state
- the peak of the activation energy curve
- amount of free energy required to bring the reactants to the transition state
how does temperature affect enzyme activity?
- 37C increases the rate of reaction
- high temperatures can denature enzymes
formation of enzyme-substrate complex
binding of enzyme to substrate –> binding to active site
active site of enzyme
consists of stretch of amino acids present in crevice or cleft of the enzyme
what are the two models of enzyme substrate complex formation?
lock and key
induced fit model
lock and key model (enzyme substrate formation)
- enzyme undergoes conformational change after binding the substrate
- shape of active site becomes complementary to shape of substrate (only after substrate binds to enzyme)
what affects enzyme rates?
concentration of enzyme, substrate or inhibitors/activators
general strategies of enzyme catalysis
- enzyme binds to two substrate molecules and orients them to encourage reaction
- enzyme binds substrate rearranging causing partial positive and negative charges that favor reaction
- enzyme strains substrate forcing it towards transition state
how is enzyme velocity determined?
- different starting substrate concentrations with the same amount of enzyme
- velocity varies with substrate concentration
Michaelis - menten enzyme kinetics
specific enzyme-substrate complex is necessary intermediate in catalysis
what does the M-M enzyme kinetic describe?
assumed that none of the product reverts to the initial substrate
relationship between substrate concentration and initial velocity
at infinite concentration, the reaction proceeds at maximal velocity
Km
- the substrate concentration at which the reaction proceeds at one half its maximal velocity
- rate at which the enzyme-substrate complex breaks down divided by the rate of ES fomation
what happens to Km if K1 is greater than K2?
Km becomes the measure of strength of ES complex and thus the affinity of the enzyme for its substrate
what is the Km value for lysozyme and carbonic anhydrase?
lysosome –> 6 x 10^-6M
carbonic anhydrase –> 8 x 10^-3M
what is the equation for Michaelis Menten?
V = (Vmax * substrate concentration)/Km + substrate concentration
when would substrate concentration equal Km?
velocity of a reaction is at half maximal
what is the significance of Km?
- equal to substrate concentration at which velocity is half maximal
- where small change in concentration would have a large effect on velocity
what is the significance of Vmax?
used to calculate turnover number
turnover number
number of moles of substrate converted into product per mole of enzyme per second
