01:694:301 Lecture Notes - Lecture 8: Enzyme Inhibitor, Zymogen, Activation Energy

65 views5 pages
Chapter 8‘Enzymes: Basic Concepts and Kinetics’
Enzymes: Highly Specific Catalysts
Understand the general statements about enzymes on 219-229
o They are very specific in both the reactions they catalyze and their choice of
reactants or ‘substrates
! This specificity is due to enzyme’s precise interaction with substrate
This precision is result of 3-D structure of enzyme protein
o Nearly all known enzymes are proteins
o The catalytic activity of many enzyme’s can depend on cofactors
! These cofactors are able to execute chemical reactions that can’t be done by aa
Metal cofactorsMg2+, Zn2+, etc.
Coenzymes – tend to be derived from vitamins; tightly or loosely bounded to
enzyme
o Tightly bounded – ‘prosthetic groups’; loose – ‘cosubstrates’; they get
released’
Note that if enzymes uses same coenzymes then usually perform similar
catalysis
o They can be regulated several ways (feedback/allosteric inhibition, regulatory
proteins, covalent modification, and zymogen cleavage)
o They can transform energy
! Ex: ATP – enzyme myosin in muscle; membrane pumps and channels
o They can’t move the equilibrium point
! Enzymes accelerate the attainment of eq. but do not shift their positions.
! The equilibrium position is a function only of the free-energy difference
between reactants and products.
o They catalyze reactions by stabilizing the transition state (‡)
! The transition state molecular structure in which substrate in
no longer a reactant but not yet a product
! Enzymes accelerate rxn by lowering activation energy
! It is the least stable and rarely occupied because it has highest
free energy
o They have an active site cleft; and they often change shape in
response to ‘correct’ substrate
! Enzyme catalyzed reaction reached maximum velocity
! Active site formed by aa residues; takes up small volume of
enzyme; non-polar micro-env.;
Enzymes bring together substrates " enzyme-substrate
complex [ES]
o Substrates are bound by multiple weak forces (H-bonds, vdW, etc.)
Interaction of the enzyme and substrate at the active site promotes the
formation of the transition state
! Koshland’s Induced Fit (pg. 228)
Active site changes shape for substrate to fit only after substrate is bound
o Binding energy is what is used by enzyme to lower activation energy
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in
! Max binding energy released with enzyme facilitates formation of
Note – 6 Enzymes classes ‘OTHLILI’
Enzymes & Free Energy
To understand how enzyme’s work need to consider 2 thermodynamic properties:
o 1) Free energy difference b/w reactants and products
! Determines whether reaction take place spontaneously
o 2) Energy required to initiate conversion of R " P
! Determines rate of reaction " (affected by enzymes)
An important point in the chapter is the discussion of Gibb’s Free Energy or !G
o At equilibrium, the enthalpy change for a reaction will equal the entropy change
times the absolute temp. " !H = T!S
For reactions not at equilibrium, these two quantities differ, and the difference shows
the available reaction energy, thus: !G = !H – T!S
o Defined this way – reactions at eq. have !G = 0
o Reactions which will move FWD spontaneously have !G < 0 (negative)
o Reactions that will REV (back up) have !G > 0 (positive)
o When STD conditions are applied, that is, all [] = [1M] then the value of free
energy change will be !, STD free energy change *at pH 7
o Note: units of energy " kcal
o !G is dependent on [P] and [R]
KNOW the 5 statements listed on pg. 222 and Equations (1) and (5) on pg. 223
o (1) Rxn can only take place spontaneously if !G is negative (exergonic)
o (2) Sys is at eq. and no net change can take place if !G = 0
o (3) Rxn does not occur spontaneously if !G is positive
(endergonic)
! Free energy is needed to drive this rxn
o (4) The !G of rxn only depends on !G of products – !G of
reactants (final-initial)
! The !G of rxn is independent of path (mechanisms) of the
transformation
o (5) The !G provides no information about the rate of a reaction.
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
Monthly
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.