lecture_06_web

MCB Instructional Program Presents MCB-Specific
Study Abroad Opportunities
discuss experiences and answer questions about
MCB Workshop Series
The Freshmen Network
Wednesday, February 3, 5-6 pm
Our first meeting of the semester is
Wednesday, Febuary 3rd , 7 pm in 217 NOYES Pleas come and learn more about this years B B IOLOGY O O PEN HOUSE Volunteer for different Open House t make the meeting, e-mail
to get more info on each committee
Just as DNA Ligase links together the gaps in the DNA backbone, our organization links together students who
share an interest in Molecular and Cellular Biology and provide a medium for students to pursue and discover
the plethora of fields associated with MCB.
and search ‘LIGASE’ or
/Community?action=getOrgHome&orgID=23439
[S]
[P]
E a
Standard Activation Energy Diagram:
[S] = energy level of substrate (reactants)
[P] = energy level of products
= activation energy, which converts substrates
into unstable transition states
[S]
[P]
E a of uncatalyzed reaction
E a of catalyzed reaction
• Enzymes decrease E
by the same amount in both directions
a
G = Free Energy of rxn -- difference in E between reactants & products • - G : rxn RELEASES energy (EXERGONIC)
• + G : rxn REQUIRES energy (ENDERGONIC)
Because most enzymes are proteins, it follows that conditions that affect protein stability also affect enzyme activity.
–Enzymes have temperature and pH optimums
–most tend to be near body temperature (37 ºC)
and neutral pH (7.0)
natural substrate, and occupies active site enzyme can’t use inhibitor as substrate - no products
are formed
can be "flooded out" by increasing concentration of
natural substrate
decreasing concentration of inhibitor also reduces
probability of inhibitor finding active site
Examples of competitive enzyme inhibitors: ethanol is a competitive inhibitor of alcohol
dehydrogenase; keeps methanol from being broken down into formaldehyde and formic acid
in bacteria (but not humans), DHPS is an enzyme
that catalyzes the conversion of p-aminobenzoic acid into folic acid, which is then used to produce monomers for biosynthetic reactions
•sulfa drugs like sulfanilamide are inhibitors of DHPS;
bacteria die because they can’t synthesize
macromolecules, but humans are unaffected by the drugs
because they don’t have DHPS
–changes conformation of enzyme, disrupts active site
–indirectly prevents substrate from binding effectively
–if change in enzyme completely prevents substrate binding, increasing substrate concentration has no effect –reversible because inhibitor can become unbound。