AP Biology
John D. O’Bryant School of
Mathematics and Science
October 15, 2012
AP Biology
Agenda
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Do Now (Quiz)
“Why is Patrick Paralyzed?” (case study)
Exam 1 discussion
“Lorenzo’s Oil” (?)
AP Biology
Do Now (Quiz)
 1. Some bacteria are metabolically active in hot springs
because
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A) they are able to maintain a cooler internal temperature.
B) high temperatures make catalysis unnecessary.
C) their enzymes have high optimal temperatures.
D) their enzymes are completely insensitive to temperature.
E) they use molecules other than proteins or RNAs as their
main catalysts.
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AP Biology
Do Now (Quiz)
 2. Which of the following statements describes enzyme
cooperativity?
A) A multi-enzyme complex contains all the enzymes of a
metabolic pathway.
B) A product of a pathway serves as a competitive inhibitor
of an early enzyme in the pathway.
C) A substrate molecule bound to an active site affects the
active site of several subunits.
D) Several substrate molecules can be catalyzed by the
same enzyme.
E) A substrate binds to an active site and inhibits
cooperation between enzymes in a pathway.
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AP Biology
Do Now (Quiz)
 3. A series of enzymes catalyze the reaction X → Y → Z →
A. Product A binds to the enzyme that converts X to Y at a
position remote from its active site. This binding decreases
the activity of the enzyme. What is substance X?
 A) a coenzyme
B) an allosteric inhibitor
C) a substrate
D) an intermediate
E) the product
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AP Biology
Do Now (Quiz)
 4. A series of enzymes catalyze the reaction X → Y → Z →
A. Product A binds to the enzyme that converts X to Y at a
position remote from its active site. This binding decreases
the activity of the enzyme. Substance A functions as
 A) a coenzyme.
B) an allosteric inhibitor.
C) the substrate.
D) an intermediate.
E) a competitive inhibitor.
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AP Biology
Do Now (Quiz)
 5. The molecule that functions as the reducing agent
(electron donor) in a redox or oxidation-reduction reaction
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A) gains electrons and gains energy.
B) loses electrons and loses energy.
C) gains electrons and loses energy.
D) loses electrons and gains energy.
E) neither gains nor loses electrons, but gains or loses
energy.
AP Biology
Do Now (Quiz)
 6. Using a series of arrows, draw the branched metabolic
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reaction pathway described by the following statements.
∙ L can form either M or N.
∙ M can form O.
∙ O can form either P or R.
∙ P can form Q.
∙ R can form S.
∙ O inhibits the reaction of L to form M.
∙ Q inhibits the reaction of O to form P.
∙ S inhibits the reaction of O to form R.
AP Biology
Do Now (Quiz)
 7. According to the figure you created from question 6,
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which reaction would prevail if both Q and S were present
in the cell in high concentrations?
A) L → M
B) M → O
C) L → N
D) O → P
E) R → S
AP Biology
Metabolism & Enzymes
AP Biology
2007-2008
Factors that Affect Enzymes
AP Biology
2007-2008
Factors Affecting Enzyme Function
 Enzyme concentration
 Substrate concentration
 Temperature
 pH
 Salinity
 Activators
 Inhibitors
AP Biology
catalase
Enzymes and temperature
 Different enzymes function in different
organisms in different environments
reaction rate
human enzyme
hot spring
bacteria enzyme
37°C
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temperature
70°C
(158°F)
How do ectotherms do it?
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pH
What’s
happening here?!
trypsin
reaction rate
pepsin
pepsin
trypsin
0
AP Biology
1
2
3
4
5
6
pH
7
8
9
10
11
12
13
14
Factors affecting enzyme function
 pH
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changes in pH
 adds or remove H+
 disrupts bonds, disrupts 3D shape
 disrupts attractions between charged amino acids
 affect 2° & 3° structure
 denatures protein (end 10/11)
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optimal pH?
 most human enzymes = pH 6-8
 depends on localized conditions
 pepsin (stomach) = pH 2-3
 trypsin (small intestines) = pH 8
AP Biology
0 1 2 3 4 5 6 7 8 9 10 11
Salinity
reaction rate
What’s
happening here?!
salt concentration
AP Biology
Factors affecting enzyme function
 Salt concentration

changes in salinity
 adds or removes cations (+) & anions (–)
 disrupts bonds, disrupts 3D shape
 disrupts attractions between charged amino acids
 affect 2° & 3° structure
 denatures protein

enzymes intolerant of extreme salinity
 Dead Sea is called dead for a reason!
AP Biology
Compounds which help enzymes
Fe in
 Activators
hemoglobin

cofactors
 non-protein, small inorganic
compounds & ions
 Mg, K, Ca, Zn, Fe, Cu
 bound within enzyme molecule

coenzymes
 non-protein, organic molecules
 bind temporarily or permanently to
enzyme near active site
AP Biology
 many vitamins
 NAD (niacin; B3)
 FAD (riboflavin; B2)
 Coenzyme A
Mg in
chlorophyll
Compounds which regulate enzymes
 Inhibitors
molecules that reduce enzyme activity
 competitive inhibition
 noncompetitive inhibition
 irreversible inhibition
 feedback inhibition

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Competitive Inhibitor
 Inhibitor & substrate “compete” for active site
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penicillin
blocks enzyme bacteria use to build cell walls
disulfiram (Antabuse)
treats chronic alcoholism
 blocks enzyme that
breaks down alcohol
 severe hangover & vomiting
5-10 minutes after drinking
 Overcome by increasing substrate
concentration

AP Biology
saturate solution with substrate
so it out-competes inhibitor
for active site on enzyme
Non-Competitive Inhibitor
 Inhibitor binds to site other than active site
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allosteric inhibitor binds to allosteric site
causes enzyme to change shape
 conformational change
 active site is no longer functional binding site
 keeps enzyme inactive
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some anti-cancer drugs
inhibit enzymes involved in DNA synthesis
 stop DNA production
 stop division of more cancer cells
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cyanide poisoning
irreversible inhibitor of Cytochrome C,
an enzyme in cellular respiration
 stops production of ATP
AP Biology
Irreversible inhibition
 Inhibitor permanently binds to enzyme
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competitor
 permanently binds to active site

allosteric
 permanently binds to allosteric site
 permanently changes shape of enzyme
 nerve gas, sarin, many insecticides
(malathion, parathion…)
 cholinesterase inhibitors

AP Biology
doesn’t breakdown the neurotransmitter,
acetylcholine
Allosteric regulation
 Conformational changes by regulatory
molecules

inhibitors
 keeps enzyme in inactive form

activators
 keeps enzyme in active form
AP Biology Conformational
changes
Allosteric regulation
Metabolic pathways
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ABCDEFG
5
6
enzyme enzyme enzyme
enzyme enzyme enzyme
enzyme
1
2
3
4
 Chemical reactions of life
are organized in pathways

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divide chemical reaction
into many small steps
 artifact of evolution
  efficiency
 intermediate branching points
  control = regulation
Efficiency
 Organized groups of enzymes
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enzymes are embedded in membrane
and arranged sequentially
 Link endergonic & exergonic reactions
Whoa!
All that going on
in those little
mitochondria!
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Feedback Inhibition
 Regulation & coordination of production
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product is used by next step in pathway
final product is inhibitor of earlier step
 allosteric inhibitor of earlier enzyme
 feedback inhibition
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no unnecessary accumulation of product
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ABCDEFG
1
2
3
4
5
6
X
enzyme enzyme enzyme enzyme enzyme enzyme
AP Biology
allosteric inhibitor of enzyme 1
threonine
Feedback inhibition
 Example
synthesis of amino
acid, isoleucine from
amino acid, threonine
 isoleucine becomes
the allosteric
inhibitor of the first
step in the pathway

 as product
accumulates it
collides with enzyme
more often than
substrate does
AP Biology
isoleucin
e
Don’t be inhibited!
Ask Questions!
AP Biology
2007-2008
Cooperativity
 Substrate acts as an activator
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substrate causes conformational
change in enzyme
 induced fit
favors binding of substrate at 2nd site
makes enzyme more active & effective
 hemoglobin
Hemoglobin
 4 polypeptide chains
 can bind 4 O2;
 1st O2 binds
 now easier for other
O2 to bind
AP3Biology
Lorenzo’s Oil
AP Biology