Download October 12 AP Biology - John D. O`Bryant School of Math & Science

AP Biology
John D. O’Bryant School of
Mathematics and Science
October 12, 2012
AP Biology
Agenda
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Do Now (Quiz)
Enzyme Action (lecture)
“Why is Patrick Paralyzed?” (case study)
“Lorenzo’s Oil” (?)
AP Biology
Do Now (Quiz)
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1. Anything that prevents ATP formation will most likely
A) result in cell death.
B) force the cell to rely on lipids for energy.
C) result in the conversion of kinetic energy to potential
energy.
 D) force the cell to rely on ADP for energy.
 E) have no effect on the cell.
AP Biology
Do Now (Quiz)
 2. Which of the following statements regarding enzyme
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function is false?
A) An enzyme's function depends on its three-dimensional
shape.
B) Enzymes are very specific for certain substrates.
C) Enzymes are used up in chemical reactions.
D) Enzymes emerge unchanged from the reactions they
catalyze.
E) An enzyme binds to its substrate at the enzyme's active
site.
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AP Biology
Do Now (Quiz)
 3. If an enzyme solution is saturated with substrate, the
most effective way to obtain a faster yield of products is to
A) add more of the enzyme.
B) heat the solution to 90°C.
C) add more substrate.
D) add an allosteric inhibitor.
E) add a noncompetitive inhibitor.
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AP Biology
Do Now (Quiz)
 4. Which of the following will have no effect on the rate of
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an enzyme-catalyzed reaction?
A) temperature
B) pH
C) competitive inhibitors
D) noncompetitive inhibitors
E) net change in energy
AP Biology
Do Now (Quiz)
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5. Inhibition of an enzyme is irreversible when
A) a competitive inhibitor is involved.
B) a noncompetitive inhibitor is involved.
C) the shape of the enzyme is changed.
D) covalent bonds form between inhibitor and enzyme.
E) weak interactions form between inhibitor and enzyme.
AP Biology
Do Now (Quiz)
 6. Bacterial production of the enzymes needed for the
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synthesis of the amino acid tryptophan declines with
increasing levels of tryptophan and increases as
tryptophan levels decline. This is an example of
A) competitive inhibition.
B) noncompetitive inhibition.
C) feedback inhibition.
D) positive feedback.
E) irreversible inhibition.
AP Biology
Do Now (Quiz)
 7. If an enzyme is added to a solution where its substrate
and product are in equilibrium, what would occur?
A) Additional product would be formed.
B) Additional substrate would be formed.
C) The reaction would change from endergonic to
exergonic.
D) The free energy of the system would change.
E) Nothing; the reaction would stay at equilibrium.
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
AP Biology
temperature
70°C
(158°F)
How do ectotherms do it?
AP Biology
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
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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
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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
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enzymes intolerant of extreme salinity
 Dead Sea is called dead for a reason!
AP Biology
Compounds which help enzymes
Fe in
 Activators
hemoglobin
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cofactors
 non-protein, small inorganic
compounds & ions
 Mg, K, Ca, Zn, Fe, Cu
 bound within enzyme molecule
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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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AP Biology
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
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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
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allosteric
 permanently binds to allosteric site
 permanently changes shape of enzyme
 nerve gas, sarin, many insecticides
(malathion, parathion…)
 cholinesterase inhibitors
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AP Biology
doesn’t breakdown the neurotransmitter,
acetylcholine
Allosteric regulation
 Conformational changes by regulatory
molecules
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inhibitors
 keeps enzyme in inactive form
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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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AP Biology
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!
AP Biology
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
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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
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 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