Download Chapter 8 Enzyme PPT

Enzymes:
“Helper” Protein molecules
AP Biology
5/23/2017
Nothing works without enzymes!
 How important are enzymes?

all chemical reactions in living
organisms require enzymes to work
 building molecules
 synthesis enzymes
enzyme
+
 breaking down molecules
 digestive enzymes
We can’t live
without enzymes!

enzymes speed up reactions
 “catalysts”
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enzyme
+
Examples
 synthesis
+
enzyme
 digestion
enzyme
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Enzymes are proteins
 Each enzyme is the specific helper to
a specific reaction
each enzyme needs to be the right shape
for the job
 enzymes are named for the reaction
they help

Oh, I get it!
They end
in -ase
 sucrase breaks down sucrose
 proteases breakdown proteins
 lipases breakdown lipids
 DNA polymerase builds DNA
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Enzymes aren’t used up
 Enzymes are not changed by the reaction
used only temporarily
 re-used again for the same reaction with
other molecules
 very little enzyme needed to help in many
reactions

substrate
active site
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product
enzyme
It’s shape that matters!
 Lock & Key model

shape of protein
allows enzyme &
substrate to fit

specific enzyme
for each specific
reaction
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Enzyme vocabulary
 Enzyme

helper protein molecule
 Substrate

molecule that enzymes work on
 Products

what the enzyme helps produce from
the reaction
 Active site

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part of enzyme
that substrate
molecule fits into
What affects enzyme action
 Correct protein structure
correct order of amino acids
 why? enzyme has to be right shape

 Temperature

why? enzyme has to be right shape
 pH (acids & bases)

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why? enzyme has to be right shape
Order of amino acids
 Wrong order = wrong shape = can’t do its job!
chain of
amino acids
DNA
folded
protein
right shape!
folded
protein
chain of
amino acids
DNA
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wrong shape!
Temperature
 Effect on rates of enzyme activity

Optimum temperature
 greatest number of collisions between
enzyme & substrate
 human enzymes
 35°- 40°C (body temp = 37°C)
Raise temperature (boiling)
 denature protein = unfold = lose shape
 Lower temperature T°
 molecules move slower
 fewer collisions between enzyme &
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substrate

Temperature
reaction rate
human
enzymes
37°
temperature
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What’s
happening
here?!
How do cold-blooded creatures do it?
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pH
 Effect on rates of enzyme activity

changes in pH changes protein shape

most human enzymes = pH 6-8
 depends on where in body
 pepsin (stomach) = pH 3
 trypsin (small intestines) = pH 8
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pH
intestines
trypsin
What’s
happening
here?!
reaction rate
stomach
pepsin
0
1
2
3
4
5
6
pH
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10 11
12 13 14
INDUCED FIT: ENZYME FITS SNUGLY
AROUND SUBSTRATE -- “CLASPING
HANDSHAKE”
COFACTORS
 Cofactors
are nonprotein enzyme helpers such as
minerals (eg. Zn, Fe, Cu)
 Coenzymes are organic cofactors (eg. vitamins)
Enzyme Inhibitors
 Competitive inhibitor: binds to the active site of
an enzyme, competes with substrate
 Noncompetitive inhibitor: binds to another part
of an enzyme  enzyme changes shape  active
site is nonfunctional
INHIBITION OF ENZYME ACTIVITY
REGULATION OF ENZYME ACTIVITY
 To
regulate metabolic pathways, the cell
switches on/off the genes that encode specific
enzymes
 Allosteric regulation: protein’s function at
one site is affected by binding of a
regulatory molecule to a separate site
(allosteric site)
 Activator – stabilizes active site
 Inhibitor – stabilizes inactive form
 Cooperativity – one substrate triggers
shape change in other active sites 
increase catalytic activity
FEEDBACK INHIBITION
 End
product of a metabolic pathway shuts down
pathway by binding to the allosteric site of an
enzyme
 Prevent wasting chemical resources, increase
efficiency of cell
FEEDBACK
INHIBITION
For enzymes…
What matters?
SHAPE!
AP Biology
5/23/2017