Ch. 6.3, 6.4 & 6.5
Energy & Enzymes
6.2 All Chemical Reactions Require Activation Energy to Begin
high
_______________________
required to start the reaction
energy level of reactants
energy
content
of
molecules
energy level of products
low
progress of reaction
An _____________________ reaction
Sparks ignite gas
https://www.youtube.com/watch?v=p-27I_osoaw&feature=related (History Lesson on Endo and Exo)
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/chemreac/energychangesrev1.shtml (ex of rxn)
(b) An exergonic reaction
6.3 How is Energy Transported Within Cells
 organisms powered by chemical energy supplied by ____________
breakdown of glucose
 energy transferred to _____________________________(i.e. ATP)
 charged by exergonic rxns and drive endergonic rxns (i.e.
rechargeable batteries
 ATP recycled approx. 1,400X/day (marathon runner uses a lb.
of ATP/min
Dehydration synthesis uses
energy when making ATP
from ADP.
 _________________________– energy carrier molecules that
______________energetic electrons & H+ ions
 donate high-energy electrons to other molecules
 NADH, FADH2
Coupled Reactions Link Exergonic with Endergonic Reactions
_____________reaction - exergonic rxns provide energy needed
to __________endergonic rxns
___________________ - plants use sunlight (____gonic) to drive
_______gonic synthesis of high-energy glucose molecules from
lower-energy reactants (CO2 + H2O)
________________ – organisms break down glucose into CO2 + H2O
(_____gonic) to drive synthesis of proteins, amino acids (_____gonic)
 energy is always __________________every time it is transformed
 energy released (exergonic) must always exceed energy needed
(endergonic)
https://www.youtube.com/watch?v=7IqgrcBkGRU
6.4 How Do Enzymes Promote Biochemical Reactions?
 activation energy determines the ________ at which a reaction
occurs
https://www.youtube.com/watch?v=VbIaK6PLrRM
Blue = exothermic
Green = endothermic
exothermic
 some important chemical
reactions are too slow or have
a high activation energy
reactants
reactants
 _____________ – substances that __________rates of
chemical reactions w/o being used up or permanently
altered
https://www.youtube.com/watch?v=hNl5WYSM5DE (Elephant Toothpaste)
https://www.youtube.com/watch?v=v9ju2rZ8YmM (how catalytic converters work – 10 min)
Enzymes are Biological Catalysts
 not advantageous to speed up dozens of rxns at once;
so it is a _________________
 _______________– natural catalysts (mostly proteins)
 each catalyzes only a few types of rxns (most only
catalyze 1 with specific molecules)
 exergonic & endergonic rxns can be catalyzed
 ATP synthase + ATPase
https://www.youtube.com/watch?v=W3KxU63gcF4 (ATP Synthase)
Structure of Enzymes Allows Them to Catalyze Specific Reactions
 ____________ of enzyme _______________ its ____________
(just like proteins)
 structure – determined by a.a. sequence/twisted/folded
 shape and charges of a.a. that form active site determines what
molecules can enter (amylase  starch not cellulose; pepsin & trypsin)
 some catalyze tens of thousands of rxns/sec and some act much
slower
https://www.youtube.com/watch?v=lfuOQZJ_MIM (firefly)
Enzymes, Like All Catalysts, Lower Activation Energy
 reactions occur in_____; each step catalyzed by different enzymes
 ____________activation energy overall  reaction can occur at
body temp
https://www.youtube.com/watch?v=tI69AVRW0DU (related to digestion)
https://www.youtube.com/watch?v=r1ryDVgx0zw
How Are Enzymes Regulated?
 metabolism – sum of all the ________________________in a cell
 metabolic pathways – reactions that are linked together
- ________________ step acts as the
________________________ step
i.e. _______________ (synthesis of high energy molecules i.e. glucose)
i.e. glycolysis (begins breakdown of glucose)
Initial reactant
Intermediates
End products
PATHWAY 1
enzyme 1
enzyme 2
enzyme 3
enzyme 4
PATHWAY 2
https://www.youtube.com/watch?v=l_vvz5fD00M – photo & resp. enzyme 5
enzyme 6
 for a given ____________ of enzyme, as substrate levels increase,
the rxn rate ______________ until active sites of all enzymes are
being continuously occupied by new substrate
 Cells must regulate
metabolic pathways by
controlling ____ produced.
a) type of enzymes
b) quantity of enzymes
c) activity levels of enzymes
 ________that code for enzymes can turn _____________
- marathon runners & high-carb meals b4 competitions
- glucose enters blood & triggers metabolic rxns (i.e.
pancreas releases insulin)
- insulin turns on genes that code for 1st enzyme in pathway
that breaks down glucose
Some enzymes only synthesized at ________________ in
organisms life (i.e. lactase)
 some enzymes are synthesized in _______________ and
then activated when needed (i.e. protein digesting pepsin &
trypsin – work best in acidic conditions)
http://lgfl.skoool.co.uk/content/keystage3/biology/pc/learningsteps/PAELC/launch.html
Enzyme Activity May be Controlled by Competitive or Noncompetitive Inhibition
 Reactions ______________ by competitive inhibition and
noncompetitive inhibition to prevent 1) substrates from being _________
and 2) producing _________________ product
 ____________________ inhibition: substance that is not the enzyme’s
normal substrate can _________________to active site of enzyme
(competing for a spot)
- structural similarities
i.e. _________________________
(block active site of acetylcholinesterase;
excess acetylcholine overstimulates muscles
causing paralysis)
https://www.youtube.com/watch?v=-gIqZ8IxctE
i.e. _______________________ inhibits synthesis of bacteria cell walls;
________________________________ inhibits synthesis of molecules
that contribute to swelling, pain, fever.
 ____________________ inhibition: molecule binds to a site
on enzyme different from active site; ___________________;
enzyme less able to catalyze rxn
 https://www.youtube.com/watch?v=PILzvT3spCQ (short comparison)
 _____________________: _______________________ inhibition
where enzymes ___________ easily between 2 different ________
that either activate or inhibit the enzyme (i.e. ADP)
https://www.youtube.com/watch?v=d5fDEUhjo-M
intermediates
enzyme 1
threonine
(initial
reactant)
enzyme 2
enzyme 3
enzyme 4
enzyme 5
As levels of isoleucine rise,
isoleucine binds to the regulatory
site on enzyme 1, inhibiting it
enzyme 1
isoleucine
isoleucine
(end product)
 ___________________: form of ________________ regulation;
causes metabolic pathways to ______________________________
when its concentration reaches an optimal level (thermostat)
https://www.youtube.com/watch?v=DHZtOKyMPRY (feedback inhibition)
Activity of Enzymes is Influenced by Their
____________________
 enzymes have a narrow range of conditions (_________________)
in which they function optimally (H-bonds btwn polar a.a.)
 _______________: when enzymes lose 3-D structure required to
function properly
 human cellular enzymes work best around pH 7.4; human
digestive enzymes work best around pH 2
http://lgfl.skoool.co.uk/viewdetails_ks3.aspx?id=452
 __________________ affects rate of enzyme catalyzed reactions
(_____________ by _______________ temps; ________________
by ________________ temps)
fast
For trypsin, maximum
activity occurs at
about pH 8
For pepsin, maximum
activity occurs at
about pH 2
For most cellular
enzymes, maximum
activity occurs
at about pH 7.4
rate
of
reaction
slow
0
1
2
3
4
5
6
pH
Effect of pH on enzyme activity
7
8
9
10
fast
For most human enzymes,
maximum activity occurs
at about 98.6F (37C)
rate
of
reaction
slow
32
0
68
20
104
40
temperature
140 (F)
60 (C)
Effect of temperature on enzyme activity