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AP Bio Unit 3: Cell Energetics Cheat Sheet by

AP Bio Unit 3: Cell Energetics


proteins (and RNA)
organic catalysts that lower the required activation energy to get reactants to products
facilitate chemical reactions:
~ increase rate of reaction without being consumed
~ reduce activation energy
~ do not change free energy released or required
~ reactant which binds to enzyme
~ enzyme­-su­bstrate complex: temporary associ­ation
~ end result of reaction
active site:
~ enzyme's catalytic site: substrate fits into actives site


changes in pH:
~ adds or removes H+
~ disrupts bond, disrupts 3D shape
~ disrupts attrac­tions between charged amino acids
~ affects 2' and 3' structure
~ denatures protein


small, inorganic compounds and ions
organic compounds
binds with enzyme
bind to enzymes near active site
Mg, K, Ca, Zn, Fe
vitamins (NAD, FAD, Coenzyme A)

Allosteric Regulation

confor­mat­ional changes by regulatory molecules
inhibi­tors: keeps enzyme in inactive form
activa­tors: keeps enzyme in active form

Metabolic Pathways

catabolic pathways:
metabolic pathways:
release energy
consume energy
cellular respir­ation

Transf­orm­ation of Energy

sunlight -> chemical bonds during photos­ynt­hesis

Exergonic vs. Endergonic Reactions

positive / negative G free energy:
released / absorbed
cellular respir­ation / photos­ynt­hesis
cellular respir­ation
uphill / downhill
not sponta­neous


regulate internal body temper­atures through metabolism
balancing heat loss and gain
five adapta­tions help animals thermo­reg­ulate:
1) insulation
2) circul­ating adapta­tions
3) cooling by evapor­ative heat loss
4) behavioral responses
5) adjusting metabolic heat production

Overview of Photos­ynt­hesis


~ glucose
~ 2 ADP +2 Pi
~ 2 NAD+
~ 2 pyruvate
~ 2 ATP
~ 2 NADH
~ 2 H2O
transfer of energy:
NADH (electrons and Hydrogen) <- C6H12O6 -> ATP
~ convert glucose to pyruvate
~ initial breakdown of sugar
~ generating ATP
~ shuttling e- and H+ to ETC

Steps of Light Reactions

1) H2O splits
~ H+: pump into thylakoid out of ATP synthase
~ e-: 2 ETCs
~ O2: released out of stomata
2) light excites e- in Photos­ystem II
3) e- to primary electron acceptor (PEA)
4) the e- travels down the ETC and replaces the e- from Photos­ystem I
5) the e- travels down another ETC and combines with NAHP+
~ energy from 1st ETC is used to pump H+ into the thylakoid space
~ a proton gradient forms and H+ leave through ATP synthase
~ H+ combines with e- and NADP+ to form NADPH
~ ATP synthase generates ATP

REDOX Reactions

molecular exchange of an electron
oxidation: lose electrons
reduction: gain electrons

REDOX reactions image


transf­orm­ation of solar light energy trapped by chloro­plasts into chemical bond energy stored in sugar and other organic molecules
1) synthe­sizes energy rich molecules
2) uses CO2 as carbon source
3) directly or indirectly supplies energy
CO2 + H2O + sunlight -> C6H12O6 + O2

Properties of Enzymes

reaction specific:
~ each enzyme works with a specific substrate chemical fit between active site and substrate
~ H bonds and ionic bonds
not consumed in reaction:
~ single enzyme molecule can catalyze thousands or more reactions per second
~ enzymes are unaffected by the reaction
affected by cellular conditions
~ ex: temper­ature, pH, salinity, etc.

Substrate Concen­tration

as substrates increase, reaction rate increases and levels off
more substrate = more frequently collide with enzyme
the reaction levels off because...
~ all enzymes have active site engaged
~ enzyme is saturated
~ maximum rate of reaction

Factors that Affect Enzyme Structure

Compet­itive Inhibitors

inhibitor competes with active site
substrate cannot bond
can overcome with substrate saturation
penicillin (competes with bacterial enzyme that builds cell wall)
directly blocks active site


the ability to do work
kinetic energy:
potential energy:
energy of motion
energy of position
water behind a dam
light energy
chemical energy stored in cells

Free Energy and Equili­brium

free energy: energy available to do work
free energy decreases when reactions proceed toward equili­brium


building complex molecules out of simple molecules
amino acids -> proteins
glucose -> glycogen


do not regulate internal body temper­ature
rely on enviro­nmental heat sources
less respir­ati­on/food

Cellular Respir­ation

C6H12O6 + O2 -> CO2 + H2O + energy
1) gylcolysis
2) interm­ediate step
3) citric acid cycle
4) oxidative phosph­ory­lation

Interm­ediate Step

mitoch­ondrial matrix
2 pyruvate
~ acetyl CoA
~ 2 NADH
~ 2 CO2
transfer of energy:
pyruvate (sugar) -> NADH (e- and H+)
convert pyruvate into more reactive Acetyl CoA

C3 vs. C4 vs. CAM plants

Oxidative Phosph­ory­lation

~ inner membrane of mitoch­ondria (ETC)
~ inner membrane spare (chemi­osm­osis)
~ O2
~ H2O
transfer of energy:
NADH/FADH2 -> proton gradient -> ATP synthase -> ATP
use REDOX reactions to make a large amount of ATP (34)


autotr­ophic nutrit­ional: nutrit­ional made of synthe­sizing organic molecules from inorganic raw materials
photoa­uto­trophs: uses light energy
chemoa­uto­trophs: oxidation of inorganics for energy


site of photos­ynt­hesis
double membrane system
thylak­oids: flattened photoc­enters
granum: stacks of thylakoids
stroma: fluid outside thylakoid

Calvin Cycle

location: stomata
production of sugar
recogn­ition of RUBP
reactants: CO2, NADPH, ATP
products: C6H12O6, NADP+, ADP+Pi, G3P

Pathways of Photos­ynt­hesis

noncyclic photop­hos­pho­ryl­ation produces ATP and NADPH
cyclic photop­hos­pho­ryl­ation is ATP production
calvin cycle consumes more ATP than NADPH

Induced Fit

"lock and key"
3-D structure of enzyme fits substrate
substrate binding cause enzyme to change shape leading to a tighter fit
"­con­for­mat­ional change­": slight change in shape
bring chemical groups in position to catalyze reactions

Enzyme Concen­tration

as enzymes increase, reaction rate increases
more enzymes = more frequently collide with substrates


optimum temper­ature:
~ as temp increases, reaction rate increases
~ greater number of molecular collisions
cold temper­ature:
~ molecules move slower
~ decrease collisions between enzymes and substrates
heat (beyond optimum)
~ increased energy level disrupts weak bond in 2' and 3' structure
~ denatu­ration: loses 3D shape

Noncom­pet­itive Inhibitors

inhibitor binds to allosteric site (not active site) which changes the shape of the active site
ex: anti-c­ancer drugs, cyanide, poisoning, DDT

Compet­itive vs. Noncom­pet­itive Inhibitors


study of energy transf­orm­ation
first law: energy of the universe is constant
second law: every process increases the entropy of the universe
entropy: "­qua­ntity of energy in universe is constant, but quality is not"

ATP Powers Cellular Work

coupling enderg­oni­c/e­xer­gonic reactions
energy coupling: phosph­ory­lated interm­edi­ates; regene­ration of ADP to ATP
3 main types of work
1) mechanical work (motor protein)
2) transport work (Na/K pump)
3) chemical work

Size and Metabolic rate

larger mammals have more body mass and require more chemical energy (higher BMR)
smaller animals require more kcal/gram, have greater rate of O2 delivery, higher breathing rate
increase activity -> increase metabolic rate -> more ATP

Overview of Cellular Respir­ation

Citric Acid Cycle

mitoch­ondrial matrix
~ acetyl CoA
~ citric acid
~ ADP + Pi
~ NAD+ and FAD
~ oxaloa­cetate
~ NADH and FADH2
~ CO2
transfer of energy:
NADH and FADH2 (e- and H+) <- citric acid -> ATP
~ complete the oxidation of glucose
~ producing NADH/FADH2 (e- and H+)


substr­ate­-level: ATP is synthe­sized by enzymes
oxidative: ATP is synthe­sized by an ETC and chemio­smosis


anaerobic process (no O2)
produces small amounts of ATP
regene­rates NAD+/NADH
alcoholic fermen­tation
~ yeast/­bac­teria
~ produces CO2 and alcohol
lactic acid
~ human muscles
~ yogurt
~ produces lactic acid


hetero­trophs: acquire organics to create energy from other creatures
~ consumers
~ decomp­osers

Light Reactions

occurs in the thylakoid
splitting of water
generation of ATP and NADPH
reactants: H2O, NADP+, ADP+Pi
products: O2, NADPH, ATP

Steps of Calvin Cycle

1) carbon fixation
~ ribulose biphos­phate: RuBP
~ rubisco: RuBP carbox­ylase: most abundant protein
2) reduction
~ adding H+ and e- from NADPH to CO2 to make sugar
3) regene­ration
~ G3P -> RuBP

Altern­ative Pathways of Carbon Fixation

photor­esp­ira­tion: fixing oxygen rather than CO2
C3 plants:
~ hot/dry days
~ stomata close (prevents H2O, inc CO2, dec O2)
C4 plants:
~ spatial separation of calvin cycle into bundle sheath cell
~ PEP carbox­ylase initially captures CO2
CAM pathways:
~ temporal separation
~ takes in CO2 at night


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