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Unit 3 Exam
Chapter Six
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Metabolism​-totality of an organism’s chemical reactions
Anabolic reactions-consume energy to build complicated molecules from smaller ones
Catabolic reactions-release energy by breaking down complex molecules to smaller ones

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Energy​-capacity to cause change or ability to rearrange a collection of matter
Potential Energy-Energy possessed because of location or structure (includes chemical energy
in food molecules)
Kinetic energy-energy associated with relative motion of objects (includes thermal energy

forms
like light and heat)
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Most energy is lost by a system as heat
First Law of Thermodynamics​-Energy can be transferred and transformed, but not created nor
destroyed
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Entropy​-a measure of disorder or randomness; for a process to occur spontaneously, it must
increase the entropy of the universe
Δ​ G​-free-energy change; portion of a system’s energy that can perform work when
temperature and pressure are uniform in a system; indicator of a reaction’s likelihood to
proceed;​Δ​G=​Δ​H-T​Δ​S
o Endergonic reaction-absorbs free energy, amount need to drive reaction, positive
delta G, nonspontaneous
o Exergonic reaction-net release of free energy, amount of work reaction can perform,
delta g is negative, spontaneous
ATP-responsible for most energy coupling (use of an exergonic process ro drive an endergonic
one); immediate source of energy that powers cellular work; contains nitrogenous base, three
phosphates, and sugar ribose
o ADP-formed when ATP is hydrolyzed and loses a phosphate; forms ATP when
undergoes endergonic phosphorylation
Coupled reactions-when one reaction is sued to drive another one (exergonic processes drive
endergonic ones); opposite types are coupled
Three primary functions of ATP (cellular work):
o Chemical work-pushing of endergonic reactions that work not spontaneously

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Transport work-pumping of substances across membranes against the direction of
spontaneous movement
Mechanical work-includes the beating of cilia, contraction of muscle cells, and
movement of chromosomes

Chapter Seven: Cellular Respiration
● Energy transformation leads to an increase in entropy
● All reactions require an input of energy, if we get no energy, reactions don’t occur and we
become disordered
● We need a constant influx of energy, and we need a way to use it
● Metabolism:bio0chemical processes that allow us to use energy; all chemical reactions in your
body
o Catabolism: break it down
o Anabolism: build it up
● ATP is the source of energy for these reactions
● Liver is the hub of your metabolism
● Cellular respiration=systematic series of catabolic reactions that break down organic
molecules into simpler products and release chemical free energy for cells to use
● Two types:
o Aerobic-requires oxygen as a reactant and leads to the most accessible energy; most
efficient form
o Anaerobic-does not require oxygen, does not lead to as much energy as aerobic
● Organic compounds + oxygen​→​carbon dioxide + water + energy
● Redox reaction (OILRIG)-organic fuels are oxidized to lead to the production of energy
o Organic compounds are oxidized
o Oxygen is reduced
● An electron travels with a proton, so technically as a hydrogen atom
● Organic compounds used : carbohydrates, proteins, and fats
● Cells break down carbohydrates/glycogen into its simplest sugar monomer, or convert lipids
and amino acids (proteins) into similar substrates
● C6H12O6 + 6O2 ​→​ 6CO2 + 6H2O + energy
● If energy from fuel is released all at once, “blast” is too great to be efficiently harnessed for
work and too much is lost as heat (eye wash blast)
● Glucose is broken down in a series of steps
● Electrons are stripped from the glucose and coupled to the generation of small packets of
energy that the cell can actually use-ATP
● Steps:
o Glycolysis-6-carbon glucose is oxidized and broken into two 3-carbon substrates,
giving off 2 net ATP
o Krebs Cycle (aerobic) or fermentation (anaerobic)
▪ Krebs: 3-carbon substrates are oxidized completely and broken into Co2,
which is released and produces a little ATP
o Electron Transport Chain (aerobic only)

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Protons and electrons from previous steps are delivered to a chain of proteins,
which release energy by passing electrons down the chain
Eventually transfer electrons to oxygen, the final electron acceptor, which
forms water
Energy is released in the form of lots of ATP

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Locations
o Cytosol-Glycolysis, Fermentation
o Mitochondrial matrix-Krebs Cycle
o Within the Inner mitochondrial membrane-Electron Transport Chain
Glucose and pyruvate-primary initial substrates for the cell
NAD+-coenzyme “electron carrier” that takes electrons (and protons) in early steps and
delivers them to the ETC
o Cycle easily between oxidized NAD+ and reduced states NAPH as it picks up or drops
off 2 electrons and 1 proton
o Electrons with NADH maintain much of their potential energy
FAD/FADH2-electron carrier involved in the Krebs Cycle, can carry 2 electrons and 2 protons
Two ways to get ATP
o Oxidative phosphorylation
▪ 90% of ATP produced
▪ Redox reactions of the electron transport chain power massive ATP
production at the end of respiration
o Substrate-level phosphorylation
▪ Small amount of ATP generated during glycolysis and the Krebs Cycle as
enzymes transfer a phosphate to local ADP
▪ Occurs because phosphate must be removed from a substrate and needs
somewhere to go

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Glycolysis
o First step
o Goal: breakdown 6-carbon glucose into two 3-carbon pyruvate molecules
o Generates a little ATP
o Reduces NAD+ to NADH
o Energy investment phase-reactions 1-4, requires input of 2 ATP
▪ Two ATPs are burned up to convert the original glucose into a fructose
1,6-bisphosphate
▪ 6-carbon F1,6B is broken into two 3-carbon units called glyceraldehyde
3-phosphate (C-C-C-P)
o Energy payoff phase-reactions 5-9, generates 4 ATP and 2 NADH
▪ Each G3P is oxidized, losing its phosphate and electrons, generating 1 NADH
and 2 ATP
● Resulting 3-carbon molecule is called pyruvate
o Total production:
▪ 4 ATP (2 for each pyruvate, use two to get started and ​2 net​)
▪ 2 NADH (1 for each pyruvate
Next stage depends on presence or absence of oxygen
o Oxygen-Krebs Cycle for aerobic
o No oxygen-Fermentation for anaerobic
Krebs Cycle (Citric Acid Cycle or TCA Cycle)
o Completes the oxidation ( or breakdown) of glucose into units of carbon dioxide (CO2)
while generating ATP and reduced electron carriers (NADH, FADH2)
o As pyruvate enter the mitochondrion, it undergoes “preparatory reaction”
▪ One of its 3 carbons is removed as CO2, forming 2 carbon acetate (acidic acid)
▪ Acetate is joined by coenzyme A, yielding the high-energy molecule acetyl CoA
(still 2C) and 1 NADH
o Acetyl-CoA (2C) can then enter the actual citric acid cycle
o In the first reaction, acetyl-CoA (2C) joins with a 4-carbon intermediate called
oxaloacetate (4C), forming citrate (6C)
o The remaining 7 reactions function to decompose citrate (6C) back into oxaloacetate
(4C), so that the cycle can repreat for a new acetyl-CoA
o In this cycle, Two carbons enter, and two carbons are released as CO2
o Cycle generates 3 more NADH, 1 FADH2, and 1 ATP
o For each pyruvate, 4 NADH, 1FADH2, and 1 ATP is generated (2 pyruvates for each
glucose, so double these number for each glucose molecule)
o By the end, the glucose is fully oxidized (pretty much “gone”), and has been converted
into CO2, generating ATP and electron carrier (NADH,FADH2
Electron Transport Chain (ETC)
o After stage 2, the cell is left with very little ATP produced (only 4 ATP from the
substrate-level phosphorylation of glycolysis and Krebs), but several loaded-up
electron carrier (NADH, FADH2)

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Each electron carrier brings two electrons to the electron transport chain, a series of
proteins found embedded in the inner mitochondrial membrane
Consists of four complexes (I-IV) , as well as a couple of accessory proteins
Most of the proteins involved are called cytochromes, which are iron-containing
proteins
NADH brings electrons to Complex I
Fadh2 bring electrons to Complex II
All electrons are then passed down the chain until they reach the “final electron
acceptor”: OXYGEN
Electrons, hydrogen, and oxygen combine to form water as a byproduct
NADH+ and FAD are regenerated, so that they can return to earlier stages and carry
electrons again
Complexes I and II both give their electrons to ubiquinone
Pumping of H+ across membrane is active transport, building a stronger gradient so
they will want to passively go through ATP synthase
Complexes are protein pumps
Cytochrome c is used
Cytochrome c oxidase deficiency is a very rare inherited genetic disorder in which
children lack the enzyme that regenerates cytochrome c in this chain
Cyanide poisoning has a similar mechanism (locks up and stops)
As the ETC passes along electrons, hydrogen ions (H+) are pumped against their
gradient into the intermembrane space, generating a proton motive force, as a
stronger H+ concentration gradient is developed
H+ can then flow back across the membrane through an enzyme called ATP synthase
ATP synthase performs oxidative phosphorylation, coupling the movement of H+ with
the generation of a ton of ATP
This entire process is using electrochemical (H+) gradient to drive cellular work
(making ATP) is called chemiosmosis
H+ move from matrix to intermembrane space through membrane, then back to the
matrix through ATP synthase
H+ movement affects pH level
Chemiosmosis is what generates the majority of our cells’ ATP by oxidative
phosphorylation
For every NADH that comes to the ETC, ATP synthase will generate 3 ATP
For every FADH2 that comes to the ETC, ATP synthase will generate 2 ATP
Different electron carriers yield different amounts of ATP because of where they
enter, affecting the number of H+ ions moved
Total energy production:
▪ Glycolysis sends 2 NADH=6ATP
▪ Krebs sends 8 NADH=24 ATP
▪ Krebs sends 2 FADH2+4 ATP
▪ Total: 34 ATP (per glucose molecule) from ETC

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Glycolysis and the Krebs Cycle each provide us with 2 ATP per glucose, so the grand total for
aerobic respiration is 38 ATP per molecule of glucose
Scientists have been unable to accurately measure the payoffs with certainty, but the
estimated range is 32-38 ATPS per glucose
It is known that only 34% of the potential chemical energy in glucose is transferred to ATP
More energy is actually lost form the system as heat
Carbohydrates are best
o Glucose goes through all of cellular respiration
o Lipids and proteins can also enter respiration, but as intermediates at later stages
Fermentation
o If there is a lack of oxygen after glycolysis, the cell can undergo anaerobic respiration
by performing fermentation
o The ultimate purpose of fermentation is NOT to generate energy, but rather to recycle
NADH back into NAD+, so that it can return to glycolysis
o No ATP is generated in the reactions of fermentation
o Anaerobic respiration (glycolysis and fermentation) only generates 2ATP for every
glucose
o Type is a matter of byproducts
▪ Mammals ( lactic acid): pyruvate (3C) + NADH ​→​ Lactic acid + NAD+
● What makes our muscles burn
▪ Yeast: Pyruvate (3C) + NADH ​→​ Ethanol + NAD+
● Generates ethanol, the alcohol we drink
● Yeast are eventually killed by the ethanol they produce
● Also makes CO2- used to be used to make sodas
▪ Obligate anaerobes
● Bacteria that can only perform anaerobic rep[siration
● Some from the genus Clostridia
▪ Facultative anaerobes
● Organisms that can operate via aerobic or anaerobic respiration
● Includes yeast and muscle cells
Regulation of cellular respiration
o Basic supply and demand
o Feedback inhibition (negative feedback control) from citrate and ATP-will send
products back and stop the process
o Also positive feedback from AMP (indicates lack of ATP) activates enzymes

Chapter 8: Photosynthesis
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Where carbohydrates get their energy

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Heterotrophs=consumers; autotrophs=producers (plants, algae, and cyanobacteria can generate
their own “food” by harnessing solar energy)
Don’t say “plants make energy”-they harness it and make carbohydrates
PLANTS ALSO DO CELLULAR RESPIRATION
Photosynthesis=metabolic process that converts solar energy into the chemical energy of a
carbohydrate
Happens in chloroplasts
o Present in all green parts of plants, but highest concentration in the leaves (500,000 per
leaf with 1mm^2 surface)
o Chloroplasts are found in mesophyll cells-the interior tissue of the leaf
▪ Liquids and dissolved solids are delivered to and from here via veins, while gases
enter and leave via stomata
o Double-membrane envelope surrounding a dense fluid stroma
o Thylakoids-membranous sacs (third level of membranes) enclosed in the chloroplast
▪ Stacks of thylakoids are called grana; where chlorophyll is
o Chlorophyll (green pigment that gives leaves color) resides in the thylakoid membranes
Sunlight Antennas
o Chlorophyll is one several pigments found in the chloroplast
o A pigment is substance that absorbs visible light
▪ Different pigments absorb different wavelengths, and those that are absorbed
“disappear”
▪ Wavelengths not absorbed are reflected, and these become the color that we see
as they enter the eye
▪ Pigments absorb all of the colors not seen
o Chlorophyll a, chlorophyll b, and several accessory pigments called carotenoids all help is
the absorption of light
o The chlorophyll absorb light in the violet-blue and orange/red range, but they reflect
green, giving plants their characteristic color
o In the fall, chlorophyll levels decrease in the leaves and the accessory pigments’ colors
show in the tissue instead
o The absorptive ability of a pigment is measured by a device called a spectrophotometer
Reactions
o One of the more interesting things about photosynthesis is that scientists do not quite
understand exactly how plants make food, but rather have described what they believe to
be the general process
o Overall reaction: 3CO2 + 3H2O + light energy ​→​ C3H6O3 + 3 O2, but can be rewritten as
6CO2 + 6 H2O + light energy ​→​ C6H12O6 + 6O2
So essentially, photosynthesis is the anabolic REDOX opposite of cellular respiration
o An input of energy (from sunlight) is required in the generation of carbihydrates
Water is split by reactions to generate O2 gas
CO2 gas is broken up to provide carbon and oxygen for carbohydrates, as well as oxygen for the
generation of some water

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This is why plants require sun and watering, but plant food (fertilizer) is not a carbon compound,
but other elements instead (N,K,P,etc)
Actually two different processes:
o Light reactions:
▪ Involve converting solar energy into chemical energy in the form of ATP and
NADPH (the photo part)
▪ Does not involve making carbohydrates
o Calvin Cycle (The Dark Reactions)
▪ Involve using the energy from the light reactions to reduce CO2 into sugar
▪ Do not require light
▪ Can happen 24/7
▪ Use potential energy of e- and ATP
Light Reactions
o Harvesting of solar energy in the form of sunlight
o Reduction NADP+ into NADPH, an electron carrier
o Generates ATP through chemiosmosis and photophosphorylation
o Frees O2 gas from the cell
o DO NOT directly involve CO2 or the formation of carbohydrates
Begins when pigments absorb photons of light energy and convert it into chemical energy
o Light is often described as discrete particle of energy called photons
Chlorophylls do the majority of photosynthetic absorption, while carotenoids are more involved in
photoprotection-the absorption of excessive light energy
Antioxidants help cell avoid damage of DNA because of carotenoids
Various wavelengths of light actually seem to drive photosynthesis better than others, as shown
on this action spectrum
When light is absorbed, we say chlorophyll is “excited”
Absorption of a particular strength of photon causes one of a molecule’s electrons to be boosted
from the “ground state” to an orbital of higher energy
An electron at this high energy state is unstable, and generally electrons will move back to the
“ground state” immediately, releasing heat/light energy, generally causing fluorescence
However, we have enzymes that pass electrons down
Inside of a chloroplast, pigments are arranged with proteins in complexes called photosystems
(design prototype for solar panels)
Each photosystem consists of:
o Reaction center (2 chlorophyll a’s)
o Light-harvesting complex (other pigments)
These ‘antenna array” clusters of pigments absorb photons of light and transfer the energy form
one molecule to the next ( a chain of electron excitations), funneling all of the energy to the
reaction center chlorophylls
Thylakoids include 2 types of photosystems: II and I
Each photosystem has a particular primary electron acceptor molecule in its reaction center
o PS II=P680
o PS I=P700

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Both photosystems are involved with using light energy to power the synthesis of ATP and
NADPH, via the passing of electrons along the thylakoid membrane
Photosynthesis begins in photosystem II, where photons are absorbed and energy is funneled to
the P680 reaction center
Here, excited high-energy electrons are passed to the primary electron acceptor, which then
passes them down an electron transport chain of carriers to photosystem I
o This chain of cytochrome proteins is much like that found in mitochondrial respiration
Meanwhile, a similar photon-harvesting process is also exciting electrons in photosystem I, which
combine with those from PS II at the P700 reaction center
P700 passes these electrons on to its primary electron acceptor, which then hand off the electrons
to a protein called ferredoxin
Ferredoxin then passes two electrons to the electron carrier NADP+, reducing it to NADPH at the
conclusion of the light reactions
o This reaction is catalyzed by an enzyme called NADP+ reductase
o NADP+ + H+ + electrons ​→​ NADPH
P680 gives up electrons early in the process, so they need to be replaced, so an enzyme will split
H2O to provide tow new electrons to P680, allowing the reactions to continue
Splitting of water also results in the generation of O2 gas, which is released
Lack of water=lack of electrons
Process also involves chemiosmosis
o As electrons are moved down the ETC between photosystems, an electrochemical
gradient is set up as H+ is pumped across the thylakoid membrane
o Then, an ATP synthase enzyme can utilize this gradient to form ATP as the H+ flow back
across
o Original energy comes from light, rather than food (photophosphorylation)
o ETC pumps H+ form the stroma into the thylakoid space, then generates ATP out in the
stroma as the H+ move back out there
Summary of the light reactions:
o Energy from the sunlight pushes electrons from water, to PSII, to PSI, and then to NADPH,
forming ATP on the side
o Light reactions generate NADPH, ATP, and oxygen gas (when we broke down water at the
beginning)
o ATP and NADPH carry this energy in chemical form to the stroma for the Calvin Cycle – a
series of anabolic reactions that are able to make sugars from carbon dioxide
The Calvin Cycle
o Generates a 3-carbon sugar called glyceraldehyde 3-phosphate (G3P)
o To form one of these, the cycle must actually be completed three times (one CO2 comes
in at a time), which is how it is always diagrammed
o Three phases:
▪ Carbon fixation
▪ Reduction
▪ Regeneration
o Carbon fixation

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Occurs when a CO2 joins a 5-carbon molecule known as ribulose-bisphosphate
(RuBP)
● This requires help of an enzyme called rubisco
▪ The 6-carbon molecule generated is so unstable that it immediately splits into two
3-carbon acids known as phosphoglycerate (PGA)
o Reduction
▪ Each molecule of 3-phosphoglycerate undergoes a reaction with ATP to become
1,3-bisphosphoglycerate
▪ Then NADPH reduces this to convert it into glyceraldehyde 3-phosphate (G3P)
● Notice that this is where the products of the light reactions come in
o Regeneration
▪ Five of the six G3P’s created must be used to regenerate RuBP so that the cycle
can continue
▪ Essential for the cell to be able to keep generating carbohydrates
o Calvin Cycle Recap:
▪ 3 CO2s joined 3 RuBPs to make 6 phosphoglycerates
▪ These six phosphoglycerates are converted into 6 G3Ps
▪ Then 5 of those 6 G3Ps must be used to regenerate RuBP so that the cycle can
continue
▪ Therefore, the Calvin Cycle only produces one G3P carbohydrate for every three
turns of the cycle and it costs 9 ATP and 6 NADPH to get there
Why do we care?
o Photosynthesis is the most important process for life on Earth
o All of the atmospheric oxygen that we breathe is the result of photosynthesis, and it’s just
a waste product to the plant
o G3P can be used to synthesize necessary plant compounds (bigger carbs, lipids, amino
acids, etc) but it ultimately serves as our food source
▪ 160 billion metric tons of carbohydrates per year
▪ Without it, we have no energy



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