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Cellular Respiration: Redox reactions and glycolysis

General chemical formula for respiration

C6H12O6 + 02= 6CO2 +6 H20 + energy

Balanced chemical formula for respiration

C6H12O6_+ 602---> 6CO2+ 6H20+ ATP+ Heat
Exergonic= energy released!
photosynthesis is endergonic

What requires energy?

Polymer assembly, pumping substances across the membrane, moving and reproducing all require energy;

Cellular respiration

process of oxidizing food molecules, like glucose, to carbon dioxide and water; the energy released is trapped in the form of ATP for use by all the energy-consuming activities

catabolic reaction

released stored energy by breaking down complex molecules

Where do organic compounds possess potential energy?

potential energy as a result of their arrangement of atoms; compounds that can participate in exergonic reactions can act as fuels; ; with the help of enzymes a cell systematically degrades complex organic molecules that are rich in potential energy to simpler waste products that have less energy (some stored as heat, some as dissipated as heat)

What is the only source of energy?

The sun!; Energy int he sun is used in photosynthesis to make glucose from CO2 and H20 with release of O2; other organisms use the O2 and energy in sugar and released CO2 and H20; together these two are responsible for the majority of life on earth.
Prokaryotes do not have mitochondria...have another way to make ATP


partial degradation of sugars that occurs without the use of oxygen

Redox reaction

release energy when electrons move closer to electronegative atoms; catabolic pathways relocate electrons in food molecules, releasing energy for AT synthesis

Oxidation-reduction (Redox) Reactions

transfer one or more electrons form one reactant ot another
Sugar loses (gives out) an electrons (therefore it oxidizes to carbon dioxide)
6O2 accepts electron


Loss of electron


Addition of an electron

Aerobic respiration

the most prevelant and efficient catabolic pathway; oxygen is consumed as a reactant along with the organic fuel; most eukaryotic cells and prokaryotic organisms can carry it out;

Cellular Respiration

technically includes aerobic and anaerobic processes, but synonym for aerobic respiration; so will use it for aerobic respiration

Breaking and Cellular respiration

Breathing is necessary for exchange of CO2 produced during cellular respiration for atmospheric O2; cellular respiration uses O2 to help harvest energy from glucose and produces CO2 in the process

Breakdown of glucose

exergonic, free energy charge of -686 kcal per mol of glucose; ; reaction can happen spontaneously (without input of energy); - Delta G
Glucose is oxidized; O2 becomes reduced

reducing agent

electron donor

oxidizing agent

electron acceptor

Summary for cellular respiration

REDOX with sodium and chlorine

Na: reducing agent
Cl: oxidizing agent
Electron donor: sodium; it is oxidized
Electron acceptor: chlorine; gets reduced
Ionic bond formed
Doesn't always have to be a full loss of electron, sometimes partial electrons are lost like in co2 (methane reacts with oxygen, forming co2, electrons end up shared less equally between carbon and its new covlanet partners (oxygen atoms);

the more electronegative an atom is, the harder it is to take an electron away from it: ENERGY MUST BE ADDED TO PULL AN ELECTRON AWAY FROM AN ATOM

Site of cellular respiration?

Mitochondria (non endomembrane system= not involved in protein synthesis) = has its own genome ((genetic material= its circular like; double stranded like prokaryotic cell); has bilayer phospholipid bilayer; it is convulted inside membrane (increases surface area= many copies of an enzyme called ATP synthase=
fluid inside=matrix
Closed system in mitochondria (only way it exhcnages is via channels and proteins)

Where do cells tap energy from?

electrons "falling" from organic fuels (glucose) to oxygen; in the case of glucose and oxygen interaction, the electrons come from hydrogen atoms; removal of electrons from glucose invovle the enzyme glucose dehydrogenase; this enzyme requires a cofactor called NAD+ (electrons shuttle)
Need dehydrase to release H+ and needs NAD+ in oxidized form to help it

Organic molecules have a lot of H which are excellent fuels because their bonds are a source of hilltop electrons whose energy may be released as those electrons fall down an energy gradient

In respiration, the oxidation of glucoes transfers electrons to a lower energy state, liberating energy that becomes available for ATP synthesis

Activation energy barrier holds back the flood of electrons to a lower energy state (this prevnets the almost instant combustion)


NAD prevent energy loss (not just an explosive thing)
Electron Shuttle


removes 2 electrons and 2 protons (2 hydrogen atoms; oxidizes sugar) from glucose= therefore oxidizing it; electrons loose very little of their potential energy; 2 protons released, but NAD+ only gets one, but still gets 2 electrons so it becomes NADH + H+; other + goes to proton pump

NADH and H+ (by receiving 2 electrons and one proton, it is neutralized and it is reduced to NADH)

After NAD now gets electron

these energetic electrons then pass from molecule to molecule in an "energy cascade" or electron transport chain; each molecule is temporarily reduced by the oxidation of the previous molecule and in turn, is oxidized when it reduces the next molecule; the ultimate electron acceptor in this part of overall process is oxygen; during hte cascade a small amount of energy is reduced; the released energy is used to pump H+

cellular respiration bvs. water formation

Cellular respiration, the hydrogen that reacts with oxygen is derived from organic molecules not H2; and instead of occuring in one explosive reaction, respiration uses an electron transport chain to break the fall of electrons to oxygen into several energy releasing steps

Electron transport chain

breaks the fall of electrons to oxygen; consists of a number of molecules (mostly proteins) built into the inner membrane of the mitochondria (each downhill carrier is more electronegative than the previous one); electrons removed from glucose are shuttled by NADH to the top, higher-energy end of hte cahin; at the bottom (lower energy); O2 captures them
Electrons transfer form NADH to oxygen in an exergonic reaction with a free energy change of -53 kcal/mol ; instead of being wasted in one explosive step, electrons cascade down the chain from one carrier to the next by a serious of redox reactions

Terminal electrons acceptor

oxygen; very great affinity for electrons; each downhill carrier is more electronegative than the previous one, making it more capable of oxidizing its uphill neighbor

How do electrons that are extracted from glucose and stored as potential energy in NADH finally reach oxygen?

The electron transport chain; breaks the fall of electrons to oxygen into several energy releasing steps ; doesn't generate ATP directly; but CREATES A PROTON GRADIENT (stores energy for chemical synthesis)

3 metabolic stages of respiration

1. glycolysis (substrate-level phosophorylation)
2. citirc acid cycle (substrate-level phosophorylation) ; krebs cycle
3. oxidative phosphorylation: electron transport and chemiosmosis


occurs in the cytosol; begins the degradation process by breaking glucose into two molecules of a compound called pyruvate
Glucose, a six-carbon sugar is split into 2 three carbon sugars; three carbon sugars are oxidized and rearranged to form two molecules of pyruvate; 10 steps in glycolysis are catalyzed by specific enzymes; occurs in two phases:
1. energy investment phase
2. payoff phase

Citric acid cycle

takes place in the mitochondrial matrix of eukartyoics; completes the breakdown of glucose by oxidizing a derivative of pyruvate to carbon dixoide

Oxidative phosphorylation

powered by redox reactions of the electron transport chain ; 90% of ATP generated; alot less in (substrate-level phosophorylation: occurs when an enzyme transfers a phosphate group from a substrate molecule to ADP, rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation)

HOw much ATP is produced by 1 molecule of glucose?

38 molecules

Why do you use an electron transport chain?

dont want to give a high energy electron to Hydrogen or there will be a combustion.
Further down the electron transport chain the more electronegative it is

How is ATP made in cellular respiration?

1. Phosphate-level phosphorylation; ADP + P= catalyzed by an enzyme (enzyme takes this P from an organic molecule -carbon containing- and removes phosphate and makes atp)
2. Oxidative phosphorylation: ADP + Pi (adding an inorganic phosphate

How was proton concentration outside the membrane made?

by redox reactions of electrons (pumped hydrogen ions against its concentration gradient from inner membrane of mitochondria to outside)

Proton Motive force

force generated by proteins in endomembrane space; Hydrogne atoms at atp synthase go down its electrochemical gradient to the reuter to produce atp

Summary of glycolysis

10 steps, each have a specific enzyme
"sugar splitting" =6 carbon glucose split into 2-3 carbon sugars; smaller sugars are oxidized
Phosphorylation: substrate
2 pyruvate + 2H20
2 NADH + 2H+
2 ATP (net)
Location: Cytoplasm
Occurs with or with out O2.
Only releases a 1/4 of the chemical energy stored in glucose

ATP kcal per mole

7.3 kcal/mol
Glucose: 686 kcal/mol
only produced 2 atp in have more to get this=this is inefficient

Glycolysis investment stage pictures
Energy investment and energy payoff phase


removes carbon

How is pyruvate modified?

Enters into mitochondria by active transport; pyurvate is first converted to acetyl CoA in mitochondiral matrix by a multienzyme comples and forms acetyl CoA; carboxyl group is removed as CO2, pairs of electrons are transferred from reamining 2 carbon fragment to NAD+ to form NADH

What can enter into mitochondira

Acetyl CoA (after pyruvate is modified)

Grooming phase

Mitochondrial matrix
NADH 1 per pyruvate (2 total)
No phosphorylation
2 Acetyl CoA

Krebs (citric acid cycle)

Substrate levle phosphorylation in the matrix
Per glucose, cranks 2x.
Produces (total): 2 Atp
2 molecules of FADH2
Krebs cycle is the crossroads for metabolic actions (make amino acids, other sugars, energy etc)
without oxygen none of these processes happen.

What is the first chemical that is interacted with by acetyl coa?

Oxaloacetate and makes citrate!
Acetyl CoA adds its 2 carbon acetyl group to oxaloacetate, producing citrate


is oxidized and can participate in more electron jobs
Protein carrier one gets reduced (gets electrons)

NADH and FADH2 account for most of the energy extracted from the food.

FADH2 to FAD; Why did FADH2 not give it to protein 1, but gave it Q

because FADH2 is more electronegative, and can't give it to first one, give sit to one that is more electronegative than FADH

Electron transport chain summary slide

oxidative phosphorylation
A collection of molecules embedded in the inner membrane of of the mitochondrion in eukaryotic cells (prokaryotic they are in the plasma membrane); (inner membrane folding increase surface area); most components of the chain are proteins which exist in multiprotein complexes; which have prosthetic groups tightly bound to them (catayltic)

Free electrons travel down the chain; electrons alternate between reduced and oxidized states as they accept and donate electrons
each component becomes reduced when it accepts electrons from its uphill neighbor, it returns to its oxidized form as it passes electrons to its downhill more electronegative neighbor

How does the mitochondrion couple this electron transport and energy release to ATP synthesis?

The answer is a mechanism called chemiosmosis
In the inner membrane of the mitochondrion are many copies of a protein complex called ATP synthase, the enzyme that actually makes ATP from ADP and inorganic phosphate.
ATP synthase works like an ion pump running in reverse. Recall from Chapter 7 that ion pumps use ATP as an energy source to transport ions against their concentration gradients.
This process, in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such as the synthesis of ATP, is called chemiosmosis.

We have previously used the word osmosis in discussing water transport, but here it refers to the flow of H+ across a membrane.


This process, in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such as the synthesis of ATP

Oxidative Phosphorylation

Do no make anymore FADH2 or NADH;
make 32-34 ATP
Cellular location: inner membrane of mitochondria


poison that inhibits the 3rd complex of electron transport chain=doesn't allow electrons to reach Oxygen; (o2 is the driving force to make concentration gradient); if you block the movement of electrons -you cannot form ATP; same with insectidice (rotenone) ;


given to patients to lose weight; DNP makes membrane very leaky, so H+ leak through the membrane=no gradient =proteins and enzymes get denatured; falling of hydrogen down gradient is a lot of release of heat = cells start burning glucose because it doesnt get energy, so it burns all the glucose adn then it starts to break down fat


blocks ATP synthase

Oxygen not present-what does cell do?

Fermentation; uses glycolysis to oxidize sugars to pyruvate; produce ATP by substarte level phosphorylation; electrons of NADH are passed to an organic molecule, regenerating NAD+; 2 ATP total

What does pyruvate get converted to in fermentation?

ethanol or lactic acid

Alcohol fermentation

pyruvate is converted to ethanol in two steps
1. pyruvate is converted to a 2 carbon compound (acetaldehyde by removal of CO2; releases Co2 from the pyruvate
2. acetadehyde is reduced by NADH to ethanol (NADH-->NAD+); used in brewing and wine making

lactic acid fermentation

pyruvated is reduced directly by NADH to form lactate (ionized form of lactic acid); used to make cheese and yogurt
Muscle cells switch to lactic acd fermentation to generate ATP when O2 is scarce; waste producte may cause muscle fatigue (lactate); but is ulimately converted bback to pyruvate in the liver

Anaerobic vs fermentation vs oxidative phosphorylation

O2 is present, pyruvate enters mitochondria from cytoplasm=cellular respiration occurs
O2 is not present=fermentatio noccurs
Both use sugars to oxidize sugars to pyruvate, produce ATP by substrate level phospholrylation
In fermentation-electrons of NADH are passed to an organic molecule regenerating NAD+
In respiration, electrons of NADH are passed to O2, producing ATP by oxidative phosphorylation 36-38 ATP total

Run out of carbs, what does our body turn to?

Fat (glycerol must be removed and then fatty acids help make acetyl coA; glycerol enters to become pyruvate) and then proteins (amino acids vs. amine group; amino acids=deanimation enters the pyruvate cycle or actyl CoA)
Humans dont tie of energy loss unless our ECT is defective

Compare and Contrast aerobic and anaerobic respiration.

Both processes include glycolysis, the citric acid cycle, and oxidative phosphorylation. In aerobic respriation, th final electron acceptor is molecular O2, but in anaerobic, it is a different substance

What if a redox reaction occurred, which compound would be oxidized and which would be reduced?

C4H6O5 would be oxidized and NAD+ would be reduced

Pyruvate to Acetyl CoA

1. pyruvates -COO- carboxyl group is removed.
2. the remaining two carbon fragment is oxidized, forming a compound named acetate; electrons transferred to NAD+
3. Finally coenzyme A (CoA), a sulfur-containing compound derived from a B vitamin is attached to the acete by an unstable bond that makes the acetyl group very reactive; makes Acetyle CoA=extremely high potential energy

During the redox reaction in glycolysis which molecule acts as the oxidizing agent? the reducing agent?

NAD+ acts as the oxidizing agnet in step 6, accepting electrons form glyceraldehyde-3 phosphate, which thus acts as the reducing agent

Citirc acid other names?

ticarboxylic acid cycle, krebs cycle

Krebs cycle function

as a metabolic furnace that oxidizes organic fuel derived from pyruvate;

Name the molecules that conserve most of the energy from the citric acid cycle's redox reactions. How is this energy converted to a form that can be used to make ATP?

NADH and FADH2; they will donate electrons to the electron transport chain

What cellular process produces the CO2 that you exhale?

CO2 is released from the pyruvate that is formed during gylcolysis, and CO2 is released during the citirc acid cycle

The conversions shown in figure 9.10 and step 4 of 0.12 are each catalyzed by a large multienzyme complex. What similarities are there in the reactions that occur in these two cases?

In boht cases, the precurosr molecules loses a CO2 molecule adn then donates electrons to an electron carrier in an oxidation step


most of the reamaining electron carries between ubiquinone and oxygen are proteins called cytochromes

Complete review of Cellular respiration

Lactic acid fermentation

pyruvate is reduced directly by NADH to form lactate (ionized form of lactic acid); process used to make cheese and yogurt with specific fungi and bacteria; muscle cells switch to lactic acid fermentation to generate ATP when O2 is scarce; waste product, lactate, causes muslce fatigue which is ultimately converted to pyruvate in the level.

what effect would an absence of O2 have on the process shows in figure 9.16 (Electron transport chain)

Oxidative phosphorylation would stop entirely, resulting in no ATP production by this process; with out oxygen to pull electrons down the ETC, H+ would be pumped into the mitochondira's intermebrane space and chemisomososis would not occur.

In absence of O2, as in question 1, what do you think would happen if you decreased the pH of hte intermembrane space of the mitochondrion? Explain.

Decreasing the pH is the addition of H+; it would establish a proton gradient even with out the function of the electron transport chain, and we would expect ATP synthase to function and synthesize ATP

obligate anaerobes

carry out only fermentation or anaerobic respiration

Facultative anaerobes

fermentation or aerobic respiration

Glycolysis evolutionary significance

oldest bacterial fossils appeared when atmosphere had little 02 (3.5 billion years ago); first prokaryotes must have used only glycolysis for ATP production (occurs in cytosol with out membrane-enclosed organelles=very widespread, suggests it evolved early in history of life

Consider the NADH formed during glycolysis. What is the final acceptor for its electrons during fermentation? What is the final acceptor for its electrons during aerobic respiration?

Fermentation final acceptor: a derivative of pyruvate such as acetaldehyde
Lactic Acid fermentation like: pyruvate
Aerobic: Oxygen

A glucose-fed yeast cell is moved from an aerobic environment to an anaerboic one. For cells to continue generating ATP at the same rate, how would its rate of glucose consumption need to change?

Cell would need to increase glucose consumption at about 19 times the consumption rate in aerobic envrionemtn (2 atp vs. 38 in aerobic)

Beta oxidation

breaks fatty acids into two carbon fragments; which enter citirc acid cycle as acetyl coA

What regulates metabolic rate?

supply/demand; the cell does not waste energy by making more than what it needs; use feedback inhibition: the end prouce of the anabolic pathway inhibits the enzyme taht catalyzes an early step of the pathway; also controls its catabolsim (if working hard, and needs more ATP, increases cellular respiration)


allosteric enzyme with receptor sites for specific inhibitors and activators-it is inhibited by ATP and stimulated by AMP which the cell derives from AMP

Compare the structure of a fat with that of a carbohydrate. what features of their strucures make fat a much better fuel?

Fat has many CH2 units and in these molecules, electrons are shared more equally and fat is much more reduced; where carbohydrate molecule are already somewhat oxidized, and shared unequally =no bound to oxygen

Under what circumstances might your body synthesize fat molecules?

When we consume more food than necessary, out body synthesizes fat as a way of storing energy for use.

What will happen in a muscle that has used up its supply of oxygen and ATP?

AMP will accumulate, stimulating phosphofructokinase, which increases the rate of glycolysis; the cell will convert pyruvate to lactate in lactic acid fermentation (to supply ATP)

What is the reducing agent in the following reaction?
Pryuvate + NADH+ H+ ---> Lactate+ NAD+

NADH (loses electrons=reduction in electrons, becomes positive)

The immediate energy source that drives ATP synthesis by ATP synthase during oxidative phosphorylation is the:

H+ concentration across the membrane holding AtP synthase

Which is metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule?


The final electron acceptor of the electron transport chain that functions in aerobic oxidative phosphorylation is the?


When electrons flow along the electron transport chain of mitochdonria, which of hte following changes occur?

The pH of the matrix increases

Cells do not catabolize carbon dixoide because

CO2 is already completely oxidized

Most CO2 from catabolsim is released during:

Citric acid cycle

Step 3 in figure 9.0 is a major point of regulation of glycolysis. The enzyme phosphofructokinase is allosterically regulated by ATP and related moleucles. Considering the overall result of glyoclysis would you expect ATP to inhibit or stiulate actiivty of this enzyme?

Since hte overall process of glycolysis results in production of ATP, it would make sense for the process to slow down when ATP levels have increased substantially. Thus we would expect ATP to allosterically inhibit phophofructokinase

Which of the following is a true distinction between fermentation and cellular respiration?

NADH is oxidized by the electron transport chain in respiration only.

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