AP Bio Unit 3 Chapter 9: Cellular Respiration and Fermentation
3 metabolic stages of cellular respiration
(1) glycolysis (2) pyruvate oxidation and the citric acid cycle (3) oxidative phosphorylation (includes the electron transport chain and chemiosmosis)
When electrons flow along the electron transport chains of mitochondria, which of the following changes occurs? (A) The pH of the matrix increases. (B) ATP synthase pumps protons by active transport. (C) The electrons gain free energy. (D) NAD⁺ is oxidized.
(A) The pH of the matrix increases (bc H+ ions are being pumped out, matrix becomes more basic/alkaline)
The final electron acceptor of the electron transport chain that functions in aerobic oxidative phosphorylation is (A) oxygen. (B) water. (C) NAD+ (D) pyruvate.
(A) oxygen
ln mitochondria, exergonic redox reactions (A) are the source of energy driving prokaryotic ATP synthesis. (B) provide the energy that establishes the proton gradient. (C) reduce carbon atoms to carbon dioxide. (D) are coupled via phosphorylated intermediates to endergonic processes.
(B) provide the energy that establishes the proton gradient
Most CO2 from catabolism is released during (A) glycolysis. (B) the citric acid cycle (C) lactate fermentation. (D) electron transport.
(B) the citric acid cycle
The IMMEDIATE energy source that drives ATP synthesis by ATP synthase during oxidative phosphorylation is the (A) Oxidation of glucose and other organic Compounds. (B) flow of electrons down the electron transport chain. (C) H+ concentration gradient across the membrane holding ATP synthase. (D) transfer of phosphate to ADP.
(C) H+ concentration gradient across the membrane holding ATP synthase (proton-motive force)
Which metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule? (A) the citric acid cycle (B) the electron transport chain (C) glycolysis (D) reduction of pyruvate to lactate
(C) glycolysis
What is the oxidizing agent in the following reaction? Pyruvate + NADH + H⁺ → Lactate + NAD⁺ (A) oxygen (B) NADH (C) lactate (D) pyruvate
(D) pyruvate
net energy yield from the citric acid cycle
-per pyruvate molecule: 3 NADH, 1 FADH2, 1 ATP -per glucose molecule (since each glucose molecule breaks down into 2 pyruvate molecules): 6 NADH, 2 FADH2, 2 ATP
how glycolysis accepts a wide range of carbohydrates for catabolism
-starch, a polysaccharide, is hydrolyzed to glucose in the digestive tract (can be broken down by cells via glycolysis/citric acid cycle) -glycogen, a polysaccharide in human/animal livers can be hydrolyzed to glucose -digestion of disaccharides like sucrose, into glucose
alcohol fermentation
-type of fermentation where pyruvate is converted to ethanol (ethyl alcohol) in 2 steps to regenerate NAD+. Pyruvate reduced indirectly by NADH. Produces CO2 as a byproduct. -used by many bacteria, yeast. Yeast used in brewing, winemaking, baking
lactic acid fermentation
-type of fermentation where pyruvate is reduced directly by NADH to form lactate as an end product, regenerating NAD+ with no release of NAD+ -used by certain fungi/bacteria, used in dairy industry (cheese/yogurt) -also used by human muscles cells to make ATP when oxygen is scarce (when sugar catabolism outpaces muscle's supply of oxygen from bloodstream)
net energy yield from glycolysis per glucose molecule
2 ATP molecules (4 ATP total, 2 net) and 2 NADH
total yield of ATP per glucose molecule
30-32 ATP (2 from glycolysis, 2 from citric acid cycle 26-28 from oxidative phosphorylation)
total yield of ATP via substrate-level phosphorylation in cellular respiration
4 ATP (2 from glycolysis, 2 from citric acid cycle)
amount of free energy released in cellular respiration
686 kcal under standard conditions (ΔG = -686 kcal/mol)
citric acid cycle (Krebs cycle)
8-step cycle that further oxidized the organic fuel derived from pyruvate (Acetyl CoA). Generates 1 ATP molecule per turn by substrate-level phosphorylation. Most of the energy is transferred to electron carriers NAD+ and FAD via redox reactions
inhibitors of phosphofructokinase
ATP and citrate (first product of citric acid cycle)
phosphorylated intermediate
ATP performs cellular work using this basic form of energy coupling through phosphorylation of an intermediate molecule
how ATP synthase catalyzes ATP synthesis
ATP synthase functions like an ion pump in reverse (uses energy of an existing ion gradient to power ATP synthesis)
why the electrons donated to the electron transport chain via FADH2 yield less ATP than electrons donated by NADH
FADH2 donates electrons from within complex II, at a lower energy level than NADH does (NADH donates at complex I). So even though both electron carriers donate the same number of electrons (2) for electron reduction, electron transport chain produces less energy when FADH2 is the electron donor
evolutionary significance of glycolysis
Glycolysis occurs in nearly all organisms, and can be used regardless of presence of O2 Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere.
chemiosmosis (general definition)
an energy-coupling mechanism that uses energy stored in the form of an H+ ion gradient across a membrane to drive cellular work
two mechanisms by which certain cells can oxidize organic fuel and generate ATP without the use of oxygen
anaerobic respiration, fermentation
before proteins can be used for fuel in cellular respiration, must first be...
broken down into amino acids (which then have to undergo deamination)
proton-motive force
capacity of the H+ ion gradient to perform work. This force drives H+ back across the inner mitochondrial membrane through the H+ channels provided by ATP synthase in cellular respiration
in addition to providing calories for ATP synthesis, food must also provide this
carbon skeletons that cells can use to make their own molecules from (via anabolic pathways, endergonic reactions)
redox reactions (oxidation-reduction reactions)
chemical reactions involving electron transfers from one reactant to another
electron carrier
coenzymes that transport electrons. Are able to cycle easily between oxidized and reduced form
Acetyl CoA (acetyl coenzyme A)
compound produced during pyruvate oxidation that is high in potential energy. Is used to transfer the acetyl group to a molecule in the citric acid cycle (reaction that is highly exergonic)
function of chemiosmosis in cellular respiration
couples the exergonic reactions of the electron transport chain with ATP synthesis
glycolysis location
cytosol
free energy in the system [increases/decreases] as electons move down the electron transport chain
decreases (exergonic reaction)
ubiquinone (coenzyme Q, CoQ)
electron carrier that is a small hydrophobic molecule, the only member of the electron transport chain that is not a protein. Is individually mobile within the membrane rather than residing in a particular complex
FADH2
electron carrier that is another source of electrons for the electron transport chain. Is a reduced product of the citric acid cycle
the nature of redox reactions in the electron transport chain
electron carriers alternate between reduced and oxidized states as they accept/donate electrons. each component of chain becomes reduced when it accepts electrons from its "uphill" (less electronegative) neighbor. Becomes oxidize again when it passes the electron to its "downhill", more electronegative neighbor
glycolysis can be divided into these 2 phases
energy investment phase (cell spends 2 ATP) and the energy payoff phase (4 ATP molecules are produced by substrate-level phosphorylation and NAD+ is reduced to NADH by electrons released from the oxidation of glucose)
substrate-level phosphorylation
mechanism in glycolysis and the citric acid cycle where smaller amounts of ATP are formed directly; occurs when an enzyme transfers a phosphate group from a substrate molecule to ADP, forming ATP (instead of adding an inorganic phosphate to ADP, as in oxidative phosphorylation). Produces a small amount of ATP
fermentation
mechanism of harvesting chemical energy without using either oxygen or any electron transport chain (without cellular respiration). Produces ATP via substrate-level phosphorylation. Involves glycolysis and the constant regeneration of NAD+ to serve as the accept electrons from glucose
glycolysis and the citric acid cycle function as _______________ that enable cells to convert some kinds of molecules to others as needed
metabolic interchanges
glycolysis
metabolic stage of cellular respiration that begins the degradation process by breaking glucose into 2 molecules of pyruvate
aerobic respiration
most efficient catabolic pathway in which oxygen is consumed as a reactant along with the organic fuel. Used by cells of most eukaryotic and many prokaryotic organisms
cytochromes
most of the remaining electron carriers between ubiquinone and oxygen are these kinds of proteins. Their prosthetic group is a heme group, an iron atom that accepts and donates electrons
prosthetic groups
nonprotein components (such as cofactors/coenzymes) tightly bound to proteins/multiprotein complexes of the electron transport chain
obligate anaerobes
organisms that carry out only fermentation or anaerobic respiration. cannot survive in presence of oxygen
cyclitic nature of the citric acid cycle
oxaloacetate, the first compound in the citric acid cycle that reacts with acetyl CoA, is regenerated when citrate is decomposed back to oxaloacetate
step in cellular respiration that generates the most ATP
oxidative phosphorylation
the final electron acceptor in the electron transport chain (in aerobic respiration)
oxygen
this atom/element is the most powerful oxidizing agent
oxygen (because it is so electronegative)
organic compounds possess ________ as a result of the arrangement of electrons in the bonds between their atoms
potential energy; allows for them to act as fuels in exergonic reactions
reaction coupling
process by which energy released by ATP hydrolysis used to power other reactions in cell; is how ATP powers work in cells. endergonic & exergonic reactions linked, often by a shared intermediate
oxidative phosphorylation
process where NADH and FADH2 produced by the citric acid cycle/glycolysis relay electrons extracted from food to the electron transport chain. Via chemiosmosis, they supply the necessary energy for the phosphorylation of ADP to ATP
pyruvate oxidation
process where pyruvate in eukaryotic cells enters a mitochondrion and is converted (further oxidized) to a compound called acetyl coenzyme A, or acetyl CoA. Requires the presence of O2. This process links glycolysis and the citric acid cycle.
ATP synthase
protein complexes (enzyme) that populates the inner membrane of mitochondria; make ATP from ADP and organic phosphate.
ion pump
pumps that use ATP as an energy source to transport ions against their gradients across a membrane
exergonic/catabolic reactions
reaction that degrades complex organic molecules that are rich in potential energy into simpler waste products that have less energy. some of this energy can be used for work; the rest dissipates as heat
each NADH molecule formed during respiration represents _________
stored energy that can be tapped into to make ATP when the electrons complete their "fall" in a series of redox reactions down an energy gradient from NADH to oxygen (in electron transport chain)
beta oxidation
the metabolic sequence that breaks fatty acids down to 2-carbon fragments, which enter the citric acid cycle as acetyl CoA. also generates NADH and FADH2, which enter electron transport chain
deamination
the removal of amino groups (NH2) from amino acids; must occur before amino acids can be used in glycolysis and the citric acid cycle
oxidizing agent
the substance in a redox reaction that is the electron acceptor (becomes reduced)
reducing agent
the substance in a redox reaction that is the electron donor (that becomes oxidized)
how catabolic pathways that decompose glucose/other organic fuels yield energy (principle of redox)
the transfer of electrons from one reactant to another during the chemical reactions (known as redox reactions releases energy stored in organic molecules, and this energy is used to synthesize ATP
most energy of a fat is stored in...
their fatty acids (hydrocarbon tails, full of C-H bonds)
[true/false]: electron transfer from NADH to oxygen is an exergonic reaction
true (because NADH is less electronegative than oxygen, and electrons following the path of least resistance down the energy gradient releases energy)
[true/false]: glycolysis occurs regardless of the presence of O2
true; however, if O2 is present, then the chemical energy stored in pyruvate and NADH can be extracted later on via pyruvate oxidation, citric acid cycle, oxidative phosphorylation
[true/false]: cellular respiration refers to both aerobic and anaerobic processes
true; however, it is commonly used as a synonym for aerobic respiration because it is related to the process of organismal respiration (process of breathing in oxygen)
oxidation
loss of electrons from a substance
similarities between fermentation and anaerobic/aerobic respiration
-all are alternative cellular pathways for producing ATP by harvesting the chemical energy of food -all use glycolysis to oxidize glucose/other organic fuels to pyruvate, with a net production of 2 ATP via substrate-level phosphorylation -NAD+ is an oxidizing agent in all 3 pathways that accepts electrons from food during glycolysis
Phosphofructokinase (PFK)
-allosteric enzyme that catalyzes step 3 of glycolysis; is the first step that commits the substrate irreversibly to the glycolytic pathway. -Is the important switch ("pacemaker") of respiration -has receptor sites for specific inhibitors and activators
how fats are used in cellular respiration
-fats (specifically triglycerides) are digested to glycerol and fatty acids -glycerol then converted to glyceraldehyde 3-phosphate
differences in amount of ATP produced (and mechanisms of ATP synthesis) between fermentation and cellular respiration (aerobic/anaerobic)
-fermentation: 2 molecules of ATP produced by substrate-level phosphorylation. Without an electron transport chain, energy stored in pyruvate unavailable :( -cellular respiration: pyruvate completely oxidized in mitochondrion. Most chemical energy shuttled by NADH/FADH2 in the form of electrons to electron transport chain. This then powers oxidative phosphorylation. So cellular respiration generates more ATP (up to 16x more) than fermentation -Also means that to make the same amount of ATP, sugar/glucose must be consumed at a much faster rate when fermenting than when respiring
contrasting mechanisms for oxidizing NADH back to NAD+ (regenerating NAD+ needed for glycolysis) between fermentation and cellular respiration (aerobic/anaerobic)
-fermentation: final electron acceptor is an organic molecule (like pyruvate in lactic acid fermentation, acetaldehyde in alcohol fermentation) -cellular respiration: electrons carried by NADH transferred to electron transport chain, regenerating NAD+
aerobic vs anaerobic respiration
-final electron acceptor in the electron transport chain of aerobic respiration is oxygen -final electron acceptor in the electron transport chain of anaerobic respiration is a less electronegative molecule
feedback inhibition
-most common mechanism for anabolic pathways -end product of the anabolic pathway inhibits the enzyme that catalyzes an earlier step of pathway
facultative anaerobes
-organisms that can make enough ATP to survive using either fermentation or aerobic respiration -in these organisms, pyruvate serves as a "fork" in the metabolic road (leads to 2 alternatives depending on presence/absence of O2: fermentation or aerobic cellular respiration)
electron transport chain
a collection of molecules, mainly proteins, embedded in the inner membrane of the mitochondrion in eukaryotes. Infoldings of inner membrane (called cristae) increases surface area. facilitates a series of redox reactions.
energy source for ATP synthase
a difference in the concentration of H+ on opposite sides of the inner mitochondrial membrane. There's a higher concentration of H+ ions in the intermembrane space than the mitochondrial matrix. ATP synthesis is powered by the flow of H+ back across the membrane into the mitochondrial matrix (H+ ion gradient created by the electron transport chain, which pumps H+ ions out of the mitochondrial matrix)
activators/stimulators of phosphofructokinase
accumulation of AMP (adenosine monophosphate)
reduction
addition of electrons to a substance (adding electrons to an atom *reduces* the amount of positive charge)
types of fermentation
alcohol fermentation and lactic acid fermentation differ in end products formed from pyruvate, both used by humans for food/industrial production
NAD+ (NADH in reduced form)
an electron carrier (nicotinamide adenine dinucleotide) that functions as an electron acceptor (so an oxidizing agent) during respiration. Is the most versatile electron acceptor in cellular respiration and functions in several redox steps during the breakdown of glucose
difference between anaerobic respiration and fermentation
an electron transport chain is used in anaerobic respiration but not in fermentation
general flow of most energy during cellular respiration
glucose → NADH → electron transport chain → proton-motive force → ATP
"uphill/downhill" energy relationship in redox reactions
energy must be added to pull electrons away from an atom (just like how energy is needed to push a ball uphill), and the more electronegative an atom is, the more energy is required to take electrons from it. Electrons lose potential energy when shifts from a less electronegative atom to a more electronegative atom, just like how a ball loses potential energy when rolling down hill (think of it as the electrons following the path of least resistance, like a ball rolling down a hill). The decrease in potential energy indicates an exergonic reaction, and the release of chemical energy that can do work
dehydrogenase
enzyme in cellular respiration that removes a pair of hydrogen atoms (2 electrons and 2 protons) from its substrate (glucose), oxidizing it. it delivers the 2 electrons and 1 proton to its coenzyme, NAD+, forming NADH (other proton released as an H+ ion)
[true/false]: cellular respiration produces energy to keep organisms alive
false; cellular respiration *releases* energy stored in food by photosynthesis
[true/false]: hydrogen atoms are transferred directly to oxygen during the oxidation of glucose in cellular respiration
false; electrons first pass to an electron carrier
[true/false]: glycolysis produces CO2 as a byproduct
false; no carbon is released as CO2 during glycolysis. All carbon originally present in glucose is accounted for in the two molecules of pyruvate.
[true/false]: all redox reactions involve the complete transfer of electrons from one reactant/substance to another
false; some redox reactions change the degree of electron sharing in covalent bonds (ex: change in electronegativity due to new bonds can cause electrons to be closer to one atom, like oxygen, such that the more electronegative atom "partially gains" electrons, and is reduced)
most of our calories are obtained in the form of...
fats, carbohydrates, carbohydrates (in the form of disaccharides like sucrose, and polysaccharides like starch) (glucose molecules not common in the diet; most of the above molecules are broken down in cells by glycolysis and the citric acid cycle)
flavoprotein
first protein in the electron transport chain that acts as the oxidizing agent when it accepts electrons from NADH. This protein has a prosthetic group called flavin mononucleotide (FMN)
this molecule is the reducing agent in cellular respiration
glucose (glucose is oxidized in cellular respiration)
why cellular respiration takes place in a series of steps
if energy is released from a fuel all at once, it cannot be harnessed efficiently for work (a lot of it would go to waste). It would also be a single big, explosive reaction
general molecular structure of reducing/oxidizing agents in redox reactions
in general, fuels with multiple C-H (hydrocarbon) bonds are oxidized into products with multiple C-O bonds. Main energy-yielding foods (carbohydrates and fats) are reservoirs of electrons associated with hydrogen, often in form of C-H bonds)
significance of hydrocarbons in redox reactions
in general, organic molecules with an abundance of hydrogen (very low electronegativity) are excellent fuels because their bonds are a source of "hilltop" electrons whose energy is released when they "fall" down the energy gradient when transferring to oxygen (very high electronegativity)... which is why triglycerides (with their hydrocarbon chains) are great fuels
electronegativity [increases/decreases] as electrons move down the electron transport chain
increases
dihydroxyacetone phosphate (DHAP)
intermediate compound generated during glycolysis that can be converted to one of the major precursors of fat
sodium-potassium pump
is an example of energy coupling. The energy derived from exergonic ATP hydrolysis is used to pump sodium and potassium ions across the cell membrane
shared intermediate
links endergonic and exergonic reactions (reaction coupling); product of one reaction is the reactant of another
how cells control/regulate catabolism (specifically ATP synthesis)
when ATP concentrations in a cell drop, respiration speeds up, and when ATP meets demand, respiration slows down (control based mainly on regulating activity of enzymes in pathway)
