106 terms

Chapter 9: Cellular Respiration

How does NAD+ change to NADH
it takes 2 hydrogen atoms from the organic sugar, but one proton (one hydrogen ion) is released into the surrounding solution. So, 2 e- and one p+ are added to NAD+ and its charge becomes neutralized.
How does the burning of methane release chemical energy that can be put to work
An electron loses potential energy when it shifts from a less electronegative atom to a more electronegative one, just as a ball loses potential energy when it rolls downhill. This redox reaction moves e- closer to oxygen so energy is released
each NADH molecule formed during respiration represents
stored energy that can be tapped to make ATP when e- complete their "fall" down the concentration gradient from NADH to oxygen.
space shuttle being launched into orbit:
H2 and 02 gases are combined, leads to explosive release of heat and light energy, boosting it into orbit. Explosion = release of energy as the electrons of hydrogen "fall" closer to the electronegative oxygen atoms.
where does glycolysis take place
in the cytosol
where does the citric acid cycle take place
in the mitochondrial matrix of eukaryotic cells or in the cytosol of prokaryotes
carbon dioxide produced where represents what
produced in citric acid cycle by oxidizing a derivative of pyruvate to carbon dioxide. represents fragments of oxidized organic molecules
oxidative phosphorylation accounts for __ ATP generated by respiration
substrate-level phosphorylation:
enzyme transfers a phosphate group from a substrate molecule to ADP, instead of adding an inorganic phosphate to ADP like in oxidative phosphorylation.
ideally, 38 molecules of ATP are made...
for every molecule of glucose degraded to carbon dioxide and water as the extra e- turn ADP to ATP.
Energy Investment Phase (EIP) #1
glucose phosphorylated by hexokinase. then its trapped in the cell and more reactive b/c of phosphorylation
had a phosphate added on to it
what does the enzyme hexokinase do?
once glucose enters the cell, hexokinase transfers a phosphate group from ATP to the sugar
how is glucose trapped in the cell after being phosphorylated
the charge of the phosphate group traps it since cell membrane is impermeable to large ions, and phosphorylation of glucose makes it more reactive
EIP #2
the enzyme phosphoglucoisomerase converts glucose 6 phosphate to its isomer fructose 6 phosphate. (glucose changed to isomer fructose)
EIP #3
another phosphate taken from ATP & added to the new fructose. 2 ATP used so far. Now with 2 P on both sides, it's ready to be split in half.
phosphofructokinase (adds p to fructose) is regulated by...
allosterically regulated by ATP and its products.
EIP #4
Aldolase enzyme breaks the sugar molecule into two different 3 carbon sugars that are isomers of each other. (dihydroxyacetone phosphate and glyceraldehyde 3 phosphate)
EIP #5
isomerase catalyzes the reversible conversion between these 3 carbon sugar isomers. The next enzyme in the reaction uses only glyceraldehyde phosphate (GP) so its removed as fast as it forms. This pulls the equilibrium in that direction, so the net result is 2 molecules of GP.
pyruvate and pyruvic acid?
same thing
glucose is broken into...
2 molecules of 3 carbon phosphoglyceraldehyde (pgals) which become 2 3carbon pyruvates.
conversions of 2 pgals to 2 pyruvates each produce
2 ATPs and 2 NADH
glycolysis starting materials:
glucose, 2NAD+, 2ATPs, 4ADPs, 4 phosphate groups.
glycolysis ending materials:
2 pyruvates, 2 NADHs, 2ADP, 4ATP
8 steps of krebs/citric acid cycle
1. Oxaloacetate is combined with Acetyl CoA to form citrate. 2.Citrate is converted to its isomer, isocitrate, because an isomerization takes place (H and OH swap places). 3. Isocitrate is oxidized and NADH is produced. A CO2 molecule is an output as well. 4. Alpha-ketoglutarate reacts with coenzyme A. Another CO2 is released from alpha-ketoglutarate and NAD+ is reduced to NADH. NADH and CO2 are thus products. 5. A phosphate group is transferred to GDP, which forms GTP. GTP is similar to ATP and is sometimes used to create ATP. 6. FAD oxidizes succinate and makes FADH2. 7. A water molecule is added to the substrate, forming malate. 8. The substrate is oxidized, NAD+ is reduced to NADH, and oxaloacetate is regenerated. The cycle begins again.
What is GTP?
Guanosine Triphosphate is similar to ATP and is used by some plant cells. can be used to make n ATP or to directly power work in the cell
How many ATPs does the ETC make
none directly
definition of cytochromes
proteins with electron-carrying heme groups (iron atom accepts & donates e-)
where do cytochromes exist
in the multiprotein complexes of the ETC: remaining electron carriers between ubiquinone (Coenzyme Q) and oxygen.
when ETC starts with FADH2...
1/3 less energy for ATP synthesis because FADH2 adds electrons at a lower energy level
where does ATP synthase exist?
in the inner membrane of the mitochondrion or the plasma membrane of prokaryotic cells
what does ATP synthase do
it uses the energy of the existing H+ gradient to power ATP syn
definition of chemiosmosis (in general)
chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of H+ gradient across a membrane to drive cellular work.
ATP synthase is... (structure) and how does it spin
ATP synthase is a multisubunit complex with four main parts, each made up of multiple polypeptides. protons move one by one into binding sites on one of these parts (the rotor) causing it to spin and catalyze ATP production.
what is a stator
the half channel in the membrane that H+ ions enter before entering binding sites on the rotor.
how is the mechanism for ATP hydrolysis different than ATP synthesis?
if it spins different ways
proton motive force is
energy generated by the transfer of protons or electrons across a membrane and can be used for chemical, osmotic or mechanical work.
In mitochondria, the energy for gradient formation comes from... and the work performed is...
exergonic redox reactions... ATP syn
why do prokaryotes tap the proton-motive force of H+ ions
to make ATP, rotate their flagella, and to pump nutrients and waste products across the membrane.
During respiration, most energy flows in this sequence:
glucose, NADH, ETC, proton-motive force, ATP.
3 reasons that ATP production isn't exact:
1. phosphorylation & redox rxns aren't directly coupled, so NADH causes production of 2.5 to 3.3 ATP and FADH2 causes production of 1.5 to 2 ATP. 2. NADH is impermeable to the inner mitochondrial membrane, so the type of e- shuttle bringing it in affects. if passed to FAD, 2 ATP, but if passed to NAD+, 3 ATP. 3. if the proton-motive force generated by the redox rxns of repiration is used for other things instead of ATP synthase.
how much of the potential energy in glucose is transferred to ATP?
40%, while the rest is lost as heat
without oxygen, the energy stored in pyruvate is...
unavailable to the cell.
obligate anaerobes (def)
organisms that carry out only fermentation or anaerobic respiration and can't survive in O2 precense
facultative anaerobes (def)
organisms that can make enough ATP to survive using either fermentation or respiration- like muscles in absence of oxygen
beta oxidation
breaks fatty acids down into 2-carbon fragments that enter citric acid cycle as acetyl coa. NADH and FADH2 are also generated & can enter ETC for ATP production
Fats make excellent fuel because
their chemical structure and the high energy level of their electrons. A gram of fat oxidized by respiration produces more than twice as much ATP as a gram of carbohydrate.
Before amino acids can feed into glycolysis or the citric acid cycle...
their amino groups must be removed by deanimation. The nitrogenous refuse from this is excreted in the form of ammonia, urea, and other waste products.
in oxidative phosphorylation, each member of the ETC is lower in ___ than the preceding member of the chain, but higher in ___. the molecule at zero free energy, which is ___, is lowest of all the molecules in free energy and the highest in electronegativity.
free energy, electronegativity, oxygen.
cell respiration equation and ∆G
C6H12O6 +6O2 -> 6CO2 +6H2O
∆G= -686kcal/mol
explain the difference between fermentation and cellular respiration:
f: partial degradation of sugars occuring without the use of oxygen CR: both aerobic and anaerobic reactions to use fuel. Mostly refers to aerobic respiration
redox rxns:
transfer of e-
the electron donor in a redox rxn is called
a reducing agent
the electron acceptor in a redox rxn is called
an oxidizing agent
in CR, e- don't go directly to O2, but are bound to H+. The H+ are held in the cell temporarily by what e- carrier?
a coenzyme called NAD+ that functions as an oxidizing agent during CR (takes e- from things)
why is oxygen the ultimate e- acceptor
it's the last e- acceptor, and it has a very large electron affinity.
4step downhill route e- follow in CR:
glucose, NAD+, NADH, terminal e- acceptor oxygen
glycolysis and citric acid cycle both perform
substrate-level phosphorylation
ETC and chemiosmosis performs
oxidative phosphorylation
how is the ETC involved in oxidative phosphorylation?
energy released at each step of the chain is used to make ATP, and final e- are given to O2. powered by redox rxns of ETC
substrate-level phosphorylation picture:
enzyme holds phosphorylated substrate and ADP. It catalyzes the reaction when substrate gives its phosphate group to ADP, forming product and ATP.
in the energy payoff phase, what happens?
4 ATP are formed and 2NADH and 2H+ are formed from 2 NAD+, 4e-, and 4H+.
in glycolysis, glucose is turned into:
2 pyruvate and 2CO2
explain the 4 steps of the transition phase in between glycolysis and the krebs cycle?
1. pyruvate's fully oxidized carboxyl group (-COO-) is removed and given off as CO2 2. the remaining 2 carbon fragment is oxidized, forming acetate (ionized form of acetic acid). An enzyme transfers the extracted e- to NAD+, storing energy in NADH 3. Coenzyme A (CoA) is attached to the acetate, making the acetate very reactive, so this new acetyl CoA has a high potential energy 4. Acetyl CoA breaks and CoA is released while the acetyl enters the cycle.
what is the relationship between glycolysis and O2?
doesn't need O2 but if there's O2 present, it sends its pyruvate and NADH into krebs cycle. If no O2, sends them to fermentation process.
how many times does the citric acid cycle run per glucose?
twice: once per pyruvate
In the citric acid cycle, how many NADH are formed?
In the citric acid cycle, how many total carbons are lost as pyruvate is oxidized?
In the citric acid cycle, how many FADH2 have been formed?
1 (FAD+ accepts 2e- and 2H+ to become FADH2)
In the citric acid cycle, how many ATP are formed?
transition phase reduces what electron carrier & how much
what happens to the 6 carbon mc's found in the original glucose molecule
they are all eventually released as CO2, since citric acid cycle only wants the electrons. starting with one 3 carbon pyruvate, 1 CO2 is released during transition phase, and 2 CO2 are released during cycle.
each member of the ETC is lower in _______ than the preceding member of the chain, but higher in ___________. The molecule at zero free energy, which is ______ is lowest of all the molecules in free energy and highest in electronegativity.
free energy, electronegativity, oxygen
the two electron carrier mc's that feed electrons into the electron transport system are...
explain how ATP synthase uses the flow of H+ to make ATP:
H+ ions want to get into the cell because of their concentration gradient, so they flow through the stator (half channel in membrane) and bind to active sites on the rotor, changing the shape of each subunit so that the rotor spins. Each H+ ion makes one complete turn before leaving the rotor and passing through a second half channel to enter mitochondrial matrix. Spinning of the rotor turns a rod in the catalytic knob, which is held stationary by the stator. turning of the rod actiates catalytic sites were ADP is bonded, and ATP can be formed.
how does the ETC form the H+ gradient across the mitochondrial membrane?
ETC uses the exergonic flow of e- from NADH and FADH2to pump H+ out across the membrane. H+ then want to get back in because of their concentration gradient, and their only option to get back in is ATP synthase.
Proton motive force and how is it involved in CR
the capacity of a gradient to perform work. energy generated by the p+ or e- movement across membrane in CR is involved in both ETC and chemiosmosis
chemiosmosis in CR:
ATP syn by ATP synthase powered by the flow of H+ back across membrane ( powered by proton-motive force)
In glycolysis, NADH produces ...
2ATP because one ATP is used to transport a molecule of NADH into the mitochondria and continue with aerobic respiration.
in pyruvate decarboxylation (transition phase) and the Krebs cycle, each NADH yields...
FADH2 yields
2 ATPs
what is the electron acceptor in fermentation
(SO4)2- and produces H2S as a byproduct
explain how alcohol fermentation starts with glucose and yields ethanol.
glucose turns to pyruvate, causing 2NADH to be formed. 2ATP are be formed simulaneously from this energy. pyruvate is then turned to 2 aldehydes and releases CO2. Then the acetaldehyde becomes ethanol (anabolic) so it takes e- from NADH to form 2NAD+. This cycle of NAD+ is important so the cell doesn't run out.
explain how lactic acid fermentation starts with glucose and yields lactate.
glucose turns 2 NAD+ and 2 ADP to 2 NADH and 2 ATP, forming pyruvate. pyruvate is reduced directly by NADH to form lactate without releasing CO2. Lactate is converted back to pyruvate by 2NADH in liver cells after strenuous exercise in animals.
what 3 organic macromolecules are often utilized to make ATP by cellular respiration and how
fats: become glycerol and are converted to intermediate of glycolysis -proteins: amino groups get removed to feed into glycolysis, and refuse= ammonia-> urea. -sucrose/ starch turn into glucose
explain the difference in energy usage between the catabolic reactions of cellular respiration and anabolic pathways of biosynthesis
biosynthetic pathways consume ATP (ex) glucose being made from pyruvate, fatty acids being made from acetyl coa. they're inversely related: metabolic interchanges allow our cells to convert certain molecules to others as we need them. (ex) if we eat more food than we need, we store fat even if our diet is fat-free because of the adaptability of metabolism.
explain how AMP stimulates CR while citrate and ATP inhibit it
Adenosine monophosphate derived from ADP. As ATP accumulates, inhibition of the enzyme slows down glycolysis. when ATP->ADP->AMP faster than ATP is being made, CR is stimulated once again. Also as citrate accumulates, glycolysis slows down because of inhibitors.
explain picture of CR
glycolysis turns glucose to 2 pyruvate, forming 2NADH and 2 net ATP. 2 pyruvate is turned to 2 acetyl coa by 2 NADH in transition phase. In citric acid cycle, 6NADH, 2 FADH2, and 2ATP are formed per glucose. In ETC, NADH or FADH2 from glycolysis or citric acid cycle form about 32 or 34 ATP through chemiosmosis and oxidativ phosphorylation.
chemosynthetic autotrophs:
get energy by oxidizing inorganic substances. don't require light. they extract e- from surrounding substances to assist in generating ATP. ex: most bacteria
state the most likely hypothetical order of evolution of anaerobic respiration, aerobic respiration, and photosyn
1st: anaerobic respiration before oxygen existed in the air. Then photosyn released O2 into the air and then CR developed, taking O2 from the air. photosyn & CR came after anaerobic CR since they require organelles, but anaerobic CR doesn't so it occured in ancient prokaryotes.
why do hydrogen atoms accompany electrons as they are transferred to the membrane
positively charged H+ ions can't pass membranes alone, so they accumulate in the two layers of the mitochondria. For the atoms to pass through the membrane, electrons' energy from broken mc's is used to stimulate their transmembrane protein channels.
why do hydrogen atoms accompany electrons as they are transferred through biological systems?
So when they reach the transmembrane proteins in ETC, electrons can stimulate them to let the H+ pass out, forming a gradient that will eventually form ATP.
Also H+ accompany e- as they are transferred in biological systems in order to make water at the end of the process.
why is it thought that glycolysis is the first catabolic pathway to have evolved int he metabolism of all cellular systems
glycolysis can produce energy with or without oxygen, and it occurs in the cytosol without need of membrane-bound organelles
what would happen if anaerobic cellular systems didn't turn to fermentation?
with each breakdown of glucose, 2pyruvate, 2 NADH, and 2 ATP are formed. If all the NAD+ is used up to make NADH though, there's no way to get it back and reuse it so the process must continue to lactate or ethanol+CO2, which turns the NADH to NAD+.
in mitochondria, exergonic redox rxns...
provide the energy that establishes the proton gradient.
The immediate energy source that drives ATP synthesis by ATP synthase during oxidative phosphorylation is the...
flow of electrons down the electron transport chain.
When electrons flow along the electron transport chains of mitochondria, what occurs?
The pH of the matrix increases.
During the reaction C6H12O6 + 6 O2 → 6 CO2 + 6 H2O, which compound is reduced as a result of the reaction?
oxygen (water is product)
why does the oxidation of organic compounds by molecular oxygen (O2) yield so much energy?
The oxygen atom has a higher affinity for electrons than the carbon atom.
A small amount of ATP is made in glycolysis by what process?
transfer of a phosphate group from a fragment of glucose to ADP by substrate-level phosphorylation
In glycolysis, there is no production of carbon dioxide as a product of the pathway, why?
The two pyruvate molecules produced from each glucose molecule each contain three carbon atoms.
Of the following molecules in the process of glycolysis, the one with the most chemical energy is _____.
In an experiment, mice were fed glucose (C6H12O6) containing a small amount of radioactive oxygen. The mice were closely monitored, and after a few minutes radioactive oxygen atoms showed up in ____.
carbon dioxide. The oxygen in water enters the mitochondrion as molecular oxygen from the atmosphere.
what is oxidative phosphorylation?
1. Electron transport chain: electron transport and pumping of H+ protons out, which creates an H+ gradient across the membrane. This uses the energy of NADH and FADH2, and indirectly turns 2H+ and O into H2O 2. Chemiosmosis: ATP synthesis powered by the flow of H+ back across the membrane through ATP synthase
explain the 5 steps chemiosmosis (ATP synthesis through ATP synthase)
1. H+ ions flowing down their gradient enter a half channel in the stator, which is anchored in the membrane. 2. H+ ions enter binding sites within a rotor, changing the shape of each subunit so that the rotor spins within the membrane. 3. Each H+ ion makes one complete turn before leaving the rotor and passing through a second half channel in the stator and into the mitochondrial matrix. 4. Spinning of the rotor causes an internal rod to spin as well. This rod extends like a stalk into the knob below it, which is held stationary by part of the stator. 5. Turning of the rod activates catalytic sites in the knob that produce ATP from ADP and Pi.
explain the 8 steps of linear electron flow in photosynthesis, through PS II and then PS I.
1. a photon strikes a pigment molecule in PS II, boosting one of its electrons to a higher energy level. As this electron falls back, it boosts a nearby electron in a nearby pigment molecule, "passing the charge" until it reaches the P680 pair of chlorophyll molecules. The electron then gets transferred to the primary electron receptor. An enzyme catalyzes the splitting of a water molecule into 2e-, 2H+, and one O. the e- replace the electron hole in P680. O combine together & form O2. Each electron then passes from PS II to PS I via electron transport chain. The exergonic fall of e- to a lower energy level provides energy for the synthesis of ATP: As electrons pass through the cytc, the pumping of H+ builds a proton gradient that is used in chemiosmosis. The same process then occurs in PS I with P700 molecules. Then, e- pass down a second electron transport chain but no proton gradient is generated so no ATP is made. Finally the e- are stored in NADPH.