Chapter 4 Flashcards
How come wood releases a lot of energy
The major component of the wood that burns= cellulose.
- Cellulose molecules, main component of plant cell walls, are complex carbs made of glucose.
- When cellulose burns, it combines with O2
in atmosphere & releases a tremendous amount of potentially life-threatening energy
Most of the energy that enters the biosphere is ___________________
solar radiation
- photosynthesis transforms this light energy into
chemical potential energy, which is then available to plants & other organisms in food webs.
What type of cells need ATP?
all cells
Aerobic cellular respiration is
AKA aerobic respiration
- the process that extracts energy from food (organic compounds) in the presence of oxygen
- The energy is used to synthesize ATP from ADP & Pi
- The ATP molecules are then used to supply energy
directly to the cells for their energy-demanding activities.
- Equation: C6H12O6 + 6O2 –> 6CO2 + 6H2O
∆G= –2870 kJ/mol
An Obligate Aerobe is
an organism that cannot live without oxygen, and they use aerobic cellular respiration exclusively or most of the time.
Aerobic cellular respiration can be divided into four stages: List them
1) Glycolysis
2) Pyruvate Oxidation
3) Citric acid cycle
4) Electron transport & oxidative phosphorylation
Each stage involves the transfer of free energy, producing ATP in 1 of 2 ways: substrate-level phosphorylation & oxidative phosphorylation.
https://www.youtube.com/watch?v=eJ9Zjc-jdys
Substrate-level phosphorylation forms ATP…
directly in an enzyme-catalyzed reaction through the transfer of a phosphate group from one molecule to an adenosine diphosphate (ADP) molecule.
Oxidative phosphorylation forms ATP…
indirectly through a series of redox reactions involving a final electron acceptor.
- In aerobic respiration, oxygen is the final electron acceptor
Glycolysis Overview
- (occurs in cytosol) –> doesn’t take place in mitochondria, & doesn’t require O2, thus all cells can do it.
- Enzymes break down one molecule of glucose into two molecules of pyruvate. Some high-energy ATP (via substrate-level phosphorylation) & NADH is synthesized.
Pyruvate Oxidation Overview
- in mitochondria
- Each of the 2 molecules of pyruvate produced in glycolysis is transported to mitochondria and is oxidized, resulting in the production of CO2 (a waste molecule), NADH, & an acetyl group that is initially
attached to coenzyme A (acetyl-CoA)
Citric acid cycle Overview
- AKA kreb’s cycle
- (in mitochondria)
- Acetyl-CoA molecules from pyruvate oxidation enter a metabolic cycle, where the acetyl group is completely oxidized to CO2. In the process, ATP (via substrate-level phosphorylation) & the e- carriers NADH & FADH2 are synthesized.
Electron transport & oxidative phosphorylation Overview
- (in mitochondria)
- The NADH & FADH2 (synthesized during glycolysis, pyruvate oxidation, and the citric acid cycle) are oxidized. Their high-energy e- & hydrogens are passed from one oxidizing agent to the next until they are transferred to O2, producing water. The free energy released during electron transport is indirectly used to synthesize a large amount of ATP by oxidative phosphorylation
The mitochondrion is referred to as the powerhouse of the cell because
as the location of the citric acid cycle and electron transport, it generates most of the ATP that is used by the cell
The mitochondrion is composed of two membranes
- the outer membrane and the inner membrane, which together define two compartments
- The intermembrane space is between the outer and inner membranes, and the matrix is the interior aqueous environment of the organelle
Some prokaryotes undergo aerobic cellular respiration without ______________. ELABORATE
mitochondria
- In prokaryotes, the process of glycolysis, pyruvate oxidation, &the citric acid cycle occur in the cytosol of the cell, whereas e- transport occurs on internal membranes derived from the plasma membrane
- These prokaryotes possess the full complement of reactions that make up aerobic cellular respiration—from glycolysis through electron transport & oxidative phosphorylation.
There are 2 general processes by which certain cells can oxidize fuel molecules & generate ATP in the absence of oxygen:
anaerobic respiration & fermentation
- Both anaerobic respiration & fermentation r catabolic (energy-yielding) processes.
Anaerobic respiration is
similar to aerobic cellular respiration in using a series of electron-transferring steps, but it uses an inorganic molecule other than oxygen as the final oxidizing agent.
Fermentation is
does not use an electron transport system. Thus, fermentation is not considered to be a form of respiration. It relies on an organic compound to act as the final oxidizing agent.
https://www.youtube.com/watch?v=YbdkbCU20_M
- This equation shows the overall reaction for 1 common fermentation pathway. The released free energy is used to make ATP. Note the products of this fermentation pathway are ethanol (CH3CH2OH) & CO2:
C6H12O6 –> 2 CH3CH2OH + 2CO2 ∆G= –218 kJ/mol - Note how fermentation releases much less free energy than aerobic respiration & thus makes less ATP
An obligate anaerobe is
an organism that cannot survive in the presence of oxygen
- use inorganic substances such as NO2, S, and Fe 3+ as final electron acceptors to obtain energy
aerobic respiration made the evolution of large animals possible because
it allowed them to meet their very high energy demands.
- RMR from amoeba sisters –> anaerobic respiration produces much less ATP
every 1 of ur billions of active cells requires access to more than ____________ ATPs per second
1 million
Glycolysis is considered to be the most fundamental & probably most ancient of all metabolic pathways. This is supported by the following facts.
1) glycolysis is nearly universal, being found in almost all organisms, both prokaryotes & eukaryotes
2) it does not require O2. Oxygen became abundant
in Earth’s atmosphere only about 2.5 billion years ago—about 1.5 billion years after scientists think that life began.
3) Third, glycolysis occurs in the cytosol of all cells and
involves soluble enzymes. Therefore, it does not require more sophisticated cellular organelles in order to operate –> indicating that it might have began before complex organelles were formed (i think)
The first experiments investigating glycolysis took place over ____ years ago.
100
- Using extracts from yeast cells, researchers showed that they could study biological reactions in an
isolated system.
- These experiments became the foundation of modern biochemistry
Glycolysis consists of ___ sequential enzyme-catalyzed reactions that lead to….
10
the oxidation of the 6-carbon sugar glucose, producing two molecules of the 3-carbon
compound pyruvate.
- The PE & e- released in the oxidation leads to the overall synthesis of both ATP & NADH.
Glycolysis has two phases: 1) an initial energy investment phase 2) an energy payoff phase
- both phases have 5 steps
energy investment phase: the 5 steps
1) hexokinase: Glucose get 1 phosphate group from 1 ATP, creating glucose-6-phosphate (phosphorylation reaction)
2) phospho-glucomutase: Glucose-6-phosphate is
rearranged to isomer fructose-6-phosphate to allow it to bind to another phosphate.
(isomerization reaction)
3) phospho-fructokinase: 1 phosphate group from 2nd ATP is attached to fructose-6-phosphate, producing fructose-1,6-bisphosphate.
(phosphorylation reaction)
4) aldolase: Fructose-1,6-bisphosphate is split into glyceraldehyde-3-phosphate (G3P) & dihydroxyacetone phosphate (DHAP). –> both r isomers & have 3C each (lysis reaction)
5) triosephosphate isomerase: The DHAP produced is converted into G3P, giving a total of 2 per 1 molecule of glucose.(isomerization reaction)
the energy payoff phase: the 5 steps
6) triosephosphate dehydrogenase: 2 e- & 2 p+ r removed from G3P. Some of the energy released in this reaction is trapped by the addition of an inorganic phosphate group from the cytosol (not derived from ATP) to the molecule. The e- r accepted by NAD+, along with one of the p+. The other p+ is released to the cytosol. (redox reaction). the molecule is now 1,3-bisphosphoglycerate
7) phosphoglycerate kinase: One of the 2 phosphate groups of 1,3-bisphosphoglycerate is transferred to ADP to produce ATP. (substrate-level phosphorylation reaction) it is now 3-phosphoglycerate
8) phospho-glucomutase: 3-phosphoglycerate is
rearranged, shifting the phosphate group from the
3-carbon to the 2-carbon to produce 2-phosphoglycerate. (mutase reaction—shifting of
a chemical group to another within the same molecule)
9) enolase: e-s r removed from one part of 2-phosphoglycerate & delivered to another part of the molecule. Most of the energy lost by the e- is retained in the product, phosphoenolpyruvate. There is also a loss of H2O. (redox reaction)
10) pyruvate kinase: The remaining phosphate group is removed from phosphoenolpyruvate & transferred to ADP. The reaction forms ATP & the final product of glycolysis, pyruvate. (substrate-level phosphorylation reaction)
there are three key points to keep in mind keep in mind about glycolysis
1) Energy Investment and Payoff Phases in Glycolysis:
-2 ATP are consumed to phosphorylate glucose and fructose-6-phosphate.The energy payoff phase releases more energy, producing 4 ATP and 2 NADH.
2) Net Yield of Glycolysis:
-Glycolysis yields a net of 2 ATP and 2 NADH per glucose molecule. No carbon is lost; all 6 carbons from glucose end up in 2 pyruvate molecules. The PE of the 2 pyruvate molecules is less than the original glucose cuz glucose has been partially oxidized. 2 H2O molecules r produced in step 9 but r later consumed in the hydrolysis of ATP and thus r not usually included in the overall equation for glycolysis
3)ATP Production via Substrate-Level Phosphorylation:
- ATP is synthesized through substrate-level phosphorylation, where an enzyme transfers a phosphate group from a high-energy substrate to ADP. Substrate-level phosphorylation is also the mode of ATP synthesis that is used during the citric acid cycle
The net equation for glycolysis is:
glucose + 2 ADP + 2 Pi + 2 NAD+ –> 2 pyruvate + 2 ATP + 2 NADH + 2H+
Energy Efficiency of Glycolysis:
- The synthesis of 2 moles of ATP stores 62 kJ of energy.
- The complete oxidation of 1 mole of glucose can release 2870 kJ of energy.
- Glycolysis converts about 2.2% ((62 KJ/2870 KJ)X100%) of the energy from glucose into ATP, while most energy remains in the two pyruvate molecules and two NADH molecules.
- Some of the energy is lost as thermal energy, but most stored in the 2 pyruvate molecules & 2 NADH molecules, which will continue through the subsequent stages of aerobic respiration. –>
Diff organisms use a variety of methods to transfer the NADH (or the e- it carries) into the mitochondria
& to the e- transport chain. These methods vary in their energy cost, so the amount of ATP generated for each NADH formed in glycolysis can vary
Glycolysis in Anaerobic Organisms:
Some organisms rely on glycolysis as their primary energy source despite its low efficiency.
The 2 molecules of pyruvate that r synthesized by glycolysis still contain about _____of the energy found in one molecule of glucose
75 %
- extraction of remaining free energy in pyruvate continues via pyruvate oxidation & the citric
acid cycle.
- In these reactions, more ATP & more of the e- carriers NADH & FADH2 r formed, while remaining glucose is completely oxidized. Carbon is released in the form of waste CO2.
The reactions of the citric acid cycle occur in the ____________________, so…
mitochondrial matrix
…the pyruvates that r produced in glycolysis must pass through both the outer & inner mitochondrial membranes.
- Large pores in the outer membrane allow pyruvate to diffuse through. For pyruvate to cross the inner membrane, however, a pyruvate-specific membrane carrier is required
Once pyruvate enters the matrix…
it is converted into an acetyl group, which is then temporarily bonded to a sulfur atom on the end of a large molecule called coenzyme A, or CoA.
–> The result is an acetyl-CoA complex.
- This multistep process is referred to as pyruvate oxidation (or pyruvic acid oxidation)
The conversion of pyruvate to acetyl-CoA
1) Decarboxylation: The carboxyl group (–COO⁻) is removed from pyruvate, forming CO₂ as a waste product (one-third of the CO₂ we exhale)
2) oxidation of the remaining 2 carbon molecules, producing an acetyl group. This dehydrogenation reaction transfers 2 e- & a p+ to NAD+, making NADH, & releases an H+ ion into solution. Lastly, the acetyl group reacts with the sulfur atom of coenzyme A, forming the high-energy intermediate acetyl-CoA.
https://www.youtube.com/watch?v=_U3yHgxyW30
The net reaction for pyruvate oxidation is:
2 pyruvate + 2 NAD+ + 2 CoA –> 2 acetyl-CoA + 2 NADH + 2 H+ + 2 CO2
Discovery of Citric Acid Cycle (Krebs Cycle):
The cycle was discovered in 1937 by Sir Hans Krebs, a biochemist at the University of Sheffield in England, discovered the metabolic reactions that became known as the Krebs cycle (now called the citric acid cycle)
number of reaction in citric acid cycle
The citric acid cycle consists of 8 enzyme-catalyzed reactions.
- 7 reactions take place in the mitochondrial matrix, & 1 on the matrix side of the inner mitochondrial membrane.
Products of Citric Acid Cycle
- Acetyl groups r oxidized to CO₂, producing ATP, NADH, & FADH₂.
- For each acetyl-CoA entering the cycle: 3 NADH, 1 FADH₂, & 1 ATP (via substrate-level phosphorylation) r produced.
- 2 CO₂ molecules r released per acetyl-CoA.
- In 1 complete cycle, one 2-carbon acetyl unit is consumed & 2 CO2 molecules r released, completing the conversion of all C atoms that were originally in glucose into CO2
- The CoA molecule that carried the acetyl
group to the cycle is released & again participates in pyruvate oxidation to pick up another acetyl group. - Net Reaction for one turn of the cycle:
acetyl-CoA + 3NAD+ + FAD + ADP + P𝑖 → 2CO2 + 3NADH + 3H+ + FADH2 + ATP + CoA
The 8 reaction of Citric Acid Cycle/ Kreb’s cycle
1) 2-carbon acetyl group carried by CoA attached to
oxaloacetate= citrate. ENZYME: citrate synthase
2) Citrate is rearranged to isomer, isocitrate. ENZYME:aconitase
3) Isocitrate oxidized to α-ketoglutarate; 1C is removed & released as CO2, & NAD+ reduced to NADH + H+. ENZYME: isocitrate dehydrogenase
4) α-Ketoglutarate oxidized to succinyl CoA; 1 carbon is removed & released as CO2, & NAD+ reduced to NADH + H+. ENZYME: α-ketoglutarate dehydrogenase
5) succinyl CoA releases CoA to make succinate: energy released makes GDP to GTP, which makes ADP to ATP by substrate-level phosphorylation. –> the only
ATP made directly in the citric acid cycle ENZYME: succinyl CoA synthetase
6) Succinate oxidized to fumarate; 2e- & 2p+ removed from succinate r transferred to FAD, making FADH2 ENZYME: succinate dehydrogenase
7) Fumarate to malate by adding 1 H2O molecule. ENZYME: fumarase
8) Malate oxidized to oxaloacetate, reducing
NAD+ to NADH + H+. Oxaloacetate can react with acetyl-CoA to re-enter the cycle. ENZYME: malate dehydrogenase
Summary of Citric Acid Cycle
2 acetyl-CoA molecules enter the citric acid cycle from glycolysis & the pyruvate oxidation of one glucose molecule.
Step 1) acetyl group enters the cycle as it reacts with oxaloacetate to form 1 molecule of citrate. –> is why process is called the citric acid cycle.
Steps 3, 4, 5, 6, & 8) some of the released energy is captured and used to form NADH, ATP, & FADH2.
Steps 3, 4, & 8) NAD+ reduced to form NADH.
Step 5) make ATP from ADP & Pi by substrate-level phosphorylation.
Step 6) reduces FAD to FADH2.
- cuz 1 glucose molecule yields 2 pyruvate molecules, 1 glucose molecule generates 2 turns of the citric acid cycle
By the end of the citric acid cycle, the original glucose molecule has…
been completely dismantled.
- The original C & O atoms r in the form of CO2
& r released as waste.
- All that remains of the original glucose molecule are the hydrogens, now carried by NADH & FADH2. –> The e- in these hydrogens retain a large amount of chemical PE.
The Electron Transport Chain purpose
citric acid cycle= all C in glucose oxidized & released as CO2.
- some ATP was formed by substrate-level phosphorylation, but most of the PE originally present in glucose was captured during the formation of NADH and FADH2.
- The electron transport chain extracts the PE
energy in these molecules & makes it usable to make more ATP
The Electron Transport Chain composition
- in eukaryotes, occurs on the inner mitochondrial membrane
- facilitates transfer of e- from NADH & FADH2 to O2
- consists of 4 protein complexes:
complex I, NADH dehydrogenase
complex II, succinate dehydrogenase;
complex III, cytochrome complex;
complex IV, cytochrome oxidase. - Complex II = single peripheral membrane protein, other 3 complexes are composed of multiple proteins.
- The flow of e- from 1 complex to another is facilitated by 2 mobile e- shuttles.
–> Ubiquinone (UQ), which is a hydrophobic molecule found in the core of the membrane, shuttles electrons from complexes I and II to complex III.
–> A second shuttle, cytochrome c (cyt c), is located on the intermembrane space side of the membrane and transfers e- from complex III to complex IV
The Driving Force behind electron transport
Electron Transport Chain= ETC (my thing)
- Complexes I, III, and IV in the ETC have increasing electronegativity, pulling e- down the chain.
- O2 has highest electronegativity & drives the entire ETC process by pulling e- through the chain.
- Energy Gradient: e- carriers in the chain r organized from high to low free energy, with each subsequent component being more electronegative than the previous one.
- NADH & O₂: NADH= most free energy & weakest pull on e- , while O₂= strongest e- acceptor & the final destination for the e-.
- Energy Release: As e- move from NADH through the ETC, they form stronger bonds with each carrier, releasing energy along the way.
- Oxidation of NADH: NADH is readily oxidized, losing electrons, which pass through the chain towards oxygen, releasing energy in the process.
In the protein transport chain, do the protein complexes carry the e-?
-These complexes have cofactors that alternate between reduced & oxidized states as they pull e- from upstream molecules & subsequently donate
e- to more electronegative downstream molecules.
-Thus, it is not the proteins themselves that transfer e-, but rather non-protein groups bound to the proteins of each complex.
The role of Oxygen in the electron transport chain
The e- transport chain is the final destination of all the O2 we breathe, which is transported around the body.
- O goes to the mitochondria to perform the single vital task of pulling e- away from complex IV
- Before O removes e- from complex IV, all the carriers & NADH r fully reduced, with stable, full e- shells.
- Nothing can happen due to their stable state –> Ex, Complex I can’t take any more e- from NADH cuz Complex I is already full. This creates a block in the process, and nothing can move forward.
- However, O is highly electronegative. When O interacts with complex IV, it removes a pair of e-. –> This creates space for Complex IV to take e- from Complex III, which then takes e- from Complex I, allowing NADH to give up its e- again. This “unblocking” happens quickly and drives the whole chain forward.
- As an O removes 2 e- from complex IV, it also reacts with 2 p+ (2 H+) in the matrix to make H2O. –> so, for
every O2 gas molecule we breathe in, 4e- are pulled through the e- transport chain & 2 H2O r produced.
During e- transport, the free E that is released does the work of…
transporting p+ (H+ ions) across the inner mitochondrial membrane, from matrix to intermembrane space. –> as a result, H+ conc is higher in intermembrane space than in matrix
proton gradient is
diff in proton (H+ ion) conc across a membrane
e- flow through the electron transport chain drives a series of p+ pumps in the inner mitochondrial membrane. ELABORATE
Complexes I & IV, specific protein components use the E that is released from electron transport for p+ pumping.
- In addition, as ubiquinone molecules (UQ) accept e- from complexes I & II, they pick up p+ from the matrix. After migrating through the membrane & donating e- to complex III, ubiquinone retains a neutral charge by releasing p+ into the intermembrane space.
proton-motive force
a force that moves p+ cuz of a chemical gradient
(AKA electrochemical gradient) of p+ across a membrane
2 component of electrochemical gradient of p+
- Chemical gradient: Unequal p+ concentrations across the membrane.
- Electrical gradient: p+ are positively charged and attracted to the negatively charged matrix.
- During oxidative phosphorylation, the PE that is released by the oxidation of NADH is used to pump protons into the intermembrane space and build up the proton-motive force
chemiosmosis is
a process in which ATP is synthesized using the energy of an electrochemical gradient and the ATP synthase enzyme
- The ability of cells to use the proton-motive force to do work= chemiosmosis
- 1st proposed as way to make ATP by British biochemist Peter Mitchell, (Nobel Prize Chemistry= 1978)
- This mode of ATP synthesis, which is linked to the oxidation of energy-rich molecules by an electron transport chain= oxidative phosphorylation which relies on the action of a large multi-protein complex= ATP synthase
Does chemiosmosis only refer to the synthesis of ATP?
No
- The proton-motive force is also used to pump substances across membranes & to drive the rotation of flagella in prokaryotes.
Where does the energy for chemiosmosis come from?
In mitochondria, = E for chemiosmosis comes from the oxidation of energy-rich molecules,
such as NADH, by the electron transport chain.
Chemiosmosis also accounts for the generation of ATP in chloroplasts, where electron transport is driven by
light energy
ATP synthase is
a large multi-protein complex that spans the inner mitochondrial membrane.
- The proton-motive force drives H⁺ ions through the basal unit channel into the matrix, down their concentration gradient.
- The flow of p+ powers ATP synthesis by causing the headpiece to rotate –> the smallest molecular rotary motor in nature
–> Binding of 3 protons to the headpiece triggers rotation, catalyzing the formation of one ATP from ADP and Pi.
- ability to harness the PE present in a p+ gradient to make ATP is fundamental to almost all life & is developed early in the evolution of life. –> This is shown by fact that structure & function
of the ATP synthase complex in mitochondria are essentially = to one in thylakoid membrane of the chloroplast & the plasma membrane of prokaryotic cells.
ATP synthase components
- Basal unit: Embedded in the membrane and forms a channel for H⁺ ions.
- Headpiece: Extends into the mitochondrial matrix and synthesizes ATP.
- Stalk: Connects the basal unit and the headpiece.
An active transport pump is, in fact, an ATP synthase that is operating in __________.
reverse
When electron transport and ATP synthesis are uncoupled..
the E that is released during electron transport via NADH oxidation is not converted to ATP energy.
- it’s released as thermal energy when p+ rush back across the inner membrane without passing through ATP synthase
One way to achieve uncoupling is…
by regulating the expression of various uncoupling proteins.
- Uncoupling proteins, when present, are in the inner mitochondrial membrane & give p+ another pathway to re-enter the matrix that does not make ATP but releases thermal energy instead
- Ex Brown adipose fat & certain other tissues have high levels of uncoupling proteins in their mitochondria, which are important for maintaining body temperature in hibernating mammals, cold-environment birds, and human infants. –> Uncoupling e- transport causes free E that would be used to generate ATP to be released as thermal E & maintain body temperature.
Ionophores
such as 2,4-dinitrophenol (DNP), can act as Electron Transport and Chemiosmosis uncouplers by creating channels for ions (including p+) to leak across membranes, leading to increased electron transport but reduced ATP synthesis, making them potentially toxic.
- DNP, once used in diet pills, accelerated fat consumption by lowering ATP production but caused harmful side effects like overheating and was eventually discontinued.
The efficiency of ___________ phosphorylation is difficult to calculate
oxidative
- rmr e- transport & oxidative phosphorylation r
distinct processes that r not always completely coupled to each other
For each NADH oxidized, how many ATP molecules are made?
1 NADH oxidation (2e- travel though ETC) pumps 10 H⁺ ions into the inner membrane space
- about 3-4 H⁺ need to flow back through ATP synthase to synthesize 1 ATP.
- Maximum ATP yield: 3 ATP per NADH oxidized
For each FADH oxidized, how many ATP molecules are made?
cuz oxidation of FADH2 bypasses the proton-pumping complex I, leads to less p+ pumped across the membrane.
- per 1 FADH2 oxidized, only about 2 ATP are made.
Given complete oxidation of 1 glucose to CO2 & H2O, & assuming that the entire H_ gradient produced by
electron transfer is used for ATP synthesis, a total of ____________________ from glycolysis, pyruvate oxidation, & the citric acid cycle r oxidized by the ETC.
10 NADH, 10 H+, and 2 FADH2
-RMR H+ oxidized means u add O
How does NADH produced in glycolysis in the cytosol get into the mitochondria for ETC?
cells use 1 of 2 “shuttle” systems that transfer the high-energy e- from NADH across the inner mitochondrial membranes into matrix
1) one system, called malate-aspartate shuttle, the
transfer= very energy efficient & used by many cells.
- NADH in the cytosol is oxidized to NAD+, and the e- are transferred across the membrane & reduce a NAD+ to NADH in the matrix.
2) the glycerol-phosphate shuttle, transfers e-across the membrane from NADH to FAD in the matrix to make FADH2, which has less free energy. Cells that use this system generate the equivalent of 2, rather than 3, ATP for every NADH produced in glycolysis
-thus total of 36 ATP will be made at the end of CR intead of 38
There r several reasons why the total yield might be less than 38 ATP.
1) the inexact NADH and FADH2 to ATP ratio
2) E from H+ flow may be lost due to uncoupling proteins or used for other mitochondrial processes in addition to the process that produces ATP (such as powering the mitochondria’s uptake of pyruvate).
3) cells that use a glycerol-phosphate shuttle system produce 2 fewer ATPs per glucose. (FLASHCARD 66)
How efficient is aerobic respiration at extracting the energy from glucose and converting it into ATP?
- hydrolysis of ATP to ADP & Pi = about 31 kJ/mol –> rmr the reversal will store the same
- Assuming that complete glucose oxidation produces 38 ATP, the total energy stored through ATP production would be 1178 kJ/mol: (31 kJ/mol X 38 ATP =1178 kJ/mol)
- glucose contains 2870 kJ/mol of E.
- On this basis, the efficiency of aerobic respiration can be calculated as follows: (1178 kJ/mol)/(12870 kJ/mol)x100 = 41.0 %
- a theoretical maximum of about 41 % of the energy in glucose is converted into ATP. The rest of the PE from glucose becomes thermal energy.
Creatine Phosphate
come cells like muscle & brain cells have fluctuating energy demands. –> Cells may need rapid ATP during high activity and less ATP at rest.
- some organisms, when excess ATP is available, it’s used to phosphorylate creatine, forming creatine phosphate, a high-energy molecule.
–> Reaction: creatine + ATP → creatine phosphate + ADP.
- During high ATP demand, creatine phosphate can quickly regenerate ATP through the reverse reaction: creatine phosphate → creatine + ATP.
-This provides a rapid ATP boost, supplementing aerobic respiration.
- Once creatine phosphate stores are depleted, they are regenerated when ATP demand is lower, using extra ATP.
metabolic rate is
the amount of energy that is expended per unit time in an organism
- is = to the overall rate of aerobic and anaerobic respiration reactions.
- E usage increases & decreases depending on the amount of work done by an organism, spanning from intense physical exertion to a state of rest
basal metabolic rate (BMR)
the metabolic rate of an organism at rest measured in kilojoules per square metre of surface area per hour (kJ/m^2/h).
- The BMR energy consumption is about 60-70%
of total daily energy used by a human body
- BMR varies between individuals & throughout our lifetime, depending on gender, growth & development, age, muscle mass, and health.
–> Ex, BMR is greatly reduced with an increased % of body fat. –>the resting metabolic rate of skeletal muscle is min 3x that of adipose (fat) tissue.
Regulating Cellular Respiration
- The rate of respiration is regulated to match ATP synthesis with the cell’s energy demands, commonly measured by O2 consumption.
-This follows the principle of supply and demand, preventing resource waste. - Most metabolic pathways, including respiration, are regulated by feedback inhibition.
feedback inhibition is when
the end products of a pathway inhibit an early enzyme in the process, controlling the rate of respiration.
Regulation of Glycolysis
- Glycolysis is regulated to match the cell’s ATP needs.
- excess ATP binds to phosphofructokinase (a key enzyme in glycolysis) as a negative regulator inhibiting glycolysis.
- The resulting decrease in the conc of fructose-1,6-bisphosphate slows or stops glycolysis and thus, the remainder of aerobic cellular respiration.
- Therefore, glycolysis does not oxidize glucose needlessly when there is an adequate supply of ATP.
Glycolysis and ATP production increases proportionately…
as ATP is converted to ADP during cellular activity.
what happens to excess sugars, such as glucose, when they are not needed for metabolism?
When glucose is not needed, it is stored as fat or glycogen in muscles.
Citric Acid Cycle Regulation:
The citric acid cycle regulates glucose oxidation, with some enzymes being allosterically inhibited by high ATP levels.
- Like ATP, NADH and citrate (an intermediate product of the cycle) also allosterically
inhibit phosphofructokinase
Inhibition by NADH and Citrate:
- NADH and citrate (a citric acid cycle intermediate) also inhibit phosphofructokinase (a key glycolysis enzyme), signaling a slowdown in downstream reactions.
- Accumulation of NADH & citrate suggests that oxidative phosphorylation may be restricted, possibly due to limited O2 availability.
Alternatives to Glucose
The reactions leading from glycolysis through pyruvate oxidation oxidize a range of carbs
- addition to glucose & other 6-carbon sugars, fats and proteins can enter the cellular respiratory pathway at various points
- The energy content of different types of food:
carbs=17kJ/g, fats=37kJ/g, proteins=17kJ/g
Oxidation of Carbohydrates:
Disaccharide carbohydrates = easily
hydrolyzed to monosaccharides (glucose, fructose, and galactose) which enter glycolysis at the early stages.
- Starch= hydrolyzed to glucose monomers using amylase & other enzymes in the digestive tract.
- Glycogen, a more complex carb, is hydrolyzed by enzymes in the liver into glucose-6-phosphate (an early substrate molecule in glycolysis)
Oxidation of Fats:
-Triglycerides r hydrolyzed into glycerol & fatty acids for energy.
- Glycerol= converted to glyceraldehyde-3-phosphate (enters glycolysis),
- fatty acids undergo beta-oxidation, forming 2C fragments, which enter the citric acid cycle as acetyl groups attached to CoA
Beta-oxidation is
AKA fatty acid oxidation
a process in which fatty acids are broken down into acetyl-CoA through catabolism
Oxidation of Proteins:
Proteins r hydrolyzed to amino acids before oxidation.
- amino group (–NH2) is removed, & remainder of the molecule enters the CR pathway as either pyruvate, acetyl units carried by CoA, or intermediates of the citric acid cycle, depending on the R-group or carbon backbone that is left
- Ex, the amino acid alanine is converted into pyruvate; leucine is converted into acetyl units; and phenylalanine is converted into fumarate, which
enters the citric acid cycle.
Weight of Carbs vs weight of fats
- Carbs r very hydrophilic, binding H2O through H-bonding.–> When eating carbs, especially in dry form (like sugar), ur body needs extra H2O to dissolve & process them, cuz the carbs naturally hold onto H2O.
- This means you must have more H2O to balance out the H2O that binds to the carbs, which makes them heavier compared to fats, which are hydrophobic
- When you eat fats, you gain only the mass of the fat. –> a gram of fat really is a gram of fuel.
- As a result, although many animals eat large quantities of carbs in their diet, the excess carbs are converted into fats for storage.
- Plants, by comparison, usually store excess energy as carbs
Besides energy, what else do food molecules provide for cells?
Carbon, which is used to synthesize essential molecules not directly provided by food.
How are glycolysis and citric acid cycle intermediates used in the cell?
They are routinely diverted to assemble compounds like amino acids and nucleic acid bases
Why is metabolic flexibility important?
It allows cells to use intermediates for both energy production and biosynthesis, as many reactions are reversible.
How are fatty acids and acetyl-CoA connected in metabolism?
Fatty acids can be oxidized to acetyl-CoA for energy, or excess acetyl-CoA can be used to synthesize fatty acids.
Fermentation backstory
- Cells can still generate ATP through glycolysis even when oxygen is low or absent.
- NAD+ is essential for glycolysis, as it removes hydrogen from glucose.
- Cells have a limited supply of NAD+, which must be regenerated after it is converted to NADH.
- In absence of O2, organisms like yeast & bacteria use fermentation to oxidize NADH to NAD+, allowing glycolysis to continue.
There are several forms of fermentation that bacteria use to obtain energy, but there are 2 forms that eukaryotes also use:
alcohol (ethanol) fermentation & lactate (lactic acid) fermentation
- some organisms, these pathways= primary
source of energy.
- In other organisms, these pathways are only used as optional or supplemental sources of energy when O2 is not available in adequate supply
Alcohol fermentation
AKA ethanol fermentation
-occurs in a variety of organisms, like certain bacteria & yeasts
- the pyruvate produced by glycolysis is decarboxylated to form acetaldehyde, which is then used to oxidize NADH
- The products of these final steps include a molecule of CO2, a molecule of ethanol, and an NAD+
REACTION: pyruvate + NADH + H+ –> NAD+ + CO2 + ethanol
- When including glycolysis, the overall equation is: glucose + 2 ADP + 2 Pi –> 2 ATP + 2 CO2 + 2 ethanol
Is fermentation more or less efficient than Aerobic respiration?
- Fermentation produces only 2 ATP, compared to up to 38 ATP produced in aerobic respiration. –>reason for less ATP is that ethanol is produced as a waste
product during fermentation, and it is a very energy-rich compound. - This is clearly demonstrated by the use of ethanol as a fuel for cooking and some race cars
- in O2 rich environments, aerobic respirating organisms will outcompete the others cuz they can extract 19x more energy from same food
Lactate fermentation is
a process in which pyruvate reacts with NADH &
is converted directly into lactate & regenerates NAD+
- primary energy pathway in some bacteria, can also be used as a supplemental system in eukaryotes
- occurs in our muscle cells when strenuous activity causes a demand for ATP at a faster rate than which O2 can be supplied to the ETC for oxidative phosphorylation.
- Glycolysis speeds up, making 2 ATP/glucose, & excess pyruvate oxidizes NADH and is converted directly into lactate & regenerates NAD+
–> This reaction commonly occurs in the cytosol.
- Significant lactate builds up during prolonged high-energy demands, but it is converted back to pyruvate when O2 levels return to normal & ATP demand is normal.
lactate fermentation equations
- this equation summarizes the final steps in lactate fermentation, beginning with a single pyruvate
pyruvate + NADH + H+ –> NAD+ + lactate - efficiency of lactate fermentation = efficiency of alcohol fermentation = 2 ATPs/glucose & a similar overall equation:
glucose + 2 ADP + 2 Pi –> 2 lactate + 2 ATP
misconception about lactate fermentation
- accumulation of lactate (in the form of lactic
acids) in muscle tissue during strenuous exercise was believed to be the primary cause of muscle stiffness &
soreness. - This is now known not to be the case. –> Lactate levels in muscles generally return to normal within an hour after intense exercise.
Sign of lactate fermentation
- Certain bacteria produce lactate as their fermentation product.
- Sour taste of buttermilk, yogurt, and dill pickles is a sign of their activity.
-lactic acid fermentation is used for making some cheeses
Lactate threshold
lactate produced is transported from the muscles to the liver, where it is oxidized back to pyruvate so that it does not build up in muscle tissue.
- The point at which lactate production is too high for transport out of muscles to keep up is called the lactate threshold. –> This value can be increased by individuals through training, and it is useful for setting exercise intensity limits in endurance sports.
- The process of lactate fermentation results in an oxygen debt. By taking deeper and more frequent breaths, the body brings in large quantities of O2 to diminish the O2 debt.
Anaerobic Respiration overview
- Although they lack mitochondria, many prokaryotes have cellular respiration ETC, located on internal membranes derived from the plasma membrane
- Some prokaryotes have ETC similar to those in eukaryotes, using oxygen (O₂) as the terminal electron acceptor.
- Other prokaryotes use substances like sulfate (SO₄²⁻), nitrate (NO₃⁻), or iron ions (Fe³⁺) as electron acceptors instead of oxygen = anaerobic respiration.
–> these organisms are found in low oxygen, such as deep soils, marsh sediments, wetlands, and lakebeds.
Why do some wetlands have a bad smell?
- Sulfur-reducing bacteria use SO₄²⁻ as the terminal electron acceptor, producing hydrogen sulfide (H₂S) instead of water, leading to the rotten egg smell in some wetlands.
