Cellular respiration
cellular respiration formula
C6H12O2 + 6O2 ------> 6CO2 + 6H20 + Energy (ATP) + heat
Respiration equation
CO2 + H2O + ATP (+ heat)
Controlling Aerobic Respiration
Can be regulated by various feedback inhibition and product activation loops:
Pyruvate Oxidation
Conversion of pyruvate to acetyl CoA and CO2 that occurs in the mitochondrial matrix in the presence of O2. Product from Glycolysis: 2 Pyruvate End-product: 2 Acetyl Coenzyme-A (Acetyl Co-A) occurs in the mitochondria Requires the 'expense' of ATP to move pyruvate across the mitochondrial membrane 1 ATP per pyruvate = 2 ATP total Carboxyl Group removed from Pyruvate, releasing CO2 NAD+ is reduced to NADH Acetyl group transferred to coenzyme A Results in Acetyl COA
Why food molecules need to be broken down into smaller molecules for energy to be harvested from them.
Glucose and other food molecules are broken down by controlled stepwise oxidation to provide chemical energy in the form of ATP and NADH.
In cellular respiration, what is oxidized and what is reduced?
Glucose is being oxidized (losing hydrogen). Oxygen is being reduced (gaining hydrogen).
Why do mammalian muscle cells perform lactic acid fermentation (instead of, say, ethanol fermentation)?
Human muscle cells make ATP by lactic acid fermentation because alcohol fermentation produces ethanol that is a toxin and would kill the cells or have to be detoxified in the liver. During strenuous exercise, when sugar catabolism outpaces the muscle's supply of oxygen from the blood, cells switch to fermentation to keep a supply of ATP by recycling NAD+ using pyruvate to lactate. It was once thought that lactate build up in the muscle caused fatigue and pain, but new research suggests that is increased levels of K+ instead. Lactate is thought to enhance muscle performance.
Oxidation and reduction reactions are coupled (REDOX Rxn)
Oxidation adding O removing H loss of electrons releases energy exergonic Reduction removing O adding H gain of electrons stores energy endergonic
the intermediate step
Pyruvic acid (from glycolysis) is oxidized and decarboyxlated
Anaerobic Respiration
Respiration that does not require oxygen Fermentation Only 2 ATP energy molecules generated (from glycolysis) Does not require oxygen Does not use Krebs cycle or electron transport chain
Distinguish between substrate-level phosphorylation and oxidative phosphorylation.
Substrate-level phosphorylation means phosphorylation of ADP to ATP without involvement of mitochondrial electron transport chain and ATP synthase. Substrate-level phosphorylation occurs at two steps in glycolysis and at one step in TCA cycle. Substrate phosphorylation means phosphorylation of a substrate into its phosphate derivative in presence of enzyme kinase, e.g. phosphorylation of glucose to glucose-6-phosphate in presence of enzyme hexokinase. Oxidative phosphorylation refers to phosphorylation of ADP to ATP associated with oxidation of NADH & FAD through mitochondrial electron transport chain.
Phosphofructokinase
The enzyme that catalyzes the phosphorylation of fructose-6-phosphate to form fructose-1-6-bisphosphate in the third step of glycolysis. This is the main regulatory step of glycolysis. PFK is feedback-inhibited by ATP. the enzyme involved in the 3rd step of glycolysis is a major control point: Inhibited by high ATP levels Stimulated by high ADP levels Inhibited by high citrate levels / stimulated by low citrate levels
substrate-level phosphorylation
The enzyme-catalyzed formation of ATP by direct transfer of a phosphate group to ADP from an intermediate substrate in catabolism.
Can a cell produce enough ATP to persist by using glycolysis alone? Why or why not?
Yes -- a single cell can exist on 2 ATP but No for an organism, glycolysis only makes 2 ATP and 2 NADH but it continues to feed the Citric Acid Cycle with it NADH and Acetyl CoA and that cycle makes 2 more and 6 NADH and 2 FADH2 -- Then it drops off electrons to power(chemiosmosis/proton-motive force) Oxidative phosphorylation: more ATP synthesis in the electron transport and chemiosmosis (about 32-34 ATP produced). All total cellular respiration accounts for about 36-38 ATP per glucose. Glycolysis alone has no way to recycle NADH to NAD+ and so the cell would eventually die due to no more components of glycolysis.
Reduction
addition of electrons (e-) to a molecule (usually in the form of hydrogen) stores energy
Pyruvate is a branching point
between aerobic and anaerobic respiration
Carbohydrate Metabolism
changes glucose to glycogen, breaks glycogen down into glucose Carbohydrate metabolism Breakdown of carbohydrate molecules to produce ENERGY Glucose: most common carbohydrate source Two types of carbohydrate metabolism 1. Anaerobic - without O2 ('Fermentation') 2. Aerobic - with O2('Cellular respiration')
Lipases
enzymes that break down fats into fatty acids and glycerol components Glycerol converted to G3P/PGAL
Metabolism of Fats
go to liver, then to fat storage, or used for energy
combustion formula
hydrocarbon + oxygen --> carbon dioxide + water
Alcohol Fermentation
pyruvate → ethanol + CO2 Bacteria, Yeast 3C NADH -> NAD+ 2C 1C beer, wine, bread Dead end process at ~12% ethanol, kills yeast or bacteria can't reverse the reaction
lactic acid fermentation
pyruvate → lactic acid 3C NADH -> NAD+ 3C Animals, bacteria, some fungi cheese, anaerobic exercise (no O2) Reversible process once O2 is available, lactate is converted back to pyruvate by the liver (O2 debt) Back to glycolysis
Oxidation
removal of electrons (e-) from a molecule (usually in the form of hydrogen) releases energy
Glycolysis
the breakdown of glucose by enzymes, releasing energy and pyruvic acid. is the first stage in aerobic respiration & fermentation Takes place in the cytoplasm of the cell Occurs in the presence or absence of oxygen Involves ten enzyme-catalyzed reactions These convert the 6-carbon glucose into two 3-carbon molecules of pyruvate
Oxidative phosphorylation
The production of ATP using energy derived from the redox reactions of an electron transport chain; the third major stage of cellular respiration. Energy released by electron transfer & proton-motive force to make ATP
Metabolism of Proteins
1) proteins are hydrolyzed into amino acids 2) amino acids are deaminated 3) these molecules enter glycolysis and the Kreb's Cycle
Fermentation
A catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid.
Beta oxidation
A metabolic sequence that breaks fatty acids down to two-carbon fragments that enter the citric acid cycle as acetyl CoA. fatty acids are broken down into two carbon segments (acetyl CoA) When fats are being used as the primary energy source such as in starvation, fasting or untreated diabetes, an excess amount of acetyl CoA is produced, and is converted into acetone and ketone bodies. This produces the sweet smell of acetone on the breath, noticeable in a diabetic state
Chemiosmosis
A process for synthesizing ATP using the energy of an electrochemical gradient and the ATP synthase enzyme. The generation of ATP by the movement of hydrogen ions across a membrane. The build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP Chemiosmosis links the Electron Transport Chain to ATP synthesis 1 NADH = 2.5 ATP 1 FADH2 = 1.5 ATP Therefore - total ATP produced through oxidative phosphorylation in the ETC: 10 NADH = 25 ATP 2 FADH2 = 3 ATP
Electron Transport Chain
A sequence of electron carrier molecules (membrane proteins) that shuttle electrons during the redox reactions that release energy used to make ATP. Captures electrons from electron carrier molecules (NADH & FADH2) Uses flow of electrons & proton-motive force to generate ATP Oxidative phosphorylation Four types of membrane protein/electron carrier complexes, composed of: Flavoproteins (example: FMN) Metal-containing proteins (example: iron-sulfur proteins) Ubiquinones (Coenzyme Q) Cytochromes
Explain the effect of each of the following substances on phosphofructokinase, and the overall effect they have on cellular respiration, and the system logic of each effect: AMP
AMP stands for adenosine monophosphate. AMP may be produced by combining two molecules of ADP during ATP synthesis. It may also be formed by the hydrolysis of one inorganic phosphate of ADP, or by the hydrolysis of ATP into AMP and pyrophosphate. PFK is allosterically inhibited by high levels of ATP but AMP reverses the inhibitory action of ATP. Therefore, the activity of the enzyme increases when the cellular ATP/AMP ratio is lowered. Glycolysis is thus stimulated when energy charge falls.
Why are pyruvate converted into acetyl-coA prior to entering the Kreb's cycle? What does this conversion do to the pyruvate molecules?
Acetyl-CoA consists of an acetyl group attached to a coenzyme A molecule. Coenzyme A is a large molecule that contains a molecule of ADP with two side chain groups stemming from its phosphate arms. Acetyl groups attach to the end of these side chains. In this way, the coenzyme A acts as a carrier of acetyl groups. When Acetyl CoA is broken down by water, large amounts of energy are released, which will drive the citric acid cycle. Acetyl-CoA is the starting product and is the fuel for the citric acid cycle. The conversion of pyruvate to acetyl coenzyme A is known as the oxidative decarboxylation of pyruvic acid. Pyruvate oxidation is a key connector that links glycolysis to the rest of cellular respiration. The citric acid cycle is also known as the Kreb's cycle.
How much more energy is produced by aerobic cellular respiration than by anaerobic cellular respiration?
Aerobic -- 36-38 ATP/glucose Anaerobic 2 ATP/glucoseAnaerobic respiration -organisms can only break a 6-carbon glucose into two 3-carbon pyruvate molecules. Glycolysis releases only enough energy to produce 2 ATPs per molecule of glucose. In anaerobic respiration, this is where ATP production stops. This anaerobic process does occur very quickly though. For example, it lets your muscles get the energy they need for short bursts of intense activity. Aerobic respiration produces ATP more slowly. It breaks glucose all the way down to CO2, producing up to 38 ATPs per molecule of glucose. Aerobic respiration consistently produces at least 15 times as much ATP as anaerobic respiration. This vast increase in energy production probably explains why aerobic organisms have come to dominate life on earth. It may also explain how organisms were able to increase in size, adding multicellularity and great diversity.
Flavin adenine dinucleotide (FAD)
An energy carrier that accepts electrons and feeds them into the electron transport chain - An electron carrying cofactor FAD reduced to FADH2 FADH2 oxidized to FAD
Nicotinamide adenine dinucleotide (NAD+)
An energy carrier that accepts electrons and feeds them into the electron transport chain An electron carrying coenzyme NAD+ is reduced and becomes NADH NADH is oxidized and becomes NAD+
Why do anaerobic cellular systems use fermentation? What would happen if they didn't?
Anaerobic systems use fermentation because it does not require oxygen -- which they don't have. Fermentation is a way of harvesting chemical energy without using either oxygen or any electron transport chain (without cellular respiration). Glycolysis can happen without oxygen -- fermentation is an expansion of glycolysis that allows continuous generation of ATP by the substrate level phosphorylation of glycolysis. It is a method used to recycle NAD+. In glycolysis 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+. Without fermentation (in anaerobic conditions), glycolysis would soon deplete the cells supply of NAD+ by reducing it all to NADH. The system would shut itself down for lack of an oxidizing agent (NAD+) -- it would run out because there would be no process to recycle it.
Aerobic Respiration Summary
Glycolysis + Krebs Cycle + Electron Transport Chain (oxidative phosphorylation). Final electron acceptor is oxygen ATP yield from Aerobic Respiration Glycolysis 2 ATP Krebs Cycle 2 ATP ETC 28 ATP TOTAL 30/32 ATP (*) *two ATP are used to move NADH produced in glycolysis into the mitochondria in eukaryotes
What is the role of electron carrier molecules in energy processing systems? Why are they necessary?
Electron carrier molecules do just what their name says. They carry electrons from one part of an energy processing system to another, providing the necessary energy and reducing power to make chemical reactions occur. The energy processing systems you are referring to are mainly aerobic cellular respiration and photosynthesis. In aerobic cellular respiration, the main electron carrier molecules are NADH and FADH2. NADH is produced during glycolysis and the Krebs cycle and then used in the electron transport chain. In the electron transport chain, NADH and FADH2 transfer their electrons to molecules that act as proton pumps. As these proton pumps are reduced by gaining the electrons from NADH and FADH2, they are able to transfer protons across the inner mitochondrial membrane to create a proton gradient that then powers the synthesis of ATP. In photosynthesis, the main electron carrier molecule is NADPH, which is similar to NADH. NADPH is produced by oxidizing NADP+ during the light dependent reactions. NADPH is then used for reducing power during the Calvin cycle, where it helps power the reactions used to make glucose.
Proteases
Enzymes that break down proteins into amino acids Amino acids are deaminated (amino groups removed) - then are modified and enter as pyruvate, acetyl-coA or enter the Krebs cycle at other points The carbon skeletons of certain amino acids (indicated in boxes) are derived from proteins and can feed into pyruvate, acetyl CoA, and the citric acid cycle.
Is glucose the only molecule that can be catabolized during cellular respiration? Why do we use glucose as the model?
Glucose is the main molecule to undergo cellular respiration (by glycolysis and then kreb's cycle) to give ATP. Other molecules include the products of the glycolysis and kreb's cycle especially acetyl-coenzyme A (acetyl CoA). Fatty acids are broken down to acetyl CoA which can then enter the kreb's cycle and give ATP. Proteins can be broken down into amino acids and transaminated to give products that can enter into the kreb's cycle to give energy. Even lactic acid (product of anaerobic respiration) can be converted back to glucose (via cori's cycle) which can then enter glycolysis to give energy. Glucose is one of the most important molecules for producing energy and it is the fuel that cells most often use. Glucose provides quick energy for cells. Fat has more energy than glucose, but it requires some chemical conversions before we can get it into the process of cellular respiration, so it takes longer to use. Glucose, on the other hand, is stored as glycogen, or long chains of glucose inside muscle.
Harvesting stored energy
Glucose is the model Catabolism/breakdown of glucose to ultimately produce ATP
Why is it thought that glycolysis is the first catabolic pathway to have evolved in the metabolism of all cellular systems?
Glycolysis produces much less ATP than does oxidative phosphorylation. Glycolysis takes place in the cytosol, does not involve oxygen, and is present in most organisms. It is found in prokaryotic cells but not in eukaryotic cells. Glycolysis is the first step that breaks down glucose and MUST be done before any further metabolic pathways can break down the glycolysis products. Glycolysis occurs in the cytoplasm which mean it would have been able to be used before the bacteria that formed the mitochondria invade the cell that gave rise to all eukaryotes, indicating it must have been a very fundamental early pathway. Glycolysis does not require any of the membrane-bound organelles of the eukaryotic cell which evolved approximately 1 billion years after the prokaryotic cells. Before there was oxygen in the earth's atmosphere, there was only anaerobic processes - So they must have developed first. The primary method for anaerobic bacteria is glycolysis because it provides energy without oxygen. Aerobic processes require a huge number of specific proteins, whereas glycolysis has a minimal number of proteins involved. The oldest known fossils of bacteria date back 3.5 billion years when appreciable quantities of oxygen were not accumulated in the atmosphere -- so therefore since glycolysis does not require Oxygen and is thought to be the first catabolic pathway to have evolved.
Cellular Respiration - A summary: Overarching Concept: Energy production through chemiosmosis Pumping of H+ ions onto one side of a membrane through protein pumps in an Electron Transport Chain (ETC) Flow of H+ ions across the membrane down the concentration gradient through ATP synthase Drives the synthesis of ATP from ADP + Pi Coupled reactions get the work done Oxidation & reduction reactions: Krebs cycles ETC & pumping of H+ (protons) Cellular Respiration Aerobic respiration Glycolysis In the cytoplasm Glucose(6C) → 2 pyruvate (3C) Produces: 2 ATP + 2 NADH ATP produced by substrate-level phosphorylation Pyruvate oxidation/intermediate step Pyruvate → acetyl CoA Produces: 2 NADH + 2CO2 (waste product) Krebs cycle In the mitochondrial matrix Acetyl CoA → enters Krebs cycle Produces: e- carriers (6 NADH & 2 FADH2) + 2 ATP + 4CO2 (waste product) ATP produced by substrate-level phosphorylation ETC
In the mitochondrial inner membrane: cristae increase surface area Protein pumps embedded in membrane: cytochromes Pumps H+ from the matrix intro the intermembrane space Establish H+ gradient in intermembrane space, so they flow into matrix through ATP synthase Produces: ~34 ATP (1 NADH = 3 ATP, 1 FADH2 = 2 ATP) ATP produced by oxidative phosphorylation O2 = final electron acceptor - ½ O2 + 2e- + 2H+ → H2O (waste product) Anaerobic respiration: glycolysis + fermentation Low ATP production (~2 ATP) Alcohol fermentation Yeast Produce alcohol (2C) + CO2 + NAD: not reversible, alcohol eventually kills yeast Recycle NAD back to glycolysis so 2ATP can be produced again and again Lactic acid fermentation bacteria (yogurt & cheese) & animals (muscle cells) produce lactic acid (3C) + NAD: reversible therefore animals can convert lactic acid back to pyruvate (oxygen debt) recycle NAD back to glycolysis so 2ATP can be produced again and again
ATP synthase
Large protein that uses energy from H+ ions to bind ADP and a phosphate group together to produce ATP Enzyme channel in mitochondrial membrane permeable to H+ H+ flow down concentration gradient flow like water over water wheel flowing H+ cause change in shape of ATP synthase enzyme powers bonding of Pi to ADP:ADP + Pi → ATP
Catabolism
Metabolic pathways that break down molecules, releasing energy.
What products of the prior phases of cellular respiration are used in the electron transport chain? How are they used?
NADH and FADH2 shuttle high-energy electrons extracted from food during glycolysis and the citric acid cycle to the electron transport chain. The electron transport chain is an energy converter that uses the exergonic flow of electrons from NADH and FADH2 to pump H+ across the membrane. The H+ gradient drives ATP synthesis by the ATP synthase protein complex. The ATP synthases are the only sites that provide a route through the membrane for H+. The energy stored in an H+ gradient across a membrane couples with the redox reaction of the electron transport chain to ATP synthesis= chemiosmosis. The events of the electron transport chain involve NADH and FADH, which act as electron transporters as they flow through the inner membrane space. In complex I, electrons removed from glucose by NAD+, during glycolysis and the citric acid cycle, are transferred to NADH to the first molecule in the electron transport chain (FMN). FMN is reduced to its oxidized form as it passes electrons to an iron sulfur protein FeS. The FeS passes electrons to ubiquinone (Q, CoQ or Coenzyme Q). Ubiquinone is the only member of the electron transport chain that is not a protein -- it is a small hydrophobic molecule. Most of the remaining electron carriers between CoQ and Oxygen are proteins called cytochromes. They have a heme group that accepts and donates electrons --The last cytochrome passes its electrons to Oxygen. Oxygen is very electronegative and picks up a pair of H+ atoms forming water. Another source of electrons is FADH, which is oxidized providing still more electrons for the chain. It is through complex II. It has a lower energy level than NADH and provides about ⅓ less energy than NADH.The movement of electrons through complexes I-IV causes protons (hydrogen atoms) to be pumped out of the intermembrane space into the cell cytosol. As a result, a net negative charge (from the electrons) builds up in the matrix space while a net positive charge (from the proton pumping) builds up in the intermembrane space. This differential electrical charge establishes an electrochemical gradient. It is this gradient that drives ATP synthesis in oxidative phosphorylation.
Where in the mitochondria does oxidative phosphorylation occur? Why does it occur there?
Oxidative phosphorylation (electron transport chain coupled with chemiosmosis) occurs in the Inner mitochondrial membrane. A mitochondrion has two membranes: an inner membrane and an outer membrane. The space surrounded by the inner membrane is termed the matrix, and invaginations of the inner membrane are termed cristae. The space between the inner and outer membrane is termed the intermembrane space. The inner membrane is highly impermeable, only allowing water, carbon dioxide, and oxygen to freely cross it. The proteins that mediate the processes of oxidative phosphorylation, including electron transport and ATP synthesis, are embedded within the inner membrane. Because only specific molecules are allowed to cross the inner mitochondrial membrane, an imbalance, or gradient, can develop between one side of the membrane versus the other. Molecules that cannot freely pass through the inner membrane must be specifically transported in order to cross. The mitochondria uses gradients to produce ATP in oxidative phosphorylation. At several sites during electron transport from NADH to O2, protons from the mitochondrial matrix are transported uphill across the inner mitochondrial membrane and a proton concentration gradient forms across it. Because the outer membrane is freely permeable to protons, the pH of the mitochondrial matrix is higher so the proton concentration is lower than that of the cytosol and intermembrane space. An electric potential across the inner membrane also results from the uphill pumping of positively charged protons outward from the matrix. Energy released during the oxidation of NADH or FADH2 is stored both as an electric potential and a proton concentration gradient across the inner membrane. The movement of protons back across the inner membrane, driven by this force, is coupled to the synthesis of ATP (energy)from ADP. Oxidative phosphorylation depends on generation of an electrochemical proton gradient across the inner membrane, with electron transport, proton pumping, and ATP formation occurring simultaneously.
Citrate
PFK is allosterically inhibited by citrate, and ATP. Citrate is a metabolite of the citric acid cycle. Citrate builds up when the Krebs Cycle enzymes approach their maximum potential. So when the Krebs cycle is producing maximum amounts of ATP and has the most energy -- citrate levels are high and slow down the process using the PFK regulatory enzyme.
ATP
PFK is allosterically inhibited by high levels of ATP. ATP concentration build up indicates an excess of energy and does have an allosteric modulation site on PFK where it decreases the affinity of PFK for its substrate. So PFK regulates to decrease the production of ATP.
Detail the movement of an electron through the electron transport chain in a mitochondrion. Include its source, destination, and all products made directly and indirectly.
Reduced electron carriers (NADH and FADH_22start subscript, 2, end subscript) from other steps of cellular respiration transfer their electrons to molecules near the beginning of the transport chain. In the process, they turn back into NAD^++start superscript, plus, end superscript and FAD, which can be reused in other steps of cellular respiration. As electrons are passed down the chain, they move from a higher to a lower energy level, releasing energy. Some of the energy is used to pump H^++start superscript, plus, end superscript ions, moving them out of the matrix and into the intermembrane space. This pumping establishes an electrochemical gradient. At the end of the electron transport chain, electrons are transferred to molecular oxygen, which splits in half and takes up H^++start superscript, plus, end superscript to form water. As H^++start superscript, plus, end superscript ions flow down their gradient and back into the matrix, they pass through an enzyme called ATP synthase, which harnesses the flow of protons to synthesize ATP.
Oxygen is not used in the Kreb's cycle, so why must the Kreb's cycle occur in aerobic cellular respiration?
The Krebs cycle does not directly require oxygen but it can only take place when oxygen is present because it relies on by-products from the electron transport chain, which requires oxygen. The Krebs cycle takes place in the mitochondrial matrix, the innermost compartment of the mitochondria. The activity of the Krebs cycle is closely linked to the availability of oxygen although none of the steps in the pathway directly use oxygen. Oxygen is required for the electron transport chain to function which recycles NADH back to NAD+ and FADH2 back to FADH providing NAD+ and ADH required by enzymes in the Krebs cycle. If the oxygen supply to a muscle cell or a yeast cell is low NAD+ and FADH levels fall, the Krebs cycle cannot proceed forward, and the cell must resort to fermentation (anaerobic) to continue making ATP. The Krebs cycle is therefore an aerobic process.
Compare and contrast the metabolism of glucose with the metabolism of complex carbohydrates, proteins & fats. Explain where each molecule (or component of the molecule) enters the aerobic cellular respiration pathway, and order each in terms of the amount of energy they produce for the cell.
The amount of energy you'll get from carbohydrate, protein and fat is measured in calories per gram. Energy provided = 4 calories/ gram of carbohydrate or protein, 9 calories/gram of fat.Fats have the most energy and proteins have the same amount of energy as carbohydrates. The body is designed to use carbohydrates as its primary fuel because carbohydrates are burned immediately. Excess energy gained from fat is stored in the body for future use. Carbohydrates are more readily digested than lipids and release their energy more rapidly. Monosaccharides and disaccharides are water soluble and easier to transport to and from storage sites than lipids. Too much stored fat can lead to obesity and other health problems. Carbohydrates are stored as glycogen in animals while lipids are stored as fats (in plants carbohydrates are stored as cellulose and lipids as oils). Complex carbohydrates are long, complex chains of sugar; take longer to break down; provide energy source for a longer time. Proteins are large organic compounds made of amino acids arranged in a linear chain. 8 of the amino acids contained in proteins are necessary in the human body to survive. The body needs protein to maintain and replace tissues and to function and grow. Protein is not usually used for energy. However, if the body is not getting enough calories from other nutrients or from the fat stored in the body, protein is used for energy. Because proteins are complex molecules, the body takes longer to break them down. As a result, they are a much slower and longer-lasting source of energy than carbohydrates.
substrate-level phosphorylation
The enzyme-catalyzed formation of ATP by direct transfer of a phosphate group to ADP from an intermediate substrate in catabolism. Transfer of phosphate from an organic molecule to make ATP. ADP + Pi → ATP
pyruvate decarboxylase
The glycolytic enzyme responsible for converting pyruvate into acetaldehyde under anaerobic conditions during alcoholic fermentation.
Why do hydrogen atoms accompany electrons as they are transferred in biological systems?
The hydrogen ions (protons) are there as a result of the reactions occurring in an aqueous (water) solution. The water, H2O, ionizes to form H+ and OH- in solution. Both pH and concentration of other ions such as K+, Na+, and Cl- also affect the balance. NAD+ is an electron shuttle. It has a "plus" form, and then, once it picks up two electrons and a hydrogen from glucose (organic food), it is reduced and called NADH. One proton (H) is released and one proton (H) is added to NAD+ along with 2 electrons. This molecule will pick up electrons at several steps and deliver them to the electron transport chain. Many biologically important oxidation and reduction reactions involve the removal or the addition of hydrogen atoms (protons plus electrons) rather than the transfer of isolated electrons. Protons are soluble in aqueous solutions (as H3O+), but electrons are not and must be transferred directly from one atom or molecule to another. Cellular respiration uses an electron transport chain to break the fall of electrons to oxygen in several energy releasing steps. An electron transport chain consists of a number of molecules, mostly proteins, built into the inner membrane of mitochondria of eukaryotic cells and the plasma membrane of aerobically respiring prokaryotes.
Proton-motive force
The potential energy stored in the form of an electrochemical gradient, generated by the pumping of hydrogen ions across biological membranes during chemiosmosis.
Oxidative phosphorylation
The production of ATP using energy derived from the redox reactions of an electron transport chain; the third major stage of cellular respiration.
Summary of Glycolysis
glucose + 2ADP + 2Pi + 2NAD+ --> 2 pyruvate + 2ATP + 2NADH + 2H+2H20 Yield from glycolysis: Energy: 2 ATP Reduced Coenzymes: 2 NADH Energy: 2 ATP Reducing power: 2 NADH
Estimate the efficiency of aerobic cellular respiration of a molecule of glucose: Energy of formation of ATP from ADP: approx. + 57 KJ/Mol Energy of combustion of glucose: approx. - 2805 KJ/Mol
how much energy was put in/how much was produced=-2805/57x36(ATP theoretically produced) Efficiency = N x EATP/Ereact x 100% where N is the number of ATP molecules formed E _react is the energy released as heat in the chemical reaction that is coupled with the reaction to form ATP. E_ATP is the energy in one high energy phophoanhydride bond in ATP, or the free energy when ATP reacts to form ADP and phosphate (ATP > ADP + phosphate). Standard: E_react = -686 kcal/mol and E_ATP= -7.3 kcal/mol. 36 molecules are formed E_react = -2805kcal/mol and E_ATP= +57 kcal/mol. Efficiency = 36 x 57/-2805
Krebs Cycle (aka Citric Acid Cycle)
second stage of cellular respiration, in which pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions Acetyl-CoA broken down to release carbon dioxide (CO2) Generates lots of NADH & FADH2 ATP produced by substrate-level phosphorylation
Aerobic Cellular Respiration
the process by which cells use oxygen to obtain usable energy from an energy source 1. Glycolysis 2. Krebs Cycle (aka Citric acid cycle) 3. Electron Transport Chain
NADH
the reduced form of NAD+; an electron-carrying molecule that functions in cellular respiration another major control mechanism: When NADH levels are highly concentrated, it allosterically inhibits pyruvate decarboxylase (enzyme necessary in the conversion of pyruvate into acetyl-coA) and reduces the amount of acetyl-CoA entering the Krebs Cycle
Summary of the Krebs Cycle
turns TWICE because of the 2 pyruvate molecules produced in glycolysis TOTAL NET GAIN PRODUCTS -2 ATP -4 CO₂ -6 NADH (carries H⁺ -2 FADH₂ to ETC) Products (Per pyruvate molecule) 2 CO2 3 NADH(x2) 1 FADH2(x2) 1 ATP(x2) = Products 4 CO2 6 NADH 2 FADH2 2 ATP
