cellular respiration Flashcards
what is catabolism?
catabolism includes the various pathways involving the breakdown of larger molecules into simpler, smaller molecules. there is an overall release of energy (exergonic)
metabolism = anabolism + catabolism
what is anabolism?
anabolism includes the various pathways involving the biosynthesis of complex molecules from simpler compounds/substnces
there is an overall energy requirement (endergonic)
metabolism = anabolism + catabolism
how do electrons relate to oxidation/reduction?
- the loss of electrons from one substance is oxidation
- the addition of electrons to another substance is reduction
- since electron transfers require both an electron donor & acceptor, oxidation & reduction always go hand in hand
oxidation: losing hydrogen. reduction: gaining hydrogen
oxidation: gaining oxygen. reduction: losing oxygen
hydrogen = 1 proton + 1 electron, so losing hydrogens involve losing one or more electrons
what is decarboxylation?
removal of carbon atoms from a compound to form carbon dioxide
what is dehydrogenation?
dehydrogenation refers to oxidation/breakdown of organic molecules, which frequently involve the removal of electrons as well as hydrogen ion/protons (H+)
enzymes that catalyse oxidative reactions are called dehydrogenases
what is oxidative decarboxylation?
oxidative decarboxylation refer to oxidation reactions whereby a carboxylate group is removed, forming carbon dioxide
what is the role of coenzymes in redox reactions in respiration & what are exampless of these coenzymes?
role:
- coenzymes are loosely associated with the enzyme during the reaction
- coenzymes act as transient carriers of electrons, hydrogen or specific functional groups
examples:
- NAD (nicotinamide adenine dinucleotide) [reduced to form NADH/reduced NAD]
- FAD (flavin adenine dinucleotide) [reduced to form FADH2/reduced FAD]
upon reduction, the reduced coenzymes serve as reservoirs of electrons & protons to form ATP via oxidative phosphorylation
electrons removed from a molecule of glucose during glycolysis, link reaction and Krebs cycle are transferred as pairs of hydrogen atoms to NAD and FAD, forming NADH & FADH2 respectively
what are the stages of harvesting energy from glucose by cellular respiration?
- glycolysis
- link reaction
- krebs cycle
- oxidative phosphorylation (electron transport & chemiosmosis)
what is glycolysis?
glycolysis converts one molecule of glucose into two molecules of pyruvate, a three carbon compound, with the generation of 2 net ATP molecules
what is the location, raw materials used and products formed during glycolysis?
location:
- occurs in cytosol/cytoplasm in all cells
raw materials used/substrates:
- glucose or other hexose sugars
- ADP
- inorganic phosphates (Pi)
- NAD
products formed (per glucose molecule)
- 2 molecules of pyruvate
- 2 net ATPs
- 2 NADH
- waste product formed: water
describe briefly the metabolism in glycolysis
- glucose, a 6-carbon (6C) sugar is split into 2 3C sugars
- each 3C sugar is rearranged to form a 3-carbon (3C) compound, pyruvate (ionised form of pyruvic acid)
- substrate level phosphorylation is important to convert ADP to ATP
- dehydrogenation is important to convert NAD to NADH
what are the 2 stages of glycolysis?
- energy-investment phase (ATP utilisation)
- energy-payoff phase (ATP formation)
idk if need to memorise so much so just memo if u sibei boliao
describe, in detail, the process of glycolysis in terms of its 2 stages
energy-investment phase:
- conversion/activation of unphosphorylated glucose to a phosphorylated fructose-1,6-bisphosphate
- hydrolysis of 2 ATPs to provide phosphate groups and also energy
- cleavage of fructose-1,6-bisphosphate to 2 3-carbon sugars, glyceraldehyde-3-phosphate (G3P)
energy-payoff phase:
- each G3P is oxidised (dehydrogenation) and NAD is reduced to NADH
- this results in a net production of 2 NADH per glucose molecule (since 2 G3Ps are made)
- one NADH supplies 2 energised electrons
- these electrons directly drive most ATP production by oxidative phosphorylation at the inner mitochondrial membrane (later on)
- substrate-level phosphorylation of ADP occurs, coupled to the dephosphorylation of an organic substrate
- directly produces 4 ATPs per glucose molecule. there is an overall net gain of 2 ATPs per glucose molecule since 2 ATPs are used during the energy-investment phase
not in LOs
why is glycolysis important?
glycolysis is a vital source of energy as it directly produces net 2 molecules of ATP by substrate-level phosphorylation
- glycolysis is the only catabolic reaction that can be completed in the absence of oxygen (anaerobic)
- glycolysis hydrolyses 1 molecule of glucose into 2 molecules of pyruvate
in the presence of oxygen,
- pyruvate produced enters the mitochondrion and are completely oxidised to produce ATP by oxidative phosphorylation
- and reduced NAD & FAD supply energised electrons for ATP production
glycolysis supplies cells with essential biosynthetic precursors
- the liver carries out glycolysis to provide precursors for the molecules it synthesises
- in the well-fed animal, once liver glycogen reserves are full, carbohydrate is converted to fats. glycolysis is predominantly associated with supplying the initial steps of fat biosynthesis with substrate, rather than acting as a source of ATP
- for microorganisms, energy & necessary biosynthetic precursors are obtained from glycolysis
phosphofructokinase
how is glycolysis regulated?
phosphofructokinase is an allosteric enzyme
1. as ATP accumulates, it acts as an allosteric inhibitor by binding to phosphofructokinase, slowing down glycolysis
2. phosphofructokinase is stimulated by AMP, which the cell derives from ADP. so the enzyme becomes active again as cellular work converts ATP to ADP (& AMP) faster than ATP is being regenerated
3. phosphofructokinase is sensitive to citrate, the first product of the krebs cycle, so if citrate accumulates in the mitochondria, some of it passes into the cytosol and inhibits phosphofructokinase. this synchronises the rates of glycolysis and the krebs cycle
what is aerobic respiration?
aerobic respiration is defined as a series of enzyme-catalysed oxidation-reduction (redox) reactions in which respiratory substrates are completely oxidised to CO2, and O2 is reduced to H2O
higher yield of ATP
some energy lost as heat
4 stages of aerobic respiration:
glycolysis
link reaction
krebs cycle
oxidative phosphorylation (electron transport + chemiosmosis)
how does the structure of the mitochondria aid its function in cellular respiration?
mitochondria are clustered in regions of cells with the most intense metabolic activity and the greatest need for ATP
outer membrane of mitochondria:
- freely permeable to ATP, ADP etc
inner membrane
- a selectively permeable membrane which is highly-folded to form cristae which increase surface area for embedding electron transport chain and ATP synthase complexes
- not permeable to NADH
- contains transport proteins for H+, ATP & ADP
- contains members of the ETC & ATP synthase complexes
- permeable to pyruvate (so it can go in since glycolysis takes place in the cytosol)
- impermeable to H+ (can establish proton gradient)
- site of oxidative phosphorylation
matrix (compartment enclosed by inner membrane of mitochondrion):
- site of the link reaction & krebs cycle
- contains enzymes required for reactions in the krebs cycle
what is the location, raw materials used and products formed in the link reaction?
location:
- mitochondrial matrix
raw materials used/substrates:
- pyruvate
- NAD
- CoA
products formed:
- acetyl CoA
- NADH
- CO2
overall reaction:
2 pyruvate + 2 NAD + 2 CoA -> 2 acetyl CoA + 2 NADH + 2 CO2
link reaction occurs 2x for each glucose as one glucose makes 2 pyruvate
the link reaction is catalysed by pyruvate dehydrogenase
not sure if we need to know in detail
describe the process of the Link Reaction
- when molecular oxygen is present, the pyruvate produced by glycolysis enters the mitochondrion
- upon entering the mitochondrion via active transport, pyruvate is converted to a 2-carbon compound called acetyl CoA, which is carried out by a multienzyme complex, which catalyses 3 reactions through oxidative decarboxylation:
1. pyruvate’s carboxyl group (COO-) that is already fully oxidised, is removed & liberated as CO2
2. the remaining 2C fragment is oxidised, forming acetate (CH3COO-). 2 electrons & a proton are removed and transferred to the coenzyme NAD, reducing it to NADH
3. coenzyme A is attached to acetate, forming acetyl CoA
link reaction happens twice for each glucose as each glucose produces 2 pyruvate
describe briefly the Krebs cycle
- the 2C acetyl group of acetyl CoA combines with a 4C molecule, oxaloacetate to form a 6C intermediate, citrate
- citrate goes through a sequence of electron-yielding oxidation reactions, during which 2 CO2 molecules split off, regenerating oxaloacetate
- the oxaloacetate is then recycled to bind to another acetyl group
what is the location, raw materials used, and products formed in the Krebs Cycle?
location:
- mitochondrial matrix
raw materials used/substrates:
- acetyl CoA (or any of the other intermediates in the pathway)
- ADP
- inorganic phosphates (Pi)
- NAD
- FAD
products (per glucose molecule/2 turns of the cycle)
- 2 ATP
- 2 FADH2
- 6 NADH
- 4CO2 (waste product)
not in LOs
describe briefly the metabolism in the Krebs Cycle
- the krebs cycle is a catabolic pathway that occurs twice for every glucose molecule broken down. glucose breakdown & oxidation is completed in 8 enzyme-controlled steps
- the krebs cycle is known as a cycle as the molecule added to incoming acetyl CoA, oxaloacetate, is regenerated at the end of one turn of the cycle to receive more acetyl groups
- the krebs cycle also plays a central role in the breakdown of multiple metabolic intermediates, eg lipids & amino acids. various compounds in the cycle can also be syphoned off for the formation of chlorophyll, amino acids etc
not very detailed so just memo :)
describe the Krebs cycle
- acetyl CoA adds its 2C acetyl group to oxaloacetate, producing citrate, a 6C compound
- citrate undergoes 1 decarboxylation & 1 oxidation reaction, producing 1 CO2 and 1 NADH respectively, and forming a 5C acid (α-ketoglutarate)
- the 5C acid undergoes 1 decarboxylation & 1 oxidation reaction, producing 1 CO2 and 1 NADH respectively, and forming a 4C acid
- the 4C acid undergoes substrate-level phosphorylation, producing 1 ATP, and 2 dehydrogenation (oxidation) reactions, producing 1 NADH & 1 FADH2, and regenerating oxaloacetate
the input of 2 carbons as acetate is balanced by the loss of 2 carbons as CO2
the cycle must occur twice to metabolise both acetyl CoA molecules derived from a single molecule of glucose
NADH & FADH2 produced are high-energy compounds, releasing a lot of energy when electrons are transferred from these coenzymes -> accounts for synthesis of most of the 36/38 ATP molecules produced during complete oxidation of a glucose molecule
what are the processes that make up oxidative phosphorylation?
electron transport (via electron transport chain) and chemiosmosis
what is the electron transport chain and where is it located?
the electron transport chain (ETC) is made up of a sequence of electron carriers, that undergo temporary reduction & oxidation as electrons from NADH & FADH2 are passed down to the final electron acceptor, molecular oxygen.
the electron transport chain is located in the inner mitochondrial membrane, which is highly folded to form cristae in all cells
is ATP directly generated from the electron transport chain?
no ATP is directly generated
- energy from electrons carried by NADH & FADH2 are used to pump protons across the inner mitochondrial membrane to the intermembrane space, generating a proton gradient across the inner mitochondrial membrane
- the flow of the protons back into the matrix along their concentration gradient through the ATP synthase complex allows for ATP synthesis by oxidative phosphorylation
describe, in detail, how the ETC transfers electrons from NADH & FADH2 to oxygen
- the ETC, embedded in the inner mitochondrial membrane, comprises of a sequence of electron carriers that have the ability to be reversibly reduced & oxidised as electrons from NADH & FADH2 are passed down the mitochondrial ETC.
- several coenzymes & cytochromes in the ETC are bound to enzymes and other essential factors, forming functional groups known as complexes. there are 4 main complexes, complexes I-IV, in the ETC
- each subsequent member ofthe ETC has a higher affinity for electrons than its predecessor, but a lower affinity than its successor. this ensures a one-way transport of electrons down the ETC, so theelectrons move along the sequence of electron carriers in order of increasing electron affinity
- electrons are eventually passed to the final electron acceptor in the ETC, molecular oxygen that has diffused into the mitochondrion. oxygen is reduced in the mitochondral matrix to produce a molecule of water
- energy released as electrons flow through the ETC is sufficient to power the pumping of H+ ions across the inner mitochondrial membrane into the intermembrane space, establishing an electrochemical proton gradient
- as members of the ETC accept electrons from NADH & FADH2, the oxidised coenzymes NAD & FAD are regenerated. this allows them to be available to accept electrons & protons from substrates during glycolysis, link reaction & Krebs cycle again.
what is the process of chemiosmosis and where does it take place?
chemiosmosis takes place in the inner mitochondrial membrane.
- energy is released as electrons are transferred along the ETC. this energy drives proton pumps to actively pump H+ unidirectionally across the inner mitochondrial membrane from the mitochondrial matrix to the intermembrane space
- the proton pumping generates a proton gradient with two components, 1) concentration gradient of H+ and 2) electrical gradient (higher conc of +vely charged protons on 1 side of membrane)
- since the inner mitochondrial membrane is impermeable to H+, protons can only re-enter through the ATP synthase complex
- the ATP synthase complex couples the exergonic passage of H+ to the endergonic phosphorylation of ADP to form ATP
how does the type of coenzyme affect the ATP yield?
amount of ATP produced depends on no. of H+ pumped into the intermembrane space, which depends on no. of electrons contributed by reduced coenzymes
for each pair of electrons stripped from NADH/reduced NAD,
- 5 pairs of (10) H+ are pumped across the inner mitochondrial membrane into the intermembrane space
- re-entry of H+ into the matrix provides the energy to generate 3 ATP molecules
for each pair of electrons stripped from FADH2/reduced FAD,
- 3 pairs of (6) H+ are pumped across the inner mitochondrial mmbrane into the intermembrane space
- re-entry of H+ into the matrix provides the energy to generate 2 ATP molecules
how to calculate the yield of 36/38 ATPs?
total no. of NADH: 10 (2 from glycolysis, 2 from link reaction, 6 from krebs cycle)
total no. of FADH2: 2 (from krebs cycle)
10 NADH x 3 ATP (electrons from each NADH produces 3 ATP) = 30 ATP
2 FADH2 x 2 ATP (electrons from each FADH2 produces 2 ATP) = 4 ATP
substrate level phosphorylation in glycolysis produces 2 ATP
substrate level phosphorylation in the krebs cycle produces 2 ATP
30 + 4 + 2 + 2 = 38 ATP
whether the cell produces 36 or 38 molecules of ATP depends on the shuttle systems (FYI) used in the mitochondrion.
what are the differences between substrate-level phosphorylation & oxidative phosphorylation?
occurrence
- SLP occurs during glycolysis in the cytoplasm and during krebs cycle in the mitochondrial matrix
- OP occurs during ETC in the inner mitochondrial membrane
ATP production
- SLP produces only a small amount of ATP
- OP produces almost 90% of ATP generated in respiration
process
- SLP: the enzymatic endergonic phosphorylation of ADP with a 5’ monophosphate coupled to exergonic dephosphorylation of an organic substrate
- OP: the enzymatic endergonic phosphorylation of ADP to form ATP by ATP synthase, coupled to exergonic electron transport from a substrate to the final electron acceptor, oxygen. exergonic passage of protons along a proton gradient
how do respiratory poisons/inhibitors affectoxidative phosphorylation?
poisons that block electron flow
- various poisons (eg carbon monoxide & cyanide) block the movement of electrons down the ETC
- this completely inhibits ATP production
poisons that inhibit ATP synthase
- these poisons (eg oligomycin, an antibiotic) directly inhibits ATP synthase by preventing the influx of protons through ATP synthase
- although the proton gradient becomes larger than normal, its potential energy cannot be tapped to make ATP
poisons that make the inner mitochondrial membrane leaky to protons
- these poisons (eg 2,4-dinitrophenol) are known as uncoupling agents. they carry protons back across the inner mitochondrial membrane.
- this causes the proton gradient to dissipate
- no proton gradient is formed, so no ATP can be made by oxidative phosphorylation. rather, the energy derived from electron transport is released as heat.
why does anaerobic respiration produce a small yield of 2 ATP molecules per glucose?
- glycolysis can take place in the absence of oxygen (so pyruvate is formed)
- under anaerobic conditions, no further oxidation of pyruvate occurs, so no acetyl CoA is formed, and no additional ATP can be generated
- because without oxygen, the link reaction, Krebs cycle and oxidative phosphorylation do not occur
- the energy needs of the cell are met by the 2 ATP molecules per glucose generated in glycolysis, so cells must consume glucose morerapidly to maintain steady-state cellular ATP levels
where does anaerobic respiration, or fermentation occur, and what are the 2 common types of fermentation?
anaerobic respiration is an oxygen-independent process
- anaerobic respiration, occuring in the cytosol, uses organic molecules as terminal electron acceptors for the regeneration of NAD
the two common types of fermentation, where pyruvate is used as an electron acceptor, are:
1. lactic acid fermentation, where pyruvate is converted to lactate
2. alcoholic fermentation, where pyruvate is converted to ethanol & CO2
not in LOs
describe lactic acid fermentation
NADH + C3H4O3 (pyruvate) -> NAD + C3H6O3 (lactate)
pyruvate is reduced directly by NADH to form lactate (ionised form of lactic acid) as a waste product, when no release of CO2
lactic acid fermentation occurs in animals and in certain fungi & bacteria
why need lactic acid fermentation?
- in animals: to regenerate NAD so it can continue glycolysis
- in certain fungi & bacteria: to make cheese and yoghurt in the dairy industry
not in LOs
describe alcoholic fermentation
NADH + C3H4O3 (pyruvate) -> NAD + C2H5OH (ethanol) + CO2
CO2 is released from pyruvate, and pyruvate is converted to acetaldehyde. then, acetaldehyde is reduced by NADH to ethanol
occurs in fungi, eg yeast, and in most plant tissues
CO2 is a waste product
what are the differences between aerobic & anaerobic respiration?
energy yield
aerobic: max 38 ATP produced per glucose molecule oxidised
anaerobic: 2 ATP per glucose molecule oxidised (only from glycolysis)
oxidation
aerobic: complete oxidation of glucose to CO2 & water
anaerobic: incomplete oxidation of glucose
condition
aerobic: occurs in the presence of oxygen
anaerobic: occurs in the absence of oxygen
idk if need to memo in detail
how to experimentally investigate respiration?
- respiration rate (uptake of oxygen per unit time) can be measured using a respirometer. the manometer in the respirometer detects changes in pressure/volume of a gas
- respiration by tiny organisms that are trapped in the respirometer chamber alters the composition of the gas
- oxygen consumption per unit time can be measured by reading the level of manometer fluid against the scale
- changes in temperature & pressure will alter the volume of air in the apparatus, so temperature of the surroundings must be kept constant while readings are taken, using a thermostatically controlled water bath. a control tube containing an equal volume of inert materials to the volume of organisms used helps compensate for changes in atmospheric pressure
- once measurements have been taken at a series of temperatures, a graph can be plotted of oxygen consumption against temperature
- the respirometer can also be used to measure the respiratory quotient (RQ) of an organism
- find oxygen consumption at the same temperature (x), then do the same but remove the chemical to absorb CO2 so the manometer scale shows whether the volumes of oxygen absorbed and CO2 produced are the same. if they are the same, level of manometer fluid won’t change and RQ = 1. if more CO2 is produced, the scale shows an increase in volume of air in the atmosphere (y)
- RQ = CO2/O2 - (x+y)/x
- if less CO2 is produced than oxygen absorbed, the volume of air in the respirometer decreases (z), so RQ = CO2/O2 - (x-z)/z
