Cellular Respiration Flashcards
name and compare the two types of chemical reactions / pathways that make up an organism’s metabolism MEMORISE
catabolism and anabolism
catabolism: large to small, exergonic (breakdown of absorbed food substances into smaller, simpler molecules = overall release of energy)
anabolism: small to large, endergonic (biosynthesis of complex molecules from simpler substances = overall energy requirement)
what is decarboxylation? MEM
removal of carbon atoms from a compound to form carbon dioxide
what is dehydrogenation? MEM
oxidation involves the removal of electrons and hydrogen ions / protons (H+)
what is oxidative decarboxylation? MEM
oxidation via removal of a carboxylate group, forming carbon dioxide
what are coenzymes, and what are the two most commonly involved in energy metabolism?
Coenzymes are loosely associated with the enzyme, acting as transient carriers of electrons, hydrogen, or specific functional groups
Nicotinamide Adenine Dinucleotide (NAD) and Flavin Adenine Dinucleotide (FAD)
what is the reduced form of NAD and FAD, and their purpose?
reduced NAD = NADH, reduced FAD = FADH2
reservoirs of electrons and protons to form ATP via oxidative phosphorylation
how do obligate aerobes behave with and without oxygen?
with (aerobic respiration): complete oxidation of glucose to CO2 and H2O, yields the max amt of 36/38 ATP
without (anaerobic respiration / fermentation): incomplete oxidation, yields net 2 ATP
what are the three metabolic stages that harvest energy from glucose by cellular respiration?
- Glycolysis
- Link reaction and Krebs cycle (Citric-acid cycle)
- Oxidative phosphorylation: electron transport and chemiosmosis
State the chemical equation of glycolysis
C6H12O6 (glucose) + 2 ADP + 2 NAD —> 2 C3H4O3 (pyruvate) + 2 ATP + 2 NADH + 2H+
what is glycolysis (in one sentence) MEM
converts one molecule of glucose into two molecules of pyruvate with the generation of two net ATP molecules
what are the two types of reactions for glycolysis?
- substrate level phosphorylation (ADP to ATP)
- dehydrogenation (NAD to NADH)
what are the substrates and products of glycolysis (per one glucose molecule)
substrates: 1 glucose, 2 ADP, 2 NAD, inorganic phosphate (Pi)
products: 2 pyruvates (three C), 2 ATP, 2 NADH (waste is water)
where do glycolysis, Link reaction, Krebs cycle, Oxidative Phosphorylation each occur?
glycolysis: cytosol / cytoplasm of all cells
Link reaction: mitochondria matrix
Krebs cycle: mitochondria matrix
Oxidative Phosphorylation: mitochondria inner membrane
what happens during the energy-investment phase of glycolysis?
- steps 1 to 3: activation of glucose
glucose is phosphorylated to form fructose-1,6-biphosphate
hydrolysis of 2 ATPs to ADPs provides phosphate groups and releases energy for this - steps 4 to 5: cleavage
cleavage of fructose-1,6-biphosphate to two 3-carbon sugars, glyceraldehyde-3-phosphate (G3P)
what is the rate-limiting step of glycolysis?
rate-limiting step is step 3, involving the enzyme phosphofructokinase (second phosphorylation of glucose to form fructose 1,6-biphosphate)
what happens during the energy-payoff phase of glycolysis?
- step 6: reduction of NAD by dehydrogenation of G3P
each G3P (two cleaved from each glucose molecule) has hydrogen removed (H added to NAD, forming NADH)
net production of 2 NADH per glucose
one NADH supplies 2 energised electrons, which drive ATP production by oxidative phosphorylation at inner mitochondrial membrane - step 7 to 10: substrate-level phosphorylation
substrate-level phosphorylation of ADP produces 4 ATPs per glucose (2 ATPs per G3P)
overall net gain of 2 ATPs per glucose (bc two ATPs used up per glucose in energy-investment phase)
detail the ten steps of glycolysis
- phosphorylation of glucose, ATP to ADP (dephosphorylated) by hexokinase
- rearrangement, glucose to fructose by phosphoglucoisomerase
- phosphorylation of fructose (diphosphate) by phosphofructokinase
- six-carbon molecule split into two three-carbon by aldolase, one G3P one non (an isomer)
- G3P and isomer r reversible reaction, isomer converted by isomerase
- oxidation and phosphorylation produces two NAD to NADH with added inorganic phosphate, each with one high-energy phosphate bond, by triose phosphate dehydrogenase
- transfer of high-energy phosphate, two ADP to ATP and two G3P to GP3 per glucose by phosphoglycerokinase
- rearrangement, 3-phosphoglycerate to 2 by phosphoglyceromutase
- removal of water to give two phosphoenolpyruvate (PEP) by enolase
- transfer of high-energy phosphate (phosphorylation), two ADP to ATP and two pyruvate by pyruvate kinase
what are the reasons glycolysis is important?
- only reaction that can occur without oxygen (anerobic respiration)
- hydrolyses 1 glucose into two pyruvate
- with oxygen, pyruvate is completely oxidised in mitochondrion to produce ATP by oxidative phosphorylation
- reduced NAD and FAD supply energised electrons for ATP production
- provides essential biosynthetic precursors
At which steps does substrate-level phosphorylation of ADP occur?
Steps 7-10
1,3 biphosphoglyceric acid to pyruvate
how does phosphofructokinase synchronise the rates of glycolysis and the Krebs cycle?
phosphofructokinase is stimulated by AMP which cell derives from ADP
sensitive to citrate (first Krebs cycle product)
citrate will inhibit phosphofructokinase
how does phosphofructokinase work to regulate glycolysis?
- allosteric enzyme
as ATP accumulates, acts as allosteric inhibitor, binding to phosphofructokinase (step 3) and changing its conformation, lowering its affinity for its substrate, slowing glycolysis
define aerobic respiration
a series of enzyme-catalysed oxidation-reduction (redox) reactions, where respiratory substrates are completely oxidised to CO2 and H2O
how does the mitochondria’s outer membrane and matrix relate to its function in cellular respiration?
outer: freely permeable to ATP, ADP, etc
matrix: compartment enclosed by inner membrane, site of Link and Krebs, enzymes required for Krebs r here
how does the mitochondria’s inner membrane relate to its function in cellular respiration?
selectively permeable, highly-folded to form cristae, increasing SA for electron transport chain and ATP synthase complexes
!!! impermeable to NADH
- contains proteins transporting H+, ATP, ADP
- contains members of ETC and ATP synthase complexes (stalked particles)
- permeable to pyruvate
!!! site of oxidative phosphorylation
what is the formula of Link reactions?
2 pyruvate (from glycolysis) + 2 NAD + 2 CoA —> 2 Acetyl CoA + 2 NADH + 2 CO2
what is the Link reaction?
the Link Reaction occurs between glycolysis and the Krebs Cycle, catalysed by pyruvate dehydrogenase
what catalyses the Link reaction
pyruvate dehydrogenase
detail how the link reaction works in cellular respiration
in aerobic respiration, pyruvate from glycolysis enters mitochondria via active transport
- pyruvate’s carboxyl group (-COO-) that is fully oxidised is removed as CO2
- remaining 2C fragment oxidised, forming acetate (CH3COO-)
- H- is transferred to coenzyme NAD, reducing it to NADH
- coenzyme A attaches to acetate, forming acetyl CoA
how do carbon atoms move with each round of Krebs?
2 enter in organic form as acetyl CoA
2 leave in inorganic form as CO2
what are the three reactions of Krebs?
reactions:
1. oxidative decarboxylation
2. substrate-level phosphorylation
3. production of reduced coenzyme
what products are formed per glucose molecule, after two turns of the Krebs cycle?
2 ATP, 2 FADH2, 6 NADH
waste: 4 CO2
what is the metabolism, substrates, and products of the Krebs cycle?
metabolism: catabolic, occurs twice per glucose molecule
- a cycle because oxaloacetate regenerated as a catalyst
- Krebs also breaks down multiple metabolic intermediates
substrates: acetyl CoA, ADP, Pi, NAD, FAD
products: ATP, FADH2, NADH (waste: CO2)
summarise the Krebs cycle in three steps
- acetyl CoA combines with oxaloacetate (4 carbon) to form citrate (6 carbon intermediate)
- citrate undergoes electron-yielding oxidation reactions, 2 CO2 molecules split off, regenerating oxaloacetate
- oxaloacetate (catalyst) recycled
detail the Krebs cycle in cellular respiration
- Condensation: Acetyl CoA (oxidised pyruvate from Link) adds 2C acetyl group to oxaloacetate (catalyst), producing citrate
- citrate changed to its isomer isocitrate
- oxidative decarboxylation NAD reduction: oxidising isocitrate by reducing NAD to NADH, losing a CO2
- oxidative decarboxylation NAD reduction: alpha-Ketoglutarate same as step 3, but coenzyme A attached to molecule by unstable bond, forms succinyl CoA
- substrate level phosphorylation: CoA displaced by phosphate, phosphate transferred to GDP and forms GTP, forms succinate
- FAD reduction: two hydrogens transferred to FAD, forming FADH2 and oxidising succinate to fumarate
- H2O added to fumarate, forms malate
- malate oxidised (NAD reduced to NADH), forms oxaloacetate again
at which steps of glycolysis does substrate-level phosphorylation of ADP occur?
Steps 7-10
1,3 biphosphoglyceric acid to pyruvate
when does oxidative decarboxylation occur during the Krebs cycle?
isocitrate to alpha-ketoglutarate to succinyl CoA, steps 3 and 4
2 NAD reduced to 2 NADH
2 CO2 lost
when does substrate-level phosphorylation occur during the Krebs cycle?
succinyl CoA to succinate –> GTP to GDP (intermediate) –> ADP to ATP, step 5
where does dehydrogenation occur during the Krebs cycle?
production of reduced coenzymes
NAD to NADH
3: isocitrate to alpha-ketoglutarate
4: alpha-ketoglutarate to succinyl CoA
8: malate to oxaloacetate
FAD to FADH2
6: succinate to fumarate
how much ATP has been produced by the end of the Krebs cycle?
4: 2 from glycolysis, 2 from Krebs (link produces none)
(most of the aerobic respiration ATP payoff comes in oxidative phosphorylation lol)
what do reduced coenzymes refer to in cellular respiration, and how many are produced per glucose molecule at the end of Krebs?
NADH: 10 (2 from glycolysis, 2 from Link, 6 from Krebs)
FADH2: 2 (only from Krebs)
what occurs in the electron transport chain during cellular respiration?
electro carriers in the chain undergo temporary reduction and oxidation as electrons (from NADH and FADH2) are passed down to the final electron acceptor, molecular oxygen
how is ATP generated in oxidative phosphorylation of cellular respiration?
energy from NADH and FADH2’s electrons used to pump protons (active transport) across the inner mitochondrial membrane to the intermembrane space, generating a proton gradient. passive flow of protons down conc gradient into matrix through ATP synthase allows for ATP synthesis by oxidative phosphorylation
how is a one-way transport of electrons down the ETC ensured?
each subsequent carrier in the ETC has a higher affinity for electrons than its predecessor, but lower than its successor: arranged in order of increasing electron affinity
what is the final electron acceptor in the ETC, and what is produced at the end?
molecular oxygen (O2), reduced to produce H2O
where does the energy for establishing a proton gradient across inner mitochondrial matrix come from in cellular respiration?
electrons released by NADH and FADH2 provide energy for active transport of H+
what is chemiosmosis?
as electrons are transferred along the ETC, energy is released to drive proton pumps in inner membrane to actively pump H+ unidirectionally from matrix to intermembrane space
what are the two components of the proton gradient in cellular respiration?
concentration gradient of H+: chemical / pH
electrical gradient: voltage
what force is created by proton gradient?
proton motive force
how do protons re-enter the matrix during chemiosmosis, and why?
inner mitochondrial membrane is impermeable to H+
H+ only enters through ATP synthase complex
what is the function of the ATP synthase complex in cellular respiration?
couple the exergonic passage of H+ (intermembrane to matrix) with endergonic phosphorylation of ADP to form ATP (with inorganic phosphate)
what is the ATP yield from each molecule of NADH and FADH2 respectively?
NADH: 10 H+ pumped, generates 3 ATP
FADH2: 6H+ pumped, 2 ATP
name the two known shuttle systems, and in what type of cells they are found, for elections and protons across the inner mitochondria membrane
glycerol phosphate shuttle (muscle and nerve)
malate-aspartate shuttle (heart and liver)
how does the glycerol phosphate shuttle work?
(enzyme, substrate, product, no of ATP)
enzyme: cytosolic glycerol-3-phosphate dehydrogenase
action: dihydroxyacetone phosphate (DHAP) to glycerol-3-phosphate
1 NADH to NAD
2 ATP per molecule of NADH
- 36 ATP molecules per glucose
how does the malate-aspartate shuttle work?
(method, no of ATP)
H- from cytosolic NADH passed to matrix NAD
3 ATP per NADH
38 ATP per glucose
when do substrate-level phosphorylation and oxidative phosphorylation respectively occur during cellular respiration?
substrate-level phosphorylation: glycolysis in the cytoplasm & Krebs cycle in matrix
oxidative phosphorylation: ETC in inner mitochondrial membrane
compare the ATP production between substrate-level and oxidative phosphorylation
substrate-level: small (4 molecules in Krebs and glycolysis combined)
oxidative: 90%
what are the three ways poisons can interfere with oxidative phosphorylation?
- block electron flow
- inhibit ATP synthase
- make inner mitochondrial membrane permeable to protons (no proton gradient)
what are the two types of fermentation, their products, and what organisms they occur in?
lactic acid (C3H6O3)
- lactic acid and NAD
- animals, some bacteria and fungi
alcoholic (ethanol C2H5OH)
- ethanol and NAD
- yeast (fungi)
what are the factors that affect the rate of cellular respiration?
substrate concentration
type of substrate
temperature
what are the roles of NAD in cellular respiration?
- coenzyme
- carries electrons / H+ to ETC from glycolysis / link / krebs
- NAD+ oxidises triose phosphate to pyruvate in glycolysis
