Bio: Cellular Respiration and Fermentation

Autotrophs

Autotrophs

• Produce their own organic molecules through photosynthesis.

Heterotrophs

• Eat organic compounds produced by other organisms

Cellular Respiration

• the process of releasing the energy contained in organic molecules (mainly Glucose) to do work.

• The process uses the energy from the organic, biological macromolecules to make ATP.

• a series of coordinated enzyme-catalyzed reactions that capture energy from biological macromolecules.

• releases heat (unusable energy) and free electrons(used to produce ATP).

Oxidation

• loss of electrons(LEO)

Reduction

• gain of electron(GER)

Dehydrogenization

• lost electrons are accompanied by protons(hydrogen)

  • a hydrogen atom is lost (1 electron, 1 proton)

    • To follow the e-, follow the H’s

Redox Reactions

• e- carry energy from one molecule to another

Nicotinamide adenine dinucleotide

• NAD+

• NADH

*Meaning of NAD+

• Oxidized form?(ready to accept electrons)

• Reduced Form?(accepted electrons)

Flavin adenine dinucleotide

• FAD+

• FADH2

*Meaning of FAD+

• Oxidized form?(ready to accept electrons)

• Reduced Form?(accepted electrons

Aerobic Respiration

• Final electron acceptor is oxygen (O2 )

Anaerobic Respiration

• Final electron acceptor is an inorganic molecule (not O2 )

Fermentation

• Final electron acceptor is an organic molecule, converted into lactic acid or ethanol + CO2

Substrate-level phosphorylation

• A mechanism for synthesis of ATP

• Transfer phosphate group directly to ADP

• Uses an enzyme (kinase)

• During glycolysis & Krebs (Citric Acid) Cycle

Glycolysis

• occurs in the cytosol/cytoplasm

• converts 1 Glucose(6 carbons) to 2 Pyruvate(3 carbons)

• can be Aerobic(32 ATP produced) or Anaerobic(2 ATP produced) so it occurs with/out the presence of O2

Energy Investment Stage(Priming Reaction)

• During this stage, 2 ATP molecules are required to act as the activation energy for each glucose molecule that enters the process.

• The ATPs are used to phosphorylate glucose. The phosphorylation makes glucose unstable.

• This ultimately leads to the breaking of glucose into 2 G3P molecules.

• First to Fifth step

*Step 1

? Hexokinase

? Glucose 6-phosphate

• _____________ transfers a phosphate group from ATP to glucose, making it more chemically reactive. The charged phosphate also traps the sugar in the cell.

? ATP

?? ADP

*Step 2

? Phosphohexose isomerase

? Fructose 6-phosphate

• This step from phosphoglucose to phosphofructose allows the eventual split of the sugar into two three-carbon molecules

*Step 3

? Phosphofructokinase -1 (PFK-1)

? Fructose 1,6-bisphosphate

• _____________________ transfers a phosphate group from ATP to the opposite end of the sugar, investing a second molecule of ATP. This is a key step for the regulation of glycolysis.

? ATP

?? ADP

*Step 4

? Aldolase

? Dihydroxyacetone phosphate(DHP)

?? Glyceraldehyde 3-phosphate(G3P)

• _________ cleaves the sugar molecule into two different three-carbon sugars.

*Step 5

? Triose Phosphate Isomerase

? Glyceraldehyde 3-phosphate(G3P)

Energy Payoff Stage

• During this stage, each of the two G3P molecules formed during the energy investment phase is oxidized.

• The energy and electrons from the 2 G3P molecules are used to create 2 molecules of NADH, 4 ATP molecules per glucose(though substrate-level phosphorylation), and 2 molecules of Pyruvate

• Sixth to Tenth step

*Step 6

? Glyceraldehyde 3-phosphate dehydrogenase

? 1,3-Bisphophoglycerate

• Two sequential reactions: (1) G3P is oxidized by transferring electrons to NAD+, forming NADH. (2) Using energy from this exergonic redox reaction, a phosphate group is attached to the oxidized substrate, making a high- energy product.

? NAD+

?? NADH(x2) + H+

*Step 7

? Phosphoglycerate kinase

? 3-Phosphoglycerate

• The phosphate group is transferred to ADP (substrate-level phosphorylation) in an exergonic reaction.

? ADP(x2)

?? ATP(x2)

*Step 8

? Phosphoglycerate mutase

? 2-Phosphoglycerate

• _______________ relocates the remaining phosphate group.

*Step 9

? Enolase

? Phosphoenolpyruvate

• _____ causes a double bond to form in the substrate by extracting a water molecule, yielding _______________, a compound with very high potential energy.

? H2O

*Step 10

? Pyruvate kinase

? Pyruvate

• The phosphate group is transferred from PEP to ADP (a second example of substrate-level phosphorylation), forming ________

? ADP(x2)

?? ATP(x2)

Pyruvate Oxidation

• performed by _______ dehydrogenase complex

• Occurs in the mitochondrial matrix in eukaryotes

• Occurs at the plasma membrane in prokaryotes

• Where pyruvate is converted to acetyl Coenzyme A(acetyl CoA)

Pyruvate(3 carbons) to Acetyl(2 carbons) + CO2(waste)

• First step of pyruvate oxidation where the 1st enzyme catalyzes decarboxylation, so a carboxyl group is removed from pyruvate

  ? 1st Enzyme: pyruvate dehydrogenase

Acetyl is attached to Coenzyme A generating Acetyl-CoA

• Second step of pyruvate oxidation where a 2nd enzyme grabs Acetyl to transfer it between reaction sites

  ? 2nd Enzyme: Dihydrolipoyl transacetylase

NAD+ is reduced to NADH + CO2

• Third step of pyruvate oxidation where 2 electrons from pyruvate oxidation are passed to coenzyme NADH catalyzed by the 3rd enzyme

  ? Enzyme: Dihydrolipoyl dehydrogenase

Krebs Cycle/Citric Acid Cycle

• Energy remains in bonds of acetyl-CoA

• completes the breakdown of pyruvate to CO2

• oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn

• Occurs:

  • In the cytoplasm of prokaryotes

  • In the mitochondrial matrix of eukaryotes

*Step 1

? Citrate synthase

? Citrate(6 carbons)

• Acetyl CoA (from pyruvate oxidation) adds its two-carbon acetyl group to four-carbon oxaloacetate, producing _______.

? H2O

?? CoA-SH

*Step 2

? Aconitase

? Isocitrate(6 carbons)

• Citrate is converted to its isomer, isocitrate, by removal of one water molecule and addition of another. This reaction does not happen immediately however, as it is converted to cis-_________ first.

*Step 3

? Isocitrate dehydrogenase

? a-Ketoglutarate(5 carbons)

• Isocitrate is oxidized, reducing NAD+

  to NADH. Then the resulting compound loses a CO2 molecule.

? NAD+

?? NADH & CO2

*Step 4

? a-ketoglutarate dehydrogenase complex

? Succinyl-CoA(4 carbons)

• Another CO2 is lost, and the resulting compound is oxidized, reducing NAD+

  to NADH. The remaining molecule is then attached to coenzyme A by an unstable bond.

? CoA-SH & NAD+

?? NADH & CO2

*Step 5

? succinyl-CoA synthetase

? Succinate(4 carbons)

• CoA is displaced by a phosphate group, which is transferred to GDP, forming GTP, a molecule with functions similar to ATP. GTP can also be used, as shown, to generate ATP.

? GDP + P

?? GTP

??? CoA-SH

*Step 6

? Succinate dehydrogenase

? Fumarate(4 carbon)

• Two hydrogens are transferred to FAD, forming FADH2

• The enzyme catalyzes the oxidizing of succinate, releasing 2 electrons that go to Coenzyme Q(carries the electrons to nearby enzymes of ETC).

*Uses the enzyme embedded in the inner mitochondrial membrane and known as Complex II of ETC *

? FAD

?? FADH2

*Step 7

? Fumarase

? Malate(4 carbons)

?? H2O

• Addition of a water molecule rearranges bonds in the substrate.

*Step 8

? Malate dehydrogenase

? Oxaloacetate(4 carbons)

• The substrate is oxidized, reducing NAD+ to NADH and regenerating ____________.

? NAD+

?? NADH + H+

Oxidative phosphorylation

• A mechanism for the synthesis of ATP

• ATP synthase uses energy from a proton gradient

• During ETC and Chemiosmosis

• produces most of the ATP generated from Cellular Respiration

Electron Transport Chain(ETC)

• is a series of membrane-bound electron carriers

• Embedded in the inner mitochondrial membrane (cristae)

• Electrons from NADH and FADH2 are transferred to the four complexes of the ETC

• Each complex

  • Has a proton pump creating proton gradient

  • Transfers electrons to the next carrier

  • Electrons end up in Oxygen -> The final electron acceptor ◦

    • Oxygen is reduced to water

ETC

• Electron carriers for Glycolysis, Pyruvate Oxidation, and Krebs cycle drop off e- at ETC membrane complexes

• H+ is pumped out, creates a gradient (more H+ outside of inner membrane)

• NADH dehydrogenase

• Succinate dehydrogenase

• Ubiquinone(Q)-Cytochrome C Reductase

• Cytochrome C Oxidase

• Complex I

• Complex II (one of the enzymes in the Krebs cycle). This complex does not have proton pumping ability.

• Complex III

• Complex IV

NADH dehydrogenase

• The NADH donated from glycolysis, and the citric acid cycle is oxidized here, transferring 2 electrons from NADH to coenzyme Q

• 1st reaction: NADH is oxidized, __releasing 2 electrons that go to coenzyme Q(__which is also reduced) and carry electrons to the next part of ETC

• 2nd reaction: the movement of charged electrons makes Complex I bend in shape, transmit energy and pump out 4 protons across the membrane

Succinate dehydrogenase

• accepts electrons from succinate (an intermediate in the citric acid cycle) and acts as a second entry point to the ETC.

• When succinate oxidizes to fumarate, 2 electrons are accepted by FAD within complex II. FADH passes them to coenzyme Q, similar to complex I.

Coenzyme Q(ubiquinone)

• Its purpose is to function as an electron carrier and transfer electrons to complex III.

• Ubiquinone(Q)-Cytochrome C Reductase

• separates electrons from coenzyme Q, passing 1 electron to cytochrome C which is reduced

• transports 4 protons across the membrane

reduced Cytochrome C

• carries the electron to the last step of ETC

Cytochrom C Oxidase

• oxidizes cytochrome c and transfers the electrons to oxygen, the final electron carrier in aerobic cellular respiration.

• a molecule of oxygen is captured, split and reduced, allowing it to accept electrons & pick up protons creating 2 molecules of water

• The free energy from the electron transfer causes 4 protons to move into the intermembrane space contributing to the proton gradient.

Chemiosmosis

• H+ flows back into the matrix through ATP Synthase, and ATP is created

• Accumulation of protons in the intermembrane space drives protons into the matrix via diffusion

• Since the membrane is relatively impermeable to ions, most protons can only reenter the matrix through ATP synthase

• Uses energy of proton gradient to make ATP from ADP + Pi

• For every 4 H+ in, one ATP is created.

• 1 NADH = 10 H+ = 2.5 ATP

• 1 FADH2 = 6 H+ = 1.5 ATP

• What is the conversion of NADH and FADH2 to ATP?

Anaerobic respiration

• Couples with glycolysis when there is no O2 for cellular respiration so that the electron transport chain will not cease to operate

• uses an electron transport chain with a final electron acceptor other than O2, for example, sulfate

Fermentation

• Couples with glycolysis when there is no O2 for cellular respiration so that the electron transport chain will not cease to operate

• uses substrate-level phosphorylation instead of an electron transport chain to generate ATP

• produces 2 ATP per glucose molecule

Alcohol fermentation

Type of fermentation:

• pyruvate is converted to ethanol in two steps, with the first releasing CO2

• _______ fermentation by yeast is used in brewing, winemaking, and baking

Lactic Acid Fermentation

Type of fermentation:

• pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2

• _______ ____ fermentation by some fungi and bacteria is used to make cheese and yogurt

• Human muscle cells use _______ ____ fermentation to generate ATP when O2

  is scarce

Obligate anaerobes

• Carry out fermentation or anaerobic respiration and cannot survive in the presence of O2

Facultative anaerobes

• pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

• able to survive using either fermentation or cellular respiration

  Ex. yeast & bacteria

Methanogens

Modes of Anaerobic Respiration

• use carbon dioxide (CO2) as the electron acceptor, reducing CO2 to CH4 (methane).

• The hydrogens are derived from organic molecules produced by other organisms.

• Are found in diverse environments, including soil and the digestive systems of ruminants like cows.

Sulfur Bacteria

Modes of Anaerobic Respiration

• In this sulfate respiration, the prokaryotes derive energy from reducing inorganic sulfates (SO4 ) to hydrogen sulfide (H2S).

• The hydrogen atoms are obtained from organic molecules other organisms produce.

• These prokaryotes, thus, are similar to methanogens, but they use SO4 as the oxidizing (that is, electron-accepting) agent in place of CO2.