BIOL 2311 Lecture Notes - Lecture 7: Oxaloacetic Acid, Chemiosmosis, Citric Acid
CH 7: Cellular Respiration
-Autotrophs harvest sunlight and convert radiant energy into chemical energy.
-Heterotrophs live off the energy produced by autotrophs.
extract energy from food via digestion and catabolism
Cellular respiration: metabolic reaction tht breaks down food to produce ATP
-Cellular respiration is a series of reactions that:
- are oxidations – loss of electrons, .
- are also dehydrogenations – lost electrons are accompanied by hydrogen
Therefore, what is actually lost is a hydrogen atom (1 electron, 1 proton).
In eukaryotes aerobic respiration occurs- oxygen is used as a reactant.
In prokaryotes aerobic respiration occurs as well, but sometimes anaerobic also occurs. Sulfate/ nitrate
is used instead of oxygen.
In overall cellular energy harvest
-Dozens of redox reactions take place
- Number of electron acceptors including NAD+
In the end, high-energy electrons from initial chemical bonds have lost much of their energy
Transferred to a final electron acceptor
Cells harvest energy by breaking bonds and shifting electrons from one molecule to another.
-aerobic respiration - final electron acceptor is oxygen
-anaerobic respiration - final electron acceptor is inorganic molecule other than oxygen
-fermentation - final electron acceptor is an organic molecule
In cellular respiration, organic molecules are oxidized by removal of higher energy e. delivered to lower
energy levels to oxygen. Some of energy released is used to make ATP.
In photosynthesis, low energy electrons derived from water are pushed to higher energy levels by
absorbing light energy . The e are reduced to carbohydrates from co2. Oxygen is released.
2H from a fuel molecule is added to NAD+ which accepts 2e and is reduced to NADH.
Respiration
The goal of respiration is to produce ATP.
- energy is released from oxidation reaction in the form of electrons
- electrons are shuttled by electron carriers (e.g., NAD+ ) to an electron transport chain
- electron energy is converted to ATP at the electron transport chain
Redox reactions
-In redox reactions, electrons release some of their energy as they pass from a donor molecule to an
acceptor molecule
-This free energy is available for cellular work, such as ATP synthesis
-Molecules that accept electrons may also combine with protons (H+ ), as oxygen does when it is
reduced to form water
ATP
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Cells use ATP to drive endergonic reactions, ΔG = -7.3 kcal/mol
-2 mechanisms for synthesis:
1. Substrate-level phosphorylation
-Transfer phosphate group directly to ADP
-During glycolysis
2. Oxidative phosphorylation
-ATP synthase uses energy from a proton gradient
Electron carriers
-Many types of carriers used
-Soluble, membrane-bound, move within membrane
-All carriers can be easily oxidized and reduced
-Some carry just electrons, some electrons and protons
-NAD+ acquires 2 electrons and a proton to become NADH
Aerobic respiration:
-C6H12O6 + 6O2 6CO2 + 6H2O
ΔG = -686kcal/mol of glucose
ΔG can be even higher than this in a cell.
-This large amount of energy must be released in small steps rather than all at once.
Glucose Catabolism
-Cells catabolize organic molecules and produce ATP in two ways:
1. substrate-level phosphorylation
2. oxidative phosphorylation – use of ATP synthase and energy derived from a proton (H+ )
gradient to make ATP
-in most organisms, both are combined
-glycolysis (in cystol- euk and pro): 6C glucose converted to 2 3C pyruvate. NADH is produced and ATP is
also synthesized. Thru dehydrogenase and substrate level phosphorylation.
-pyruvate oxidation (in mitochondria matrix- euk, cytosol-pro): covert each 3C pyruvate to 2C acteyl
group
-Krebs cycle (mitochondria matrix- euk, cytosol-pro): each 2C acetyl group oxidized to co2. Some NADH
and some ATP formed here also.
-electron transport chain A.K.A oxidative phosphorylation ( in inner mitochondrial membrane-euk,
plasma membrane-pro): high energy e from previous steps are delivered to oxygen thru e carriers in the
electron transport chain. Free energy released by electron flow generates the h+ gradient called
chemiosmosis.
ATP is synthesized by the enzyme ATP synthase
- The energy is derived from the proton gradient
-This gradient is formed by high energy electrons during the oxidation of glucose
-These energy depleted electrons are then donated to oxygen and hence oxidative phosphorylation
AEROBIC RESPIRATION (OXIDATION OF GLUCOSE)
- Reaction locations:
-Glycolysis – in the cytosol
-Pyruvate oxidation and citric acid cycle – in the mitochondrial matrix
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-Electron transfer system and ATP synthase enzymes – in the inner mitochondrial membrane
MEMBRANES AND COMPARTMENTS OF A MITOCHONDRION
OXIDATION OF GLUCOSE – 4 STAGES
1.Glycolysis
2.Pyruvate Oxidations
3.Krebs Cycle
4.Eclectron transport chain
Glycolysis
-Glycolysis converts 6C glucose to 2 molecules of 3C pyruvate.
- a 10-step biochemical pathway - occurs in the cytoplasm
- 2 molecules of pyruvate are formed
- net production of 2 ATP molecules by substrate-level phosphorylation
- 2 NADH produced by the reduction of NAD+
Stage one:
-For each molecule of glucose that passes through glycolysis, the cell nets two ATP molecules.
-Priming glucose priming
1.cleavage and rearrangement
-Substrate-level phosphorylation
1.oxidation
2.ATP generation
For glycolysis to continue
NADH must be recycled to NAD+ by either:
1. Aerobic respiration:
- Oxygen is available as the final electron acceptor
-Produces significant amount of ATP
2. Fermentation:
- Occurs when oxygen is not available
-Organic molecule is the final electron acceptor
In the presence of oxygen, pyruvate is oxidized
-Occurs in the mitochondria in eukaryotes
-multienzyme complex called pyruvate dehydrogenase catalyzes the reaction (removing –COO and
converting it to acetyl group).
-Occurs at the plasma membrane in prokaryotes
Fate of Pyruvate
1.Depends on oxygen availability.
-When oxygen is present, pyruvate is oxidized to acetyl-CoA which enters the Krebs cycle
-Aerobic respiration
2.Without oxygen, pyruvate is reduced in order to oxidize NADH back to NAD+
-Fermentation
Pyruvate Oxidation and citric acid cycle
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Document Summary
Autotrophs harvest sunlight and convert radiant energy into chemical energy. Heterotrophs live off the energy produced by autotrophs. extract energy from food via digestion and catabolism. Cellular respiration: metabolic reaction tht breaks down food to produce atp. Cellular respiration is a series of reactions that: Are oxidations loss of electrons, . Are also dehydrogenations lost electrons are accompanied by hydrogen. Therefore, what is actually lost is a hydrogen atom (1 electron, 1 proton). In eukaryotes aerobic respiration occurs- oxygen is used as a reactant. In prokaryotes aerobic respiration occurs as well, but sometimes anaerobic also occurs. In the end, high-energy electrons from initial chemical bonds have lost much of their energy. Cells harvest energy by breaking bonds and shifting electrons from one molecule to another. Aerobic respiration - final electron acceptor is oxygen. Anaerobic respiration - final electron acceptor is inorganic molecule other than oxygen. Fermentation - final electron acceptor is an organic molecule.
