Fermentation: Catabolic process that makes ATP from glucose( or other fuels) that doesn't use ETC.
Cellular Respiration: Catabolic pathway that breaks down organic molecules and uses ETC for the production of ATP.
Aerobic
- Air life
- Uses O2 as final e- acceptor
- Most efficient
- Most EUK
- Some PRO
Anaerobic
- W/O air life
- Uses inorganic molecules other than O2 as final e- acceptor
- Less efficient
- Some PRO
Organic compounds + O2 → CO2 + H2O + Energy
How catabolic reactions release energy
Redox: oxidation reduction reaction - relocating e-.
Oxidation = DONOR
- Loses e-
- Charge inc. (more +)
Reduction = ACCEPTOR
- Gains e-
- Reduces the total net charge bc e- are (-)
Enzymes
-Lowers the activation energy
-Allows oxidation of sugar so energy can be harvested
NAD+ : Electron carrier, works well bc easily oxidized/reduce
NAD+
- Accepts e-
- Oxidizing agent
- Only a small energy "fall" from sugar for e-
NADH
- Donates e-
- Reducing agent
ETC
-Carrier to carrier
-Gets more electronegative as it goes towards O2, energy gets released at each step
Aerobic Cellular Respiration
- Glycolysis "sugar splitting"
-In cytosol, 1 sugar → 2 pyruvate
- Pyruvate oxidation & citric acid cycle
-In EUK: pyruvate enters mitochondria. oxidized into acetyl CoA then citric acid
-In PRO: this happens in cytosol
- Oxidation phosphorylation: e- transport and chemiosmosis
- Substrate level phosphorylation
-ATP synthesis from adding inorganic P to ADP
-Contains e- transport & chemiosmosis
-Makes most of ATP (90%) from cell respir.
-Powered by ETC
9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
• Glycolysis- sugar splitting
• One glucose becomes two pyruvates
• 2 ATP and 2 NADH are made (net)
• No C released as carbon dioxide
– glucose (6 C) → 2 pyruvate (3 C)
• No O2 needed
• Occurs in cytoplasm
• Two phases
– Investment: energy need to split the glucose
– Payoff: more energy is released than consumed
• Nets 2 ATP
9.3 After pyruvate is oxidized, the citric acid
• If cycle completes the energy-yielding oxidation of organic molecules
• If oxygen is available, more energy can be extracted
– In eukaryotes: actively transport the pyruvate to the mitochondria
– In prokaryotes: stay in cytosol
• Pyruvate converted to Acetyl coenzyme A by a multi-enzyme complex
– This is oxidation
Pyruvate oxidation
• Carboxyl group (already oxidized, has little energy) is released as CO2
• The 2 C product is oxidized so now it is acetate
• Electrons moved to NAD+
• Coenzyme A attached to the acetate forming Acetyl CoA
– Acetyl CoA has high potential energy
Citric Acid Cycle
• Acetyl CoA delivers the acetyl into the Krebs cycle
• Remember that one glucose makes two pyruvates and thus two acetyl groups
• Each “turn” of the cycle makes
– one ATP by substrate phosphorylation
– 2 CO2
– 3 NADH
– a FADH2
9.4 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
• So far each glucose yields 4 ATP by substrate phosphorylation, most of the energy remains in the electron carriers
• Which are sent to the electron transport chain which is a collection of molecules embedded in a membrane (plasma for prokaryotes and inner mitochondrial membrane for eukaryotes)
ETC
• Ubiquinone aka Coenzyme Q
– Hydrophobic, lipid soluble so it “floats” in the membrane
• Cytochromes
– Protein electron carriers
ATP Synthase
• Enzyme that makes ATP from ADP and inorganic phosphate
• Uses energy in the form of a H+ concentration gradient
– Difference in pH
• Like an ion pump running in reverse
• Chemiosmosis: energy in the form of a H+concentration gradient across a membrane is used to power cellular work
• The ETC maintains the H+ gradient by using the energy released by the electron “drop” to
pump the protons across the membrane
• This gradient is called a proton-motive force because it sends the H+ back through the ATP synthase “mill”
• Cellular respiration is one example of chemiosmosis
*Glycolysis oxidizes glucose to pyruvate but oxygen isn’t involved and it can occur in the absence of oxygen
9.5 Fermentation and anaerobic respiration enables cells to produce ATP W/O use of O2
Anaerobic respiration
- No O2 needed
- Uses ETC
- Less electronegative e- acceptor is used
- Some PRO
- Some marine bacteria
-Sulfate ion as final e- acceptor
-Hydrogen sulfide produced instead of H2O
-Rotten egg smell
Fermentation
- No O2 needed
- No ETC
- NAD+ as e- acceptor
- Is glycolysis + some way to recycle NAD+ ie. alcohol & lactic acid
Fermentation Examples
• Alcohol
– Bacteria
– Yeast
– Humans used yeast to make wine, beer, & bread.
• Lactic acid
– Bacteria
– Fungi
– Dairy industry to make cheese and yogurt
– Human muscle cells in low O2 conditions
• Obligate anaerobes- can not use oxygen
• Facultative anaerobes- can go either way depending on conditions
– Yeast
– Our muscle cells
9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways
• A variety of molecules can be utilized for cellular respiration
• Intermediates may be shuttled to anabolic pathways (biosynthesis)
• Cellular respiration is controlled by allosteric enzymes at key points
