Glycolysis, Respiration, and Fermentation | MIT 7.01SC Fundamentals of Biology
MIT OpenCourseWare・2 minutes read
Primitive organisms evolved energy-producing systems triggered by lightning and cosmic radiation, with Glycolysis, a universal process found in bacteria, yeast, and humans, enabling energy production without oxygen through 10 chemical reactions. Oxygen led to the evolution of more efficient energy production methods like the citric acid cycle and oxidative phosphorylation, generating 36 ATP from glucose, 18 times more efficient than fermentation.
Insights
- Glycolysis, a universal process found in various organisms, evolved around 3.7 billion years ago to produce energy from glucose without oxygen, involving 10 interconnected reactions catalyzed by specific enzymes.
- The evolution of oxygen through photosynthesis led to increased metabolic opportunities, enabling cells to access energy stored in NADH more efficiently, eventually evolving the citric acid cycle and oxidative phosphorylation, which are 18 times more efficient than fermentation in generating ATP.
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Recent questions
What is the process of glycolysis?
Glycolysis is a pathway that evolved around 3.7 billion years ago, involving 10 chemical reactions catalyzed by different enzymes to produce pyruvate, ATP, and NADH. It is a universal process found in bacteria, yeast, and humans, enabling energy production from glucose without oxygen. The pathway requires initial investments of ATP to drive reactions uphill before yielding a net of 2 ATP and NADH. Each of the 10 steps in glycolysis is interconnected and catalyzed by specific enzymes, with the process involving coupling ATP hydrolysis to drive energy-consuming reactions and produce ATP.
How is NADH recycled in glycolysis?
To continue glycolysis, NADH must be converted back to NAD+ to recycle and maintain the reaction. Two methods to regenerate NAD+ involve converting NADH to lactic acid or ethanol and CO2, crucial for cells lacking oxygen. Lactic acid fermentation is seen in yogurt production and during anaerobic exercise, while ethanol fermentation is common in yeast for alcohol production. These fermentation processes are essential for recycling NADH and sustaining energy production in the absence of oxygen.
What is the significance of oxygen in cellular respiration?
Oxygen levels increased metabolic opportunities, allowing cells to access energy stored in NADH. In the absence of oxygen, NADH leads to fermentations that produce 2 ATP. With oxygen available, cells evolved the citric acid cycle and oxidative phosphorylation, generating 36 ATP from 2 3-carbon compounds. Respiration using oxygen is 18 times more efficient than fermentation, highlighting the crucial role of oxygen in cellular energy production.
How does the Chemiosmotic Hypothesis explain ATP synthesis?
The Chemiosmotic Hypothesis, proposed by Peter Mitchell in 1961, explains how energy can be interconverted through chemical bonds, concentration gradients, and electrical potential. The proton motive force, a combination of proton concentration gradient and electrical potential, drives the synthesis of ATP. The ATP synthase, derived from the flagella motor, rotates as protons pass through, synthesizing ATP. Respiration involves two stages: a proton pump establishes a gradient, and an ATP synthase uses the gradient to synthesize ATP.
What is the citric acid cycle and its role in energy production?
The citric acid cycle processes pyruvate to produce acetyl-CoA, leading to the complete burning of glucose to carbon dioxide and water. It involves a 2-carbon compound derived from pyruvate being added to a 4-carbon compound in the cycle, resulting in a 6-carbon compound that eventually converts to a 4-carbon compound with the release of CO2. This cycle produces ATP, NADH, and another reduced electron carrier, ultimately leading to a net yield of 36 ATPs from a single glucose molecule.
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Summary
00:00
Evolution of Glycolysis: Energy Production Without Oxygen
- The first energy-producing system likely evolved when primitive organisms resembling bacteria emerged on Earth, utilizing organic compounds triggered by lightning and cosmic radiation.
- Glycolysis, a pathway that evolved around 3.7 billion years ago, involves 10 chemical reactions catalyzed by different enzymes to produce pyruvate, ATP, and NADH.
- Glycolysis is a universal process found in bacteria, yeast, and humans, enabling energy production from glucose without oxygen.
- The pathway involves initial investments of ATP to drive reactions uphill before yielding a net of 2 ATP and NADH.
- The reactions in glycolysis are interconnected and require all 10 steps to function, each catalyzed by a specific enzyme.
- The process of glycolysis involves coupling ATP hydrolysis to drive energy-consuming reactions and produce ATP.
- To continue glycolysis, NADH must be converted back to NAD+ to recycle and maintain the reaction.
- Two methods to regenerate NAD+ involve converting NADH to lactic acid or ethanol and CO2, crucial for cells lacking oxygen.
- Lactic acid fermentation is seen in yogurt production and during anaerobic exercise, while ethanol fermentation is common in yeast for alcohol production.
- These fermentation processes are essential for recycling NADH and sustaining energy production in the absence of oxygen.
18:27
Evolution of Oxygen and Cellular Respiration
- Photosynthesis evolved oxygen as a waste product, leading to a gradual rise in oxygen levels on Earth over millennia.
- Oxygen levels increased metabolic opportunities, allowing cells to access energy stored in NADH.
- In the absence of oxygen, NADH is a nuisance, leading to fermentations that produce 2 ATP.
- With oxygen available, cells evolved the citric acid cycle and oxidative phosphorylation, generating 36 ATP from 2 3-carbon compounds.
- Respiration using oxygen is 18 times more efficient than fermentation.
- The Chemiosmotic Hypothesis, proposed by Peter Mitchell in 1961, explains how energy can be interconverted through chemical bonds, concentration gradients, and electrical potential.
- The proton motive force, a combination of proton concentration gradient and electrical potential, drives the synthesis of ATP.
- The ATP synthase, derived from the flagella motor, rotates as protons pass through, synthesizing ATP.
- Respiration involves two stages: a proton pump establishes a gradient, and an ATP synthase uses the gradient to synthesize ATP.
- The citric acid cycle processes pyruvate to produce acetyl-CoA, leading to the complete burning of glucose to carbon dioxide and water.
39:24
"Energy Production in Citric Acid Cycle"
- The citric acid cycle involves a 2-carbon compound derived from pyruvate being added to a 4-carbon compound in the cycle, resulting in a 6-carbon compound that eventually converts to a 4-carbon compound with the release of CO2. This cycle produces ATP, NADH, and another reduced electron carrier, ultimately leading to a net yield of 36 ATPs from a single glucose molecule.
