Unit 6: Bioenergetics, Glycolysis, and Fermentation
ATP as a currency, not a battery, and the first pathway every cell uses to cash it in from glucose.
8 topics · 26 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
ATP Structure and Hydrolysis
- How it worksHow does ATP's chain of three phosphate groups pack in electrostatic repulsion that gets released on hydrolysis?
- How it worksWalk me through ATP hydrolysis breaking its terminal phosphate bond and releasing ADP plus inorganic phosphate.
- Going furtherWhat happens to a cell's ATP-to-ADP ratio the instant its energy demand spikes?
Your turn1 of 2
ATP's three phosphate groups sit clustered together, each carrying a negative charge, right next to each other along the same small molecule. A student wonders why cells would build a molecule with so much negative charge packed into one place instead of spreading it out. What does this crowded arrangement actually accomplish?Why ATP Hydrolysis Releases Free Energy
- How it worksHow does relieving the electrostatic repulsion between ATP's clustered phosphates release a large negative delta G on hydrolysis?
- Common mistakeWhy isn't ATP's energy stored inside one single special high-energy phosphate bond?
- Worked exampleFind the free energy released when 3 moles of ATP hydrolyze at negative 30.5 kilojoules per mole each.
Your turn1 of 2
Find the free energy released when 18 moles of ATP hydrolyze, at -29 kilojoules per mole each.Redox Reactions and NAD+/NADH
- How it worksHow does NAD+ accept a hydride ion and two electrons to become NADH during an oxidation reaction?
- Going furtherWhat happens to a pathway's rate once its supply of oxidized NAD+ runs out?
- Common mistakeWhy isn't NADH itself the final destination for the energy a cell extracts from food?
Your turn1 of 2
During glycolysis, NAD+ picks up electrons from an oxidized sugar intermediate and becomes NADH. A student assumes NAD+ must simply grab a single free electron floating nearby, the way a positively charged ion might attract one. What does NAD+ actually accept?Glycolysis: The Energy Investment Phase
- How it worksHow do glycolysis's first steps add phosphate groups that trap glucose inside the cell and destabilize it for splitting?
- Worked exampleFind the net ATP spent by the time glycolysis's investment phase splits one glucose into two three-carbon sugars.
- Going furtherWhat happens to glycolysis's investment phase when hexokinase gets inhibited by a buildup of its own product?
Your turn1 of 2
Glycolysis's investment phase spends 2 ATP per glucose molecule before any payoff begins. Find the total ATP spent when a cell processes 43 glucose molecules through this phase.Glycolysis: The Energy Payoff Phase
- How it worksHow does oxidizing each three-carbon sugar generate NADH while also setting up a high-energy phosphate transfer?
- How it worksWalk me through substrate-level phosphorylation directly transferring a phosphate from a sugar intermediate onto ADP.
- Worked exampleFind the net ATP and NADH produced from one glucose molecule by the end of glycolysis, after subtracting the 2 ATP invested.
- Going furtherWhat happens to glycolysis's output the moment a cell's oxygen supply runs out?
Your turn1 of 2
Each three-carbon sugar oxidized in glycolysis's payoff phase generates 1 NADH, and one glucose molecule yields two such three-carbon sugars. Find the total NADH produced when a cell processes 35 glucose molecules through glycolysis.Regulation of Glycolysis by Phosphofructokinase
- How it worksHow does phosphofructokinase get shut off allosterically once the cell's ATP levels are already high?
- Common mistakeWhy isn't glycolysis regulated equally at every one of its ten steps?
- Going furtherWhat happens to glycolysis's rate when a cell's ATP is abundant but its AMP levels spike anyway?
Your turn1 of 2
A student assumes glycolysis must be regulated evenly across all ten of its steps, with every enzyme in the pathway contributing about equally to controlling the overall rate. Why is this picture of glycolysis's regulation wrong?Fermentation: Lactic Acid and Alcoholic
- How it worksHow does converting pyruvate to lactate regenerate the NAD+ that glycolysis needs to keep running?
- How it worksWalk me through how yeast ferments pyruvate into ethanol and carbon dioxide instead of lactate.
- Going furtherWhat happens to a fermenting cell's ATP output compared to a cell that has oxygen available?
Your turn1 of 2
During intense exercise, a muscle cell converts pyruvate into lactate even though this step by itself yields no additional ATP. A student assumes this conversion must be pointless, since no extra energy comes out of that particular reaction. Why does the cell still do it?Why Cells Ferment Without Oxygen
- How it worksHow does fermentation let glycolysis keep running by recycling NAD+ without any oxygen involved?
- Worked exampleFind the net ATP yield per glucose for a fermenting cell relying on glycolysis alone, compared with about 30 for a respiring cell.
- Common mistakeWhy isn't fermentation just glycolysis running the same energy extraction without oxygen?
- Ties togetherHow does fermentation's NAD+ recycling connect back to the same redox chemistry that oxidative phosphorylation depends on?
Your turn1 of 2
A fermenting cell nets about 2.2 ATP per glucose relying on glycolysis alone, while a respiring cell nets about 30 ATP per glucose. Find how many times larger the respiring cell's ATP yield is.