Unit 9: Bioenergetics and Glycolysis
ATP as the cell's spendable energy currency, and the ten-step pathway that pulls the first small yield of it out of a glucose molecule.
6 topics · 21 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.
Free Energy, ATP, and the Energy Currency of the Cell
- How it worksHow does breaking ATP's terminal phosphate bond release energy a cell can capture for other work?
- Common mistakeWhy isn't energy created when ATP is hydrolyzed, only released from a molecule that already stored it?
- Common mistakeWhy don't mitochondria 'make energy' rather than convert one form of it into ATP, with the total conserved?
- Going furtherWhat happens to a cell's ATP-to-ADP ratio during a sudden burst of intense activity?
Your turn1 of 2
A student explains ATP hydrolysis by saying the reaction "creates" the energy a cell uses to do work. What is the correct way to describe what's actually happening?Coupled Reactions and ATP Hydrolysis
- How it worksHow does coupling ATP hydrolysis to an unfavorable reaction make the combined reaction favorable overall?
- Worked exampleFind the overall free energy change of a reaction requiring +5 kcal/mol when it's coupled to ATP hydrolysis releasing -7.3 kcal/mol.
- Common mistakeWhy isn't ATP hydrolysis directly grabbing and physically moving the substrate of the reaction it's coupled to?
Your turn1 of 2
Find the overall free energy change of a reaction requiring +9 kcal/mol when it's coupled to ATP hydrolysis releasing -7.55 kcal/mol.Glycolysis: Substrate-Level Phosphorylation Step by Step
- How it worksWalk me through how glucose is split and rearranged through ten enzyme steps into two molecules of pyruvate.
- Worked exampleFind the net ATP yield of glycolysis per glucose molecule, given that 2 ATP are invested and 4 ATP are produced.
- Common mistakeWhy isn't glycolysis itself the process that uses oxygen to make most of a cell's ATP?
- Going furtherWhat happens to the pyruvate produced by glycolysis when no oxygen is available to the cell?
Your turn1 of 2
Find the net ATP yield of glycolysis per glucose molecule, given that 3 ATP are invested and 6 ATP are produced.Regulation of Glycolysis by Phosphofructokinase
- How it worksHow does a buildup of ATP allosterically inhibit phosphofructokinase to slow glycolysis down?
- How it worksHow does a buildup of AMP override that inhibition to speed glycolysis back up?
- Common mistakeWhy isn't phosphofructokinase regulation the same thing as the cell simply running out of substrate?
Your turn1 of 2
A cell's glycolytic rate slows dramatically even though plenty of glucose and glucose-6-phosphate are still available. A student assumes this slowdown must mean the cell has simply run out of some necessary substrate. Why is this the wrong explanation?Fermentation and Anaerobic ATP Production
- How it worksHow does lactic acid fermentation regenerate the NAD+ that glycolysis needs to keep running without oxygen?
- How it worksHow does alcoholic fermentation in yeast regenerate NAD+ through a different pathway that ends in ethanol?
- Common mistakeWhy isn't fermentation just a less efficient way of making the same amount of ATP that cellular respiration would from the same glucose?
- Ties togetherHow does fermentation's real job of regenerating NAD+ connect back to why glycolysis stalls without it?
Your turn1 of 2
A student describes fermentation as simply a less efficient version of cellular respiration, making the same total amount of ATP from the same glucose but through a clumsier pathway. Why is this an inaccurate description?The Pentose Phosphate Pathway and NADPH
- How it worksHow does the pentose phosphate pathway divert glucose-6-phosphate to generate NADPH and five-carbon sugars?
- Common mistakeWhy isn't NADPH interchangeable with NADH inside the cell even though the two molecules differ by one phosphate group?
- Going furtherWhat happens to a red blood cell's defense against oxidative damage when its pentose phosphate pathway enzyme is deficient?
Your turn1 of 2
NADH and NADPH differ by only a single phosphate group, and both molecules can donate a pair of high-energy electrons. A student assumes the two must be interchangeable inside the cell. Why is this wrong?