The Electron Transport Chain & ATP Synthesis

9.4 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis pp. 172-177

Directions: as always, answer these reading comprehension questions in your journal. Rephrase the Q's in the A's OR glue this paper in your journal on its own page nearby.

1. In the electron transport chain (ETC), a) Where do the “starting” electrons come from? From NADH and FADH2, but ultimately… glucose!

b) What causes electrons to move from one electron carrier to another in the chain? Increased stability as each new carrier gets reduced (accepts e-).

c) What molecule is the final electron acceptor for the ETC? (It's not considered part of the chain; it "swoops in" at the last moment to whisk away the electrons that have reached the end of the chain.) And what substance forms as a result? Oxygen is the final e- acceptor, and the substance that forms is water.

d) What substance accumulates between the inner and outer mitochondrial membranes as a result of the moving of electrons along the ETC? Protons, a.k.a. hydrogen ions, a.k.a. H+ ions

2. Identify the underlined elements of this simile: “The making of ATP in the mitochondria is like the making of a cake; one needs ingredients, energy, and a chef to do the manual labor.” Ingredients: ADPs and phosphates; energy, the H+ gradient; chef, ATP synthase enzyme.

3. If a eukaryotic cell was unable to get enough oxygen… a) Would its ETC operate? Why or why not? No, e- wouldn't be able to be unloaded at end of the chain. b) Would it be able to make ATP within its mitochondria? No – if ETC doesn't operate, no proton gradient. c) Would the cell be able to have Krebs cycles or perform glycolysis? Why or why not? No Krebs because w/o a running ETC, NADH and FADH2 don't get oxidized. Krebs needs NAD+ and FAD. Glycolysis also needs NAD+, so technically no glycolysis either… but some cells have a trick to enable them to keep running glycolysis in the absence of oxygen. It's called fermentation. Section 9-5 in your text.

4. Prokaryotic cells have cellular respiration, even though they do not have mitochondria. Where is the ETC of a prokaryotic cell located? Along the plasma membrane. The proton gradient builds up in the prokaryote's cell wall space.

5. CLEARLY define the five terms below. They are loosely related but you need to understand how they are different! a) chemiosmosis: process in which H+ ions pass through ATP synthase, causing the enzyme to spin; the spinning enzyme synthesizes ATP. b) electron transport: Alternate series of reductions and oxidations as NADH and FADH2 hand off their electrons all the way to – eventually – oxygen, forming water. c) oxidative phosphorylation = ETC + chemiosmosis d) proton motive force = hydrogen ion gradient utilized in chemiosmosis e) substrate level phosphorylation = entirely different way of adding a phosphate group to ADP, forming ATP. Happens at one step in glycolysis or Kreb's. Done by an enzyme. No hydrogen gradient utilized.