7.1: Introduction
- Page ID
- 88932
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)We saw that glycolysis generates two pyruvates per glucose, and that subsequent oxidation of each pyruvate generates two Ac-S-CoA molecules. In aerobic cells, oxidation of each Ac-SCoA by the Krebs cycle captures about 4% (30/687 Kcal) available in a mole of glucose—in just two ATP molecules; not much for all that biochemical effort! But a total of twenty-four \(\rm H^{+}\) ions (protons) in glucose have captured in reduced electron carriers (NADH, \(\rm FADH_2\)) in redox reactions. Here we’ll see how oxidation of NADH and \(\rm FADH_2\) by an electron transport system releases free energy that fuels the creation of a proton (\(\rm H^{+}\)) gradient. Then we’ll see how dissipation of this gradient powers oxidative phosphorylation and ATP synthesis. Electron transport and oxidative phosphorylation account for the cellular capture most nutrient free energy in ATP. We’ll contrast oxidative phosphorylation with glycolytic and Krebs cycle substrate-level phosphorylation and look at an energy balance sheet for respiration. Then we’ll look at cellular free energy capture from alternate nutrients. Finally, we look at photosynthesis, and then compare ATP production in what are essentially, opposite pathways.
When you have mastered the information in this chapter, you should be able to:
- explain the centrality of the Krebs Cycle to aerobic metabolism.
- identify sources of electrons in redox reactions leading to and within the Krebs cycle.
- illustrate the path of electrons from the Krebs cycle to and through the electron transport chain.
- trace the evolution of the electron transport chain from its location on an aerobic bacterial membrane to its location in eukaryotic cells.
- list the expected properties of a proton gate and a proton pump.
- interpret experiments involving redox reactions, ATP synthesis and ATP hydrolysis conducted with intact mitochondria and separated mitochondrial membranes.
- distinguish between the pH, \(\rm H^{+}\) and electrical gradients established by electron transport.
- explain the chemiosmotic mechanism of ATP synthesis and contrast it with substrate- level phosphorylation.
- compare and contrast the role of electron transport in respiration and photosynthesis and discuss the evolution of each.
- trace and explain the different paths that electrons can take in photosynthesis.
- explain the presence of similar (or even identical) biochemical intermediates in respiration and photosynthesis.