5: Metabolism I – Catabolic Reactions
- Page ID
- 16120
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Life requires energy. As our discussion of biomolecules pointed out, the major functional components of the cell are mostly polymers - long chains of smaller individual molecular units. Each addition of a small link to the chain costs energy. Chemical reactions that build up complex molecules from simple ones are known as anabolic reactions. Conversely, heterotrophic organisms such as animals ingest food made up of these large polymers, which, when broken down in the digestive process, release energy for maintaining and building that organism. Such chemical reactions, in which complex molecules are broken down to simpler components, are classified as catabolic reactions. Taken as a group of reactions within a cell or even an organism, they can be referred to as the cell’s or organism’s anabolism or catabolism. The sum total of both types of reactions is the cell’s metabolism.
- 5.1: Glycolysis
- This page details the role of enzymes in metabolic reactions, particularly glycolysis, which is vital for ATP production in both prokaryotic and eukaryotic cells. It outlines the process where glucose is converted into energy, emphasizing the energy investment and subsequent yield of ATP and NADH. The page compares glycolysis to aerobic respiration, noting its lower ATP yield and the importance of pyruvate and NADH fate under varying oxygen conditions.
- 5.2: Fermentation
- This page discusses fermentation as a metabolic process that regenerates NAD+ from NADH to sustain glycolysis without oxygen. It outlines two main types: lactate fermentation, which converts pyruvate to lactate, and alcohol fermentation, which transforms pyruvate into ethanol. Both methods play a crucial role in enabling ATP production during anaerobic conditions, with lactate being either excreted or reused in the liver.
- 5.3: 5.3 The TCA Cycle
- This page covers the conversion of pyruvate to acetyl-CoA by the pyruvate dehydrogenase complex, essential for ATP production in cellular respiration. It details the transport into the mitochondrial matrix, the enzyme's structure, and the influence of vitamins and toxins on metabolism. The TCA cycle is then explored, detailing key steps such as the transformation of α-ketoglutarate to succinyl-CoA, the generation of NADH, and the roles of specific enzymes.
- 5.4: Oxidative Phosphorylation
- This page discusses oxidative phosphorylation, the conversion of ADP to ATP using energy from the electron transport chain, primarily from NADH oxidation. It highlights the role of four major complexes in the inner mitochondrial membrane and the importance of oxygen for electron transport. Additionally, it details ATP synthase's function, where protons moving down their gradient induce rotational movement, leading to ATP production through conformational changes.
- 5.5: Uncoupling Electron Transport from ATP Synthesis
- This page explains oxidative phosphorylation's role in ATP synthesis through a proton gradient, influenced by ATP levels. It contrasts typical ATP synthesis with brown adipose tissue, which can uncouple electron transport to produce heat via thermogenin and norepinephrine regulation. Additionally, it discusses 2,4-dinitrophenol (DNP) as an uncoupler that raises body temperature and respiration rates but carries significant health risks.
- 5.6: Structure of Electron Carriers
- This page outlines the essential components of the electron transport chain, detailing the structures and functions of flavin mononucleotide (FMN), ubiquinone, heme groups, and iron-sulfur clusters. It explains how FMN and ubiquinone facilitate electron transfer through their multiple oxidation states, the role of heme groups in reducing O2 to water, and the function of iron-sulfur clusters as electron carriers. Collectively, these elements are crucial for cellular respiration.
- 5.7: 5.7 Starch and Glycogen Depolymerization
- This page explains the catabolism of starch and glycogen, essential glucose polymers for energy. Starch digestion starts in the mouth with salivary a-amylase, progressing in the small intestine to produce maltose and dextrins. Glycogen is broken down in cells by glycogen phosphorylase to yield glucose-1-phosphate for glycolysis, aided by enzymes like the debranching enzyme.
- 5.8: 5.8 Fatty Acid Breakdown
- This page discusses the role of hormone-sensitive lipase in breaking down stored fats in adipose tissue into glycerol and fatty acids, which then enter the bloodstream. It details the process of β-oxidation in mitochondria, the importance of carnitine, and the consequences of its deficiency. The page also explains how β-oxidation generates acetyl-CoA for the TCA cycle and addresses the formation of ketone bodies during starvation, highlighting the risk of ketoacidosis from rapid production.
- 5.9: Amino Acid Degradation
- This page discusses the degradation of proteins by various proteases, which hydrolyze peptide bonds to produce smaller peptides and amino acids for new proteins or metabolism. Six classes of proteases are identified based on active site structure and specificity, serving extracellular functions like digestion and immune responses, as well as intracellular roles in metabolism.
Thumbnail: Biochemical processes that break things down from larger to smaller are called catabolic processes. Catabolic processes are often oxidative in nature and energy releasing. Some, but not all of that energy is captured as ATP. (CC BY-SA-NC; Kevin Ahern & Indira Rajagopal).