Lecture-9-Cellular-R_38381 - Cellular respiration: converts...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Cellular respiration: converts the potential energy stored in fuel molecules to a usable form (i.e., ATP’s) that can do cellular work. Photosynthesis (chloroplasts) Stored chemical energy (carbohydrates, fats, (organic molecules) proteins, nucleic acids) Aerobic (+ O2) Anaerobic (– O2) Broken down by the catabolic pathways of... Fermentation • Incomplete breakdown • Products: small organic molecules • Net energy trapped: 2 ATP Cellular Respiration • Complete breakdown • Products: H20, CO2 • Net energy trapped: 38 ATP Glucose most often used as a fuel source C6H12O6 + 6 O2 6 H2O + 6 CO2 + Energy ΔG = – 686 kcal/mol energy released by cells: • Catabolic pathways yield energy through redox reactions; such reactions relocate electrons & release energy stored in organic molecules use energy to make ATP’s – Redox reactions involve the transfer of electrons (e–) from one reactant to another: Oxidation: substance loses electrons Oxidizing agent (Y) is Reduction: substance gains electrons the electron acceptor Reducing agent is the electron donor • Redox reactions can also result in changing the degree of electron sharing in a covalent bond • Electron transfers in redox reactions require energy to pull an electron from an atom. – The energy required correlates to the electronegativity of an atom – Electrons lose potential energy when transferred from less, to more, electronegative atoms release of chemical energy (‐∆G; can do work) e– Transfer to another molecule • Redox reactions comprise cellular respiration: [Glucose] • Hydrogen‐rich organic molecules are “fuel” sources for metabolism: hydrogen bonds are sources of electrons with high potential energy; carbohydrates, fats, proteins. – Oxidize these to release chemical energy Harvest of Energy from Fuel Molecules Occurs in Steps • Energy from glucose can be released all at once via combustion: C6H12O6 O2 CO2 H2O Releases 686 kcal/mol of energy • Such a process cannot result in the efficient transfer of energy to do work rather catabolize glucose in series of enzyme catalyzed reactions, some of which remove electrons (as H atoms) transferred ultimately to oxygen (at the end). • Energy harnessed in electron transfers • Requires electron carriers to execute: NAD+ (coenzyme) • NAD+ (nicotinamide adenine dinucleotide); oxidized form – works with dehydrogenase enzymes: 2H [2e‐, 2 protons] Glucose [Reduced form] Portion of NAD molecule where chemistry occurs • Reduced electron carriers (NADH’s) formed during glucose catabolism go to the electron transport chain. • NADH’s give up their electrons to proteins of the electron transport chain, where the e–’s are transferred in steps & energy is released, forming ATP’s: • Oxygen serves as the terminal (last) electron acceptor in this chain; is reduced to H2O. • Electron transport chain proteins located in the inner mitochondrial membrane (cristae) Cellular respiration Stages of Cellular Respiration Glycolysis (outside mitochondrion) 1 Glucose 2ATP (6 carbons) Energy Investing Rxns: Requires energy to split glucose C6H12O6 2 ADP 2 x 3 carbon molecules 2 NAD+ 2 NADH 2 ATP 2 x C3H5O3P Substrate level phosphorylation 2 ATP Energy Harvesting Form ATP’s and NADH 2 ADP 2 ADP Glycolysis can occur in the absence of oxygen (anaerobic) 2 Pyruvates (3 carbon molecule) Summary [2 x C3H4O2] • Substrate level phosphorylation during cellular respiration yields ATP by a substrate acting as the donor of the phosphate to ADP. • Yields much less ATP than oxidative phosphorylation (electron transport chain) • In the presence of oxygen, pyruvate formed from glycolysis enters the mitochon‐ drion. Pyruvate is oxidized to acetyl‐CoA & loses CO2. • Attachment of Coenzyme A (CoA) 2 Acetyl‐CoA’s 2 Pyruvates makes molecule Forms 2 NADH more reactive. Citric acid cycle (in mitochondria) End Result: Oxidation of glucose is completed Energy capture → (NADH, FADH2, ATP) 1 turn of cycle = 1 acetyl‐CoA enters cycle; make 1 ATP, 3 NADH, 1 FADH2 per turn Per 1 glucose: 2 ATP, 6 NADH, 2 FADH2 FADH is an electron carrier similar to NAD+ Acetyl‐CoA CO2 also formed Oxidative Phosphorylation Yields the Bulk of ATP in Cellular Respiration • Glycolysis and the citric acid cycle directly yield a total of 4 ATPs per glucose molecule via substrate level phosphorylation. – Most of the energy extracted from glucose is contained in the reduced electron carriers, NADH (10) and FADH2 (2) • NADH & FADH2 transfer chain give up electrons to the electron – NADH, FADH2 are oxidized here – Electron transfers yield energy that are coupled to ATP formation, a type termed oxidative phosphorylation • Electron transfer chain molecules located in the inner mitochondrial membrane (cristae) • Electron transport chain components: multi‐protein complexes I, II, III, and IV; III & IV are cytochromes. non‐protein: Q (ubiquinone) • Electron carriers are alternately reduced & oxidized; energy released along the way. • NADH & FADH2 are oxidized at different entry points. • Electronegativity of components arranged from low to high (oxygen is highest) “downhill”; energy releasing; ‐∆G 2H+ + ½ O2 H2O Chemiosmosis • ATP synthase is multi‐protein complex found in multiple copies within the inner mitochondrial membrane. • ATP synthase is a proton (H+) pump which uses the energy of an existing proton gradient to power ATP synthesis. • This process is termed chemiosmosis • ATP synthase is a molecular motor that binds H+ ions causing it to spin. Turning activates catalytic sites producing ATP from ADP + P. • The H+ gradient that drives ATP synthase is the function of the electron transfer chain. [H+ gradient = pH gradient] H+ H+ H+ H+ H+ Electron Transport Chain Intermembrane space ATP Synthesis High [H+] Inner mitochon. membrane Matrix Lower [H+] • Complexes I, III, and IV of the electron transport chain couple energy release from electron transfer to the pumping of protons into the intermembrane space. A proton gradient is generated. • Protons can travel down their gradient through ATP synthase. Final Tally of ATPs • • • • Total = 36 – 38 ATPs 2.5‐3.3 ATP per NADH x 10; 1.5‐2.0 ATP per FADH2 x 2 Oxidative phosphorylation accounts for 90% of ATP formed Efficiency of respiration: 40% Location of Cell Respiration Processes in Mitochondria Glycolysis electron transport chain & ATP synthases citric acid cycle reactions • Fermentation enable cells to produce ATP in the absence of oxygen; they are incomplete oxidations. • Fermentation relies on glycolysis, plus reactions that regenerate NAD+: – NAD+ NADH transfer e–’s to pyruvate or similar molecule – ATP’s formed by glycolysis (substrate level phosphorylation) • Compared to cellular respiration, fermentation produces 19X less ATP (2 vs. 38); lacks oxidative phosphorylation. Alcohol fermentation Lactic acid fermentation Metabolism of Other Fuel Molecules • A variety of molecules beyond glucose are used as fuel sources: other sugars, proteins, lipids, etc. • These fuel molecules funnel into different points of the cellular respiration reactions. • Alternately, intermediates of cellular respiration are used for anabolic pathways (biosynthesis) Summary: Cell Respiration • Glucose + 6 O2 6 H2O + 6 CO2 + Energy – Redox reactions (What is oxidized/reduced above?) • Three stages: (glycolysis, citric acid cycle, electron transport chain) – Cytoplasmic & Mitochondrial locations of reactions – Release of free energy as reactions proceed are captured to produce ATP’s, NADH, & FADH2 • Chemiosmosis oxidation of NADH, FADH2 by electron transport chain create proton gradient – Protons diffuse thru ATP synthase (ADP + P ATP); oxidative phosphorylation (contrast with substrate level phosphorylation) • ATP totals of process; efficiency of glucose oxidation. • Fermentation: anaerobic, less efficient; are incomplete oxidations that rely on regenerating NAD+. • Proteins, lipids feed into cellular respiration reactions ...
View Full Document

Ask a homework question - tutors are online