Learning Goals By the end of the lesson you will be able to 1. Understand what a redox reac;on is and how it
applies to cellular respira;on 2. Explain the main goal(s) of cellular respira;on 3. Describe the stages of cellular respira;on 4. Ar;culate how the body’s energy currency, ATP
is formed
Metabolism
• The sum total of all the anabolic and catabolic processes in a cell or organism
• Redox reac1ons underlie a number of these processes
• A redox rxn. is a chemical rxn that involves the xfr of e-‐‘s between two substances
• 2 elements to redox rxn.’s; reduc1on & oxida1on – Oxida1on: loss of one or more e-‐‘s – Reduc1on; gain of one or more e-‐‘s
• Substance that loses the e-‐‘s is oxidized and is thus the reducing agent
• Substance that gains the e-‐‘s is reduced and is thus the oxidizing agent
• Redox rxn.’s can also happen w/ par;al xfr of e-‐‘s (i.e. sharing in covalent bond, but e-‐‘s drawn closer to more electronega;ve atom like oxygen)
• Some;mes a series of redox rxn.’s occur that fn’s to transport e-‐‘s through a series of increasingly stronger e-‐ carriers
(Draw diagram)
• Free energy released in each step because e-‐ moving to progressively stronger e-‐ acceptor. Therefore an exergonic process.
• OVERALL, THE CONTROLLED COMBUSTION OF GLUCOSE IN CELLULAR RESPIRATION IS AN EXERGONIC REDOX RXN (similar to combus1on of methane)!!!
Cellular Respira1on (Big Picture)
• Process by which organisms break down glucose (C6H12O6) to produce energy (in the form of ATP) to sustain life
• Summary of aerobic respira;on (uses oxygen). The actual process is about 20 rxn.’s w/ enzymes catalyzing each step.
• Considered glucose oxida;on because i. H’s from glucose carry e-‐‘s to O, forming H2O. In
H2O, O has stronger pull on e-‐‘s than H, than C in glucose.
ii. Oxyen bound to carbon exerts strong electronega;ve pull on e-‐‘s, essen;ally cons;tu;ng as a loss of e-‐‘s for the carbon. Thus also.
• Overall rxn. decreases free energy because of loss of poten;al energy (i.e. more stable bond)
• Overall rxn. also increases entropy. This is a “downhill” process that yields 2870KJ of free E/mole of glucose.
• Exergonic rxn.’s normally release heat & light, but cells have a way of capturing some of this energy (~34%) by moving the posi;on of the e-‐‘s in certain molecules to higher free E states (i.e. ATP).
• These molecules now become ready sources of free E that cell can use.
• Even though cell. resp. is an exergonic process, it is not spontaneous. Why?
i. Ac;va;on energy prevents spontaneous
combus;on and allows living things to control oxida;on process.
ii. Use of enzymes also allows cell to control rxn.’s of cellular respira;on
Cellular Respira1on (Beginning Details)
• ULTIMATE GOAL; extract E from nutrient molecules, harness & store E in a form that the cell can use (i.e. like baferies)
• 3 main sub-‐goals of i. Break bonds between the 6 carbons of glucose to
form 6 CO2 molecules ii. To move hydrogen atom e-‐‘s from glucose to oxygen,
forming 6 H2O molecules iii. Trap as much of the free E released in the process as
possible in the form of ATP
• 4 stages in 3 loca;ons Name # of Steps Cellular Loca1on
Stage 1 Glycolysis 10 Steps Cytoplasm
Stage 2 Pyruvate Oxida;on 1 Step Mitochondrial Matrix
Stage 3 Kreb’s Cycle 8 Steps Mitochondrial Matrix
Stage 4 Electron Transport Chain & Chemiosmosis
Mul;-‐step Inner Mitochondrial Membrane
Adenosine Triphosphate (ATP)
• The energy currency of the body
• When cell needs energy for an endergonic reac;on, ATPase catalyzes hydrolysis of terminal phosphate in ATP
• Cleaved energe;c phosphate is afached to molecule associated with work to be done (i.e. phosphorylated), thus energizing and ac;va;ng the molecule
• 2 ways to create ATP, both of which involve transferring and capturing exergonic energy i. Substrate-‐level phosphoryla1on (Direct ATP
forma1on)
With the help of an enzyme a compound with a phosphate xfr’s that phosphate to ADP à ATP + dephosphorylated compound
• 2 ways to create ATP, both of which involve transferring and capturing exergonic energy ii. Oxida1ve phosphoryla1on (Indirect ATP forma1on)
-‐Crea;on of carrier molecules -‐involves a series of redox rxn’s w/ oxygen as the final e-‐ acceptor -‐yields more ATP molecules/glucose molecule -‐u;lized an enzyme and co-‐enzymes NAD+ & FAD
– NAD (nico;namide adenine dinucleo;de) removes 2H’s from original glucose, becoming NADH + H+ (NADH for short) • This rxn. occurs in once in glycolysis, once in pyruvate oxida;on and 3 ;mes in Kreb’s cycle
– FAD (flavin adenine dinucleo;de) does similar thing as NAD+ and is reduced to FADH2 • -‐occurs in one rxn of Kreb’s cycle
• 2 ways to create ATP, both of which involve transferring and capturing exergonic energy in the molecule ii. Oxida;ve phosphoryla;on (Indirect ATP forma;on)
• These reduced co-‐enzymes (NADH & FADH2) act as mobile E carriers w/n the cell, moving free E from one molecule to another.
• They will eventually xfr their free E to ATP using free oxygen. This happens in stage 4 of cellular respira;on (Electron Transport Chain & Chemiosmosis)
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