Lect15_respiration

Lect15_respiration - Respiration extracting more energy...

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1 Day 15 Respiration – extracting more energy from electrons Gradients: Another way to store energy • Order is a consequence of energy input – Without constant energy flow, disorder is favored • Creating order across a membrane – more stuff on one side than on the other – is another way a cell can store energy. • Chemical bond energy (e.g., ATP) can be transformed into a concentration gradient (and vice versa) Purves et al. 5th edition. Life: the Science of Biology Membranes as dams • A pump (a protein powered by ATP) transports something – say H+ – across the membrane – The H+ cannot flow back in (the membrane is impermeable to it) – This is analogous to water behind a dam – gravity causes it to ‘want’ to flow downhill – Like the water, H+ ‘wants’ to flow down its concentration (and charge!) gradient • When flow is allowed, it releases energy and the energy can be used to do work (like a hydroelectric plant) Electro-chemical gradients • When an ion (such as H+) is pumped across a membrane, TWO gradients form – A concentration gradient – there is a pH difference across the membrane – A charge gradient – there are fewer positive charges inside than outside the cell • A proton gradient is a strong source of potential energy – ‘proton-motive force’
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2 Gradients can be used to perform work • Gradients across membranes are used to – Transport materials up a concentration gradient – Run bacterial flagella – Make ATP (more about this later) H+ H+ H+ H+ Sucrose ATP H+ H+ H+ H+ H+ H+ Summary so far • Redox reactions release energy • Some of the energy can be captured onto ATP and NADH and used to do work • Energy can also be stored in gradients (electrochemical ones, particularly) Summary so far • Leftover NADH must be recycled to NAD+ – A cell can do this by dumping electrons onto leftover parts of fuel molecules (e.g., pyruvate) (fermentation) – OR, by using an external electron acceptor = RESPIRATION
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3 Respiration How to get “better mileage” from fuel by putting the excess electrons to work One of the most fundamental innovations of life (and an ancient one – the first forms of life likely used gradients like those described here) (We’re talking ANAEROBIC respiration right now -- doesn’t require breathing or oxygen) Why don’t cells just take the reducing power from NADH and convert it into hydrogen gas and spit that out? (2e - + 2H + --> H 2 ) a. Because this reaction can’t happen b. This does happen but its an unfavorable reaction because hydrogen is a better donor (reaction goes to the left) c. For unknown reasons, life never happened to develop this capacity d. It could work if there’s someone there to remove the hydrogen e. Both b and d Respiration • Involves using an outside electron acceptor (to which NADH donates its electrons) • Allows further oxidation of the fuel – Meaning, for instance, that more energy can be obtained from pyruvate • Involves the development of two significant innovations – The Electron Transport Chain –A T P
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This note was uploaded on 03/08/2011 for the course BIS 2A taught by Professor Grossberg during the Fall '08 term at UC Davis.

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Lect15_respiration - Respiration extracting more energy...

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