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Energy and Life Processes (or a whiz bang condensed version of Chs. 5 & 6!). Spring 2012. The organization of living systems has a continuous energy “ cost ” Living processes obey the laws of chemistry and physics. Energy flows while matter cycles.
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Energy and Life Processes(or a whiz bang condensed version of Chs. 5 & 6!) Spring 2012
The organization of living systems has a continuous energy “cost” Living processes obey the laws of chemistry and physics. Energy flows while matter cycles. “Metabolism,” the sum of all of the biochemical events occurring inside cells, can be divided into catabolic and anabolic events. All of these involve the simultaneous conversion of one chemical compound into another, which necessarily involves energy changes as well (energy flow and matter cycling are interdependent). Attempts to define “Life” must include an understanding of the essentials of energy processing.
Catabolism and anabolism involve energy changes, and are linked by energy considerations. Catabolic“breakdown reactions” convert complex chemicals to less complex forms and convert chemical bond energy in ways that makes some high quality energy available for general use (in the form of ATP). Anabolic“synthesis” or build-up” reactions create more complex forms from simpler ones which requires an external input of high quality energy, (usually in the form of ATP).
The laws of thermodynamicsdescribe what we know (from observation) about the ways energy behaves in nature. Energy can’t be created or destroyed, it can only change form = the First law. When energy in a system changes form, the change always results in less “high quality” energy being available after the change than existed previously = the Second Law. ( or systems tend to maximum disorganization over time, i.e “poop flows down hill”)
The chemical bonds in the food we eat contain energy, just like the chemical bonds in the hydrocarbons of gasoline. When living cells harvest this energy some is saved in the form of ATP, but, in accordance with the laws of thermodynamics, most is wasted in the form of heat.
For energy to be useful in cells it most often has to be converted to ATP
ATP hydrolysis powers almost everything that goes on in cells
ATP is the energy intermediate of cells; its cyclic production and use link catabolism and anabolism.
Enzymes are biological catalysts that allow the chemical reactions of life to occur much faster than they could otherwise (with a much lower energy input). They are mostly catalytic proteins. Very specific (have specific substrates) Not consumed Activity can be modulated (controlled) They don’t alter the nature of the energy change that a given reaction entails, they merely make “possible” reactions go faster.
Chemical reactions from reactant(s) to product(s) always involve an energy change. A -> B A -> B + C A + B -> C A + B -> C + D
Some reactions are “spontaneous” - they go with the flow, while other reactions are not. A spontaneous reaction involves an energy change that is in keeping with the second law of thermodynamics which means that as the reaction proceeds energy is released and the system contains less high quality energy after the reaction than before. A nonspontaneous reaction works has the opposite properties and so requires a high quality energy input. Both are possible in cells, and both can be catalyzed by enzymes.
The energy “profile” of spontaneous and non-spontaneous reactions
Are “spontaneous” reactions really spontaneous (the role of enzymatic catalysis)?
The “ball -in-glove” fit of a substrate into the enzyme’s active site allows the reaction to proceed with less activation energy required, and so it goes faster
Enzymes are arranged into metabolic pathways where the product of one becomes the substrate for the next. ABCDE F Enz.4 Because products are removed as fast as they are made, the materials in pathway “flow” in the forward direction. Equilibrium, where the changes (and the accompanying energy changes)effectively come to a standstill = cellular death. Pathways can be linear as shown (see glycolysis which follows) or cyclic, where F, with addition of another input, resynthesizes A and the the pathway cycles (see the citric acid cycle which follows). Enz.3 Enz.1 Enz.2 Enz.5
An overview of plasma membrane structure and function Membrane proteins do all the “work” of controlling transport, signal reception, etc.
Ion and small molecule movement across bio-membranes requires specific transport proteins which either make or useconcentration gradients.
Passive transport is powered by diffusion which in turn is “powered” by thermodynamic considerations: a mixed solution is less organized and therefore exists at a lower energy state
Lets look at small molecule transport in more detail:To say that “passive” transport requires no energy is a bit of a lie. Actually, all transport requires energy, just in different forms More solute = a gradient Less solute
Active transport is accomplished by protein “pumps” that consume ATP to create a concentration gradient of some solute across a membrane. Like passive mechanisms, active transport is highly specific.
Energy flow in cells depends on using external energy =SUNLIGHTor the chemical bonds in food molecules, to make a concentration gradient across a membrane within chloroplasts or mitochondria, then using this gradient to generate ATP.
In terms of the overall energy flow in aerobic respiration, and the part of photosynthesis that generates ATP (the “light reaction”) you have basically the same sequence of events: High energy electrons hydrogen ions to be pumped across a membrane to produce an H+ gradient. The H+ gradient allows ATP synthetase enzyme to join ADP + P to ATP ATP synthesis in respiration and photosynthesis The difference is the source of the electrons (sugar vs. light acting on water through a photosystem) and the location of the membrane (mitochondrion inner membrane vs. chloroplast thylakoid membrane).
The Electron Transport Chain and the “Chemi-osmotic” production of ATP. FAD “compact” pickups unload H+ and e- atthe second protein complex (not shown), as a result each NADH delivery results in the production of 3ATPs while each FADH results in the production of 2ATPs. A similar “chain” makes ATP in the Light Reaction of Photosynthesis.
NAD and FAD (not shown) are “pickup trucks” that carry H and electrons to the electron transport chain. NAD is “heavy duty” and carries high energy electrons, while FAD is a “compact” and carries only lower energy electrons. FAD, a “compact pickup NAD, a “full-size pickup”
An aerobic respiration overview ( * the transistion rxn, between glycolysis and the citric acid cycle is not shown) *
e- e- e- Glucose 2 2 2 Acetyl CoA 2
Four ATPs are “recovered” by substrate-level phosphorylation for a net gain of +2 ATPs.
Substrate-level phosphorylation is carried out by an enzyme and doesn’t involve electron transport or an H+ gradient.
e- e- e- Glucose 2 2 2 Acetyl CoA 2
The Transition or Preparatory rxn. next converts pyruvate to acetyl Co A.
The Electron Transport Chain and the “Chemi-osmotic” production of ATP. FAD “compact” pickups unload H+ and e- atthe second protein complex (not shown), as a result each NADH delivery results in the production of 3ATPs while each FADH results in the production of 2ATPs.
Other compounds in food can also be processed to yield ATP, and respiration intermediates can be taken out (reverse the arrows) to provide intermediates for the synthesis of cellular components .
OK so all of this requires Oxygen to “haul the trash” or it shuts down. What happens when O2 is in short supply or just not available?
Muscle activity demands ATP consumption at accelerated rates which demands faster O2 supply and CO2 clearing from the cardiovascular system
Like muscles forced to work beyond their oxygen supply, yeast growing without adequate oxygen are forced to use an organic compound in place of O2 as a terminal e- acceptor (to unload and recycle NAD); this is defined as fermentation.
