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What does a cell need? Building blocks biological molecules, ions, metals, water, etc. Catalysts (enzymes) reactions h

What does a cell need? Building blocks biological molecules, ions, metals, water, etc. Catalysts (enzymes) reactions happen rapidly enough to sustain life Information nucleic acids Energy. What do we need energy for? synthesis mechanical work active transport

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What does a cell need? Building blocks biological molecules, ions, metals, water, etc. Catalysts (enzymes) reactions h

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  1. What does a cell need? Building blocks biological molecules, ions, metals, water, etc. Catalysts (enzymes) reactions happen rapidly enough to sustain life Information nucleic acids Energy

  2. What do we need energy for? synthesis mechanical work active transport concentration gradient electrochemical gradient heat (homeotherms) bioluminescence fireflies, luminous fungi, deep-sea creatures…

  3. Most organisms obtain energy directly from the sun (autotrophs, spec. phototrophs) or from organic molecules (heterotrophs) aerobic or anerobic Not all plant cells are autotrophic; what part(s) of the plant would not be autotrophic?

  4. Thus autotrophs and heterotrophs obtain energy from environment but get it in different ways. Decreased entropy; higher free energy Organic compounds; O2 heat heat heterotrophs autotrophs CO2, NO3-, H2O Increased entropy; lower free energy

  5. Energy flows through biosphere; so does matter Carbon cycles Water Nitrogen Phosphate Etc.

  6. What is energy and how is it used for work? Why do some reactions occur spontaneously? Why are some reactions NOT spontaneous but can occur anyway?

  7. Forms of energy Kinetic- energy of movement (light and heat) Potential energy- stored (e.g., on chemical bonds) Energy is converted from one form to another (first law of thermodynamics). Amount of energy in the system stays the same. Energy tends to move from more-ordered to less-ordered forms.

  8. What is the meaning of the second law? In every physical or chemical change, the universe always tends toward greater disorder Open system: order can increase in one area, but decreases in another Can be termed the law of thermodynamic spontaneity; spontaneous reactions increase disorder and tend toward stability

  9. Measured by changes in free energy and entropy Free energy: amount of energy “available” to do work, if temperature is uniform (as in a cell) Total energy in a system is termed enthalpy or heat content. Termed H H=E + PV H changes if a biological reaction occurs (H) reactantsproducts

  10. H= Hproducts- H reactants If reaction gives off heat H is negative reaction is exothermic If reaction takes up heat H is positive reaction is endothermic

  11. Free energy (G) is a portion of H, adjusted for entropy and the temperature of the system G=H-TS T tends to stay constant in a biological systm (temperature) S (entropy) changes; increases or decreases G= H-TS

  12. Spontaneous reactions result in an increase in entropy and a decrease in free energy of the system. These reactions are exergonic. Consider: C6H12O66CO2 + 6H2O + energy G = H- TS = -673 kcal/mol-13 kcal/mol = -686 kcal/mol (G is way less than zero!)

  13. Building sugar from carbon dioxide and water requires an input of 686 kcal/mol. (Energy is stored in those chemical bonds.) Where does this energy come from? “Energy coupling”: energy produced by an exergonic reaction is used to drive an endergonic reaction Most common reaction is the hydrolysis of ATP.

  14. Bonds between phosphate groups are unstable Under “standard conditions” (not physiological) ATP + H2O  ADP + Pi G = -7.3 kcal/mol ADP is much more stable Why does this reaction perform work?

  15. ATP can be continuously regenerated. In fact, our muscles have a unique compound (creatine phosphate) that facilitates this Phosphorylation of ADP is endergonic.

  16. G can be measured for a specific reaction under specific conditions: Temperature Concentrations of reactants and products. Calculations can yield conditions under which reaction is at equilibrium (Keq) Often these are fairly constant in the cell.

  17. Reactions tend to move toward equilibrium. G indicates how far and in what direction from equilibrium a reaction lies under the conditions. If a reaction is at equilibrium G equals zero. No further reactions are possible. In a cell, this means death. So how can cellular reactions be maintained out of equilibrium?

  18. Living cells maintain themselves in steady state. Levels of reactants and products are far from equilibrium, so they can happen continuously. How? Cells continuously acquire energy (open system). Cells use that energy to perform work. How do reactions occur at a rate that sustains life???

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