Energy and Metabolism Chapter 6
Flow of Energy • Energy: the capacity to do work -kinetic energy: the energy of motion -potential energy: stored energy • Energy can take many forms: chemical, mechanical, electric current, heat, light
Flow of Energy • Most forms of energy can be converted to heat energy. • Heat energy is measured in kilocalories. • One calorie = the amount of heat required to raise the temp of water by 1oC 1 kilocalorie (kcal) = 1000 calories (Cal.)
Laws of Thermodynamics First Law of Thermodynamics – energy cannot be created or destroyed -energy can only be converted from one form to another For example: sunlight energy chemical energy photosynthesis
Laws of Thermodynamics • Second Law of Thermodynamics: disorder is more likely than order entropy: disorder in the universe • The 2nd Law of Thermodynamics states that entropy is always increasing. • Energy is required to keep order, to do work • keep cells together and organized • perform life processes
Laws of Thermodynamics • Enthalpy: All of the energy contained in a molecule’s chemical bonds • Free energy: the energy available to do work, to reduce disorder (enthalpy) • denoted by the symbol G (Gibb’s free energy) • free energy = enthalpy – (entropy x temp.) G = H - TS
Laws of Thermodynamics • Chemical reactions can create changes in free energy: ΔG = ΔH - T ΔS • When products of chemical reactions contain more free energy than reactants – ΔG is positive. • When reactants contain more free energy than products – ΔG is negative.
Laws of Thermodynamics • Chemical reactions can be described by the transfer of energy that occurs: • endergonic reaction: a reaction requiring an input of energy • ΔG is positive • exergonic reaction: a reaction that releases free energy • ΔG is negative
Laws of Thermodynamics • Most reactions require some energy to get started - activation energy. • activation energy: extra energy needed to get a reaction started -destabilizes existing chemical bonds -required even for exergonic reactions • catalysts: substances that lower the activation energy of a reaction (enzymes)
Flow of Energy • Potential energy stored in chemical bonds can be transferred from one molecule to another by way of electrons. oxidation: loss of electrons reduction: gain of electrons • Redox reactions are coupled to each other.
Oxidation-Reduction Reactions • A chemical reaction that transfers electrons from one atom to another • Oxidation = loss of an electron • Reduction = gain of an electron
Oxidation-Reduction Reactions • Oxidation • A chemical reaction in which a molecule gives up electrons • Oxidation releases energy • The molecule loosing the electron is oxidized 79
Oxidation-Reduction Reactions • Reduction • A chemical reaction in which a molecule gains electrons and energy • The molecule that accepts electrons is reduced • The molecule being reduced receives energy 80
Oxidation-Reduction Reactions • LEO the lion says GER • If it Looses Electrons during the reaction, it’s Oxidized • If it Gains Electrons during the reaction, it’s Reduced
Redox Reactions • Oxidation and Reduction reactions always occur in pairs • If an atom or molecule is reduced, another atom or molecule must have been oxidized • If an atom or molecule is oxidized, another atom or molecule must have been reduced • For this reason Oxidation and Reduction Reactions are known as Redox Reactions
ATP - Energy Currency of Cells • ATP is the molecule that cells use to store, transfer, and provide energy • The energy from ATP is used to fuel anabolic reactions • recall: for growth, repair, and reproduction • ATP = Adenosine TriphosPhate • Adenosine (same molecule from DNA and RNA) + • Three inorganic phosphates (functional group PO4) 21
ATP - Energy Currency of Cells • ATP= adenosine triphosphate • the energy “currency” of cells • ATP structure: • ribose, a 5-carbon sugar • adenine • three phosphates
ATP - Energy Currency of Cells • ATP - 1 PO4 = ADP (Adenosine Diphosphate) • ADP - 1 PO4 = AMP (Adenosine Monophosphate) • ADP + 1 PO4 = ATP 25
ATP • ATP is a molecule that is used as an Energy Currency in cells • ATP’s can be broken down to provide energy for endergonic reactions • Cells use energy to build ATP’s • Enzymes of allow cells to efficiently build ATP’s - Cells can make ATP’s for less energy than ATP’s can provide
ATP - Energy Currency of Cells • ATP stores energy in the covalent bonds between phosphates: • Phosphates are highly negative, therefore: • the phosphates repel each other • much energy is required to keep the phosphates bound to each other • Energy is released when the bond between two phosphates is broken
Energy Currency of Cells • When the bond between phosphates is broken: ATP ADP + Pi energy is released • ADP = adenosine diphosphate • Pi = inorganic phosphate • This reaction is reversible...
Text art 5_06 ATP/ADP Cycling
Energy Currency of Cells • When the bond between phosphates is formed: ADP + Pi ATP energy is consumed • ATP - ADP Cycle
Text art 5_07 ATP/ADP Cycling
Energy Currency of Cells • It costs energy to build ATPs ADP + 1PATP (Adenosine Diphosphate +1 phosphate)
ATP/ADP Cycling ATP ADP
Energy Currency of Cells • The energy released when ATP is broken down to ADP can be used to fuel endergonic reactions. • The energy released from an exergonic reaction can be used to fuel the production of ATP from ADP + Pi.
Other Functions of ATP • ATP regulates enzyme activity • Phosphorylation and dephosphorylation - process of adding or removing phosphate groups - can activate or deactivate enzymes • ATP serves as a source of phosphate groups 38
Enzymes • Enzymes: molecules that catalyze - speed up - biochemical reactions in living cells • Three rules to be considered an enzyme • Most are proteins (some RNA enzymes) • Lower the energy of activationrequired for a reaction to occur • Are not changed or consumed by the reaction • Cofactors, Coenzymes 40
Metabolism • Enzymes catalyze cellular chemical reactions • Metabolism - the chemical reactions in a cell: • Two categories of cellular chemical reactions: • Anabolic Reactions • Build larger molecules for growth, repair, reproduction • Dehydration Synthesis Reactions • require energy and nutrients • Catabolic Reactions • Breakdown larger molecules • Hydrolysis Reactions • mobilize nutrients for energy making it available to the cell 41
Metabolism • Metabolism is the sum total of all anabolic and catabolic reactions that occur in the cell • The metabolism of cells is carried out and controlled by the enzymes • There are catabolic enzymes – those that cleave larger molecules into smaller ones • Ex. Hydrolysis Reactions • There are also anabolic enzymes – those that assemble smaller molecules into larger ones • Ex. Dehydration Reactions 42
Enzymes • Enzymes interact with substrates. • substrate: molecule that will undergo a reaction • active site:region of the enzyme that binds to the substrate • Binding of an enzyme to a substrate causes the enzyme to change shape, producing a better induced fit between the molecules.
Enzymes Enzymes interact with substrates • Substrates: molecules that will undergo a reaction when bound to the enzyme • lactose, hydrogen peroxide (H2O2) • On the Enzymes: • Active site: region of the enzyme that binds to the substrate • Allosteric site: region of the enzyme that binds substances other that the substrate 44
Enzymes • Enzymes are very specific: • Enzymes will only interact with a specific substrates • The substrate fits into the active site like a key fits into a lock (Lock and Key Hypothesis) • Substrate binding causes the enzyme to change shape, producing a better induced fit between the molecules (Induced Fit Hypothesis) • Changing the shape of an enzyme affects its ability to function 46
Enzymes • Enzyme/Substrate Complex: E + S ES EP E + P • The Enzyme and the Substrate come together (E+S) • The Enzyme/Substrate Complex is formed (ES) • The Enzyme’s Substrate is changed to the Enzyme’s • Product in the active site of the enzyme (EP) • The Enzyme and Product Separate (E+P) • The Enzyme is free to bind to another Substrate 48