Energy and Metabolism Chapter 8

Energy

Metabolism All the chemical reactions carried out by the cell

Metabolism Catabolic reactions: Break down large molecules into smaller substances Exergonic: Releases energy

Metabolism Anabolic reactions: Synthesis of large molecules from smaller substances Endergonic: Requires energy

Metabolism Biochemical pathways: Reactions in a cell Occur in sequence Product of one reaction Becomes substrate in the next Pathways are highly regulated & coordinated Feedback inhibition: End product of a reaction blocks the pathway from producing more.

Energy

Bioenergetics: Analysis of how energy powers activities of living systems Growth, order, reproduction, responsiveness & regulation

Energy Energy: The capacity to cause change The capacity to do work Kinetic energy: Energy of motion Potential energy: Energy of position or stored energy

Energy Thermodynamics: Study of energy “heat changes” Most work done by living organisms Transformation of PE to KE

Energy Sun main source of energy Combines smaller molecules Make larger molecules Energy is stored in the chemical bond

Energy Heat Energy: Random motion of molecules Heat can be lost in the system during conversions Sun replaces energy lost as heat

Energy Redox(oxidation-reduction) reactions: Transfer of an electron or electrons Important in the flow of energy in biological systems An electron is passed from one atom to another energy is passed

Law of thermodynamics Laws of thermodynamics govern all energy changes in the universe. First law of thermodynamics: Energy cannot be created or destroyed Change from one form to another. (potential to kinetic) Total amount of energy stays the same

First law In living organisms: Eating transfers energy from the bonds in food to organism PE is transferred to KE

Second law Second law of thermodynamics: Transformation of PE to heat (random motion of molecules). Entropy (disorder) in the universe is increasing

Second law Energy transformations tend to proceed spontaneously Convert matter from a more ordered state to a less ordered More stable state.

Figure 8.3 (a)(b) First law of thermo- dynamics Second law of thermodynamics Chemical energy Heat CO 2 H2OH2O

Second law Entropy(s): Disorder in a system Enthalpy (H): Heat content Free energy(G): Amount of energy available to do work in any system. Amount of energy available to break and then make other chemical bonds

Second law G=Gibbs free energy  G =  H - T  S (T=Kelvin temp)  G is positive Products have more energy than reactants More energy in the bonds or less randomness Endergonic reaction

Second law  G is negative Products have less energy than reactants H is lower (bond energy) or S is greater- more randomness Exergonic: Reaction that releases energy

Exergonic reaction

Exergonic reactions

Activation Energy Energy needed to initiate a reaction All reactions require activation energy. Reactions with higher AE tend to move forward more slowly

Enzymes Catalyst in living organisms Large three-dimensional globular protein Ribozymes: RNA catalysts are specific & speed up reactions

Enzymes Substrate: Molecule that is going to undergo the reaction Active sites: Specific spots on the enzyme that substrates binds Enzyme-substrate complex: Enzymes bind to substrates with a precise fit. Induced fit: Substrate causes the enzyme to adjust to make a better fit E+S ES E + P

Fig Substrates Enzyme Products are released. Products Substrates are converted to products. Active site can lower E A and speed up a reaction. Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. Substrates enter active site; enzyme changes shape such that its active site enfolds the substrates (induced fit). Active site is available for two new substrate molecules. Enzyme-substrate complex

Enzymes Only small amounts are necessary Can be recycled Specific Speeds up the reactions Different types of cells have different enzymes Determines course of chemical reactions in the cell

Enzyme examples Lipase, protease Carbonic anhydrase –CO 2 + H 2 O H 2 CO 3 Lactate dehydrogenase –Lactate to pyruvate Pyruvate dehydrogenase –Enzyme that starts the Kreb cycle

Enzymes Factors that affect the rate of enzyme 1. Concentration of enzyme & substrate 2. Factors that affect 3-D shape of the enzyme Temperature, pH, salt concentration and regulatory molecules

Enzymes Inhibitor: Binds the enzyme Prevents it from working Occurs at end of a pathway to stop reactions Two types of inhibitors Competitive Noncompetitive

Fig (a) Normal binding (c) Noncompetitive inhibition (b) Competitive inhibition Noncompetitive inhibitor Active site Competitive inhibitor Substrate Enzyme

Enzymes Allosteric site: On/off switch for the enzyme Usually at different location than the active site Allosteric inhibitor: Binds at the allosteric site Stops the enzyme activity Activators: Binds & increases the activity

Active site available Isoleucine used up by cell Isoleucine binds to allosteric site. Active site no longer available; pathway is halted. Enzyme 1 (threonine deaminase) Feedback inhibition Intermediate A Intermediate B Intermediate C Intermediate D Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 End product (isoleucine) Threonine in active site

Enzymes Cofactor: Assists enzyme function such as Zn, Mg, Cu Coenzymes: Organic molecules that are not proteins Help transfer electrons & energy associated with the electrons Vitamins are coenzymes NAD + important coenzyme

Energy

ATP ATP powers the energy requiring processes in the cell 1. Chemical work (making polymers) 2. Transporting substances 3. Mechanical work Muscle movement, cilia

ATP ADP Losses a inorganic phosphate Hydrolysis 7.3kcal/mole of energy is released.

Figur e 8.9 (a) The structure of ATP (b) The hydrolysis of ATP Adenosine triphosphate (ATP) Ribose Adenine Triphosphate group (3 phosphate groups) Adenosine diphosphate (ADP) Energy Inorganic phosphate H2OH2O

Figure 8.11 Transport protein Solute Solute transported (a) Transport work: ATP phosphorylates transport proteins. Mechanical work: ATP binds noncovalently to motor proteins and then is hydrolyzed. Protein and vesicle movedMotor protein Cytoskeletal track ATP ADP P i P i P i P ATP (b) Vesicle

Figure 8.12 Energy from catabolism (exergonic, energy- releasing processes) Energy for cellular work (endergonic energy-consuming processes) ADPP i H2OH2O ATP