Bio 178 Lecture 13 Energy and Metabolism

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Presentation transcript:

Bio 178 Lecture 13 Energy and Metabolism

Reading Chapter 8 Quiz Material Questions on P 158 Chapter 8 Quiz on Text Website (

Outline Energy and Metabolism ð Free Energy ð ATP ð Enzymes

Endergonic and Exergonic Reactions

Activation Energy (A E ) The energy required to start a reaction. Why do spontaneous reactions require A E ? Existing bonds must be broken. Catalysis Process of influencing chemical bonds in a way that lowers the A E of a reaction, eg. Stressing bonds.  Speed up reactions Importance of A E Prevents macromolecules from breaking down spontaneously.

Activation Energy

Adenosine Triphosphate (ATP)

Used to power the majority of energy-requiring processes in cells. Energy storage Electrostatic repulsion of phosphates  Unstable (low A E to break the bonds). ATP  ADP + P i + Energy (7.3 kcal/mole). Mechanism ATP hydrolysis occurs simultaneously with endergonic reactions. If there is a net release of energy the reaction is exergonic and will proceed.

ATP (Cntd.) Why is ATP not used as a long-term energy storage molecule? Too unstable - cells continually produce ATP for immediate use.

Enzymes What are enzymes? Biological catalysts made of protein. Enzyme Catalysis Weaken bonds (apply stress) Bring substrates close together  Lower activation energy of a reaction

How do Enzymes Work? Active Site Precisely and specifically fits the substrate - aa enzyme side groups interact with substrate  usually stressing bonds. Induced Fit Enzyme adjusts its shape to fit the substrate. Catalytic Cycle Enzymes are not used up in the reaction.

Catalytic Cycle of an Enzyme

Multienzyme Complexes Description A sequence of reactions may be controlled by a sequence of enzymes. These may be bonded together noncovalently. Advantages Close proximity allows the product of one reaction to be passed to the next in rapid sequence. Central control of entire sequence of reactions. Example - Pyruvate dehydrogenase 60 protein subunits (multiple copies of 3 enzymes).

Pyruvate Dehydrogenase

Non-Protein Biological Catalysts Ribozymes Catalysts made of RNA. Types of Ribozymes Intramolecular Catalyze reactions on themselves Intermolecular Catalyze reactions on other molecules Which came first - Protein or RNA?

Environmental Effects on Enzyme Catalysis Affected by anything that alters its 3D shape: pH, [salt], temperature, regulatory molecules Temperature Optimum Temperature Temperature at which reaction rate is greatest. Below Optimum Increasing temp increases substrate-enzyme collisions & can stress bonds. Bonds not flexible to permit induced fit  not optimum. Above Optimum Denaturation.

Effect of Temperature on Enzyme Catalysis

Environmental Effects on Enzyme Catalysis pH Optimum pH pH at which reaction rate is greatest. Above/Below Optimum Change in [H + ] affects charge balance between charged amino acids, which affects intramolecular bonding.

Effect of pH on Enzyme Catalysis

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