Energy and Enzymes

Metabolism

• The sum of all chemical reactions occurring in a biological system at a given time

• Metabolic reactions involve energy changes

  • energy is constantly being used to build up molecules while also being releases as molecules are broken down

  • Therefore, metabolism encompasses the simultaneous occurrences of anabolic and catabolic reactions (go hand in hand)

Free Energy

• Available energy to do work

• delta G = G_final - G_initial

Anabolic Reactions

• Building up of complex molecules from simple molecules

  • requires an input of energy

  • E.g., condensation reactions

  • “think like attached”

Catabolic Reactions

• Breaking down of complex molecules into simple molecules

  • releases energy

  • E.g., hydrolysis reactions

  • “think like catastrophe”

Endergonic Reactions

• Consume free energy

• delta G is POSITIVE

• Example: anabolic reactions (condensation)

• Often reverse reactions

  • products → reactants

  • Require a lot more energy to occur than exergonic reactions

• Must be coupled with an exergonic reaction to occur since activation energy is so high

Exergonic Reactions

• Release free energy

• delta G is NEGATIVE

• Example: catabolic reactions (hydrolysis)

• Often forward reactions

  • reactants → products

Activation Energy

• The energy barrier that needs to be overcome for a reaction to start

  • The amount of free energy needed

• Some or all chemical bonds must be broken as reactants so that new bonds in the products can form

  • In this process, molecules are in a higher energy state called the transition state (more unstable)

Enzyme + Active Site

• Biological catalysts that help lower the activation energy for chemical reactions

  • Primarily proteins

    • end in “-ase”

• Help stabilize the structure of the transition state (since not as much energy would be needed)

• Increase the rate of chemical reactions

• Are not consumed, can be reused over and over again in a reaction

• Enzyme site where substrates can bind to

  • The shape of such sites determine the functionality of the enzymes

• Many enzymes directly participate in the catalytic process

  • Refers to active interaction between substrates and active sites

Reaction Coupling

• When an endergonic reaction needs to be combined with an exergonic reaction in order for the endergonic reaction to take place

• Common example: ATP Hydrolysis + endergonic reactions

ATP Hydrolysis

• ATP (Adenosine Triphosphate)

• ATP is broken down into ADP and Pi

  • which releases a lot of energy that endergonic reaction that it is coupled with can use

    • b/c it takes a lot of energy to hold together the three phosphate groups in ATP that are all negatively charged and want to repel each other

• ATP can be regenerated in cells by other exergonic reactions that are taking place

• Activated carrier: Captures free energy and transfers it