Metabolic Reactions and Energy

• Some chemical reactions release energy

  • exergonic

  • breaking polymers

  • hydrolysis = catabolism

    • cellular respiration

• Some chemical reactions require input of energy

  • endergonic

  • building polymers

  • dehydration synthesis = anabolism

    • synthesis of proteins (dehydration synthesis)

Endergonic vs. Exergonic Reactions

• Exergonic

  • energy released

  • -delta G

• Endergonic

  • energy invested

  • +delta G

• Delta G

  • change in free energy and the ability to do work

2nd Law of Thermodynamics and Free Energy (Delta G)

• Entropy

  • measure of disorder

• Every energy transfer increases the entropy

• A living system’s free energy is energy that can do work when temperature and pressure are in uniform, as in living

• Delta G Formula

  • Delta G = Delta H - (T)Delta S

    • ΔH = change in enthalpy 

    • ΔS = change in entropy

    • T = absolute temp (K)

      • Kelvin = Celsius + 273

• -ΔG = loss of energy (exergonic) and is spontaneous 

• +ΔG = gain in energy (endergonic) and is nonspontaneous

• All cells move towards equilibrium ΔG decreases

Equilibrium and Metabolism

• Reactions in closed systems eventually reach equilibrium = no work

• Cells are open systems and are not in equilibrium

  • This is due to their constant flow of materials

• metabolism is never at equilibrium

• A catabolic pathway in a cell releases free energy in a series of reactions

Energy and life

• organisms require energy to live

  • where does that energy come from?

    • coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy)

Energy Needs of Life

• organisms are endergonic systems

• Energy is needed for

  • synthesis (biomolecules), reproduction, active transport, movement, temperature regulation

Living Economy

• Fueling the economy

  • eat high energy organic molecules (food)

  • break them down = catabolism (digest)

  • capture energy in form cell can use

• Need an energy currency

  • a way to pass energy around

  • ATP

    • chemical form of energy known as adenosine triphosphate

BELOW IS NOT IN THE FLASHCARD DECK AS OF 9/22

ATP

• Adenosine Triphosphate

  • modified nucleotide

    • adenine + ribose + Pi → AMP

    • AMP + Pi → ADP 

    • ADP + Pi → ATP

• Energy is released from ATP when the terminal phosphate bond is broken

How does ATP store/release energy?

• In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction

• ATP drives endergonic reactions by phosphorylation

  • phosphorylation

    • transferring a phosphate group to some other

Regeneration of ATP (ATP/ADP Cycle)

• ATP = renewable and regenerated by addition of a phosphate group to ADP

• The energy to phosphorylate ADP = Catabloic Reactions

• ATP/ADP Cycle = energy transferred from catabolic to anabolic pathways

• A working muscle recycles over 10 million ATPs per sec

Enzymes and Metabolic Reactions

• breaking down large molecules requires an initial input of energy = activation energy (EA)

• 2nd Law of Thermodynamics

  • why don’t proteins, carbohydrates and other biomolecules breakdown?

  • at temperatures typical of the cell, molecules don’t make is over the hump of activation energy

• heat speeds up reactions, but … would denature proteins and kill cells

How do enzymes lower EA?

• orienting substrates correctly

• straining substrate bonds

• providing a favorable microenvironment

• covalently bonding to the substrate

The Effectiveness of Enzymes

• Can be affected by pH, Temperature, and some chemicals

  • Optimal enzyme temp for humans: 35-40C

  • Optimal enzyme pH for humans: 6-8

Cofactors

• Non-Protein enzyme helpers

  • Inorganic Example: metal in ionic form

  • Organic Example: vitamins

Enzyme Inhibitors

• Competitive

  • bind to the active site, competing with the substrate

• Noncompetitive

  • bind to another part of an enzyme, making the active site less effective

    • toxins, poisions, pesticides, and antibiotics

Allosteric Regulation of Enzymes

• either inhibit or stimulate an enzyme’s activity

• occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site

Activators - stabilizes the active form of the enzyme

Inhibitors - stabilizes the inactive form of the enzyme

• attractive for drug candidates for enzyme regulation due to their specificity