Introduction to Metabolism Chapter 6

Metabolism u The totality of an organism’s chemical processes. u Concerned with managing the material and energy resources of the cell.

Catabolic Pathways u Pathways that break down complex molecules into smaller ones, releasing energy. u Example: Respiration

Anabolic Pathways u Pathways that consume energy, building complex molecules from smaller ones. u Example: Photosynthesis

Energy u Ability to do work. u The ability to rearrange a collection of matter. u Forms of energy: u Kinetic u Potential u Activation

Kinetic Energy u Energy of action or motion.

Potential Energy u Stored energy or the capacity to do work.

Activation Energy u Energy needed to convert potential energy into kinetic energy. Potential Energy Activation Energy

Energy Transformation u Governed by the Laws of Thermodynamics.

1st Law of Thermodynamics u Energy can be transferred and transformed, but it cannot be created or destroyed. u Also known as the law of Conservation of Energy.

2nd Law of Thermodynamics u Each energy transfer or transformation increases the entropy of the universe.

Entropy u Measure of disorder.

Summary u The quantity of energy in the universe is constant, but its quality is not.

Question? u How do living organisms overcome Entropy? u By using energy from the environment or external sources (e.g. food, light).

Free Energy u The portion of a system's energy that can perform work.

Free Energy G = H - TS G = free energy of a system H = total energy of a system T = temperature in o K S = entropy of a system

Free Energy of a System u If the system has: u more free energy u it is less stable u It has greater work capacity

Chemical Reactions u Are the source of energy for living systems. u Are based on free energy changes.

Reaction Types u Exergonic u Exergonic: chemical reactions with a net release of free energy. u Endergonic u Endergonic: chemical reactions that absorb free energy from the surroundings.

Exergonic/Endergonic

Biological Examples u Exergonic - respiration u Endergonic - photosynthesis

Cell - Types of Work u Mechanical - muscle contractions u Transport - pumping across membranes u Chemical - making polymers

Cells use ATP as their energy source u Adenosine Triphosphate u Made of: - Adenine (nitrogenous base) - Ribose (pentose sugar) - 3 phosphate groups

Adenine Ribose Phosphates

Key to ATP u Is in the high energy bonds between the three phosphate groups. u Negative charges on the phosphate groups repel each other and makes the phosphates unstable.

ATP Cycles u Energy released from ATP drives anabolic reactions. u Energy from catabolic reactions “recharges” ATP.

ATP Cycle ATP ADP + P + Energy

ATP in Cells u A cell's ATP content is recycled every minute. u Humans use close to their body weight in ATP daily. u No ATP production equals quick death.

Redox reactions

Oxidation - definitions u Loss of electrons. u Loss of energy. u Loss of Hydrogens from Carbons.

Reduction - definitions u Gain of electrons. u Gain of energy. u Gain of Hydrogens to Carbons. Comment - be careful not to use “reduction” in lay terms.

Redox reactions u Reactions are usually paired or linked together. u Many of the reactions will be done by phosphorylation.

Phosphorylation u Adding a phosphate group to a molecule. u The phosphate group adds “energy” to the molecule for chemical reactions.

ATP u ATP energizes other molecules by transferring phosphate groups to them….. The process is called phosphorylation.

Phosphorylation