Cell Metabolism

CELL METABOLISM

• Collective total of chemical processes that occur within living cells to accomplish the activities of life

• Follow physical and chemical laws

Energy and the Laws of Thermodynamics

• Energy is the capacity to do work

– Kinetic energy: energy of motion

• Examples: light energy (movement of photons), electricity (movement of charged particles), thermal or heat energy (random movement of atoms or molecules)

– Potential energy: stored energy

• Example: chemical energy (potential energy stored in chemical bonds)

• Energy can be transformed from one state to another

• Much of the work done by living organisms involves the conversion of potential energy to kinetic energy and vice versa

Concept Check

• Describe the forms of energy found in an apple as it grows on a tree, then falls and is digested by someone who eats it.

Free Energy

• Free energy is the energy available in a system to do work

– Exergonic reactions release free energy

• Spontaneous ; releases ATP

• Proceeds “downhill” since free energy is lost from the system

– Endergonic reactions require the addition of free energy

• Not spontaneous; requires ATP

• Proceeds “uphill” since free energy is added to the system

Concept Check

• Cellular respiration uses glucose and oxygen, which have high levels of free energy, and releases CO2 and water, which have low levels of free energy. Is respiration spontaneous or not? Is it exergonic or endergonic? What happens to the energy released from glucose?

Free Energy

• Chemical reactions in cells happen in three ways:

– Cells regulate chemical reactions through the use of protein catalysts called enzymes

– Cells couple reactions together, driving energy-requiring endergonic reactions with the energy released by exergonic reactions...