Chapter 8 Metabolism & Enzymes. METABOLISM ENERGY AND LIFE. What is life?. Life is a collection of chemical reactions. LIFE IS WORK. Cells need energy to do work. Figure 6.1 The complexity of metabolism. METABOLIC PATHWAY. -series of steps -enzyme directed
Life is a
-series of steps
-the management of material and energy resources
Potential to Kinetic
the study of energy transformations
Closed system? Open?
Energy can be changed but not created or destroyed
Energy of universe is constant
A qualitative change - not quantitative
Entropy of the universe is constantly increasing
randomness or disorder
WHAT CAUSES IT?-
energy transfers or transformations
energy available for work
WHAT IS WORK?
Coupling exergonic reactions (releasing energy)
with endergonic reactions (needing energy)
Fate of all energy is to end up as heat energy - not available for work
Organisms are open systems that exchange energy and materials with their surroundings.
They create ordered structures using energy that flows into environment as light.
They take in ordered structures and create less ordered ones and release heat.
Living systems then increase entropy.
Complex organisms developed from simpler ones. Entropy?
REACTIONS! materials with their surroundings.
With or without outside help?
When a spontaneous process occurs in a system, stability of the system is increased.
Unstable systems tend to change to become more stable.
More free energyLess stableGreater work capacity
G = free energy the system is increased.
H = total energy
S = entropy
T = ‘C + 273 = K
G = H - TS
G = H - T S the system is increased.
G = free energy
G = Gfinal state - Ginitial state
H = total energy (enthalpy)
T = degrees Kelvin
S = entropy
Spontaneous?? the system is increased.
Systems that are-
High free energy &/or low entropy
In a spontaneous process, the system is increased.
free energy decreases
G < 0
Nature runs downhill! the system is increased.
To occur spontaneously, the system must either give up energy (a decrease in H), give up order (an increase in S) or both. G < 0
END the system is increased.
ENZYMES the system is increased.
Interesting Enzymes the system is increased.
1 ounce of pepsin per 4000 lbs of egg white in a few hours-- would take 10 to 20 tons of acid for 24-48 hours at high temp
Endergonic vs. Exergonic per minute
ΔG = change in free energy = ability to do work
G = H - T S per minute
G = ( -) or (< 0 ) G = ( +) or (> 0 )
spontaneous/ downhill nonspontaneous
energy released energy stored
Low G High G
High S Low S
T = absolute temperature K
H = change in total bond energy of reactants and products in a system
G = free energy
S = change in entropy = disorder or randomness
assume as "0" then ΔG = H
Free energy = total potential energy
increase entropy = decrease in free energy
or increase temperature = increase in entropy
PROTEIN KINASES per minute
Enzymes that catalyze phosphorylation
Act as “switches” to turn on or off proteins
END per minute
Shown to the right are two plots of the energy levels of molecules involved in a reaction such as
A + B > C
over the course of the reaction.
The blue curve depicts the course of the reaction in the absence of an enzyme which facilitates the reaction while the red curve depicts the course of the reaction in the presence of the reaction specific enzyme. The difference in energy level between the beginning state (left side) and the energy necessary to start the reaction (peaks of the curves) is the activation energy of the reaction.
The presence of the enzyme lowers the energy of
The second plot depicts the distribution of energy levels of the reactants at a temperature higher than body temperature but in the absence of an enzyme. The distribution is shifted to a higher average energy level but the activation energy remains the same. Clearly, there is a higher proportion of molecules at an energy level high enough to participate in the reaction than if the molecules were at body temperature.
The third plot is the same as the first one but with the presence of an enzyme the activation energy for the reaction has been lowered significantly. Thus, the proportion of molecules at an energy level above the activation is greatly increased which means the reaction will proceed at a much higher rate.