chapter 8 metabolism & enzymes

What is life?

Figure 6.1  The complexity of metabolism

-series of steps

-enzyme directed

-enzyme managed

-the management of material and energy resources

Catabolic Anabolic

– forming bonds between molecules• dehydration synthesis• anabolic reactions

– breaking bonds between molecules• hydrolysis• catabolic reactions

RELEASES ENERGY

COUPLED RXN’s

USES/STORES ENERGY

THERMODYNAMICS

the study of energy transformations

Closed system? Open?

(Bioenergetics)

1st LAW OF THERMODYNAMICS:

Energy can be changed but not created or destroyed

Energy of universe is constant

A qualitative change - not quantitative

2ND LAW OF THERMO.:

Entropy of the universe is constantly

increasing

Which of these happens spontaneously?

DEFINE ENTROPY-

randomness or disorder

WHAT CAUSES IT?-

energy transfers or transformations

WHAT IS FREE ENERGY?

energy available for work

WHAT IS WORK?

any change!

Order as a characteristic of life

Organisms require energy to live

– Sources of energy?Coupling exergonic reactions (releasing energy)

with endergonic reactions (needing energy)

+ + energy

+ + energy

1st + 2nd = Quantity of energy is conserved but

not the quality

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!

SPONTANEOUS

OR

NOT?

With or without outside help?

Kinetic and potential energy: dam

The relationship of free energy to stability, work capacity, and spontaneous change

Disequilibrium and work in closed and open systems

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 stable

Greater work capacity

In a spontaneous change

•free energy decreases (ΔG<0)

•system becomes more stable

•released free energy can be used to do work

More free energyLess stable

Greater work capacity

Energy changes in exergonic and endergonic reactions

EXERGONIC REACTIONS:

• ENERGY RELEASING REACTIONS

• PROCEEDS WITH A NET LOSS OF FREE ENERGY

• DOWNHILL; SPONTANEOUS

• NEGATIVE FREE ENERGY

ENDERGONIC REACTIONS-

• ENERGY REQUIRING

• PROCEEDS WITH A NET GAIN OF FREE ENERGY

• UPHILL; NONSPONTANEOUS

• POSITIVE FREE ENERGY

G = free energy

H = total energy

S = entropy

T = ‘C + 273 = K

G = H - TS

G = H - T S

G = free energy

G = Gfinal state - Ginitial state

H = total energy (enthalpy)

T = degrees Kelvin

S = entropy

Disequilibrium and work in closed and open systems

Spontaneous??

Systems that are-

High free energy &/or low entropy

Unstable

Highly ordered

G < 0

Nature runs downhill!

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

The structure and hydrolysis of ATP

ATP

Energy coupling by phosphate transfer

The ATP cycle

Interesting Enzymes•Mars Rovers search for traces of enzymes

•PKU test - phenylketonuria

•meat tenderizer, cleansers

•heart attack indicator

•improve dough quality in bread

•improve clarity in beer and liquors

•environmental cleanup and biotech

•10,000 to 20,000 daltons in size

•125-3000 amino acid units

•10176 to 109020 possible combinations

•only 10103 molecules in universe

•age of universe is 1017 seconds old

•<1040 enzyme codons have been read since life began

Catalase can digest 5 million hydrogen peroxide molecules per minute

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

ΔG = change in free energy = ability to do work

Chemical reaction & energy

• Some reactions release energy– Exergonic

• Digesting polymers

• Hydrolysis = catabolism

• Some reactions require input of energy– Endergonic

• Building polymers

• Dehydration synthesis = anabolic

G = H - T S G = ( -) or (< 0 ) G = ( +) or (> 0 ) spontaneous/ downhill nonspontaneousexergonic endergoniccatabolic anabolicRespiration Photosynthesisenergy released energy storedexothermic endothermicLow G High GHigh S Low S

initial final

final initial s

T = absolute temperature KH = change in total bond energy of reactants and products in a systemG = free energy S = change in entropy = disorder or randomness

assume as "0" then ΔG = H Free energy = total potential energyincrease entropy = decrease in free energy

or increase temperature = increase in entropy

PROTEIN KINASES

Enzymes that catalyze phosphorylation

PHOSPHATASES

Catalyze dephosphorylation

Act as “switches” to turn on or off proteins

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

Activation Energy and Enzymes II

Shown to the right are three plots of the energy levels of molecules involved in a reaction such as

A + B > C

The first plot depicts the distribution of energy levels of the reactants at body temperature without the presence of an enzyme. The vertical blue line indicates the activation energy level which must be attained for the reaction to occur. The shaded portion of the distribution on the left indicates the proportion of A and B molecules having sufficient energy levels to participate in the reaction.

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.