chapter 8 metabolism & enzymes
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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.