Chapter 8 Metabolism Slide 2 / 64 Metabolic Pathways Metabolism - - PDF document
Slide 1 / 64 Chapter 8 Metabolism Slide 2 / 64 Metabolic Pathways Metabolism is the totality of an organisms chemical reactions. Metabolism is a property of all life. Slide 3 / 64 Metabolic Pathways There are two types of metabolic
Metabolism is the totality of an organism’s chemical reactions. Metabolism is a property of all life.
There are two types of metabolic pathways: Catabolic pathways release energy by breaking down complex molecules into simpler compounds. Anabolic pathways consume energy to build complex molecules from simpler ones.
A metabolic pathway begins with a specific molecule and ends with a product Each step is catalyzed by a specific enzyme No enzyme, no reaction
enzyme 1 enzyme 2 enzyme 3
A
B C D
Starting Molecule Product Reaction 1 Reaction 3 Reaction 2
Living things use anabolic pathways to synthesize more complex organic molecules using the energy derived from catabolic pathways. Molecules from the environment are broken down. Their energy and matter are used to: · build structures · drive processes But living things still obey the Laws of Thermodynamics.
Energy is neither created nor destroyed. The total energy of the universe is a constant; if a system loses energy, it must be gained by the surroundings, and vice versa.
Initial state Final state
E of system decreases Internal energy, E Energy lost to surroundings
EFinal < Einitial ∆E < 0 ( negative)
E Final E Initial
Initial state Final state
E of system increases Internal energy, E Energy gained from surroundings
E final > E initial # E > 0 (positive)
E initial E final
The system includes whatever we want to study, living
The surroundings are everything else. System I Surroundings System II
When heat is absorbed by the system, the process is endothermic. Exothermic
System Endothermic
Surroundings
Heat Heat
System
When heat is released by the system, the process is exothermic. Remember that a change in heat is a change of enthalpy.
1 If a hot rock is placed in cold water, and your system is the rock, the process is _____. A endothermic B exothermic C neither, there is no change in energy D it depends on the temperature
2 If a hot rock is placed in cold water, and your system is the water, the process is _____. A endothermic B exothermic C neither, there is no change in energy D it depends on the temperature
3 If an ice cube is placed in warm water, and your system is the ice cube, the process is _____. A endothermic B exothermic C neither, there is no change in energy D it depends on the temperature
4 If an ice cube is placed in warm water, and your system is the warm water, the process is _____. A endothermic B exothermic C neither, there is no change in energy D it depends on the temperature
5 Water droplets evaporating from the skin surface will make you feel cold. For your skin, this process is _____. A endothermic B expothermic C neither, there is no change in energy D it depends on the temperature
Life creates ordered structures from less ordered materials in anabolic reactions. Life also consumes ordered forms of matter and breaks them down, releasing energy, with catabolic reactions. Living things are highly ordered.
Organisms increase the disorder of the universe in order to increase their own order. Entropy may decrease in an organism, but the universe’s total entropy increases. Life obeys the Second Law of Thermodynamics.
The First Law tells us that energy cannot be created nor destroyed; the total energy of the universe is a constant. The First Law allows any process in which the total energy is conserved, including those where energy changes forms. However, the First Law alone cannot explain what we see around us every day.
For instance, the First Law would allow the broken cup shown below to reassemble itself, but it never will. The absence of processes like this shows that the conservation of energy is not the whole story. If it were, movies run backwards would look perfectly normal to us!
The Second Law is a statement about which processes occur and which do not. · Heat can flow spontaneously from a hot object to a cold
· It is impossible to build a perpetual motion machine. · The universe always gets more disordered with time. · Your bedroom will get increasingly messy unless you keep cleaning it up.
· Stir sugar into coffee and you get coffee that is uniformly
· When a tornado hits a building, there is major damage. You never see a tornado pass through a pile of rubble and leave a building behind. · You never walk past a lake on a summer day and see a puff of steam rise up, leaving a frozen lake behind.
The Second Law tell us what will happen spontaneously, without outside intervention. Spontaneous doesn't mean fast, it just means that it will naturally occur if a system is left on its own.
· Spontaneous processes are those that can proceed without any
· The gas in vessel B will spontaneously effuse into vessel A, but once the gas is in both vessels, it will not spontaneously return to vessel B.
Processes that are spontaneous in
the reverse direction.
· Processes that are spontaneous at one temperature may be nonspontaneous at other temperatures. · Above 0 °C it is spontaneous for ice to melt. · Below 0 °C the reverse process is spontaneous.
6 A reaction that is spontaneous _____. A is very rapid B will proceed without outsode intervention C is also spontaneous in the reverse direction D has an equilibrium position that lies far to the left E is very slow
7 Which of the following statements is true? A Processes that are spontaneous in one direction are spontaneous in the opposite direction. B Processes are spontaneous because they occur at an
C Spontaneity can depend on the temperature. D All of the above statements are true.
Entropy is a measure of the randomness or disorder of a system. The second law of thermodynamics states that the entropy of the universe increases for spontaneous processes.
8 The thermodynamic quantity that expresses the degree of disorder in a system is ______. A enthalpy B internal energy C bond energy D entropy E heat flow
9 The entropy of the universe is __________. A constant B continually decreasing C continually increasing D zero E the same as the energy, E
Growth of an individual, and evolution of a species, are both processes of increasing order. Do they violate the second law of thermodynamics?
No! Life is not an isolated system. Even though life itself shows increasing order, it creates an increasing amount of disorder in its surroundings: the total disorder of the universe is increased by life.
Do they violate the second law of thermodynamics?
10 If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously? A The entropy of the organism's environment must also be decreasing. B Heat is being used by the organism as a source of energy. C Energy input into the organism must be occuring in order to drive the decrease in entropy. D In this situation, the second law of thermodynamics must not apply.
11 According to the second law of thermodynamics, which of the following is true? A Energy conversions increase the order in the universe. B The total amount of energy in the universe is constant. C The decrease in entropy in life must be offset by an increase in entropy in the environment. D The entropy of the universe is constantly decreasing.
Biologists want to know which reactions occur spontaneously and which require the input of energy. To do so, they need to determine the energy and entropy changes that must occur. As you learned last year, this determines the change in the Gibbs Free Energy: ΔG.
A process will occur spontaneously if the result is a reduction of the Gibbs Free Energy (G) of the system. G takes into account the resulting change in the energy of a system and the change in its entropy. If the effect of a reaction is to reduce G, the process will proceed spontaneously. If ∆G is negative, the reaction will occur spontaneously. If ∆G is zero or positive, it will not occur spontaneously.
Exergonic reactions have a negative ∆G and occur spontaneously Endergonic reactions have a positive ∆G and do not occur spontaneously
Reactants Energy Products Progress of the reaction Amount of free energy released (ΔG < 0) Free energy
Reactants Energy Products Progress of the reaction Amount of free energy required (ΔG > 0) Free energy
A
B cannot occur outside of a living cell C releases free energy when proceeding in the forward direction D is common in anabolic pathways E leads to a decrease in the entropy of the universe
The concept of free energy applies to life: Processes in living systems that lower the Gibbs free energy are spontaneous; they are exergonic. Processes that raise the Gibbs free energy are nonspontaneous; they are endergonic.
Biological systems often need an endergonic reaction to
But if it is coupled to a reaction that is exergonic, so that together, they are exergonic, it will take place.
NH2 Glu Non-spontaneous reaction: # G is positive # G = +3.4 kcal/mol NH3 Glu Glutamic acid Ammonia +
ATP
+
H2O ADP Spontaneous Reaction:ΔG is negative
+
Pi ΔG = -7.3 kcal/mol
NH2 Glu Non-spontaneous reaction: # G is positive # G = +3.4 kcal/mol NH3 Glu Glutamic acid Ammonia + ATP + H2O ADP Spontaneous Reaction:ΔG is negative + Pi ΔG = -7.3 kcal/mol
# G = –3.9 kcal/mol together, reactions are spontaneous
13 Which of the following correctly states the relationship between anabolic and catabolic pathways? A Degradation of organic molecules by anabolic pathways provides the energy to drive catabolic pathways. B Energy derived from catabolic pathways is used to drive the breakdown of organis molecules in anabolic pathways. C Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.
A cell does three main kinds of work: · Mechanical (motion) · Transport (crossing a barrier) · Chemical (changing a molecule) To do work, cells manage energy resources by energy coupling, using an exergonic reaction to drive an endergonic one NOTE: both processes don't have to occur at the same time, it's possible to store the energy from an exergonic process to drive an endergonic process at a later time.
ATP (adenosine triphosphate) is the currency of energy in living systems. It stores the energy gained in exergonic reactions to power endergonic reactions at a later time. ATP provides the energy for the processes of life.
ATP (adenosine triphosphate) includes three phosphate groups (PO4
Each Phosphate group has an ionic charge of -3e. In this space filling model of ATP, each PO4
blue.
The phosphate groups repel each
negative charge. Therefore it requires Work to add the second phosphate group; to go from AMP (monophosphate) to ADP (diphosphate). To add the third group, to go from ADP to ATP (triphosphate), requires even more work since it is repelled by both of the other phosphate groups.
This is like the work in compressing a spring. The energy from the work needed to bring each phosphate group to the molecule is stored in that phosphate bond. When the bond is broken to go from ATP to ADP, significant energy is released. Going from ADP to AMP releases less energy, since there is less total charge in ADP than ATP.
ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant. The recipient molecule is now "phosphorylated". The three types of cellular work are powered by the hydrolysis
NH2 Glu P
i
Pi P i P
i
Glu NH3 P P P ATP ADP Motor protein Mechanical work: ATP phosphorylates motor proteins Protein moved Membrane protein Solute Transport work: ATP phosphorylates transport proteins Solute transported Chemical work: ATP phosphorylates key reactants Reactants: Glutamic acid and ammonia Product (glutamine) made
+ + +
ATP is a renewable resource that is regenerated by addition
The energy to phosphorylate ADP comes from catabolic reactions in the cell The chemical potential energy temporarily stored in ATP drives most cellular work Each cell is converting millions of ATP to ADP and back again every second.
P
i
ADP Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (energonic, energy- yielding processes) +
ATP
exergonic
14 In general, the hydrolysis of ATP drives cellular work by _____. A changing to ADP and phosphate B releasing free energy that can be coupled to other reactions C releasing heat D acting as a catalyst E lowering the free energy of the reaction
15 What best characterizes the role of ATP in cellular metabolism? A The releasse of free energy during the hydrolysis of ATP heats the surrounding environment. B The free energy releasedby ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate. C It is catabolized to carbon dioxide and water. D The ΔG associated with its hydrolysis is positive.
16 Which of the following is not an example of the cellular work accomplished with the free energy derived from the hydrolysis
A Mechanical work, such as the moving of flagella. B Transport work, such as the active transport of an ion into a cell. C Chemical work, such as the synthesis of new proteins. D The production of heat, which raises the temperature of the cell. E All of the above.
# G = 0 A closed hydroelectric system # G < 0
An open hydroelectric system
A multistep open hydroelectric system # G < 0 # G < 0 # G < 0
The multistep, open hydroelectric system is like life. Materials being used must be replaced in order for energy to be produced and work to be done. Remember... Life is not in equilibrium Life is an open system experiencing a constant flow of materials and energy.
17 Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description? A The metabolism of an organism is isolated from its surroundings. B Organisms aquire energy from their surroundings. C Heat produced by the organism is conserved in the organism and not lost to the environment. D Because energy must be conserved, organisms constantly recycle energy and thus need no input of energy.