Energy and Metabolism
Adapted from: faculty.sgc.edu/asafer/BIOL1107/chapt06_lecture.ppt
Metabolism
• The sum of all the chemical reactions occurring in an organism at one time
• Concerned with the management of material and energy resources within the cell
• Anabolic pathways• Catabolic Pathways
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Bioenergetics
Study of how organisms manage their energy resources
Energy: the capacity to do work, to move matter
-kinetic energy: the energy of motion
-potential energy: stored energy
Energy can take many forms:
mechanical electric current
heat light
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Flow of EnergyPotential energy stored in chemical bonds can be
transferred from one molecule to another by way of electrons.
**the rearrangement of atoms in molecules may results in the potential energy of the molecule being converted into kinetic energy.
oxidation: loss of electrons
reduction: gain of electrons
redox reactions are coupled to each other.
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Laws of Thermodynamics
The terms of open or closed systems refer to whether or not energy can be transferred between the system and its surroundings (can energy be imported or exported)
First Law of Thermodynamics – energy cannot be created or destroyed
-energy can only be converted from one form to another
For example:
sunlight energy chemical energy
photosynthesis
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Laws of ThermodynamicsA change in free energy can occur with
metabolism:• endergonic reaction: a reaction requiring an input
(gain) of energy (products contain more energy)
exergonic reaction: a reaction that releases (lose) free energy (reactants contain more energy)
Metabolic reactions are often coupled where an exergonic reaction fuels an endergonic reaction.
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Laws of Thermodynamics
Most reactions require some energy to get started. Can you think of two examples?
activation energy: extra energy needed to get a reaction started
-destabilizes existing chemical bonds
-required even for exergonic reactions
catalysts: substances that lower the activation energy of a reaction
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Objectives
• Explain the role of ATP in the cell• Describe ATP’s composition and how it performs
cellular work• Explain the importance of chemical
disequilibrium• Understand the energy profile of a reaction
including: activation energy, free energy change & transition state.
• Explain how metabolic pathways are regulated.
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Energy is required to form bonds.
Atoms or molecules
EnergyEnergy
+ Energy Larger molecule
The energy that was used to form the bonds is now stored in this molecule.
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Energy is released when bonds are broken.
EnergyEnergy
The energy is now released. It may be in a form such as heat or light or it may be transferred to another molecule.
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Energy Currency of Cells
ATP = adenosine triphosphate
-the energy “currency” of cells
ATP structure:
-ribose, a 5-carbon sugar
-adenine
-three phosphates
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ATP (Adenosine Triphosphate)
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ATP (Simplified Drawing)
A Base (adenine)
Sugar (ribose)
3 phosphate groups
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A
ATP
ATP Stores EnergyThe phosphate bonds are high-energy bonds.
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Energy
ADP + Pi + Energy
Breaking the bonds releases the energy.
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Energy Currency of Cells
Phosphates are highly negative, therefore:
-the phosphates repel each other
-much energy is required to keep the phosphates bound to each other
-much energy is released when the bond between two phosphates is broken
ATP has a high G
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Energy Currency of Cells
When the bond between phosphates is broken:
ATP ADP + Pi
energy is released (G=-7.3Kcal/mol in the lab, -13 Kcal/mol in the cell)
ADP = adenosine diphosphate
Pi = inorganic phosphate
Is this reaction catabolic or anabolic? This reaction is reversible.
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Coupled Reactions
ATP is Recycled The energy used to produce ATP comes from glucose or other high-
energy compounds. ATP is continuously produced and consumed as illustrated below.
Phosphorylation
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ATP is synthesized from ADP + Pi. The process of synthesizing ATP is called phosphorylation.
Two kinds of phosphorylation Substrate-Level Phosphorylation– Chemiosmotic Phosphorylation
Electron Carriers
• Compounds that pick up electrons from high energy compounds and transfer then to low-energy compounds.– LEO & GER– Electrons carry reducing power– Eg. NAD+ and FAD (oxidized forms), NADH
and FADH2 (reduced forms)
• Coupled reaction
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Enzymes
Multienzyme complexes offer certain advantages:
1. The product of one reaction can be directly delivered to the next enzyme.
2. The possibility of unwanted side reactions is eliminated.
3. All of the reactions can be controlled as a unit.
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Metabolism
Biochemical pathways are a series of reactions in which the product of one reaction becomes the substrate for the next reaction.
Biochemical pathways are often regulated by feedback inhibition in which the end product of the pathway is an allosteric inhibitor of an earlier enzyme in the pathway.
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