Metabolism AP Biology Chapter 8
Energy
Energy management Bioenergetics is the study of how organisms manage their energy resources. Energy is the capacity to do work. Energy exists in various forms Cells transform energy from one type into another.
Kinetic energy Kinetic energy is the energy associated with the relative motion of objects. Objects in motion can perform work by imparting motion to other matter. Newton s Cradle Photons of light can be captured and their energy harnessed to power photosynthesis in green plants. Heat or thermal energy is kinetic energy associated with the random movement of atoms or molecules.
Potential energy Potential energy is the energy that matter possesses because of its location or structure. Chemical energy is a form of potential energy stored in molecules because of the arrangement of their atoms.
Learning Check Which statement does NOT describe chemical energy? The energy required by chemicals A type of potential energy The energy stored in the bonds of the molecule Stored energy that can be used to do work
Learning Check What is the most general definition of energy? Heat The capacity to do work The motion of molecules Sunlight
Learning Check Which of the following is an example of potential energy? Heat Light Chemical Energy All of these are correct
The energy transformations of life are subject to laws of thermodynamics Thermodynamics is the study of energy transformations In this field, the term system refers to the matter under study and the surroundings include everything outside the system. A closed system is isolated from its surroundings. In an open system, energy and matter can be transferred between the system and its surroundings.
Types of Systems Matter Exchanged? Open Yes Yes Closed No Yes Isolated No No Energy Exchanged?
Open systems Organisms are open systems. They absorb energy (light or chemical energy in the form of organic molecules) and release heat and metabolic waste products (such as urea or CO 2 ) to their surroundings.
First law of thermodynamics Energy can be transferred and transformed, but it cannot be created or destroyed. Law of Conservation of Energy. Energy of the universe is constant
nd 2 Law of Thermodynamics Every transformation results in a reduction of the FREE ENERGY (useable energy). Energy transfers and transformations increase ENTROPY (disorder, randomness or chaos). Law of Entropy. Energy always tends to go from a more usable (higher quality) form to a less usable (lower quality) form.
Most conversions are less than 100% efficient and therefore some energy is lost or wasted. Energy is lost in the form of HEAT (random energy of molecular movement). Solar energy Chemical energy (photosynthesis) Chemical energy (food) Mechanical energy (moving, thinking, living) Waste heat Waste heat Waste heat Waste heat
Only 25% of chemical energy stored in gasoline is transformed into motion of the car and 75% is lost as heat!!
Without adding energy to a system, the system will break down.
Learning Check The transformation of energy always results in the loss of some energy in the form of: ATP Chemical Energy Heat Light
Learning Check Imagine a glass box (terrarium) containing living plants and animals and sitting on a windowsill. The growth of the plants provides food for snails, insects, fungi, and bacteria that live in the box. Vents allow good air circulation. What will happen if you put a black cloth over the box, cutting off all light?
Spontaneous processes For a process to occur on its own, without outside help in the form of energy input, it must increase the entropy of the universe. The word spontaneous describes a process that can occur without an input of energy. Spontaneous processes need not occur quickly. Some spontaneous processes are instantaneous, such as an explosion. Some are very slow, such as the rusting of an old car.
Metabolic Disequilibrium A cell that has reached metabolic equilibrium is dead! No energy is available to do work Cells maintain disequilibrium because they are open systems. The constant flow of materials into and out of the cell keeps metabolic pathways from ever reaching equilibrium.
ATP Powers Cellular Work A cell does three main kinds of work: Mechanical work- the beating of cilia, contraction of muscle cells, movement of chromosomes during cellular reproduction. Transport work-pumping of substances across membranes against the direction of spontaneous movement. Chemical work- driving endergonic reactions such as the synthesis of polymers from monomers.
Energy Coupling Cells manage their energy resources to do work by energy coupling Energy from an exergonic (gives off energy) process is used to drive an endergonic (takes in energy) process In most cases, the immediate source of energy to power cellular work is ATP.
ATP
ATP ATP (adenosine triphosphate) = a type of nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups.
ATP The bonds between phosphate groups can be broken by hydrolysis. ATP à ADP + P i
ATP cycling ATP is a renewable resource that can be regenerated by the addition of a phosphate group to ADP. Regeneration of ATP is an endergonic process, requiring an investment of energy. DG = 7.3 kcal/mol.
Learning Check How are ATP and ADP structurally different? Which of the following are examples of cellular work that require ATP as a source of energy? Muscle contractions Synthesis of complex molecules Active transport of materials across membranes
Learning Check ATP is continuously built to replace what is consumed by the activities of the cell. What can you predict about a reaction that would build ATP from ADP and P? Would it release or require energy?
Metabolism
Metabolism is an Emergent Property of Life Metabolism: totality of an organism s chemical reactions Chemistry of life is organized into metabolic pathways Begins with a specific molecule, which is then altered in a series of defined steps to form a specific product. A specific enzyme catalyzes each step of the pathway.
Metabolic pathways Catabolic pathways release energy by breaking down complex molecules to simpler compounds. Ex: cellular respiration Anabolic pathways consume energy to build complicated molecules from simpler compounds. Ex: The synthesis of protein The energy released by catabolic pathways can be stored and then used to drive anabolic pathways.
Which is which? Learning Check
Learning Check Anabolic Catabolic Cellular Respiration Photosynthesis Synthesize Starch from Glucose Digest Food Molecules Build Complex Products Release Energy Requires Energy Break down complex molecules
Learning Check Put in the correct order Anabolic Reaction Catabolic Reaction ATP ADP + P
Learning Check Anabolic reactions require ATP. But it takes energy to make ATP. Where does the energy for ATP synthesis come from?