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An Introduction to Metabolism - Coggle Diagram
An Introduction to Metabolism
How do the laws of thermodynamics relate to biological processes?
Energy use by living things demonstrates the first
law of thermodynamics
– Energy can be transferred or transformed, but not
created or destroyed
CONCEPT 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions
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A cell does three main kinds of work:
Chemical work—pushing endergonic reactions
Transport work—pumping substances across membranes against the direction of spontaneous movement
Mechanical work—such as beating cilia or contracting muscle cells
Cells manage energy resources to do work through energy coupling, the use of an exergonic process to drive an endergonic one
Most energy coupling in cells is mediated by ATP
The Structure and Hydrolysis of ATP
ATP (adenosine triphosphate) is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups
In addition to energy coupling, ATP functions as one of the nucleoside triphosphates used to make RNA
CONCEPT 8.1: An organism’s metabolism transforms matter and energy
Metabolism is the totality of an organism’s chemical reactions
It is an emergent property of life that arises from orderly interactions between molecules
Metabolic Pathways
In a metabolic pathway, a specific molecule is altered in a series of steps to produce a product
Each step is catalyzed by a specific enzyme, a macromolecule that speeds up a specific reaction
Catabolic pathways release energy by breaking down complex molecules into simpler compounds
Cellular respiration, the breakdown of glucose
in the presence of O₂, is an example of a pathway of catabolism
Anabolic pathways consume energy to build complex molecules from simpler ones
For example, the synthesis of protein from amino acids is an anabolic pathway
Catabolic pathways are described as “downhill” reactions, whereas anabolic pathways are “uphill”
Living things use energy released from the downhill reactions of catabolic pathways to power the uphill reactions of anabolic pathways
Bioenergetics is the study of how energy flows through living organisms
Forms of Energy
Energy, the capacity to cause change, can be used to do work—move matter against opposing forces, such as gravity and friction
Energy exists in various forms
Living cells must transform energy from one form to another to do the work of life
Kinetic energy is energy associated with motion
Moving objects perform work by imparting motion to other matter
For example, water gushing through a dam turns turbines
Thermal energy is the kinetic energy associated with random movement of atoms or molecules
Thermal energy in transfer from one object to another is called heat
Light is another type of energy that can be harnessed to do work, such as photosynthesis
Potential energy is energy that matter possesses because of its location or structure
For example, water behind a dam possesses energy because of its altitude above sea level
Molecules possess energy due to the arrangement of electrons in bonds between their atoms
Energy can be converted from one form to another
For example, chemical energy from food is used to perform the work of climbing up to a diving platform
The kinetic energy of muscle movement is transformed into potential energy as the diver climbs higher above the water
The potential energy is then transformed to kinetic energy as the diver falls back down to the water
Chemical energy is potential energy available for release in a chemical reaction
Complex molecules, such as glucose, are high in chemical energy because energy is released as they are broken down to simpler products
The Laws of Energy Transformation
Thermodynamics is the study of energy transformations in a collection of matter
An isolated system, such as the liquid in a thermos bottle, is unable to exchange energy or matter with its surroundings
In an open system, energy and matter can be transferred between the system and its surroundings
Organisms are open systems; they absorb energy from light or food and release heat and metabolic wastes, such as CO₂, to the surroundings
The First Law of Thermodynamics
According to the first law of thermodynamics, the energy of the universe is constant
Energy can be transferred and transformed, but it cannot be created or destroyed
The first law is also called the principle of conservation of energy
The Second Law of Thermodynamics
During every energy transfer or transformation, some energy is converted to thermal energy and lost as heat, becoming unavailable to do work
According to the second law of thermodynamics,
Every energy transfer or transformation increases the entropy of the universe
Entropy is a measure of molecular disorder, or randomness
Biological Order and Disorder
Cells create ordered structures from less organized starting materials
For example, simple molecules are ordered into amino acids, which are assembled into ordered polypeptides
Complex, ordered structures are also produced from simpler starting materials at the organismal level
CONCEPT 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously
Biologists follow the energy and entropy changes during chemical reactions to determine whether they require an input of energy or occur spontaneously
Free-Energy Change, G
Gibbs free energy, G, can be simplified and referred to as free energy
Free energy is the portion of a system’s energy that can do work when temperature and pressure are uniform throughout the system, as in a living cell
The ΔG for a process can be used to determine whether it is spontaneous or not
ΔG is negative for all spontaneous processes
ΔG is zero or positive for nonspontaneous processes
Every spontaneous process decreases the system’s free energy
Spontaneous processes can be harnessed by the cell to perform work
Free Energy, Stability, and Equilibrium
Free Energy and Metabolism
The concept of free energy can be applied to the chemistry of life’s processes
Exergonic and Endergonic Reactions in Metabolism
Chemical reactions can be classified based on their free-energy changes
An exergonic reaction (“energy outward”) proceeds with a net release of free energy to the surroundings
An endergonic reaction (“energy inward”) absorbs free energy from the surroundings
Equilibrium and Metabolism
Reactions in a closed system, such as an isolated hydroelectric system, eventually reach equilibrium and can then do no work
CONCEPT 8.4: Enzymes speed up metabolic reactions by lowering energy barriers
Spontaneous reactions do not need added energy, but they can be slow enough to be imperceptible
For example, the hydrolysis of sucrose to glucose and fructose is spontaneous
At room temperature, a solution of sucrose in sterile water would sit for years without appreciable hydrolysis
A catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction
An enzyme is a macromolecule (typically protein) that acts as a catalyst to speed up a specific reaction
For example, adding the enzyme sucrase to a sucrose solution at room temperature will catalyze the complete hydrolysis of sucrose within seconds
The Activation Energy Barrier
Every chemical reaction between molecules involves bond breaking and bond forming
A molecule must be contorted into a highly unstable state before bonds can break to start the reaction
To reach this state, the molecule must absorb energy from its surroundings
The initial energy needed to break the bonds of the reactants is called the activation energy (EA)
Heat in the form of thermal energy absorbed from the surroundings often supplies activation energy
Molecules become unstable when enough energy is absorbed to break bonds; this is the transition state
Allosteric Regulation of Enzymes
Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site
This type of regulation may either inhibit or stimulate enzyme activity