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Chapter 8: An Introduction to Metabolism - Coggle Diagram
Chapter 8: An Introduction to Metabolism
8.1: An organism's metabolism transforms matter and energy
Metabolism
The totality of an organism's chemical reactions
Metabolic Pathways
Pathway in which a specific molecule is altered in a series of steps each catalyzed by enzymes
Intersecting pathways make up the road map of metabolism
Catabolic pathways
Breaks down complex molecules into simpler ones; releases energy
Ex. cellular respiration
Anabolic pathways
Builds complex molecules from simple ones; uses energy
Ex. protein synthesis
Bioenergetics
The study of the flow of energy through organisms
Forms of Energy
Chemical energy
Potential energy available for release in a chemical reaction
Thermal energy
Kinetic energy associated with the random movement atoms/moles; transfer of thermal energy is called heat
Kinetic energy
Energy of movement
Potential energy
Energy of position
The Laws of Energy Transformation
Thermodynamics
The study of energy transformations that occur in a collection of matter
Second law of thermodynamics
Every energy transfer or transformation increases the entropy of the universe
Ex. most of the chemical energy from food is released as heat
First law of thermodynamics
Energy can be transferred or transformed but not created or destroyed; conservation of energy
Ex. chemical energy within food being transferred into kinetic energy
Entropy
The measure of molecular disorder
Spontaneous process
Process that does not require an input of energy
Ex. rusting of a car
Systems
Open system
Energy and matter can be exchanged with surroundings
Ex. organisms
Isolated system
Unable to exchange energy or matter with surroundings
Ex. liquid in thermos bottle
Biological order and disorder
The building of complex structures from simpler ones is balanced by the organism's tendency to replace organized forms of energy from its surroundings with less ordered ones.
Ex. Co2 and H2O is released upon acquiring the complex molecules from food
8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously
Free Energy Change, :small_red_triangle:G
Free energy
Portion of a system's energy that can perform work when temperature and pressure is uniform
Ex. living cell
The total free energy, :small_red_triangle:G, will change when the system changes, such as in a chemical reaction
:small_red_triangle:G = :small_red_triangle:H - T:small_red_triangle:S
Free energy change = Enthalpy (total energy) - Temperature in kelvin of the change in entropy
:small_red_triangle:G
Non-spontaneous reaction
Endergonic reaction
-:small_red_triangle:G
Spontaneous reactions
:small_red_triangle:H must be negative, and/or T:small_red_triangle:S must be positive
Exergonic reaction
Free Energy, Stability, and Equilibrium
:small_red_triangle:G = G final state - G initial state
Free energy can be thought of as a measure of instability
Ex. a bead of dye (more likely to disperse) is less stable than when dispersed through water
Equillibrium
Forward and reverse reactions occur at the same rate
G is at lowest possible value in the system
A process is spontaneous and can perform work only when it is moving toward equilibrium
Free Energy and Metabolism
Exergonic and Endergonic Reactions in Metabolism
Exergonic reaction
Net release of free energy
-:small_red_triangle:G
Spontaneous
Endergonic
Absorbs free energy
:small_red_triangle:G
Non-spontaneous
8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions
Energy coupling
The use of an exergonic reaction to pair an endergonic one
The Structure and Hydrolysis of ATP
ATP
Bonds between phosphate groups can be broken by hydrolysis
Exergonic reaction creates ADP and energy
Three negatively charged phosphate groups and their mutual repulsion creates instability, equivalent to a compressed spring
How ATP Provides Energy that Performs Work
Cells use energy released during ATP hydrolysis primarily to drive chemical, transport, and mechanical work
Energy from ATP can make endergonic reactions exergonic
Involves phosphorylation
Recipient molecule is phosphorylated intermediate
ATP hydrolysis may change shape of protein and thus it's ability to bind to another molecule
ATP may bind noncovalently to a motor protein before hydrolysis - once hydrolyzed, another ATP can bind
The Regeneration of ATP
ATP cycle
The phosphorylation of ADP is powered by catabolic reactions
8.4: Enzymes speed up metabolic reactions by lowering energy barriers
The Activation Energy Barrier
Activation energy
The energy required to push the reactants to the top of an energy barrier so that a reaction can undergo
Typically, so high that reactions will not proceed
How Enzymes Speed Up Reactions
Enzymes lower the activation energy barrier so that the transition state may be reached without additional heat
Enzymes cannot change the :small_red_triangle:G of a reaction; they cannot make endergonic reactions exergonic
Substrate Specificity of Enyzmes
Substrate
The reactant an enzyme acts on
Forms an enzyme-substrate complex
Enzymes convert substrates to products
Enzymes are very specific
Ex. sucrase will only act on sucrose
Due to their shape caused by amino acid sequence
Active site
A pocket/groove region of enzyme that binds to the substrate
Induced fit
The tightening of the active site once in contact with the substrate
Catalysis in the Enzyme's Active Site
Net effect is always in the direction of equilibrium
Enzymes convert reactant to products quickly and with no effect to their own shape/form
Active sites provide templates in reactions of two or more reactants
Enzymes may stress and break their reactants to help it approach the activation energy barrier
Enzyme may provide microenvironment conducive to the reaction
May include amino acid participation in which the substrate briefly binds covalently to the enzyme
Effects of Local Conditions on Enzyme Activity
Effects of temperature and pH
Enzymatic function increases with temperature to a point; once reaches, enzymatic function drops severely
Causes the protein to denature
Enzymes have ideal pH range in which they function most effectively
Cofactors
Adjuncts bound to either the enzyme or the substrate that act as non-protein helpers
Enzyme Inhibitors
Chemicals that inhibit enzymatic function; typically, loosely bound to allow for reversibility
Competitive inhibitors
Mimic substrates to compete for active site
The Evolution of Enzymes
Thousands of enzymes have risen primarily from mutations
8.5: Regulation of enzyme activity helps control metabolism
Allosteric Regulation of Enzymes
A case in which a protein's function at one site is affected by the binding of a regulatory molecule at another site
May result in inhibition OR stimulation
Allosteric Activation and Inhibition
Complexed of allosterically regulated enzymes oscillate between a catalytically active and catalytically inactive shape; the binding of an activator to the regulatory (allosteric) site stabilizes the enzymatic shape with active sites, whereas a bound inhibitor will stabilize the inactive shape of the enzyme
Cooperativity
A substrate molecule changes the enzymatic shape of all subunits by binding to the active site, increasing its catalytic activity
Feedback Inhibition
Metabolic pathway is halted by inhibitory binding of its product to an earlier enzyme on an anabolic pathway
Prevents production of unnecessary product
Localization of Enzymes Within the Cell
Cells are compartmentalized
Multienzyme complexes may form within metabolic pathways
Some enzymes have fixed, structural locations
Some enzymes operate within the solution of membrane bound organelles