CAS BI 105 Lecture Notes - Lecture 13: Exergonic Reaction, Chemical Bond, Chemical Reaction
Energy and Enzymes
Metabolism
•The sum of all chemical reactions in one organism
•Chemical reactions - using energy to break a bond or gaining energy when a bond is broken
Energy
•The capacity to do work
•What is work?
•Chemical Work: making and breaking chemical bonds, building and breaking molecules
•Kinetic Work: move ions, molecules, large things in/out of the cell or the entire cell across a
surface/tissue
Types of Energy
•Kinetic Energy: the energy of motion
•ex: moving sodium across the membrane, down its concentration gradient
•ex: rolling a ball down a hill
•Potential Energy: stored energy
•An object wants to move and will move if allowed (the POTENTIAL to move)
•ex: disequilibrium of sodium ready to move down its concentrating radiant
•ex: ball poised at the top of the hill, ready to roll down
•Thermal Energy: heat
•Reactions often lose energy in the form of heat
•Chemical Energy: potential energy in food/storage molecules
•Fewer chemical reactions - body temperature drops
•More chemical reactions - body temperature rises
Energy Transformations
•Constant changes of energy from one form to another
•ex: chemical energy (wood) —> thermal energy (fire)
•Thermodynamics: the study of energy transformations
•2 laws of thermodynamics
•1st law - energy can neither be created nor destroyed, only converted from one form to another
•Exergonic Reaction - energy released when you break a bond
•Need to capture energy in order to use in ADP-ATP conversion
•Endergonic Reaction - energy required to make a bond
•Where do we get energy for these reactions?
•By coupling an endergonic and exergonic reaction at the same place & time (one energy
fuels the other)
•By storing energy as potential energy in electrons carried on nucleotides (ex: NADH/
FADH2)
•Energy transfer molecules carry the energy until it can be used in the ADP-ATP
conversion
•2nd law - every energy transfer of transformation increases entropy, thus the entropy of the
universe is always increasing
•entropy = disorder/chaos = energy lost when trying to convert from one form to another (heat
lost)
•*entropy results in unusable energy
•ex: entropy increases as more heat and small molecules are released
Intermediates
•Sometimes a reaction is not as simple as A + B —> C
•If there are many sets involved the molecules are known as intermediates
•ex: A + B —> C —> D —> E
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Energy in a Reaction
•Making a chemical bond takes energy - endogenic
•Breaking a chemical bond releases energy - exergonic
•constantly cycles back and forth between ATP and ADP states
Metabolism
•All chemical reactions in an organism
•Energy is extracted from nutrients
•Synthesize or breakdown of molecules
•Catabolism: reactions that release energy by breaking down molecules
•Anabolism: reactions that required energy to build molecules
•Energy used and taken in
Cellular Reactions
•Often reversible
•Different enzymes are required for each direction/new level of control
•Will be either catabolic or anabolic
•ex: A + B <—> C + D
•Often a reaction is slow & impossible to complete without help
•Activation Energy - the energy needed to bring molecules close together/align them in a certain
arrangement
•This is the typical cause of resistance to a reaction
•The energy needed to start a reaction
•Enzymes try to reduce activation energy and make reactions easier
Enzymes
•Some reactions occur slowly on their own
•Enzymes: proteins that catalyze (speed up) reactions
•Substrate: the molecule that the enzyme acts on
•*All ligands are substrates, not all substrates are ligands
•Co-factor: another binding partner that may control the enzyme
•Control - to maintain homeostasis we must control enzyme activity
•Can keep the enzyme inactive, activate when needed (cofactors)
•Inhibit enzyme when not needed
•ex: CO2 + H2O —> Carbonic Acid
•Reaction Rate = 1 molecule/100 seconds
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Metabolism: the sum of all chemical reactions in one organism, chemical reactions - using energy to break a bond or gaining energy when a bond is broken. Energy: the capacity to do work, what is work, chemical work: making and breaking chemical bonds, building and breaking molecules, kinetic work: move ions, molecules, large things in/out of the cell or the entire cell across a surface/tissue. Intermediates: sometimes a reaction is not as simple as a + b > c, if there are many sets involved the molecules are known as intermediates, ex: a + b > c > d > e. Energy in a reaction: making a chemical bond takes energy - endogenic, breaking a chemical bond releases energy - exergonic, constantly cycles back and forth between atp and adp states. Enzyme binds substrate and forms an enzyme-substrate complex: 2. Chemical reaction occurs - enzyme is not bound to product anymore: 3.