Chapter 6 Energy, Enzymes, and Metabolism Biology 101 Tri-County Technical College Pendleton, SC.
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Transcript of Chapter 6 Energy, Enzymes, and Metabolism Biology 101 Tri-County Technical College Pendleton, SC.
Chapter 6 Energy, Enzymes, and Metabolism
Biology 101
Tri-County Technical College
Pendleton, SC
Metabolism and more…
Metabolism defined as sum of all chemical reactions in a cell
Anabolism is part of metabolism concerned with building up complexity in cell Requires energy to accomplish
Catabolism is part of metabolism concerned with breaking down complex substances into simpler ones and releasing energy in process
Reactions are often linked (coupled)
Thermodynamics
Energy defined as ability to do workWork defined as movement of mass through spaceKinetic versus potential energyIn biochemistry, energy represents capacity for changeFirst Law: energy (matter) cannot be created nor destroyed Can be converted from one form to another
Thermodynamics, cont.
Chemical to light; mechanical to electrical; potential to kinetic; and vise versaLaw applies to the universe or any closed systemOpen system merely one part of larger closed systemLaw states that in any interconversion, the total energy before and after the conversion is the SAME
Thermodynamics III
Second law states that “in every energy conversion, some of the energy becomes unavailable to do work” Some lost to entropy (disorder)/some as heat
Total energy called enthalpy (H)Usable energy (doing work) is called free energy (G)Unusable energy called entropy (S) which is multiplied by absolute temperature
Thermodynamics IV
H = G + TS Can be rewritten to G = H – TSEnergy changes measured in calories (cal) or joules (j)Change in value represented by Δ (delta) and can be negative or positiveIf ΔG is negative, free energy released; if positive, free energy consumed Endergonic versus exergonic reactions
Exo versus Ender Visual
Energy Coin of the Realm
Adenosine triphosphate (ATP)
Can be hydrolyzed and can donate a phosphate group to many different compounds
ADP-ATP cycle classic example of energy coupling and biochemical reaction Couples endergonic and exergonic reactions
Time for an Estesism…Hot damn!!!
ATP Visual
ADP-ATP Cycle Visual
…but how does it work
Phosphate groups are negatively charged
Lots of free energy required to overcome tendencies of phosphates to repel each other
Energy invested to make ADP from AMP and ATP from ADP
When phosphate removed, energy used to put it there released and used to do work
Active cells requires millions of ATPs per second to drive its machinery
Energy Coupling Visual
Here and there..mostly there
Catalyst is any substance that speeds up chemical reaction w/o itself being used upMost biological catalysts are proteins called enzymes Certain RNA molecules (ribozymes) TOO
**Reactions would proceed eventually given infinityNot fast enough or often enough to sustain life
Enzymes, cont.
ApoenzymeHoloenzymeCoenzymes and cofactorsFor reaction to proceed, energy barrier must be overcome**Exergonic reactions proceed ONLY after they are pushed over energy barrier by small amount of added energyNeeded energy called activation energy (EA)
Enzymes III
EA changes reactants into unstable molecular forms called transition-state species
Could lower EA by >ing temperatureSucrose and bunsen burner..care for a light?
Enzymes work by lowering EA so reaction can proceed at temperature favorable to lifeSome can catalyze 400 million reactions/sec Liver enzyme catalyse
Activation Energy Visual
Enzymes and Substrates
In enzyme-catalyzed reactions, reactants are called substrates
Substrates bind to a particular site on enzyme called the active site
Specificity of enzyme results from exact 3-dimensional shape and structure of enzyme
Reason enzyme recognizes its substrate is because it “fits”
Most enzyme names end in “ase”
Enzymes, cont.
Enzyme-substrate complexreaction
Enzymes lower EA by one/more processes Orient substrates Add charges to substrates Induce strain in the substrates
Competitive and noncompetitive inhibition
Two models of enzyme specificity “Lock and key” and “induced fit”
Induced fit most widely accepted model
Enzyme-Substrate Visual
Induced Fit Visual
Factors Affecting Rate
No enzyme present, reaction rate would be directly proportional to [ ] of substrate Higher [ ], the more collisions=more reactions
Addition of enzyme speeds up reaction and changes plot of reaction
Rate >es as substrate >es but then levels off
Enzyme has become saturated (working as fast as it can)
Factors, cont.
Turnover number = number of molecules converted to product in one secondIf enzyme saturated, adding more substrate will NOT > reaction rate any furtherMost enzymes have optimal pH rangeTemperature affects enzyme activity Warming >es rate but only to a point; becomes too
warm, enzyme begins to denature (nonfunctional)
Isozymes (enzymes that catalyze same reaction but have different optimal temps) made by many organisms
And finally, brethren…
Let’s briefly discuss negative feedback model