Chapter 8 notes
description
Transcript of Chapter 8 notes
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Chapter 8 notesAn Introduction to
Metabolism
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Concept 8.1Metabolism: the totality of an
organism’s chemical reactionsA metabolic pathway begins with a
specific molecule and is altered into a product- each step is catalyzed by an enzyme
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Concept 8.1Catabolic pathway: release energy
in the breaking down of complex molecules into simpler compounds- ex. glucose CO2 + H2O
Anabolic pathway: consume energy to build complicated molecules from simpler ones- ex. amino acids proteins
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Concept 8.1Energy: the capacity to do work
Reactions are either exergonic (energy outward) or endergonic
(energy inward)
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Concept 8.2Exergonic reactions proceed with a
net release of energy - occur spontaneously
Endergonic reactions absorb free energy from their surroundings- nonspontaneous
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Concept 8.2
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Concept 8.2Cells do three kinds of work:
- mechanical work (ex. contraction of a muscle cell)- transport work (ex. pumping of substances across a memebrance)- chemical work (ex. synthesis of polymers from monomers)
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Concept 8.3Energy coupling: the use of an
exergonic process to drive an endergonic one.
ATP (adenosine triphosphate) is the energy source used in most reactions.- contains a ribose (sugar), adenine (base), and 3 phosphate molecules
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Concept 8.3
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Concept 8.3Energy is released from ATP when the
terminal phosphate bond is brokenATP ADP + Pi + Energy- work is accomplished by phosphorylation- the transferring of the Pi to another
molecule (ex. channel protein)
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Concept 8.3ATP is regenerated in the cell by
phosphorylating ADP through an exergonic reaction in the cell
- in a muscle cell 10 million ATP
are consumed and regenerated per second per cell
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Concept 8.3
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Concept 8.4Spontaneous reactions may occur at
veryslow rates- sucrose glucose + fructose- if an enzyme is added, the same
reaction can be completed in seconds .
Catalyst : a chemical agent that speeds up reaction w/out being consumed
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Concept 8.4Enzyme : a biological catalyst
Activation energy , the energy needed to begin a reaction, prevents many reactions from occurring quickly
Heat is used to speed up reactions because it increases the speed of reactant molecules (they collide more often).
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Concept 8.4In biological systems heat alone would
not work- too much heat denatures proteins and kills cells
An enzyme (catalyst) lowers the amount of activation energy needed- enzymes are very selective
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Concept 8.4
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Concept 8.4The reactant an enzyme binds to is
called the substrate- binds to the active site of the enzyme- the enzyme converts the substrate to product- the product is released
Enzyme animation
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Concept 8.4Up to a point, the rate of an
enzymatic reaction will increase with temperature- eventually it will drop because of thermal agitation and protein denaturing
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Concept 8.4Most human enzymes function best at 35 - 40 oC.- some bacteria that live in hot springs
have proteins that work best at 70 oC.
Most human enzymes also work best at 6-8 pH .
- pepsin in the stomach work best at pH of 2.
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Concept 8.4
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Concept 8.4Certain chemicals can selectively
inhibit the activity of specific enzymes
Competitive inhibitors: reduce enzyme activity by blocking the substrate from binding to the active site- can be overcome by increasing the substrate
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Concept 8.4Noncompetitive inhibitors: impede
the reaction by attaching to another part of the enzyme, thus changing its shape- ex. toxins and poisons