Chapter 8 notesAn Introduction to

Metabolism

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

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

Concept 8.1Energy: the capacity to do work

Reactions are either exergonic (energy outward) or endergonic

(energy inward)

Concept 8.2Exergonic reactions proceed with a

net release of energy - occur spontaneously

Endergonic reactions absorb free energy from their surroundings- nonspontaneous

Concept 8.2

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)

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

Concept 8.3

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)

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

Concept 8.3

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

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).

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

Concept 8.4

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

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

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.

Concept 8.4

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

Concept 8.4Noncompetitive inhibitors: impede

the reaction by attaching to another part of the enzyme, thus changing its shape- ex. toxins and poisons