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Chapter 8 notes. An Introduction to Metabolism. Concept 8.1. Metabolism : the totality of an organism’s chemical reactions A metabolic pathway begins with a specific molecule and is altered into a product - each step is catalyzed by an enzyme. Concept 8.1.

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chapter 8 notes

Chapter 8 notes

An Introduction to Metabolism

concept 8 1
Concept 8.1

Metabolism: the totality of an organism’s chemical reactions

A metabolic pathway begins with a specific molecule and is altered into a product

- each step is catalyzed by an enzyme

concept 8 13
Concept 8.1

Catabolic 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 14
Concept 8.1

Energy: the capacity to do work

Reactions (Rxns.) are either exergonic (energy outward) or endergonic (energy inward)

concept 8 2
Concept 8.2

Exergonic rxns. proceed with a net release of energy

- occur spontaneously

Endergonic rxns. absorb free energy from their surroundings

- nonspontaneous

concept 8 27
Concept 8.2

Cells 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 3
Concept 8.3

Energy coupling: the use of an exergonic process to drive an endergonic one

ATP is the energy source used in most rxns.

- contains a ribose (sugar), adenine (base), and 3 phosphate molecules

concept 8 310
Concept 8.3

Energy is released from ATP when the terminal phosphate bond is broken

ATP  ADP + Pi + Energy

- work is accomplished by phosphorylation

- the transferring of the Pi to another molecule (ex. channel protein)

concept 8 312
Concept 8.3

ATP is regenerated in the cell by phosphorylating ADP through an exergonic rxn. in the cell

- in a muscle cell 10 million ATP are consumed and regenerated per second per cell

concept 8 4
Concept 8.4

Spontaneous rxns. May occur at very slow rates

- sucrose  glucose + fructose

- if an enzyme is added, the same rxn. can completed in seconds

Catalyst: a chemical agent that speeds up reaction w/out being consumed

concept 8 415
Concept 8.4

Enzyme: a biological catalyst

Activation energy, the energy needed to begin a rxn, prevents many rxns from occurring quickly

Heat is used to speed up rxns b/c it increases the speed of reactant molecules (to collide more often)

concept 8 417
Concept 8.4

In biological systems heat alone would not work

- too much heat denatures proteins and kills cells

An enzyme (catalyst) lowers the amt. of activation energy needed

- enzymes are very selective

concept 8 420
Concept 8.4

The 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 8 421
Concept 8.4

Up 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 8 422
Concept 8.4

Most 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 2

concept 8 424
Concept 8.4

Certain 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 [substrate]

concept 8 425
Concept 8.4

Noncompetitive inhibitors: impede the reaction by attaching to another part of the enzyme, thus changing its shape

- ex. toxins and poisons