Chapter 9: Introduction To Metabolism

Front 1

Metabolism

Back 1

Metabolism is the sum of the chemical reactions in an organism.

Front 2

Catabolism

Back 2

Catabolism is the energy-releasing processes.

Front 3

Anabolism

Back 3

Anabolism is the energy-using processes.

Front 4

Metabolic pathway

Back 4

A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell.
Metabolic pathways are determined by enzymes.
Enzymes are encoded by genes.

Front 5

Collision theory

Back 5

The collision theory states that chemical reactions can occur when atoms, ions, and molecules collide.

Front 6

Activation energy

Back 6

Activation energy is needed to disrupt electronic configurations.

Front 7

Reaction rate

Back 7

Reaction rate is the frequency of collisions with enough energy to bring about a reaction.
Reaction rate can be increased by enzymes or by increasing temperature or pressure.

Front 8

Enzymes

Back 8

carry out reactions at physiological conditions so they proceed in a timely manner

enzymes speed up the rate at which a reaction proceeds toward its final equilibrium

Front 9

The Mechanism of Enzyme Reactions

Back 9

A + B -> AB‡ -> C + D

AB‡ transition-state complex –
resembles both the substrates and the products

a typical exergonic reaction

Front 10

How Enzymes Lower Ea

Back 10

by increasing concentrations of substrates at active site of enzyme

by orienting substrates properly with respect to each other in order to form the transition-state complex

two models for enzyme-substrate interaction
-lock and key and induced fit

Front 11

protein catalysts

Back 11

have great specificity for the reaction catalyzed and the molecules acted on

Front 12

catalyst

Back 12

substance that increases the rate of a reaction without being permanently altered

Front 13

substrates

Back 13

reacting molecules

Front 14

products

Back 14

substances formed by reaction

Front 15

Structure and Classification of Enzymes

Back 15

some enzymes are composed solely of one or more polypeptides

some enzymes are composed of one or more polypeptides and nonprotein components

Front 16

apoenzyme

Back 16

protein component of an enzyme

Front 17

cofactor

Back 17

nonprotein component of an enzyme
*prosthetic group – firmly attached
*coenzyme – loosely attached

Front 18

holoenzyme

Back 18

holoenzyme = apoenzyme + cofactor

Front 19

Important Coenzymes

Back 19

NAD+
NADP+
FAD
Coenzyme A

Front 20

Coenzymes as Carriers

Back 20

often act as carriers, transporting substances around the cell

Front 21

Environmental Effects on Enzyme Activity

Back 21

enzyme activity is significantly impacted by :
-substrate concentration
-pH
-temperature

Front 22

Effect of [substrate]

Back 22

rate increases as [substrate] increases

no further increase occurs after all enzyme molecules are saturated with substrate

Front 23

Effect of pH and Temperature

Back 23

each enzyme has specific pH and temperature optima

Front 24

denaturation

Back 24

loss of enzyme’s structure and activity when temperature and pH rise too much above optima

Front 25

competitive inhibitor

Back 25

directly competes with binding of substrate to active site

Front 26

noncompetitive inhibitor

Back 26

binds enzyme at site other than active site

changes enzyme’s shape so that it becomes less active

Front 27

Ribozymes

Back 27

Thomas Cech and Sidney Altman discovered that some RNA molecules also can catalyze reactions

Front 28

Regulation of Metabolism

Back 28

important for conservation of energy and materials

maintenance of metabolic balance despite changes in environment

Front 29

Metabolic Regulation

Back 29

three major mechanisms
1. metabolic channeling
2. regulation of the synthesis of a particular enzyme (transcriptional and translational)
3. direct stimulation or inhibition of the activity of a critical enzyme
-post-translational

Front 30

Metabolic Channeling

Back 30

differential localization of enzymes and metabolites

Front 31

compartmentation

Back 31

differential distribution of enzymes and metabolites among separate cell structures or organelles

can generate marked variations in metabolite concentrations

Front 32

Post-Translational Regulation of Enzyme Activity

Back 32

two important reversible control measures
1. allosteric regulation
2. covalent modification

Front 33

Allosteric Regulation

Back 33

most regulatory enzymes

activity altered by small molecule

Front 34

allosteric effector

Back 34

binds non-covalently at regulatory site

changes shape of enzyme and alters activity of catalytic site

positive effector increases enzyme activity

negative effector inhibits the enzyme

Front 35

Covalent Modification of Enzymes

Back 35

reversible on and off switch

addition or removal of a chemical group (phosphate, methyl, adenyl)

Front 36

Advantages of Covalent Modification of Enzymes

Back 36

respond to more stimuli in varied and sophisticated ways

regulation on enzymes that catalyze covalent modification adds second level

Front 37

Feedback Inhibition

Back 37

also called end-product inhibition

inhibition of one or more critical enzymes in a pathway regulates entire pathway

-pacemaker enzyme

each end product regulates its own branch of the pathway

each end product regulates the initial pacemaker enzyme

Front 38

pacemaker enzyme

Back 38

catalyzes the slowest or rate-limiting reaction in the pathway

Front 39

isoenzymes

Back 39

different enzymes that catalyze same reaction