energy and metabolism

An Introduction to Metabolism

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Overview: The Energy of Life

• Sel hidup

– Merupakan pabrik kimiawi mini, tempat terjadinya ribuan reaksi dalam ruang berukuran mikroskopik

– Mengubah energi dalam banyak cara


• Beberapa organisme

– Convert energy to light, as in bioluminescence

Figure 8.1


Concept 1:

• Metabolisme organisme mentransformasi materi dan energi berdasarkan hukum termodinamika

• Metabolisme

– Merupakan keseluruhan reaksi kimia dalam organisme

– Muncul dari interaksi antar molekul dalam lingkungan sel yang teratur


Organisasi Kimia Kehidupan dalam Jalur-jalur Metabolik

• Jalur metabolik (metabolic pathway) memiliki karakteristik :

– Dimulai dari molekul spesifik yang kemudian diubah dalam serangkaian langkah yang jelas sehingga menghasilkan produk tertentu

– Dikatalis oleh enzim tertentu

Enzyme 1 Enzyme 2 Enzyme 3

A B C DReaction 1 Reaction 2 Reaction 3

Startingmolecule

Product


• Jalur katabolik

– Memecahmolekul komplek menjadi molekul sederhana

– Melepaskan energi

– Misalnya respirasi seluler yang menguraikan gula glukosa dan molekul organik lain menjadi karbon dioksida dan air dengan kehadiran oksigen.

– Energi yang tersimpan dalam molekul organik bisa digunakan sel untuk melakukan kerja, misalnya untuk transpor membran


• Jalur anabolik

– Membangun molekul komplek dari molekul sederhana

– Mengkonsumsi energi

– Misalnya sintesis protein dari asam-asam amino


Forms of Energy

• Energi

– Merupakan kemampuan untuk mengakibatkan perubahan atau kemampuan untuk menyusun-ulang materi

– Terdapat dalam beberapa bentuk

– Kerja kehidupan tergantung poada kemampuan sel untuk mentransformasi energi dari satu bentuk ke bentuk lainnya


• Energi Kinetik

– Merupakan energi yang berkaitan dengangerak

– Benda yang bergerak dapat melakukan kerja dengan memberikan gerak pada materi lain, misal kontraksi otot kaki mendorong pedal sepeda

– Panas atau kalor (energi termal) adalah energi kinetik yg berasosiasi dgn pergerakan acak atom atau molekul

– Cahaya juga merupakan jenis energi yg dpt ditangkap utk melakukan kerja, misal pd fotosintesis


• Potential energy

– Energi yg tersimpan dalam materi krn lokasi atau strukturnya, misal molekul memiliki energi karena atom-atomnya.

– Energi kimia adalah energi potensial yg tersedia untuk dilepaskan dalam reaksi kimia

– Glukosa mengandung banyak energi kimia, yg selama reaksi katabolik, atom-atom disusun ulang dan energi dipaskan sehingga menghasilkan produk penguraian yang berenergi lebih rendah.


• Struktur dan jalur biokimiawi sel memungkinkan sel melepaskan energi kimia dari molekul makanan yang memberikan tenaga bagi proses-proses kehidupan


• Energi bisa diubah, dari satu bentuk ke bentuk lainnya

Pada tempat datar, penyelam punya lebih banyak EP

Terjun, mengubah EP menjadi EK

Mendaki, mengubah EK pergerakan otot menjadi EP

Di dalam air. Penyelam mempunyai EP yg lebih sedikit daripada di darat

Figure 2


The Laws of Energy Transformation

• Thermodynamics

– Is the study of energy transformations

– Organisme merupakan sistem terbuka, dimana energi dan materi dapat ditransfer antara sistem dan lingkungan

– Organisme menyerap energi, misal energi cahaya atau kimia dalam bentuk molekul organik, dan melepaskan panas dan sisa metabolik seperti CO2 ke lingkungan


The First Law of Thermodynamics

• Energi di semesta bersifat konstan

• Energi dapat ditransfer dan diubah, tapi tidak dapat diciptakan maupun dihilangkan.

• Misal : dengan mengubah cahaya matahari menjadi energi kimia, tumbuhan hijau bekerja sebagai transformer energi, bukan pembuat energi


• An example of energy conversion

Figure.3

Hukum I Termodinamika: Chitah mengubah energi kimia dari molekul organik dalam makanannya menjadi EK dan bentuk energi lain saat dia melakukan proses biologisnya.

(a)

Chemicalenergy


The Second Law of Thermodynamics

– Pada setiap transfer atau transformasi energi, sejumlah energi menjadi energi yg tidak dpt digunakan (anusable) dan tdk dpt tersedia untuk kerja, tetapi akan diubah menjadi panas, atau energi yg berasosiasi dg pergerakan acak atom dan molekul

Figure 8.3

Hukum II termodinamika, setiap transfer atau transformasi energi akan meningkatkan ketidakteraturan (entropi) semesta. Misal pada chitah, entropi ditambahkan dalam bentuk panas dan molekul kecil produk sampingan metabolosme

(b)

Heat co2

H2O+


• Concept 2: Perubahan energi bebas suatu reaksi menunjukkan apakah reaksi tersebut berlangsung spontan atau tidak


Perubahan energi bebas ( G )

• Energi bebas suatu sistem kehidupan

– merupakan energi yang dapat melakukan kerja dalam tingkat seluler, ketika suhu dan tekanan seragam di seluruh sistem


• Perubahan energi bebas dapat dihitung untuk suatu reaksi kimia sbb :

– Is related directly to the enthalpy change (∆H) and the change in entropy

– ΔH = perubahan entalpi sistem ( energi total)

– ΔS= perubahan entropi sistem

– T = suhu mutlak dalam Kelvin (K=oC +273)

∆G = ∆H – T∆S


• Hanya proses dengan ΔG negatif yg bersifat spontan (proses terjadi tanpa masukan energi dari luat)


Free Energy, Stability, and Equilibrium

• Organisme hidup dengan mengorbankan energi bebas

• Pada reaksi spontan

– Energi bebas berkurang, dan stabilitas sistem meningkat.


• At maximum stability

– The system is at equilibrium

Reaksi kimia. Molekul gula dalam sel diuraikan jd molekul sederhana

.

Difusi. Molekul dalam setetes zat warna berdifusi sampai tersebar acak

Pergerakan gravitasi. Obyek bergerak spontan dari tempat tinggi ke rendah.

•Lebih banyak energi bebas(G)• Kurang stabil• Kapasitas kerja lebih besar

• Energi bebas lebih rendah(lower G)• Lebih stabil•Kapasitas kerja lebih kecil

pada perubahan spontan• energi bebas sistem berkurang(∆G<0) • Lebih stabil• Energi bebas yg dilepas bisa untuk kerja

() (c)

Figure 4


Exergonic and Endergonic Reactions in Metabolism

• An exergonic reaction

– Berlangsung diiringi pelepasan netto energi bebas, terjadi secara spontan

Figure 8.6

Reactants

Products

Energy

Progress of the reaction

Amount ofenergyreleased (∆G <0)

Fre

e e

ne

rgy

(a) Exergonic reaction: energy released


• An endergonic reaction

– Reaksi yg menyerap energi bebas dari lingkungannya, tidak spontan

Figure 8.6

Energy

Products

Amount ofenergyreleased (∆G>0)

Reactants


Fre

e e

ne

rgy

(b) Endergonic reaction: energy required


Equilibrium and Metabolism

• Reactions in a closed system

– Eventually reach equilibrium

Figure 8.7 A

(a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium.

∆G < 0 ∆G = 0


• Cells in our body

– Experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium

Figure 8.7

(b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equlibrium.

∆G < 0


• An analogy for cellular respiration

Figure 8.7 (c) A multistep open hydroelectric system. Cellular respiration is analogous to this system: Glucoce is brocken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium.

∆G < 0

∆G < 0

∆G < 0


• Concept 8.3: ATP memberikan tenaga bagi kerja seluler dengan menggabungkan reaksi eksergonik dan endergonik

• A cell does three main kinds of work

– Kerja kimiawi, mendorong rekasi endergonik yg tdk spontan, misal sintesis polimer

– Transport, pemompaan zat melintasi membran melawan pergerakan spontan

– Chemical, misal kontraksi sel otot


• Energy coupling

– Merupakan kunci dalam pengelolaan sumber daya energi sel untuk melakukan kerja

– Penggunaan reaksi eksergonik untuk menggerakkan reaksi endergonik.

– ATP sbg perantara sebagian besar penggandengan energi dalam sel dan sebagai sumber energi langsung yg memberikan tenaga bagi kerja selulet


The Structure and Hydrolysis of ATP

• ATP (adenosine triphosphate)

– Is the cell’s energy shuttle

– Provides energy for cellular functions

Figure 8.8

O O O O CH2

H

OH OH

H

N

H H

O

NC

HC

N CC

N

NH2Adenine

RibosePhosphate groups

O

O O

O

O

O

-- - -

CH


• Energy is released from ATP

– When the terminal phosphate bond is broken

Figure 8.9

P

Adenosine triphosphate (ATP)

H2O

+ Energy

Inorganic phosphate Adenosine diphosphate (ADP)

PP

P PP i


• ATP hydrolysis

– Can be coupled to other reactionsEndergonic reaction: ∆G is positive, reaction is not spontaneous

∆G = +3.4 kcal/molGlu Glu

∆G = + 7.3 kcal/molATP H2O+

+ NH3

ADP +

NH2

Glutamicacid

Ammonia Glutamine

Exergonic reaction: ∆ G is negative, reaction is spontaneous

P

Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/molFigure 8.10


How ATP Performs Work

• ATP drives endergonic reactions

– By phosphorylation, transferring a phosphate to other molecules


• The three types of cellular work

– Are powered by the hydrolysis of ATP

(c) Chemical work: ATP phosphorylates key reactants

P

Membraneprotein

Motor protein

P i

Protein moved(a) Mechanical work: ATP phosphorylates motor proteins

ATP

(b) Transport work: ATP phosphorylates transport proteins

Solute

P P i

transportedSolute

GluGlu

NH3

NH2

P i

P i

+ +

Reactants: Glutamic acid and ammonia

Product (glutamine)made

ADP+

P

Figure 8.11


The Regeneration of ATP

• Catabolic pathways

– Drive the regeneration of ATP from ADP and phosphate

ATP synthesis from ADP + P i requires energy

ATP

ADP + P i

Energy for cellular work(endergonic, energy-consuming processes)

Energy from catabolism(exergonic, energy yieldingprocesses)

ATP hydrolysis to ADP + P i yields energy

Figure 8.12


• Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers

• A catalyst

– Is a chemical agent that speeds up a reaction without being consumed by the reaction


• An enzyme

– Is a catalytic protein


The Activation Barrier

• Every chemical reaction between molecules

– Involves both bond breaking and bond forming


• The hydrolysis

– Is an example of a chemical reaction

Figure 8.13

H2O

H

H

H

H

HO

OH

OH

OH

O

O OO OHH H H

H

H

H

CH2OH CH2OH

OHCH2OH

Sucrase

HOHO

OH OHCH2OH

H

CH2OH

H

CH2OH

H

O

Sucrose Glucose Fructose

C12H22O11 C6H12O6 C6H12O6

+HOH H


• The activation energy, EA

– Is the initial amount of energy needed to start a chemical reaction

– Is often supplied in the form of heat from the surroundings in a system


• The energy profile for an exergonic reaction

Fre

e en

ergy


∆G < O

EA

Figure 8.14

A B

C D

Reactants

A

C D

B

Transition state

A B

C D

Products


How Enzymes Lower the EA Barrier

• An enzyme catalyzes reactions

– By lowering the EA barrier


• The effect of enzymes on reaction rate


Products

Course of reaction without enzyme

Reactants

Course of reaction with enzyme

EA

withoutenzyme

EA with enzymeis lower

∆G is unaffected by enzymeF

ree

ener

gy

Figure 8.15


Substrate Specificity of Enzymes

• The substrate

– Is the reactant an enzyme acts on

• The enzyme

– Binds to its substrate, forming an enzyme-substrate complex


• The active site

– Is the region on the enzyme where the substrate binds

Figure 8.16

Substate

Active site

Enzyme

(a)


• Induced fit of a substrate

– Brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction

Figure 8.16 (b)

Enzyme- substratecomplex


Catalysis in the Enzyme’s Active Site

• In an enzymatic reaction

– The substrate binds to the active site


• The catalytic cycle of an enzyme

Substrates

Products

Enzyme

Enzyme-substratecomplex

1 Substrat memasuki situs aktiff, enzim berubah bentuk shg situs aktif mengelilingi substrat

2 Substrat ditahan pada situs aktif oleh interaksi lemah spt ikatan hidrogen dan ion

3 Situs aktif dapat menurunkan EA dan mempercepat reaksi dg :

• Bekerja sbg cetakan utk orientasi substrat

• Menekan substrat dan menstabilkan transisi

• Menyediakan lingkungan mikro yg kondusif

• Berpartisipasi langsung dalam reaksi katalitik

4 Substrat diubah jd produk5 Products are

Released.

6 Situs aktif dapat kembali diisi 2 molekul substrat baru

Figure 8.17


• The active site can lower an EA barrier by

– Orienting substrates correctly

– Straining substrate bonds

– Providing a favorable microenvironment

– Covalently bonding to the substrate


Effects of Local Conditions on Enzyme Activity

• The activity of an enzyme

– Is affected by general environmental factors


Effects of Temperature and pH

• Each enzyme

– Has an optimal temperature in which it can function

Figure 8.18

Optimal temperature for enzyme of thermophilic

Rat

e o

f re

actio

n

0 20 40 80 100Temperature (Cº)

(a) Optimal temperature for two enzymes

Optimal temperature fortypical human enzyme

(heat-tolerant) bacteria


– Has an optimal pH in which it can function

Figure 8.18

Rat

e o

f re

actio

n

(b) Optimal pH for two enzymes

Optimal pH for pepsin (stomach enzyme)

Optimal pHfor trypsin(intestinalenzyme)

10 2 3 4 5 6 7 8 9


Cofactors

• Cofactors

– Are nonprotein enzyme helpers

• Coenzymes

– Are organic cofactors


Enzyme Inhibitors

• Competitive inhibitors

– Bind to the active site of an enzyme, competing with the substrate

Figure 8.19 (b) Competitive inhibition

A competitiveinhibitor mimics the

substrate, competingfor the active site.

Competitiveinhibitor

A substrate canbind normally to the

active site of anenzyme.

Substrate

Active site

Enzyme

(a) Normal binding


• Noncompetitive inhibitors

– Bind to another part of an enzyme, changing the function

Figure 8.19

A noncompetitiveinhibitor binds to the

enzyme away fromthe active site, altering

the conformation ofthe enzyme so that its

active site no longerfunctions.

Noncompetitive inhibitor

(c) Noncompetitive inhibition


• Concept 8.5: Regulation of enzyme activity helps control metabolism

• A cell’s metabolic pathways

– Must be tightly regulated


Allosteric Regulation of Enzymes

• Allosteric regulation

– Is the term used to describe any case in which a protein’s function at one site is affected by binding of a regulatory molecule at another site


Allosteric Activation and Inhibition

• Many enzymes are allosterically regulated


– They change shape when regulatory molecules bind to specific sites, affecting function

Stabilized inactiveform

Allosteric activaterstabilizes active fromAllosteric enyzme

with four subunitsActive site

(one of four)

Regulatorysite (oneof four)

Active formActivator

Stabilized active form

Allosteric activaterstabilizes active form

InhibitorInactive formNon-functionalactivesite

(a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again.

Oscillation

Figure 8.20


• Cooperativity

– Is a form of allosteric regulation that can amplify enzyme activity

Figure 8.20

Binding of one substrate molecule toactive site of one subunit locks all subunits in active conformation.

Substrate

Inactive form Stabilized active form

(b) Cooperativity: another type of allosteric activation. Note that the inactive form shown on the left oscillates back and forth with the active form when the active form is not stabilized by substrate.


Feedback Inhibition

• In feedback inhibition

– The end product of a metabolic pathway shuts down the pathway


• Feedback inhibition

Active siteavailable

Isoleucineused up bycell

Feedbackinhibition

Isoleucine binds to allosteric site

Active site of enzyme 1 no longer binds threonine;pathway is switched off

Initial substrate(threonine)

Threoninein active site

Enzyme 1(threoninedeaminase)

Intermediate A

Intermediate B

Intermediate C

Intermediate D

Enzyme 2

Enzyme 3

Enzyme 4

Enzyme 5

End product(isoleucine)

Figure 8.21


Specific Localization of Enzymes Within the Cell

• Within the cell, enzymes may be

– Grouped into complexes

– Incorporated into membranes


– Contained inside organelles

1 µm

Mitochondria,sites of cellular respiraion

Figure 8.22

energy and metabolism

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