Chapter 8

An Introduction to Microbial Metabolism

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2

8.1 The Metabolism of Microbes

Metabolism – all chemical and physical workings of a cell

Two types of chemical reactions:

Catabolism – degradative; breaks the bonds of larger molecules forming smaller molecules; releases energy

Anabolism – biosynthesis; process that forms larger macromolecules from smaller molecules; requires energy input

Synthesis of Cell Structures

Sources of energy

Carbohydrates

Lipids

Proteins

End products with

reduced energy

CO2, H2O

Macromolecules

Carbohydrates

Proteins

Lipids

Simple building

blocks

Sugars

Amino acids

Catabolism

Releases energy

Anabolism

Requires energy

ATP

NADH

Incre

asin

g c

om

ple

xity

Figure 8.1 Simplified

model of metabolism

3

Enzymes: Catalyzing the Chemical Reactions of Life

• Enzymes are biological catalysts that increase the rate of a

chemical reaction by lowering the energy of activation (the

resistance to a reaction)

• The enzyme is not permanently altered in the reaction

• Enzyme promotes a reaction by serving as a physical site

for specific substrate molecules to position

Progress of Reaction

Energy of activation in the

absence of enzyme

Energy of activation in the

presence of enzyme

Products

Final state

Reactant

Initial

state

En

erg

y S

tate

of

Re

ac

tio

n

Insight 8.1

4

Enzyme Structure

• Simple enzymes – consist of protein alone

• Conjugated enzymes or holoenzymes – contain protein and nonprotein molecules – Apoenzyme: protein portion

– Cofactors: nonprotein portion • Metallic cofactors: iron, copper, magnesium

• Coenzymes, organic molecules: vitamins

Coenzyme

Apoenzymes

Coenzyme

Metallic

cofactor

Metallic

cofactor Figure 8.2

Conjugated enzyme

structure

5

Apoenzymes: Specificity and the Active Site

• Exhibits primary, secondary, tertiary, and some, quaternary structure

• Site for substrate binding is active site, or catalytic site

AS

AS

Levels of Structure

AS

AS

Primary Secondary Tertiary

Quaternary

(a) As the polypeptide

forms intrachain bonds

and folds, it assumes a

three-dimensional

(tertiary) state that

displays an active site

(AS).

(b) Because each

different polypeptide

folds differently, each

apoenzyme will have a

differently shaped active

site.

(c) More complex

enzymes have a

quaternary structure

consisting of more than

one polypeptide. The

active sites may be

formed by the junction of

two polypeptides.

Figure 8.3

6

Apoenzymes: Specificity and the Active Site

• A temporary enzyme-substrate union occurs when substrate moves into active site – induced fit

• Appropriate reaction occurs; product is formed and released

(a) (b) (c)

(d)

Substrate (S)

Products

S

Does

not fit

E E E

Enzyme (E) ES complex E

Figure 8.4 Enzyme-substrate reactions

7

Cofactors: Supporting the Work of Enzymes

• Micronutrients,

such as metal ions,

are needed as

cofactors to assist

the enzyme

• Coenzymes act as

carriers to assist

the enzyme in its

activity, such as

electron transfer

1. An enzyme

with a coenzyme

positioned to

react with two

substrates.

2. Coenzyme

picks up a

chemical group

from substrate 1.

4. Final action

is for group to

be bound to

substrate 2;

altered substrates

are released

from enzyme.

3. Coenzyme

readies the

chemical group

for transfer to

substrate 2.

Substrate 2 (S2 )

Coenzyme

(C)

Chemical

group (Ch)

Substrate 1 (S1)

Enzyme

complex

(E)

S2

S1

C E

Ch

C E

S1

S1

C E

Ch

Ch

S2

S1

Figure 8.5 Function of coenzymes

8

Location and Regularity of Enzyme Action

• Exoenzymes – transported extracellularly, where they

break down large food molecules or harmful chemicals

– Cellulase, amylase, penicillinase

• Endoenzymes – retained intracellularly and function there

– Most enzymes are endoenzymes

(a) (b)

Exoenzymes Endoenzymes

Active

enzyme

Products Substrate

Enzyme

Substrate

Products

Inactive

enzymes

Figure 8.6 Location of

action of enzymes

9

• Constitutive enzymes – always present, always produced in equal amounts or at equal rates, regardless of the amount of substrate

• Regulated enzymes – not constantly present; production is turned on (induced) or turned off (repressed) in response to changes in the substrate concentration

Regularity of Enzyme Action

(a)

Constitutive

enzymes

or

(b)

Regulated

enzymes

Enzyme level

increases

Add more

substrate

Add more

substrate

Remove

substrate

Enzyme level

is reduced

Figure 8.7

10

Synthesis and Hydrolysis Reactions

• Synthesis or

condensation reactions

– anabolic reactions to

form covalent bonds

between smaller

substrate molecules,

require ATP, release one

molecule of water for

each bond formed

O

C

C

H H

OH

G G

Enzyme

(a) Condensation Reaction. Forming a glycosidic bond

between two glucose molecules to generate maltose

requires the removal of a water molecule and energy from

ATP.

Glycosidic bond

2 glucose

molecules

OH HO

OH

H

G G

G G

O C H

H

OH

H

H2O

H2O

Enzyme

1 maltose

molecule Enzyme

Figure 8.8 a

11

Synthesis and Hydrolysis Reactions

• Hydrolysis reactions

– catabolic reactions

that break down

substrates into small

molecules; requires the

input of water to break

bonds

(b) Hydrolysis Reaction. Breaking a peptide bond between two

amino acids requires a water molecule that adds OH to one

amino acid and H to the other.

H2O

Peptide bond

Enzyme

Enzyme

aa1

aa1 aa2

aa2

NH

C

C

N H

O

O

OH

Enzyme

aa1 aa2

NH C

O

OH

H

H

Figure 8.8 b.

Sensitivity of Enzymes to Their Environment

• Activity of an enzyme is influenced by the

cell’s environment

• Enzymes operate under temperature, pH,

and osmotic pressure of organism’s habitat

• When enzymes are subjected to changes in

organism’s habitat they become unstable

– Labile: chemically unstable enzymes

– Denaturation: weak bonds that maintain

the shape of the apoenzyme are broken

12

13

Regulation of Enzymatic Activity and Metabolic Pathways

Multienzyme Systems

Linear

A

B

C

D

E

Cyclic

U

T input V

W

X

Z

Y

S product

Branched

O2

O

O1

Divergent

M

N

P

Q

R

Convergent

M

A

B

C

N

X

Y

Z

Figure 8.9 Patterns of

metabolic pathways

14

Direct Controls on the Actions of Enzymes

1. Competitive inhibition – substance that resembles the normal substrate competes with the substrate for the active site

2. Noncompetitive inhibition – enzymes are regulated by the binding of molecules other than the substrate away from the active site • Enzyme repression – inhibits at the genetic

level by controlling synthesis of key enzymes

• Enzyme induction – enzymes are made only when suitable substrates are present

Figure 8.10 Regulation of enzyme action

15

Substrate

Reaction proceeds

Noncompetitive Inhibition

Active site

Regulatory

molecule

(product)

Product

Regulatory site

Reaction is blocked because

binding of regulatory molecule in

regulatory site changes

conformation of active site so

that substrate cannot enter .

Normal

substrate Competitive

inhibitor with

similar shape

Enzyme

Enzyme Enzyme

Both molecules

compete for

the active site.

Reaction proceeds Reaction is blocked

because competitive

inhibitor is incapable

of becoming a product.

Competitive Inhibition

Figure 8.11 Enzyme repression – feedback inhibition

16

DNA RNA

Enzyme

Protein Folds to form functional

enzyme structure

Excess product binds to

DNA and shuts down further

enzyme production.

+

Substrate

Products

1 2 3 4

DNA RNA Protein No enzyme 7

5

6

8.2 The Pursuit and Utilization of Energy

• Energy: the capacity to do work or to

cause change

• Forms of energy include

– Thermal, radiant, electrical, mechanical,

atomic, and chemical

17

18

Cell Energetics

• Cells manage energy in the form of chemical reactions that make or break bonds and transfer electrons

• Endergonic reactions – consume energy

• Exergonic reactions – release energy

• Energy released is temporarily stored in high energy phosphate molecules. The energy of these molecules is used in endergonic cell reactions.

A B C Energy Enzyme

+ +

X Y Z Energy Enzyme

+ +

19

A Closer Look at Biological Oxidation and Reduction

• Redox reactions – always occur in pairs

• There is an electron donor and electron acceptor which constitute a redox pair

• Process salvages electrons and their energy

• Released energy can be captured to phosphorylate ADP or another compound

Oxidation

Glucose Reduction

C6H12O6 + 6O2 → 6CO2 + H2O + Energy

Oil Rig

20

Electron and Proton Carriers

• Repeatedly accept and release electrons and hydrogen to facilitate the transfer of redox energy

• Most carriers are coenzymes:

NAD, FAD, NADP, coenzyme A, and compounds of the respiratory chain

Oxidized nicotinamide Reduced nicotinamide

From substrate

2H

2e:

N

NH2

O

H

C

C C

C C

C

P

P

NADH + H+

N

H

C

C C

C C

C

O

P

P

Adenine

Ribose

H: H+

NAD+

NH2

Figure 8.13 NAD reduction

21

Adenosine Triphosphate: ATP, Metabolic Money

• Metabolic “currency”

• Three part molecule consisting of:

– Adenine – a nitrogenous base

– Ribose – a 5-carbon sugar

– 3 phosphate groups

• Removal of the terminal phosphate releases energy

• ATP utilization and replenishment is a constant cycle in active cells

N O–

P O –O

O

O

O

P O C

O

H

H

H

Adenine

O

OH OH

Ribose

Adenosine monophosphate (AMP)

Adenosine diphosphate (ADP)

Adenosine triphosphate (ATP)

N

N

N

H H

Bond that releases

energy when broken

P

N

H H H

O– O–

Figure 8.14

22

Figure 8.15 Phosphorylation of Glucose by ATP

Glucose

ATP ADP

Glucose-6-P

Glucose-6-phosphate Glucose

ATP ADP

Hexokinase

G

G

G

23

Figure 8.16 Formation of ATP

ATP can be formed by three different mechanisms:

1. Substrate-level phosphorylation – transfer of phosphate group from a phosphorylated compound (substrate) directly to ADP

2. Oxidative phosphorylation – series of redox reactions occurring during respiratory pathway

3. Photophosphorylation – ATP is formed utilizing the energy of sunlight

1 1

Phosphorylated

substrate

Substrate

Enzyme

PO4 ATP ADP

24

8.3 Pathways of Bioenergetics

• Bioenergetics – study of the mechanisms of

cellular energy release

• Includes catabolic and anabolic reactions

• Primary catabolism of fuels (glucose) proceeds

through a series of three coupled pathways:

1. Glycolysis

2. Kreb’s cycle

3. Respiratory chain, electron transport

25

Energy Strategies in Microorganisms

• Nutrient processing is varied, yet in many cases is based on three catabolic pathways that convert glucose to CO2 and gives off energy

• Aerobic respiration – glycolysis, the Kreb’s cycle, respiratory chain

• Anaerobic respiration – glycolysis, the Kreb’s cycle, respiratory chain; molecular oxygen is not the final electron acceptor

• Fermentation – glycolysis, organic compounds are the final electron acceptors

26

Overview of Catabolic Pathways

Glycolysis

AEROBIC RESPIRATION ANAEROBIC RESPIRATION

Glucose (6 C)

2 pyruvate (3 C)

Acetyl Co A

Electrons

Electron transport

O2is final electron

acceptor.

Maximum

ATP produced = 38

Maximum

ATP produced = 2 – 36

Maximum

ATP produced = 2

ATP

NADH

NADH

FADH2

Acetyl Co A

NADH

FADH2

CO2

CO2

ATP ATP

CO2

Glycolysis

Glucose (6 C)

2 pyruvate (3 C)

Lactic acid Acetaldehyde

Ethanol

+CO2

Electrons

Electron transport

Nonoxygen electron acceptors

(examples: SO42–, NO3

–,CO32–)

An organic molecule is final

electron acceptor (pyruvate,

acetaldehyde, etc.).

ATP

NADH

CO2

FERMENTATION

Glycolysis

Fermentation

Or other alcohols,

acids, gases

Glucose (6 C)

2 pyruvate (3 C)

ATP

NADH

CO2

Krebs Krebs

(a) (b) (c)

Figure 8.17

27

Aerobic Respiration

• Series or enzyme-catalyzed reactions in which electrons are transferred from fuel molecules (glucose) to oxygen as a final electron acceptor

• Glycolysis – glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C), NADH is generated

• TCA/Krebs – processes pyruvic acid and generates 3 CO2 molecules , NADH and FADH2 are generated

• Electron transport chain – accepts electrons from NADH and FADH; generates energy through sequential redox reactions called oxidative phosphorylation

Glycolysis

AEROBIC RESPIRATION

Glucose (6 C)

2 pyruvate (3 C)

Acetyl Co A

Electrons

Electron transport

O2is final electron

acceptor.

Maximum

ATP produced = 38

ATP

NADH

NADH

FADH2

CO2

CO2

ATP

Krebs

(a)

28

Glycolysis: The Starting Lineup

Fructose-6-phosphate

Fructose-1,6-diphosphate

(F-1,6-P)

4

5

6

7

8

9

1

3

2

Dihydroxyacetone

Phosphate

(DHAP)

Split of F-1,6-P; subsequent

reactions in duplicate Glyceraldehyde-

3-P

(G-3-P)

ADP ADP

Krebs cycle or fermentation

(see figures 8.20 and 8.25)

Krebs cycle or fermentation

Goes to Goes to

Glucose

Glucose-6-phosphate

Second phosphorylation

First phosphorylation

Glyceraldehyde-3

phosphate

Disphosphoglyceric

acid

Substrate-level

phosphorylation

3-phosphoglyceric

acid

Phosphoenolpyruvic acid

Pyruvic acid

ADP

2-phosphoglyceric acid

Substrate-level

phosphorylation

1C OCOCOCOCOC

COCOC COCOCOPO4

COCOCOPO4 COCOCOPO4

PO4OCOCOCOPO4 PO4 COCOCO PO4

COCOCOPO4 COCOCOPO4

COCOC COCOC

COCOC COCOC

COCOC COCOC

PO4

PO4 PO4

PO4 PO4

PO4 PO4

PO4

PO4

NAD H

NAD+ NAD+

NAD H

To

ele

ctr

on

tra

nsp

ort

To

ele

ctro

n tra

nsp

ort

H2O H2O

ADP

ATP ATP

ATP ATP

ATP

ATP

ADP

ADP

AEROBIC RESPIRATION

Glucose

ATP

NADH

CO2

CO2

NADH

FADH2

Glycolysis

ATP

Electron transport

O2 is final electron

acceptor

ATP produced = 38

Acetyl CoA

Krebs

Electrons

(6 C)

2 pyruvate (3 C)

PO4–3

1C OCOCOCOCOC

1C OCOCOCOCOC

1C OCOCOCOCOC

PO4–3

29

Pyruvic Acid – A Central Metabolite

Amino acids

Sugars

Fat metabolites

Glycolysis

Pyruvic acid

HO C C C H

O O H

H

l ll ll

l

Acetaldehyde

Acids, gas

Alcohol

Acetone

2, 3 butanediol Acetyl CoA

Krebs

cycle

Anabolic pathways Respiration Fermentation

Figure 8.19 Pyruvic

acid is the “hub”,

three different fates

from here

30

The Krebs Cycle – A Carbon and Energy Wheel

From glycolysis

Pyruvic acid

NAD+

NAD H+

Acetyl CoA

Oxaloacetic acid

CoA

Citric acid

Malic acid

Krebs Cycle

Isocitric acid

NAD+

NAD H+

CO2

a-Ketoglutaric acid

NAD

NAD H+

CO2

Succinyl CoA

ADP

CO2

FADH2

FAD

Step after first arrow is the reaction that

links glycolysis and the Krebs cycle and

converts pyruvic acid to acetyl coenzyme A.

This involves a reduction of NAD+

The 2C acetyl CoA

molecule combines with

oxaloacetic acid, forming

6C citrate, and releasing

CoA.

Citric acid changes

the arrangement of

atoms to form

isocitric acid.

Succinyl CoA is converted

to succinic acid and

Regenerates CoA. This

releases energy that is

captured in ATP.

Succinic acid loses 2 H+

and 2 e–, yielding fumaric

acid and generatiang

FADH2.

Fumaric acid

reacts with

water to form

malic acid.

An additional NADH

is formed when malic acid

is converted to oxaloacetic

acid, which is the final

product to enter the cycle

again, by reacting with

acetyl CoA.

a-ketoglutaric acid

Loges the second CO2

and generates

another NADH+

plus 4C succinyl CoA

Isocitric acid is

converted to 5C

a-ketogluaric

acid,which

yield NADH

and CO2

O

C OH

CoA

CH3

C

C OO–

C =O

C H2

C OO–

C OO

C H2

HO C OO–

C H2

C OO–

S

O

C

CH3

C OO–

C H

H C

C OO–

C OO–

C H2

C H2

H C

HO C H

C OO–

COO–

C H2

O C

C OO–

O

C O–

C H2

C H2

C

O S C0A

C OO–

CH2

CH2

C OO2

C0A

C OO–

C H

H C

COO –

Fumaric acid

H +

H+ NAD H +

C

H

H

1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

8

PO4 – 3

H2O

HO

ATP

AEROBIC RESPIRATION

Glucose (6 C)

2 pyruvate (3 C)

ATP

NADH

CO2

CO2

NADH

FADH2

Glycolysis

ATP

Electron transport

O2 is final electron

acceptor

ATP produced = 38

Acetyl CoA

Krebs

Electrons

Figure 8.20

31

The Respiratory Chain: Electron Transport and Oxidative Phosphorylation

• Final processing of electrons and hydrogen and

the major generator of ATP

• Chain of redox carriers that receive electrons

from reduced carriers (NADH and FADH2)

• ETS shuttles electrons down the chain, energy is

released and subsequently captured and used

by ATP synthase complexes to produce ATP –

Oxidative phosphorylation

32

Figure 8.21Electron Transport and Chemiosmosis

Matrix (inner

compartment)

Outer mitochondrial membrane

Inner mitochondrial membrane

Cristae

FMN

Coenzyme Q

Cytochrome b

Cytochrome c1

Cytochrome c

Cytochrome a

Cytochrome a3

Outer membrane

Intermembrane

space of

matrix

Matrix

Crista

F Q b

c1

c

a a3

NADH

dehydrogenase

FMN Coenzyme Q

Cytochrome b

Cytochrome c1

Cytochrome c

Intermembrane

space (outer

compartment)

NADH

dehydrogenase

Cytochrome a

Cytochrome a3

e–

2 H+

Outer compartment (intermembrane space)

Inner compartment (mitochondrial matrix)

2 2

2 H+

FADH2

1/2 O 2

From Krebs From Krebs

and glycolysis

Crista ATP

synthase

H+

H+

H+

e– e–

e– e–

e– e–

e– e–

e– e–

e–

e– e–

e– e–

e– e–

H2O

Outer

membrane

of the

mitochondrion

NAD H

NAD

ATP

33

The Formation of ATP and

Chemiosmosis

• Chemiosmosis – as the electron transport carriers shuttle electrons, they actively pump hydrogen ions (protons) across the membrane setting up a gradient of hydrogen ions – proton motive force

• Hydrogen ions diffuse back through the ATP synthase complex causing it to rotate, causing a 3-D change resulting in the production of ATP

34

H + H+

Cytochrome

aa3

Crista

H+ ions

Outer compartment

Inner

compartment

Intermembrane

space

(a)

ADP + Pi

ATP

ATP

synthase

F0 F1

e–

H+

H H

O

O

1/2 O 2

(b)

1 Charged

As the carriers in the mitochondrial cristae transport

electrons, they also actively pump H+ ions (protons) to the

intermembrane space, producing a chemical and charge

gradient between the outer and inner mitochondrial

compartments.

The distribution of electric potential and the concentration

gradient of protons across the membrane drive the synthesis of

ATP by ATP synthase. The rotation of this enzyme couples

Diffusion of H+ to the inner compartment with the bonding of ADP

And Pi. The final event of electron transport is the reaction of the

electrons with the H+ and O2 to form metabolic H2O. This step is

catalyzed by cytochrome oxidase (cytochrome aa3).

H+ H+

H+

H+

H+

H+

H+

H+ H+

H+

H+

H+

H+ H+

H+ H+ H+

e–

2 Charged

Figure 8.22 Chemiosmosis

Electron Transport and ATP Synthesis

in Bacterial Cell Envelope

35

H

H

H H

H

H H

H

ATP

AD P

Cell wall

Cell membrane

with ETS

Cytoplasm

ATP synthase

H

H

H

H H

H

H H

H

H

H H

H

Enlarged view of bacterial cell envelope to show the

relationship of electron transport andATP synthesis.

Bacteria have the ETS an ATP synthase stationed in

the cell membrane. ETS carriers transport H+ and

electrons from the cytoplasm to the exterior of the

membrane. Here, it is collected to create a gradient

just as it occurs in mitochondria.

(c)

Figure 8.22 c

36

The Terminal Step of Electron Transport

• Oxygen accepts 2 electrons from the ETS and

then picks up 2 hydrogen ions from the solution

to form a molecule of water. Oxygen is the final

electron acceptor

2H+ + 2e- + ½O2 → H2O

37

Figure 8.23 Theoretic ATP Yield for Aerobic Respiration

Glucose

GLYCOLYSIS

Fructose 1, 6-bis PO 4

2 Glyceraldehyde 3 PO 4

2 Pyruvate

2 NADHs 6 ATPs

2ATPs

6 NADHs

2FADH2s

Oxidative

phosphorylation

6ATPs Oxidative

phosphorylation

in ETS

in ETS

in ETS

Substrate-level

phosphorylation

2ATPs* Substrate-level

phosphorylation

38 ATP maximum T otal aerobic yield

18ATPs Oxidative

phosphorylation

4ATPs Oxidative

phosphorylation

2 NADHs

2 Acetyl-CoA

2 Krebs cycles

38

Anaerobic Respiration

• Functions like aerobic respiration except it utilizes oxygen containing ions, rather than free oxygen, as the final electron acceptor

– Nitrate (NO3-) and nitrite

(NO2-)

• Most obligate anaerobes use the H

+ generated during

glycolysis and the Kreb’s cycle to reduce some compound other than O2

ANAEROBIC RESPIRATION

Maximum

ATP produced = 2 – 36

Acetyl Co A

NADH

FADH2

ATP

CO2

Glycolysis

Glucose (6 C)

2 pyruvate (3 C)

Electrons

Electron transport

Nonoxygen electron acceptors

(examples: SO42–, NO3

–,CO32–)

ATP

NADH

CO2

Krebs

(b)

39

The Importance of Fermentation

• Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen

• Uses organic compounds as terminal electron acceptors

• Yields a small amount of ATP

• Production of ethyl alcohol by yeasts acting on glucose

• Formation of acid, gas, and other products by the action of various bacteria on pyruvic acid

Maximum

ATP produced = 2

Lactic acid Acetaldehyde

Ethanol

+CO2

An organic molecule is final

electron acceptor (pyruvate,

acetaldehyde, etc.).

FERMENTATION

Glycolysis

Fermentation

Or other alcohols,

acids, gases

Glucose (6 C)

2 pyruvate (3 C)

ATP

NADH

CO2

(c)

40

Figure 8.24 Alcoholic & Acidic Fermentation

Glucose

Pyruvic acid

Glycolysis

Ethyl alcohol

Acetaldehyde

System: Homolactic bacteria

Human muscle

System: Yeasts

C C OH

O O

C

H

H

H

OH C C

H

H

H

H

H

C C

O

H

H

H

H

C C C

H

Lactic acid

H

H

H

OH O

OH

NAD+

NAD H

NAD+

NAD H NAD H

CO2

H H

41

Figure 8.25 Products of Pyruvate Fermentation

Propionibacterium Enterobacter

Acetobacterium

Acetoacetic acid

Butyric acid Clostridium

Formic acid

CO2 + H2 Proteus

Mixed

acids Streptococcus , Lactobacillus

Oxaloacetic acid

Acetylmethylcarbinol

2,3 butanediol

Acetyl CoA

Ethanol

Succinic acid

Propionic acid

Pyruvate

Acetic acid

Escher ichia,

Shigella

Lactic acid

Yeasts

NAD H

42

8.4 Biosynthesis and the Crossing Pathways of Metabolism

• Many pathways of metabolism are bi-directional or amphibolic

Carbohydrates

Cell wall

Storage

Starch

Cellulose

Nucleotides

Chromosomes

Nucleic

acids

Fatty acids

Cell

structure

Macromolecule

Building block

Metabolic

pathways

Simple

products

Membranes

Storage

Lipids

Fats

Amino acids

Deamination Beta

oxidation

GLUCOSE

Enzymes

Membranes

Proteins

Krebs

cycle

NH3 CO2 H2O

Acetyl coenzyme A

Pyruvic acid

Cata

bolis

m

Anabolis

m

Gly

coly

sis

Biosynthesis and the Crossing

Pathways of Metabolism • Catabolic pathways contain molecular intermediates

(metabolites) that can be diverted into anabolic pathways

– Pyruvic acid can be converted into amino acids through amination

– Amino acids can be converted into energy sources through deamination

– Glyceraldehyde-3-phosphate can be converted into precursors for amino acids, carbohydrates, and fats

Carbohydrates

Cell wall

Storage

Starch

Cellulose

Nucleotides

Chromosomes

Nucleic

acids

Fatty acids

Cell

structure

Macromolecule

Building block

Metabolic

pathways

Simple

products

Membranes

Storage

Lipids

Fats

Amino acids

Deamination Beta

oxidation

GLUCOSE

Enzymes

Membranes

Proteins

Krebs

cycle

NH3 CO2 H2O

Acetyl coenzyme A

Pyruvic acid

Cata

bolis

m

Anabolis

m

Gly

coly

sis