Chapter 8
An Introduction to Microbial Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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