Download - Metabolism e
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Metabolism
Processes by which living organisms obtain and utilize energy
Two parts to metabolismp
Catabolism
Degradation, pathways by which nutrients and cellular components are broken down for reuse or to generate energy
Anabolism
Biosynthesis, building up of biomolecules from simpler components
Trophic Strategies
Comes from Greek trophos meaning to feed
Classification of organisms based on anabolic patterns
Autotrophs synthesize all cellular components from simple inorganic molecules (e.g. H2O, CO2, NH3, H2S)
Chemolithotrophs energy derived from oxidation of inorganic compounds (e.g. NH3, H2S, Fe2+)
Photoautotrophs energy derived via photosynthesis
Heterotrophs energy derived from oxidation of organic compounds; existence dependent on autotrophs
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Trophic Strategies (continued)
Classification based on ultimate electron acceptor
Obligate aerobes use O2 and only O2 as electron acceptor
Anaerobes can use electron acceptors other than O2 (e.g. SO4, NO4 or organic compounds); i.e. do not require O2 to live.
Facultative anaerobes can grow either aerobically or anaerobically
Obligate anaerobes poisoned by O2; must grow without O2
Overview of Catabolism
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Thermodynamics, as Related to Metabolism
A + B C + D
+=
]][[]][[ln'
BADCRTGG o
Two types of reactions in metabolism
Reactions near equilibrium G close to zero
majority of reactions
Reactions far from equilibrium G
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Three Major Implications of Thermodynamics for Metabolism
Metabolic pathways are irreversible.
Biological systems are governed by thermodynamics!Biological systems are governed by thermodynamics!For a process to be spontaneous G must be negative
Every metabolic pathway has a committed step.
Usually the first irreversible step unique to a pathway.Usually an important site of regulation
Catabolic and anabolic pathways differ
1 2A
XY
Control of Metabolism is Regulation of Enzymes
SEkSVSKSEk
SKSVv
m
Tcat
m +=
+= max
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Allosteric Control
A B CD
E F
+
E F
Genetic Control
Alterations in the rate of transcription or translation result in alterations in the amount of protein made (i.e. [E]T).
Covalent Modification
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Substrate Cycles
vf and vr catalyzed by different enzymes
Net flux (vf-vr) can be increased by increasing vf or decreasing vr.
Such systems are more sensitive than single (unopposed) enzymes.
ATP A High Energy Compound
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ATP A Rationalization
l t bili tiless resonance stabilizationand
more electrostatic repulsion
than here!
ATP is not the Only High Energy Compound
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Coupled Reactions
Hydrolysis of Pyrophosphate is Used to Provide Extra Energy for Some Reactions
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Phosphocreatine An ATP Buffer
OOCCH2NC
CH3
NHNH P
OO
O+ ADP OOCCH2NC
CH3
NHNH2 + ATP
G0 = -12.6 kJ/mol
Nucleoside Diphosphate Kinase
ATP + NDP ADP + NTP
Adenylate Kinase
ATP + AMP 2 ADP
Thioesters Coenzyme A
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Redox Carriers NAD+
N
N N
NH
O
O
H3C
H3C
Redox Carriers Flavins (FAD / FMN)
Ribose-5-phosphate
N
N N
NH
O
O
H3C
H3C
Ribose-5-phosphate
H
H
H
FNM
FNMH
N
N N
NH
O
O
H3C
H3C
Ribose-5-phosphate
H
H
HFNMH
(radical)2
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Electrochemical Cells
For reaction:
Aox + Bred Ared + Box
+=
]][[]][[ln
redox
oxredO
BABARTGG
=
]][[]][[ln
redox
oxredO
BABA
nFRTEE