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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