Basic Metabolism and Energetics

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Basic Metabolism and Energetics

• Ichiro Matsumura
• October 3, 2002

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Overview

• Enzyme kinetics
• Metabolism and energetics

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Equilibrium
Mountain top
Mountain height
elevation
Valley depth
kF A kR B
The valley of the balls
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Enzymes accelerate reactions by decreasing DG
mountain top activation energy
Catalysts get the reaction to the equilibrium
faster, but dont affect Keq.
But Life is not at equilibrium!
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The Michaelis-Menten Equation explains the
saturation behavior of enzymes
Initial reaction velocity
Substrate concentration
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Some real life examples
High energy Carbohydrates, fats, oxygen
Our bodies work by converting high energy food
into low energy compounds and using that released
energy to perform its biological functions
Free Energy
Low energy CO2, H2O
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The paradox Life must sometimes go backwards
Proteins, DNA, RNA
Yet our bodies seem to work in the opposite
direction we take simple molecules and make
large complex structures out of them.
Free Energy
Amino acids, nucleotides.
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We burn food to make ourselves.
Food O2
Protein
Catabolism of food is coupled to anabolic
biosynthesis and the other processes of life.
Free Energy
Amino Acids
CO2 H2O
Total DG is negative - Life is a favorable
reaction!
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The secret some enzymes catalyze coupled
reactions.
The reaction is favorable as long as the total DG
is negative.
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Metabolism and energetics

• Metabolism
• Catabolism
• Anabolism
• Energetics
• ATP
• NAD, FAD
• Coupled reactions

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An example of a metabolic pathway
Most of the chemical transformations necessary
for Life cannot be catalyzed by single enzymes.
This metabolic pathway is called glycolysis.
You will learn about it later in great detail.
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ANABOLIC (BIOSYNTHETIC) PATHWAYS

• Energy utilization
• MUSCLE CONTRACTION
• ACTIVE ION TRANSPORT
• GENE EXPRESSION
• HORMONE SECRETION
• CELL DIVISION

ADP P
ATP
i
CATABOLIC (BREAK-DOWN) PATHWAYS

• Energy production
• OXIDATIVE PHOSPHORYLATION

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Catabolic pathways break down complex molecules
and produce energy.
FOOD
O2
ENERGY !!!
think about biochemistry
run to the bar
Jump for Joy
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Stages of Catabolism
STAGE
I- Complex to Building Blocks
II- Building Blocks to Acetyl CoA
Catabolic pathways tend to converge.
III- Oxidation of Acetyl CoA
Each arrow represents a catabolic pathway.
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can be hormone controlled
ANABOLIC (BIOSYNTHETIC) PATHWAYS

• Energy utilizing
• MUSCLE CONTRACTION
• ACTIVE ION TRANSPORT
• GENE EXPRESSION
• HORMONE SECRETION
• CELL DIVISION

Testosterone activates many anabolic pathways.
Other effects of anabolic steroids Heart attacks
and strokes Liver damage Acne Hair loss Breast
development (men) Genital shrinkage (men)
CA gubernatorial candidate
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Anabolic Reactions

• Building things out of the components
• Divergent pathways
• Requires Energy (ATP)
• Biosynthetic pathway is usually distinct from the
  catabolic mechanism
• Allows for differential regulation

A
B
A
B
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Comparison
Anabolic
Catabolic

• Divergent process
• End products are complex molecules
• Requires Energy
• Builds something

• Convergent process
• End products are simple molecules
• Releases Energy
• Breaks something down

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The body must balance catabolism and anabolism
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Some enzymes utilize cofactors

• Metals
• Coenzymes
• Prosthetic groups
• Heme
• Thiamine (B1), riboflavin (B2), pyridoxine (B6)
• Transiently associated cofactors
• ATP
• NADH
• FADH2

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Production of energy cofactors during catabolism
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Cofactors enable the coupling of most catabolic
and anabolic pathways.
Energy-yielding Nutrients
Complex Molecules
Proteins Polysaccharides Lipids Nucleic Acids
Carbohydrates Fats Proteins
Chemical Energy
Catabolism
ATP NADH
Anabolism
Energy Poor End Products
Precursor Molecules
Amino Acids Sugars Fatty acids Bases
CO2 H2O NH3
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ATP the energy currency of Life
For convenience, energy from catabolism is
usually stored as chemical energy in a
high-energy intermediate. Everybodys favorite is

High energy phosphate bonds 1. Electrostatic
repulsion 2. Resonance stabilization
Enzyme handle
O-
O-
P
HO
O
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Redox Energy Carrier
reactive center
H
NAD
NAD (Nicotinamide Adenine Dinucleotide)
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Redox Energy Carrier
vitamin B2
reactive center
FAD (Flavin Adenine Dinucleotide)
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The cell often uses reducing equivalent transfer
reducing-equivalent (proton electron) transfer
NADH H pyruvate
NAD lactate
(oxidation half-reaction)
NADH
NAD H 2e-
(reduction half-reaction)
lactate
pyruvate 2H 2e-
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Redox energy carriers can be exchanged for ATP
(during ox-phos)
Taking NADH back to NAD, you can get 2 or 3 ATP
molecules back for each NADH. FADH2 gives you 2
ATP per FAD.
ATP
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Important Points

• Metabolism is a balance between Catabolism and
  Anabolism
• ATP is often the energy used to drive unfavorable
  reactions (?G -7.3 kcal/mol)
• Redox co-factors also carry energy in the form of
  high energy electrons.