Download CH06-Metabolism-Fueling Cell Growth

Chapter 06
Metabolism: Fueling Cell Growth
 Two fundamental
tasks needed to
grow.
 Synthesis of
macromolecules
 Metabolism
 Important to
humans
 Food, medicine,
energy,
research
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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A Glimpse of History
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Biologists had noticed that in vats of grape juice,
alcohol and CO2 are produced while yeast cells
increase in number
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Biologists concluded that multiplying cells were
converting sugar in the juice to alcohol and CO2
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But idea not widely accepted
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Mocked by influential chemists and others
In 1850s, Louis Pasteur set out to determine how
alcohol develops from grape juice
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Simplified setup: clear solution of sugar, ammonia, mineral
salts, trace elements
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Added a few yeast cells—as they grew, sugar decreased,
alcohol level increased
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Strongly supported idea, but Pasteur failed to extract
something from inside the cells that would convert sugar
In 1897, Eduard Buchner, a German chemist,
showed that crushed yeast cells could convert sugar
to ethanol and CO2; awarded Nobel Prize in 1907
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Enzymes were extracted…..
Microbial Metabolism
 All cells need to accomplish two fundamental tasks
1) Synthesize new parts
• Cell walls, membranes, ribosomes, nucleic acids
2) Harvest energy to power reactions
• Sum total of these is called metabolism
• Human implications
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Used to make biofuels
Used to produce food
Important in laboratory
Invaluable models for study
Unique pathways potential
drug targets
6.1. Principles of Metabolism
 Can separate metabolism into two parts
1)
Catabolism
• Processes that degrade compounds to release
energy
• Cells capture to make ATP
2)
Anabolism/Biosynthesis
• Biosynthetic processes
• Assemble subunits of macromolecules
• Use ATP to drive reactions
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Processes intimately linked
Harvesting Energy
 Energy is the capacity to do work
 Two types of energy
1) Potential: stored energy (e.g., chemical bonds, rock on hill,
water behind dam)
2) Kinetic: energy of movement (e.g., moving water)
 Energy in universe cannot be created or destroyed,
but it can be converted between forms
Harvesting Energy
 Photosynthetic organisms
harvest energy in sunlight
• Power synthesis of organic
compounds from CO2
• Convert kinetic energy of
photons to potential energy of
chemical bonds
 Chemoorganotrophs obtain
energy from organic
compounds
• Depend on activities of
photosynthetic organisms
Harvesting Energy
 Free energy - is energy available to do work after a
chemical reaction has occured
• E.g., energy released when chemical bond is broken
• Compare free energy of reactants to free energy of products
1)Exergonic reactions: reactants have more free energy
• Energy is released in reaction
2)Endergonic reactions: products
have more free energy
• Reaction requires input of energy
Components of Metabolic Pathways
 Role of Enzymes (Proteins) – suffix “ase”…
• Biological catalysts: accelerate conversion of substrate
into product by lowering activation energy
• Highly specific: one at each step
• Reactions would occur without, but extremely slowly
Components of Metabolic Pathways
 Role of ATP
• Adenosine triphospate (ATP) is energy currency
• Composed of ribose, adenine, three phosphate groups
• Adenosine diphospate (ADP) acceptor of free energy
• Cells produce ATP by adding Pi to ADP using energy
• Release energy from ATP to yield ADP and Pi
Precursor Metabolites
 Precursor metabolites are intermediates of
catabolism that can be used in anabolism
• Serve as carbon skeletons for building macromolecules
• E.g., pyruvate can be converted into amino acids alanine,
leucine, or valine
6.2. Enzymes
 Environmental Factors Influencing Enzyme Activity
• Enzymes have narrow range of optimal conditions
• Temperature, pH, salt concentration
• 10°C increase doubles speed of enzymatic reaction up
until maximum
• Proteins denature at higher temperatures
• Low salt, neutral pH usually optimal
6.5. Fermentation
 Fermentation end products varied;
helpful in identification,
commercially useful
• E. coli is facultative anaerobe
• Lactic acid
• Ethanol
• Aerobic respiration, anaerobic
respiration, and fermentation
• Butyric acid
• Propionic acid
• Streptococcus pneumoniae
• 2,3-Butanediol
• Fermentation only option
• Mixed acids
 Fermentation used when
respiration not an option
6.8. Photosynthesis
 Photosynthesis
• Plants, algae, several groups of bacteria
• General reaction is
Light Energy
6 CO2 + 12 H2X
C6H12O6 + 12 X + 6 H2O
where X indicates element such as oxygen or sulfur
• Can be considered in two distinct stages
• Light reactions (light-dependent reactions)
– Capture energy and convert it to ATP
• Light-independent reactions (dark reactions)
– Use ATP to synthesize organic compounds
– Involves carbon fixation
Chapter 06
Metabolism: Fueling Cell Growth
 Two fundamental
tasks needed to
grow.
 Synthesis of
macromolecules
 Metabolism
 Important to
humans
 Food, medicine,
energy,
research
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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