Metabolism: Energy and Enzymes
• Cells and Energy Flow
• Metabolic Reac?ons and
Energy Transforma?on
• Metabolic Pathways
• Enzymes
• Oxida?on and Reduc?on

Energy
Capacity to do work or bring about change
• All organisms have a constant need for energy
• KINETIC ENERGY
– Energy of Mo?on
– Mechanical energy
• POTENTIAL ENERGY
– Stored energy
– Food = Chemical energy
• Poten?al energy can be converted into kine?c energy


Flow of Energy
1st law of thermodynamics:
Energy cannot be created or
destroyed, but only change form

2nd Law of Thermodynamics
• Energy cannot be changed from one form to another
without a loss of usable energy
• OUen, this loss is in the form of heat

One Way Flow of Energy:
Sun loses E to Earth’s environment
E gained by organisms from environment
E lost by organisms back to environment

The sun is the original source of
energy for the food chain. Sun light
allows plants to grow.
(100,000 Units of Energy)
Plants capture approximately 1%
of the light energy from the sun.
This is done by photosynthesis.
(1,000 Units of Energy)
In a typical foodchain, Herbivores
(Vegetarians) eat approximately
10% of the plants produced.
(100 Units of Energy)
Carnivores (meat eaters) eat the
herbivores. They use around 10%
of the energy stored by the
herbivores.
(10 Units of Energy)

2nd Law of Thermodynamics
• Every energy transforma>on makes the universe
less organized
• Entropy – amount of disorganiza?on
• Randomness of the universe will only increase.

Metabolism
The sum of all of the chemical reac?ons that
occur in a cell
• Anabolic reac?ons: building/synthesis; requires
energy
– Transcrip?on, transla?on, DNA replica?on,
photosynthesis, synthesis of lipids, glycogen, etc.
• Catabolic reac?ons: breaking down; releases
energy
– Cellular respira?on, glycolysis, diges?on


Energy Use
• Chemical Work
– Energy for synthesis/anabolism
• Transport Work
– Energy to pump molecules across membranes
• Mechanical Work
– Energy for movement of cell or within cell
• Muscle contrac?on, cilia movement, chromosome movement

Enzymes
• Proteins that catalyze/speed up biochemical reac?ons
– Enzyme is not changed and is recycled.
– Some enzymes are RNA (rRNA).
• Characteris?c 3D shape determines func?on
– Substrate: reactant for an enzyme
• Specificity: Enzyme only binds to one substrate/set of substrates
– Ac>ve site: region of enzyme that interacts with substrate


1. Substrate binds to ac?ve site of enzyme
2. Enzyme‐substrate (temporary) complex is formed.
3. Substrate is transformed.
4. Products are released. Enzyme is unchanged.
5. Enzyme reacts with another substrate molecule.

How Do Enzymes Work?
• Molecules are in a state of mo?on
• Molecules must come collide with enough energy for a
reac?on to occur (Ac>va>on Energy)
• Temperature or pressure increase the energy of
molecules
– Cells can’t handle changes in these factors
• Enzymes:
– Help bring substrates together
– Posi?on/orient substrates to facilitate interac?on
– Lower the Ac>va>on Energy of a chemical reac?on


Enzyme Names
• End in –ase
• Substrate or type of reac?on catalyzed
Sucrase‐ sucrose  glucose + fructose + H2O
Transferase‐ transfers func?onal groups
Dehydrogenase‐ removes H
– Ex. Lactate dehydrogenase
Oxidase‐ adds O

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