Metabolism: Energy and Enzymes
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Cell energy
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Metabolic reactions
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Energy transformation
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Metabolic pathways and Enzymes
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Oxidation-reduction of energy flow
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Cells and the flow of energy
BIO100 - chp 5
Energy is:
a.
b.
c.
The ability to do work or bring about a change
Living things are constantly changing and need to acquire energy
Cells use acquired energy to maintain:
 cellular organization
 carry out reactions that allow organisms to develop grow and reproduce.
There are Two forms of energy:
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Kinetic energy - energy of movement
Potential energy -stored energy
Cells and the flow of energy: There are 2 Laws of thermodynamics
1. 1st law
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
Law of energy conservation
Energy cannot be created or destroyed, but it can be changed from one
form to another
Total amt. of energy remains constant
2. 2nd law

Energy cannot be changed from one form to another without a loss of
usable energy
Flow of Energy
Metabolic reactions and energy transformations
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Energy Reactions in Metabolism. There are 3 chemical reactions that occur in cells
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Reactants are the substances that participate in chemical reactions
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Products- substances that are formed in a chemical reaction
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Free energy- amount of energy that is available to do work after a chemical reaction has
occurred. Seen as the release of ATP
ATP- the energy for cells (Adenosine triphosphate)
The Advantages of ATP as an energy carrier:
1. Provides a common energy currency for many metabolic reactions
2. Breakdown of ATP releases sufficient energy for biological processes - little is wasted
3. ATP breakdown is coupled to endergonic reactions in such a way that it minimizes
energy loss
How does energy flow in chemical reactions?
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Some chemical reaction release energy; while others consume energy
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Exergonic reaction = 2 substrates combine
and the reactions produce a byproduct plus energy.
This example show the production of 2 byproducts
and ATP energy is released.
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Endergonic reaction = this type of reaction takes
2 or more products and uses up energy to change
or produce a product
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Functions of ATP energy:
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Chemical work - supplies energy for synthesizing macromolecules that make up the cell
and the organism.
Transport work - supplies energy for active transport mechanisms across the plasma
membrane
Mechanical work - supplies energy for muscle contraction, cilia movement, chromosome
migration, etc.
Metabolic pathways and the role of enzymes
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Metabolic pathways are a series of linked reactions
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They begin with a specific reactant and produce an end product
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There are more efficient means of capturing metabolic energy than releasing it all in one
step – one reaction leads to the next reaction …. to the next reaction….
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Each step is catalyzed by a specific enzyme
Enzymes
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Protein molecule that functions as an organic catalyst to speed up rate of chemical
reaction
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Reactants in an enzymatic reaction are called substrates
Enzymes + Substrates + reaction
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Enzymes are protein molecules that speed chemical reactions by lowering the energy activation.
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They do this by forming enzyme substrate complex
Substrate
Enzyme
lipid
Lipase
Urea
Urease
Maltose
Maltase
Ribonucleic acid
Lactose
Ribonuclease
Lactase
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Enzymes are Biological Catalysts – ( a protein)
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The structure of enzymes allows them to catalyze (break down) specific reactions
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The cycle of enzyme-substrate interactions
Enzymes - there are Factors affecting enzymatic speed
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The concentration of the Substrates
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The concentration of the Enzyme
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Temperature and pH (too hot denatures it, to cold, slows or even halts the process)
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Enzyme inhibition
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Enzyme cofactors
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Factors affecting enzymatic speed
Substrate concentration
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Enzyme activity increases as substrate concentration increases - because there are more
collisions between substrate and enzyme
Enzyme concentration
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Cell regulates metabolism by regulating which enzymes are active
Genes producing enzymes can be turned on or off to regulate enzyme concentration
In some cases a signaling molecule is used to activate an enzyme
Temperature
1. Activity increases as temperature increases
2. Due to increased enzyme-substrate collisions
3. High heat will denature an enzyme by breaking down the tertiary structure (p.33)
4. Effect of temperature on rate of reaction – for example, the rate of enzymatic reaction doubles
with every 10°C but it will peaks at 40°C, in which then the metabolic reactions declines with
warmer temperatures – and can denatured the protein enzymes
Factors that can affect the rate of enzymes:
Enzyme inhibition (resistance of enzyme reaction) and cofactors
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It can occur when enzymes cannot bind its substrates
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Activity of cell enzymes is regulated by feedback inhibition, When product is used up,
it’s removed from active site (Poisons - enzyme inhibitors)
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Cofactors assist enzymes
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Coenzymes are organic, nonprotein helper like vitamins
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A deficiency of any vitamins results in lack of certain enzymatic actions