BIO100 - chp 5
Metabolism, Energy and Enzymes
Energy is the ability to do work or bring about a change. All living things are constantly changing
and need to acquire energy. Cells use acquired energy to maintain: a) cellular organization and
b) carry out reactions that allow organisms to develop, grow and reproduce.

There are two forms of energy:
1.
Kinetic energy - energy of movement
2. Potential energy -stored energy

Energy has properties & exhibits energy behavior. This is defined through the laws of
thermodynamics.
Laws of thermodynamics
–
1st law - is the Law of energy conservation. That means that:
 Energy cannot be created or destroyed, but it can be changed from one form to
another
 The total amount of energy in the universe remains constant
–
2nd law


Energy cannot be changed from one form to another without a loss of usable energy.
The amt. of energy in useful form will decrease
Matter is Organization. Entropy: means that energy is less organized and that there is an increase in
the randomness of energy dispersement. Energy is more organized when energy is concentrated,
therefore, energy is less organized when energy is widely dispersed. For examples:
 In gasoline, the one 8-carbon atom molecule that is stable and more concentrated
during potential energy.
 On the other hand, eight carbon atoms moving separately during kinetic energy in
carbon dioxide molecules released during kinetic energy.
•
Matter tends toward increasing randomness and disorder.
Living things, on the other hand, use solar energy to construct complex molecules and maintain
orderly structures – in order to battle against or resist disorder.
Solar energy (produced by nuclear reactions in the sun) provides almost all the energy used by
life on earth. These solar reaction produce huge increases in entropy
Flow of Energy
The ultimate source of energy for most forms of life on
earth is solar energy
Living things use the energy of sunlight to create low
entropy condition.
How does Energy Flow? - Through Metabolic Reactions & Energy Transformations
•
Chemical reaction – converts one chemical substance (reactants) into another (product)
•
Chemical reactions - is the process that forms and breaks chemical bonds that hold atoms
together.
•
These chemical reactions occur in cells
•
–
Reactants are the substances that participate in chemical reactions
–
Products- substances that are formed in a chemical reaction
–
Free energy- amount of energy that is available to do work after a chemical reaction has
occurred
p.75
Some chemical reaction release energy; others consume energy
1.
2.
•
Exergonic reactions release energy
Endergonic reactions consume energy
See types of energy transformations on pg. 76
Metabolic Reactions and Energy Transformations
•
Molecules do not react with one another unless they are activated in some way.
•
All chemical reactions require an initial input of energy just to get started- “the push”
•
Activation energy – the energy that must be added to make molecules react. This energy of
activation – is Kinetic energy, which is the usual source of activation energy. It is like forcing
together the outer electron shells of two atoms to react with each other. Molecules moving
with speed collide with each other to force their electron shells to mingle or react. As molecules
move fast, temperature increases, therefore, increasing chemical reactions
Coupled Reaction - Reactions that occur simultaneously. One is an exergonic reaction – releasing
energy and the other is endergonic reaction – consuming the energy released by the exergonic reaction.
An example is:
an exergonic reaction in the sun releases energy (light) that drives the endergonic
reactions in the plant to produce sugar (stored energy), as seen in photosynthesis.
Metabolic Reactions and Energy Transformations
•
ATP- (Adenosine triphosphate) is the most common energy for cells. The advantages of ATP as
energy carrier is to:
1. Provides energy for a wide variety of endergonic reations
2. Provides a common energy currency for many reactions
3. Breakdown of ATP releases sufficient energy for biological processes - little is wasted
Function of ATP:
1. Chemical work - supplies energy for synthesizing macromolecules that make up the cell and the
organism.
2. Transport work - supplies energy for active transport mechanisms across the plasma membrane
3. Mechanical work - supplies energy for muscle contraction, cilia movement, chromosome
migration, etc.
The utilization of ATP during membrane transports energy in Cells:
•
Exergonic reaction, like in glycolysis, powers the endergonic systhesis of ATP
•
This endergonic reaction converts ADP to ATP
•
This endergonic reaction of muscle cells is powered by the energy that is transferred from the
exergonic breakdown of ATP
•
During this coupled reaction, heat is released and lost as unusuable energy
•
Electron carriers - other carrier molecules that also transport energy within a cell
Metabolic pathways and enzymes
Enzymes are: 1) Are protein molecule that functions as an organic catalyst to speed up rate of
chemical reaction; and 2) Reactants in an enzymatic reaction are called substrates
•
Enzymes + Substrates + reaction
Substrate + enzyme = a reaction & products
Substrates + enzyme = a reaction &a product
Degredation
Synthesis
•
Enzymes are protein molecules that speed chemical reactions by lowering the energy activation.
•
They do this by forming enzyme substrate complex such as the following examples:
Substrate
Enzyme
lipid
lipase
Urea
Urease
Substrate
Maltose
Maltase
Ribonucleic acid
Ribonuclease
Lactose
•
Enzyme
Lactase
Metabolic pathways and enzymes pg. 78
Metabolic pathways are series of linked reactions. They begin with a specific reactant and produce an
end product. The 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…. Each step is catalyzed by a specific
enzyme
–
•
Enzymes are biological Catalysts proteins. Their structure of allows them to catalyze
specific reactions, which gives you the cycle of enzyme-substrate interactions
Factors affecting enzymatic speed: the concentration of substrates, the concentration of the
enzyme, the temperature and pH, the enzyme inhibition properties, or enzyme cofactors.
The substrate concentration affects the enzyme activity; it increases as the substrate concentration
increases - because there are more collisions between substrate and enzyme
Factors affecting enzymatic speed: Concentration:
•
•
•
•
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
Metabolic reactions
Factors affecting enzymatic speed: Temperature
•
•
•
•
Activity increases as temperature increases
Due to increased enzyme-substrate collisions
High heat will denature an enzyme by breaking down the tertiery structure (p.33)
Effect of temperature on rate of reaction
Factors affecting enzymatic rate: Enzyme inhibition and cofactors
•
•
•
•
•
Occurs when enzyme cannot bind its substrate
Activity of cell enzymes is regulated by feedback inhibition, When product is used up, it’s
removed from active site (Poisons - enzyme inhibitors)
Cofactors assist enzymes
Coenzymes are organic, non-protein helpers like vitamins
A deficiency of any vitamins results in lack of certain enzymatic actions