Unit One
“Science Introduction and
Cellular Function”
“Energy and Life”
Energy
• Energy – the ability to do work
• Potential Energy – the capacity to do
work
• Kinetic Energy – energy of motion
• The study of energy is called
“Thermodynamics” because the most
convenient way to measure it is in the form
of heat
• There are many other forms of energy:
light, sound, radiation, electrical current
etc.
Laws of Thermodynamics
• First Law – energy can be converted from
one state to another but it is never
destroyed, and it never disappears
• Second Law - the universe is tending
toward disorder; no organisms or machine
is 100% efficient in its use of energy
– Entropy – is a measure of the degree of
disorder of a system; the second law can
simply be stated as “entropy increases”
Chemical Reactions
• CO2 + H2O + Sunlight  C6H12O6 + ATP + O2
• The substances to the left of the arrow are
called the Reactants
• The substances to the right of the arrow are
called the Products
• The arrow is synonymous with the word
“Yields”
• Reactions either require energy as they go
toward completion or release energy as they
go toward completion
Chemical Reactions
• Endergonic/Endothermic – reactions that
require energy to occur
• Exergonic/Exothermic – reactions that give
off energy in the form of heat as they occur
• In endergonic reactions, there is more
product energy than reactant energy; this
makes it more difficult for reaction to occur
• In exergonic reactions, there is more reactant
energy than product energy; this makes it
easier for reaction to occur
Chemical Reactions
• A “spark” is always needed to start a reaction,
whether it is an exergonic or endergonic reaction
• This “spark” is referred to as Activation Energy,
and is the chemical nudge needed to initiate the
reaction
• Recall from chapter 3 that proteins can be
enzymes which act as Catalysts
• A Catalyst speeds up a reaction making go
toward completion at a faster rate than it would on
its own
• In a reaction that has a catalyst present, the
activation energy is lower therefore speeding up
the reaction
Proteins = Enzymes = Catalysts
• Enzymes regulate cellular function; they ensure
reactions occur when they are needed
• The shape of the enzyme determines its
effectiveness at regulating reactions
• Enzymes are effective only in a certain range in
reference to temperature and pH
• The optimal temperature at which enzymes
function is approximately 98.6 F/ 37 C
• The optimal pH at which enzymes function is from
approximately 6 to 8 on scale (close to neutral)
Proteins = Enzymes = Catalysts
• Enzymes are often regulated by
Feedback Inhibition = the product of the
reaction acts to slow the effectiveness of
the enzyme
– A good example of feedback inhibition is a
factory assembly line
• Workers assemble a product
• Workers begin to assemble product too fast
• Workers are instructed to slow down production
Proteins = Enzymes = Catalysts
• Two types of Feedback Inhibition:
– Competitive Inhibitors – does not change
the shape of the enzyme but renders it
ineffective by interfering with its ability to
communicate chemically
– Noncompetitive Inhibitors – changes the
shape of the enzyme, and shape has
everything to do with its effectiveness as a
catalyst
ATP, the energy of the cell
• ATP = Adenosine Triphosphate
• ATP is the energy currency of the cell
• ATP has three main parts: 5 Carbon sugar
(y), 3 Phosphate groups (g), and a
Nitrogenous base (b)
ATP, the energy of the cell
• ATP releases energy for use by the cell via
the loss a phosphate group
• The resulting molecule is ADP =
Adenosine Diphosphate (“di” because it
has lost a phosphate group)
• ATP powers many of the cell’s functions:
– Movement of the flagella
– Expulsion of waste
– Heat production
ATP, the energy of the cell
• In plants, ATP is produced via
Photosynthesis and Cellular
Respiration (to be discussed in more
detail later)
• In animals, ATP is produced via Cellular
Respiration (to be discussed in more
detail later)