Transcript BIO 10 Lecture 2

BIO 10
Lecture 6
THE VITAL FORCE:
AN INTRODUCTION TO ENERGY
WHAT IS ENERGY?
• Energy = the capacity to do work
• Energy is a tricky subject to understand
because it can be measured but not seen.
• Two main forms:
– Potential energy: stored energy
• a rock on a hill
• a lump of coal
– Kinetic energy: energy in motion
• a rolling rock
• heat from a burning lump of coal
Energy is the “Vital Force”
• Vital = “of or concerned with life”
• Life needs energy to work against entropy
• Where does the energy come from?
– The whole Universe was wound up like a giant music box
by the Big Bang
– The “winding up” is the potential energy created when
matter was first separated in space and time
– This potential energy is converted to kinetic energy as
matter falls together by gravity and stars “shine”
• Life on Earth sucks energy from the radiation emitted
by the Sun, Earth’s nearest star
– A few organisms suck energy from thermal processes
created by the heat of Earth’s own gravitational collapse
Life harvests the energy of high energy (short
wavelength) photons from the Sun to work against
entropy to create highly ordered systems.
The leftover energy is then re-radiated back into
space at a longer (less energetic) wavelength.
Thermodynamics:
The Study of Energy
• First law of thermodynamics: energy
is neither lost nor gained, but only
transformed.
– Examples: solar energy (kinetic) used to
create carbohydrates (potential) in plants,
and steam engine burning coal (potential)
to generate heat to move pistons (kinetic).
• Second law of thermodynamics:
explains what is observed when energy is
transferred, and why certain reactions
occur spontaneously (e.g. coal will burn,
but ashes will not)
– Start with coal (potential energy), add a flame, and a
reaction occurs spontaneously to produce ashes and
hot air (kinetic energy)
– Transfer always goes spontaneously from an
ordered, concentrated form (e.g. chemical bonds
between carbons in coal) to a disordered, dispersed
form (e.g. heat and gases).
• Coal does not spontaneously reform from ashes and hot
air. Why? Because energy transformation occurs
spontaneously only when it goes from greater to
lesser order
• The second law of thermodynamics describes how
energy is transferred, and it states that when energy is
transferred it always results in a greater amount of
disorder in the universe.
Entropy is a measure of the
amount of disorder in a system.
Transformation of energy
The less energy is lost in an unusable form
during the transformation of from one form to
another, the most efficient the process is at
generating WORK
Living organisms need energy in order to
maintain the order (fight entropy) and do
the work required to preserve and
perpetuate the DNA molecules they
contain.
They suck this energy from
the Sun or Earth (either
directly or indirectly), which
sucks it from the Universe
(via gravitational collapse)
Energy Reactions and
Cycles in Living Organisms
• Synthesis reactions (like making
carbohydrates—more ordered and
complex than carbon dioxide gas)
takes energy
– These are “uphill” reactions because
they fight against the second law of
thermodynamics
– Also called endergonic reactions
• “energy in” because they require energy to
go
• Degradation Reactions (like breaking
down carbohydrates into carbon
dioxide again) release energy
These are “downhill”
reactions because they
increase entropy
Are also called exergonic
reactions: “energy out”
because they go
spontaneously without the
input of energy from the
surroundings
Coupling of Reactions
• Since both endergonic and exergonic reactions take
place in living organisms, they are often chemically
linked.
• Example: The creation of the complex molecule
glycogen is endergonic (requires the input of energy)
• The energy is provided by breaking down another
molecule to release energy. That molecule is ATP.
ATP: Life’s Energy Currency
• The ATP molecule stores energy, much like your
bank account stores dollars until you need to use
them.
– Negatively charged phosphates repel each other, ATP (three
phosphates), ADP (two phosphates).
– Linking them requires overcoming this repulsion using
energy (jack-in-the-box analogy), so making ATP from ADP
and a third phosphate requires energy (endergonic), but
releasing the third phosphate from ATP to make ADP
generates energy (exergonic).
– ATP has more energy than ADP.
• Example of how ATP
can be used to perform
cellular work:
– Cell needs to move
calcium ions up their
concentration gradient into
a muscle cell.
– ATP splits into ADP and
phosphate, a downhill
reaction that releases
energy.
– The energy is used to
transfer a phosphate
molecule onto a protein,
causing a shape change
that drives calcium across
the membrane.
The Need for Enzymes
– Exergonic reactions may not happen very
quickly, even though they are
spontaneous
• In living organisms the reactions are hastened
by enzymes.
– Many different enzymes may be needed to
accomplish one task. Series of steps and
the enzymes that hasten them are called
metabolic pathways.
– Substrate = substance being worked on by
each specific enzyme.
• Enzymes hasten
reactions by lowering
the amount of energy
needed to get
chemical reactions
going (activation
energy).
• Enzymes are catalysts
(retain their original
chemical composition
while bringing about a
change in a specific
substrate).
• Almost all enzymes are proteins.
• Have complex 3-D structures
– Active site = place that binds substrate
– “Lock and key” model – highly specific
Example:
• Chymotrypsin
breaks down
proteins in the
small intestine
• A shape change
caused by the
binding of the
substrate leads to
the breakage
Short Review of Lecture 6
• What is energy and why is it so important to
living things?
• What two forms does energy come in?
• What do the two Laws of Thermodynamics
state?
• Plants breathe in CO2 and then harvest
radiation energy from the sun to turn it into
carbohydrates
– Is this an endergonic or exergonic reaction?
– Are carbohydrates more or less ordered than CO2?
• How are carbohydrates and ATP molecules
functionally similar?