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Samenvatting Celfysiology Campbell
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Summary of all material for the course Cell Physiology from the book Campbell Biology
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Samenvatting Campbell CelfysiologieCF 1-2: Chapter 6; concept 6.1,6.2,6.3
Concept 6.1 An organism’s metabolism transforms matter of energy
The totality of an organism’s chemical reactions is called metabolism. A metabolic
pathway is a map of many chemical reactions of a cell, arranged as intersecting
metabolic pathways.
Catabolic pathways are metabolic pathways that release energy by breaking down
complex molecules to simpler compounds, like respiration (glucose gets broken
down to carbon dioxide and water).
Anabolic pathways (sometimes called biosynthetic pathways) consume energy to
build complicated molecules from simpler ones.
Catabolic and anabolic pathways are the “downhill” and “uphill” avenues of the
metabolic landscape. Energy released from downhill reactions of catabolic pathways
can be stored and then used to drive uphill reactions of anabolic pathways.
Bioenergetics are the study of how energy flows through living organisms.
Energy is the capacity to cause
change, but it’s also the ability to
rearrange a collection of matter.
Energy which can be associated with
the relative motion of objects is
called kinetic energy. Moving
objects can per-form work by
imparting motion to other matter.
Thermal energy is kinetic energy
associated with the random
movement of atoms or molecules;
thermal energy in transfer from one
object to another is called heat.
Light is also a type of energy that
,can be harnessed to perform work, such as powering photosynthesis in green plants.
Potential energy is the energy that matter possesses (bezitten) because of its
location or structure (example: water behind a dam).
Chemical energy is a term used by biologists to refer to the potential energy
available for release in a chemical reaction. Some catabolic pathways release energy
by breaking down complex molecules. Biologists say that these complex molecules,
such as glucose, are high in chemical energy.
Thermodynamics is the study of the energy transformations that occur in a
collection of matter is called. Scientists use the word system to denote the matter
under study; they refer to the rest of the universe—everything outside the system—as
the surroundings. An isolated system, such as that approximated by liquid in a
thermos bottle, is unable to exchange either energy or matter with its surroundings
outside the thermos. In an open system, energy and matter can be transferred
between the system and its surroundings. Organisms are open systems.
Entropy is a measure of molecular disorder or randomness. The more randomly
arranged a collection of matter is, the greater the entropy.
First law of thermodynamics: Energy can be transferred and transformed, but
it cannot be created or destroyed , so the energy of the universe is constant.
The law is also known as the principle of conservation of energy
Second law of thermodynamics: Every energy transfer or transformation
increases the entropy of the universe.
Spontaneous process is an process which can proceed without requiring an input of
energy. A process that, on its own, leads to a decrease in entropy is said to be
nonspontaneous: It will happen only if energy is supplied.
, For instance, we know that water flows downhill spontaneously but moves uphill only
with an input of energy, such as when a machine pumps the water against gravity.
Some of that energy is inevitably lost as heat, increasing entropy in the surroundings,
so usage of energy during a nonspontaneous process also leads to an increase in the
entropy of the universe as a whole.
Concept 6.2 The free-energy change of a reaction tells us whether or not the reaction
occurs spontaneously.
Free energy is the portion of a system’s energy that can perform work when
temperature and pressure are uniform throughout the system, as in a living cell. The
change in free energy, ΔG, can be calculated for a chemical reaction by applying the
following equation:
∆G=∆H-T∆S
This equation uses only properties of the system itself: ∆H symbolizes the change in
the system’s enthalpy (in biological systems, equivalent to total energy); ∆S is the
change in the system’s entropy; and T is the absolute temperature in Kelvin (K) units.
Only processes with a negative ∆G are spontaneous. So every spontaneous process
decreases the systems free energy and processes that have a positive or zero ∆G are
never spontaneous.
∆G also describes the difference between the free energy of the final state and the
free energy of the initial state: ∆G = Gfinalstate - Ginitialstate
For a reaction to have a negative ∆G, the system must lose free energy during the
change from initial state to final state. Because it has less free energy, the system in
its final state is less likely to change and is therefore more stable than it was
previously.
We can think of free energy as a measure of a system’s instability—its tendency to
change to a more stable state. Unstable systems (higher G) tend to change in such a
way that they become more stable (lower G).
Another term that describes a state of maximum stability is equilibrium (the forward
and reverse reactions occur at the same rate, and there is no further net change in
the relative concentration of products and reactants). G is at its lowest possible value
in that system.
A process is spontaneous and can perform work only when it is moving toward a
equilibrium.
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