Transcript Metabolism & Energy

Metabolism & Energy
METABOLISM?
• The term metabolism refers to the sum of all
the chemical reactions that occur within the
cell.
• Many times, due to energy constraints, the
reaction required takes place in a sequential
series of chemical reactions called a
metabolic pathway. (ABCDE)
• Metabolic reactions can be categorized as:
– Catabolic – those which break larger substances
down into smaller ones to release energy.
– Anabolic – those which consume energy to build
large molecules from smaller ones.
ENERGY
• Energy is simply the capacity to do work.
• We can categorize energy into two main types:
– Kinetic Energy – The energy of motion.
– Potential Energy – Stored energy.
• The cell often will transform potential energy into
kinetic energy. (Remember the electrostatic
gradient?...)
• Other types of energy fall into one of these two
categories. For example…
– Heat – Kinetic energy of moving particles.
– Chemical Energy – Potential energy contained within
the bonds of a molecule.
BOND ENERGY
• Whenever a bond is formed between two atoms – energy
is released. And it is the same amount of energy required
to break the bond.
• Bond energy is the energy required to break (or form) a
chemical bond.
• Here is the weird part…
– Because unbonded, free atoms can form bonds and
give off energy – they are considered to have more
chemical energy that the compounds they form…
– Think about it – if energy is given off when the bonds of
a compound form – where did it come from?…The free
atoms that built the compound!!!
• BUT – most atoms will want to form compounds for the
sake of stability so we often are comparing the bond
energy values of compounds as they turn into other
compounds.
THE WEIRDNESS CONTINUES!
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CHHHHOOOO
Energy released
when bonds form
Energy released
when bonds form
CH4 + 2O2
Net energy released
in the combustion
reaction
CO2 + 2H2O
LAWS of THERMODYNAMICS
• We are energy beings – without it, we die real
quick! Most energy transfer in the cell is done
so as heat. Too much heat denatures proteins
so the question is how do we run all of the
reactions needed without too much heat build
up or loss?
• Thermodynamics – the study of the transfer and
transformation of thermal energy (heat).
• These laws discuss the energy transfer
between a “system” and its “surroundings” –
the cell is the system and extracellular fluid is
the surroundings.
• It is important to note that biological systems are
considered to be “open systems” because they can
exchange matter and energy.
FIRST LAW OF THERMODYNAMICS
• “Energy cannot be created or destroyed, but
it can be transformed from one type of energy
into another and transferred from one object
to another.”
• This simply means that when a chemical reaction
occurs – the amount of energy that enters the
reaction must exit the reaction.
• Jogging…
– Chemical energy from food converts to
kinetic energy of muscle movement.
– Heat built up in body is lost to the
environment when you cool off.
SECOND LAW OF THERMODYNAMICS
• “During any process, the universe tends toward
disorder.”
• Entropy (S) – measure of disorder in a system.
• This means that energy transformations tend convert
matter from order to disorder.
• WAIT A FREAKIN’ SECOND!!! We know that life is
highly organized – this breaks the law…does anarchy
reign supreme?
– No – the second law only applies to closed systems –
biological systems are open systems.
– We use inputs of matter & energy to reduce entropy
(randomness).
– All energy we need to survive comes from the Sun!
TURNING UP THE HEAT
• Heat makes it easier to break chemical bonds – it
increases the kinetic energy of the atoms so they are
easier to pull apart. Heat is measured using
temperature (T).
• Chemical bonds have energy and forming these
bonds reduces entropy. The value of the energy in
the bonds of a molecule is called enthalpy (H).
• So…When a chemical reaction occurs…
– There is a change in entropy (ΔS) – order or disorder.
– There is a change in enthalpy (ΔH) – bonds are broken
and made into new bonds with different energies.
– There could be a change in temperature – BUT – many
living things maintain a stable internal body
temperature. (37°C for ourselves)
FREE ENERGY
• Free energy (G) is the energy from a
chemical reaction that is available to do work.
We know that reactions can give off or absorb
energy.
• Free energy of a chemical reaction is
calculated using the formula:
ΔG = ΔH - TΔS
• The free energy value (ΔG) tells us a lot
about a reaction.
ENDERGONIC & EXERGONIC
• If ΔG has a positive value, it means that the
bond energy of the products is higher than
that of the reactants.
– This means that energy was absorbed by the
reaction and you have gone from disorder to
order. These reactions are termed endergonic.
• If ΔG has a negative value, it means that the
bond energy of the products is lower than that
of the reactants.
– This means that energy was given off by the
reaction and you have gone from order to
disorder. These reactions are termed exergonic.
THERMODYNAMICS & METABOLISM
• Reactions in our cells can have a very large
gap between the energy of the reactants and
products. This means a large absorption or
release of energy within the cells.
• This energy is often transferred as heat so
this could significantly alter the stable
temperature of the cell and disrupt protein
function leading to cell death.
• The cell has several clever ways of getting
around this problem while still ensuring the
reactions it needs are still being carried out.
KEEPING IT STABLE
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One of the best ways a cell can cope with energy
transfer is to have a series of smaller reactions take
place in stead of one big reaction.
Cellular Respiration
C6H12O6 + 6O2  6CO2 + 6H2O
If this were to occur in one step – like burning the
glucose with a match – the sudden, massive energy
release would literally combust the cell…So instead
we do this…
C6H12O6 + 6O2  6CO2 + 6H2O
The energy is now released in a series of reactions
in smaller bursts that are more manageable for the
cell. The overall energy yield is the same because
we are using bond energies to calculate this and the
reactants and products are still the same.
FIN