Transcript Energy and Metabolism

Chapter 6
Energy and Metabolism
Energy:
• The capacity to do work – any change in the state
of motion or matter
• Measured as heat energy
• Unit is the kilocalorie (K)
• Heat energy flows from an object of higher
temperature to an object of lower temperature
• Cells cannot use heat energy for work because
they are too small for a significant temperature
gradient
Types of energy:
• Potential energy - the capacity to do work based
on position or state
– Chemical energy is potential energy stored in chemical
bonds
– Food is a type of chemical (potential) energy
• Kinetic energy – the energy of motion
– Mechanical energy is kinetic energy of motion
– Muscular movement is mechanical (kinetic) energy
Types of energy systems:
• Closed – the system does not exchange energy
with its surroundings
• Open – the system does exchange energy with its
surroundings
• Are biological systems closed or open? Why?
Thermodynamics
• The study of energy and its transformations
• First law of thermodynamics
– Energy cannot be created or destroyed
– Energy can be transferred or changed in form
– Organisms cannot create energy but can capture it
• Second law of thermodynamics
– No energy transfer is 100% efficient
– Some energy is lost as heat and cannot be used to do
work
– Organisms fight entropy only with constant input of
energy from their surroundings
Metabolism
•
•
Needed for organism’s life processes
The sum of all chemical activities within an
organism
• Two processes:
1. Anabolism – requires energy input
•
Complex molecules are synthesized from simpler
substances
2. Catabolism – releases energy
•
•
Larger molecules are broken down to smaller ones
In living systems catabolism usually supplies the
energy needed for anabolism
Types of reactions:
• Exergonic – spontaneous or downhill
– Releases energy that can perform work
– Products have less energy than the reactants
• Endergonic – nonspontaneous
– Energy must be supplied from the environment
– Products will have more energy than the reactants
ATP: Adenosine triphosphate
• Holds energy for very short periods
• Releases energy when third phosphate group is
removed: ATP  ADP + P
• Links exergonic and endergonic reactions – used
for catabolism and anabolism
ATP and ADP
• Nucleotides:
– Adenine
– Ribose
– Phosphate groups
• ATP = three phosphates
• ADP = two phosphates
• Moving from ATP to ADP
releases energy in an
exergonic reaction
Redox Reactions
• OIL RIG:
– Oxidation is lost; reduction is gain
• Energy moves with the electrons:
– The substance that becomes oxidized gives up energy
(and an electron)
– The substance that becomes reduced gains energy
(and an electron)
• Always paired in biological systems – free
electrons cannot exist in nature
• Redox reactions in cells generally involve the
transfer of a whole hydrogen atom rather than just
an electron
Acceptor molecules...
• NAD+ gains H atom (is reduced) to form NADH
• NADH stores large amounts of energy
• This energy is transferred in a series of reactions
to other molecules that will eventually form ATP
• NADP+ is chemically similar
• Reduced to form NADPH, but this is not involved
in ATP formation
NAD+(oxidized) to NADH (reduced)
Enzymes
• Are biological catalysts
• Cells need enzymes to regulate the rate of
chemical reactions
• These work by lowering the activation energy of
a chemical reaction (energy required to break
existing bonds)
• Although most enzymes are proteins, some types
of RNA molecules have catalytic activity as well
Enzymes…
• Enzyme + substrate  enzyme-substrate complex
• ES complex  enzyme + product(s)
• The enzyme is not permanently altered by the
reaction and can be reused
• The substrate joins to the enzyme at the active
site
• As the substrate joins the enzyme – it causes a
shape change – induced fit
• Enzymes are specific – the shape of the substrate
must fit
Enzymes…
• Work best at specific temperature and pH
conditions
• Catalyze virtually every chemical reaction that
takes place in an organism
• Some enzymes consist only of protein
• Some enzymes have two components
– Protein called apoenzyme
– Cofactor
Control of reactions: Inhibition
• Feedback
inhibition:
• Formation of an
end product
inhibits an
earlier reaction
in the metabolic
pathway
Inhibition…
• Competitive inhibition
– Inhibitor competes for the substrate for the
active site
• Noncompetitive inhibition
– Inhibitor binds with enzyme at a site other than
active site
• Irreversible inhibition
– Inhibitor combines with an enzyme and
permanently inactivates it
Competitive and noncompetitive
inhibition