Chapter 6 Energy and Metabolism
metabolism – 1000s of chemical reactions
Chemical processes necessary for life
Enzymes selectively accelerate each step
Outline
•
•
•
•
•
•
Flow of Energy in Living Things
Laws of Thermodynamics
Free Energy
Activation Energy
Enzymes
ATP
METABOLIC TERMS
• Catabolic pathways release energy - break
down complex molecules
• Anabolic pathways consume energy - build
complicated molecules
• Energy released by catabolic pathways DRIVES
anabolic pathways
energy coupling
Organisms transform energy
• Energy - capacity to do work – move and rearrange matter
• Kinetic energy - energy of
motion
– photons, heat.
• Potential energy - energy based
on location or structure
– Chemical energy potential energy
based on arrangement of atoms
• catabolic pathways RELEASE ENERGY
• Cellular respiration
– unleash chemical energy from sugar
• Where does sugar energy come from?
• Potential energy
• energy based on location or structure
– Chemical energy
potential energy based on arrangement of atoms
Figure 8.2 Transformations between kinetic and potential energy
•Energy can be converted
•Climb hill - kinetic energy to potential energy
•Top of hill - potential energy
•Rolling down
back to
kinetic energy
•potential energy for
climb came from?
Terms
• System - matter under study
• surroundings - everything outside the system
• closed system - isolated from surroundings
• open system - energy can be transferred between
the system and surroundings.
• Organisms are ________systems
Flow of Energy in Living Things
• Oxidation - Reduction
– Oxidation atom or molecule loses an electron.
– Reduction atom or molecule gains an electron.
•Redox reactions electron lost by one
atom is gained by another.
Fig. 8.4 (TEArt)
Loss of electron (oxidation)
o
A
o
B
–
+
e–
A
B
A*
B*
Gain of electron (reduction)
Low energy
High energy
–Redox reactions electron lost by one atom is gained by another.
–RECALL OIL RIG
Generally
• Oxidation is exerogonic
Gives up electron
• In metabolism we’d say catabolic
•Reduction is endergonic
RECEIVES electron
•In metabolism we’d say anabolic
•Thermodynamics - changes in heat
• 1st law of thermodynamics - energy can be
transferred and transformed, but not created or
destroyed
– Plants transform light to chemical energy
– Do they do produce energy?
2nd law of thermodynamics - every energy
transformation makes universe more disordered
Entropy - a measure of disorder, randomness.
•Order can increase
locally
•BUT unstoppable trend
toward randomization of
the universe
•Living cells convert organized energy to disordered (heat).
Heat -energy in most random state
• energy transformations - part heat energy
– Automobiles - gas - 25% motion; rest lost as ?
Combining two laws, the quantity of energy is
constant; the quality is not.
• Do we violate the second law of
thermodynamics?
–Organisms - islands of low entropy in
an increasingly random universe.
• Spontaneous?
—wood burns, ashes don’t
wood (potential energy) +flame = spontaneous yield of
ashes and hot air (kinetic energy)
– Transfer from ordered (concentrated chemical bonds) to
disordered (dispersed heat and gases).
– wood does not spontaneously reform
Why? energy transformation occurs spontaneously only
from greater to less order
Entropy—a measure of disorder in a system.
• Energy Living Things
– High order of organisms decreases entropy,
but requires a great energy input.
– Mechanical work (muscles contracting)
– transport work (ions across membranes)
– synthesis work (manufacturing organic molecules)
– all require energy
– called endergonic reactions—“energy in.”
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Energy released Energy supplied
ENERGY TERMS
Fig. 8.6 (TEArt)
Product
Energy
must be
supplied.
Reactant
Reactant
Energy is
released.
Product
Exergonic
Endergonic
Exergonic
Is
Catabolic
Free Energy
• - amount of energy actually available to
break and subsequently form other chemical
bonds
– Gibbs’ free energy (G)
• Delta Δ G - change in free energy
–endergonic - requires an input of energy
–exergonic - releases free energy
• The free energy (G) in a system is related to the total
energy (H) Note: includes heat
• and its entropy (S) : note: not available for work
• G = H - TS
T –Temperature in Kelvin units
– Increases in temperature amplify entropy
– Not all energy in a system is available for work entropy
component must be subtracted.
– What remains is free energy G
FREE energy
• G = energy liberated or absorbed in a reversible
process
• changes – ΔG - indicates when chemical reaction
will occur
• if + reaction will require more energy (ATP)
• if – reaction will occur spontaneously
(until equilibrium) neg is energy releasing
delta ΔG is an important
concept in biology
•A system at equilibrium is at maximum stability.
•at equilibrium, rate of forward and backward reactions
are equal
•At equilibrium, delta G = 0 and the system can do no
work. (net)
• Chemical reactions exergonic or endergonic based on free energy
• exergonic reaction proceeds with a net release
of free energy - delta G
is___?_____.
• endergonic reaction absorbs (requires) free
energy from its
surroundings.
– Endergonic – chemical
reactions store energy
– delta G is ?
– reactions are
nonspontaneous.
Fig. 8.6a
Enzymes!!
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Energy released Energy supplied
•enzymes speed up chemical reactions
Fig. 8.7 (TEArt)
Uncatalyzed
Activation
energy
Catalyzed
Activation
energy
Reactant
Reactant
Product
Product
energy and enzymes
• Enzyme speed reactions -
lower EA.
hasten reactions that would occur
eventually
– enzymes
are selective
– determine
chemical
processes
• Enzymes
– Many different
enzymes might be
needed to
accomplish one
task.
Active site
Substrate
– Series of steps metabolic pathways
Substrate
–substance being worked on
by each specific enzyme
The substrate,
sucrose, consists
of glucose and
fructose bonded
together.
Fig. 8.9
(TEArt)
2 The substrate
1
binds to the
enzyme, forming
an enzyme-
Glucose
Fructose
substrate
complex.
Bond
4 Products are
released, and
the enzyme is
free to bind
other
substrates.
3 The binding of
the substrate
and enzyme
places stress on
the glucosefructose bond,
and the bond
breaks.
H2 O
Active site
Enzyme
RNA – enzyme?
• Ribozymes (RNA segment acts as enzyme)
• Which came first? Protein or RNA?
• RNA (likely – because it can be a ribozyme)
• RNA and evolution
Because very substrate specific, now testing ways to treat
*VIRUSES *CANCER* GENETIC DISORDERS
Activation Energy
• Activation energy - extra energy required to
destabilize existing chemical bonds and initiate a
chemical reaction.
–catalyst - substance that lowers the activation energy
• cannot violate laws of thermodynamics.
– direction of chemical reaction determined by
difference in free energy between the reactants and
the products
• Enzymes and Shape
– Precisely shaped active
site is region of an
enzyme that binds to
the substrate
– INDUCED FIT
substrate specific
– Sucrase binds to sucrose and breaks
disaccharide into fructose and glucose
The active site is enzyme’s
catalytic center
• usually held in the active site by weak
interactions (hydrogen bonds and ionic bonds).
– R groups of a few amino acids on the active site
catalyze the conversion of substrate to product.
• catalyze thousands or more reactions a second
• reusable
• both forward and reverse direction
– direction depends on the relative concentrations of
products and reactants.
– Enzymes catalyze reactions in the direction of
equilibrium.
• rate - substrate concentrations.
• BUT - is
more always better??
• active sites can be engaged- enzyme saturation
• How could we increase productivity?
physical and chemical environment
• structures depend on environmental conditions.
• Changes in shape influence the reaction rate.
• optimal - or not
physical and chemical environment
• Temperature
– increases collisions
– but proteins denature
– optimal temperature??
Fig. 8.11a
• pH
• typically 6 - 8
• stomach pH 2
• intestine pH 8
• matching work
environments
Fig. 8.11b
• cofactors - nonprotein helpers for enzymes
– zinc, iron, and copper – bind to enzyme
• - coenzymes
nonprotein
– Vitamins (B1)
– NAD+ accepts hydrogen and electron = NADH
• inhibitors
– If covalent
bonds,
irreversible.
– If weak,
reversible.
– If same site competitive
inhibition
Regulation of Biochemical Pathways
• pathways - coordinated
and regulated
– temporarily shut down
when products not
needed
• feedback inhibition When the cell produces
increasing quantities of a
particular product, it
automatically inhibits its
ability to produce more.
• If not on active site noncompetitive
inhibition.
• Reversible inhibition natural part of
metabolism
• Why??
Allosteric regulation
• ATP Energy Currency :
• adenosine triphosphate
•
•
•
•
nucleotide
nitrogenous base (adenine)
sugar (ribose)
three phosphate groups
Fig. 8.14
Figure 8.14a ATP
•phosphate bonds -weak - each has negative charge
•repulsion contributes to instability
– Negatives repel – Phosphates are negative
– ATP (three phosphates), ADP (two phosphates)
– Linking them requires overcoming repulsion
– Requires energy
– ATP from ADP and a third phosphate requires
energy (endergonic)
– Releasing phosphate from ATP generates
energy (exergonic)
• bonds between phosphate groups broken by
hydrolysis
– Hydrolysis forms adenosine diphosphate
–
– [ATP -> ADP + Pi]
– releases 7.3 kcal of energy per mole of ATP
– delta G is -13 kcal/mol in actual conditions
Cell
membrane
•How IT WORKS IN
extracellular
muscle cells
–Calcium ions move to enzyme
Enzyme
Calcium
ions
ATP binding
site
–ATP splits -ADP and
phosphate
Ca++
Ca++
ATP
P
ADP
–energy transfers phosphate
onto protein
Ca++
Cytosol
intracellualr
–
P
P
–shape change drives calcium
across membrane
P
biochemical pathways
Ca++
2
H2O2
=>
2
H2O
+
O2
200,000
per
second!
Staph bacteria produce lots of catalase
Infantile Refsum’s diesase – no peroxisomes