Transcript Chapt. 6 Energy & Metabolism

Energy & Metabolism
Chapt. 6
• All living things require energy
• One of the primary functions of
macromolecules is to provide E.
• Energy is the ability to do Work
• Energy exists in two forms:
– Kinetic Energy
– Potential Energy
Kinetic Energy
Kinetic energy is the energy of motion. An
object which has motion - whether it be
vertical or horizontal motion - has
kinetic energy. There are many forms of
kinetic energy - vibrational (the energy
due to vibrational motion), rotational
(the energy due to rotational motion),
and translational (the energy due to
motion from one location to another).
The amount of translational kinetic energy
which an object has depends upon two
variables: the mass (m) of the object
and the speed (v) of the object.
Kinetic energy is an expression of the fact
that a moving object can do work on
anything it hits; Moving objects cause
other objects to move…
Movement is work
•
Text pg 96
Potential Energy
• Stored energy
• Objects with the capacity to
do work but not active now
have PE.
• Kid on the top of a slide
• Bolder perched on an edge
• Chemical bonds…
• Much of life relates to
converting PE to KE
PE= mass x gravity x height
Forms of Energy
• Mechanical
• Sound
• Electricity
• Light
• Radiation
• Heat
Heat
• Useful way to study energy because all
other E. forms can be converted to heat
• This is the study of Thermodynamics
• Heat Energy measured in units of
calories or kilocalories
Thermodynamics
• Thermodynamics is a branch of physics
which deals with the energy and work of a
system…
Energy Flow
• Ultimately, all E. for life on earth comes
from the sun
• Sunlight shines 40 million billion
calories/second on earth!
• Plants, algae and photosynthetic bacteria
convert sun E. to sugars
Sunlight to Chemical Bonds
• Photosynthesis converts a small (~10%)
amount of sun E. into covalent bonds
• Where does the rest (~90%) of sunlight E.
go?
Energy from Chemical Bonds
• Chemicals may be considered from a potential
energy or kinetic energy standpoint. One pound
of sugar has a certain potential energy. If that
pound of sugar is burned the energy is released
all at once. The energy released is kinetic
energy (heat). So much energy is released that
organisms would burn up if all the energy was
released at once.
• Organisms must release the energy a little bit at
a time.
Covalent Bonds
• Sharing of electrons
between atoms
• Covalent bonds are a form
of PE
• Energy is stored in each
covalent bond
• Breaking covalent bonds
releases E. ~98Kcal/Mole
for C-H bonds
• Bond energy is the energy
in each orbiting e-
Electron Energies
• In Oxidation/Reduction
reactions e- are passed
from one atom to another
• Oxidized atom gives e- to
reduced atom
• Reduced form now has
more energy than
oxidized one
• The amount of E passed
on by e- depends on how
far it was from the
nucleus
Reduction is the gain of an electron. Sometimes we also have
H ions along for the ride, so reduction also becomes the gain of H.
Oxidation is the loss of an electron (or hydrogen).
Photon of Light
Red/Ox Reaction:
NADH/ NAD+
Example of the Energy in
Covalent Bonds
Photosynthesis:
6CO2 + 12H2O + Light E.  C6H12O6 +6O2 + 6H2O
Light Energy requirements = ~3,000-7,000 Kcal
Respiration:
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
Energy released = 686 Kcal
Energy Loss in each Energy Transfer
• Photosynthesis uses lots of energy (30007000 Kcal) to produce one glucose
molecule…
• But, the energy released from one glucose
molecule produces only 686Kcal
• Most of the excess energy is lost as Heat.
..but the energy is never really gone…
All Energy transfers follow certain rules…
The Laws of Thermodynamics
• First Law… Energy can never be created nor
destroyed.
• The total amount of Energy in the universe
remains always the same, it just changes
forms…
How do we know this?
This is an empirical law, which means that we know that energy is conserved
because of many repeated experiments by scientists. It's been observed that you
can't get any more energy out of a system than you put into it .
James Prescott Joule did a famous experiment which demonstrated the
conservation of energy and showed that heat and work were both of the same
nature: energy.
His experiment involved water in a thermally insulated container and a paddle
which was connected to the outside world (surroundings). Joule found that the
amount of energy could change from one form to another (work to heat);
however, no net change of energy in the system plus the surroundings occurred
and thus Energy is conserved.
http://www.secondlaw.com/two.html
The First Law of Thermodynamics
• The first law is very simple: You can't create or
destroy energy.
• You can just change it from one form to another,
for example, electricity to heat, heat that will boil
water and make steam, hot steam to push a
piston (mechanical energy) or turn a turbine that
makes electricity which can be changed to light
(in a light bulb) or, using only a tiny quantity
changed to sound in an audio speaker system,
and so forth.
The Second Law
• Energy spontaneously tends to flow only from
being concentrated in one place to becoming
diffused or dispersed and spread out.
• A blowout in a tire and lightning -- what could
seem to be more unlike than those! Yet the
reason for their occurring is the same, the
tendency for concentrated energy not to stay
localized, to disperse if it has a chance and isn't
hindered somehow.
The Second Law
• Energy is constantly being converted to
random molecular motion (heat Energy)
• This random motion is less ordered
(disordered) and is always increasing
• The universe is becoming more disordered
all the time
• Disorder = Entropy
• And Entropy is always increasing
And so…
The Universe is Breaking Down
• Entropy is increasing
• It takes constant E. inputs to keep a road in
good shape, your car running and your dorm
room clean…
• Leave things alone… and things fall apart
• Playing cards rarely form a card house without
your help… card houses, once built, usually fall
apart.
So What’s This Got to do
with Life?
• Metabolism….involves E. transfers
• Biological Reactions follow this format:
Reactants --> Products
A
B
• Energy transfers go along with this
1. Reactants --> Products + Energy
2. Energy + Reactants --> Products
Energy from Food
• Some living things
can convert sun E. to
food E.
• Food E. transfers
from Plant to Deer to
Coyote…
• Each E. transfer step
loses ~90% to heat
(random molecular
motion).
How to measure the Energy
in a molecule?
• Energy in a molecule (G) equals the
energy in the chemical bonds (H) minus
the energy lost as heat (S)
G= H - S
• Also...The heat factor increases with
Temp (T)
G = H - ST
In Chemical Reactions, usually it’s the
Change in E. between Reactants and
Products that matters
∆G = ∆H - T∆S
Energy + Reactants --> Products
• If products contain MORE energy than
reactants
• Energy input is required for reaction
• Reactions will NOT occur spontaneously
• Termed Endergonic reactions
• ∆G value is positive
• Text pg. 99
Endergonic Reactions
∆G = ∆H - T∆S
Products contain MORE energy than
reactants
∆G value is positive
Reactants --> Products + E
• Products contain LESS energy than
reactants, excess E. is released
• Energy is released to do work
• Reactions will occur spontaneously
• Termed Exergonic reactions
• ∆G value is negative
• Text pg. 99
Exergonic Reactions
∆G = ∆H - T∆S
Products contain LESS energy than
reactants
∆G value is negative
Activation Energy
• If so many reactions are exergonic and
release energy spontaneously, why
haven’t they already all occurred?
• They all require a bit of E. input…
• This is the Activation Energy
• A kid on the slide needs a slight push…
• Text pgs. 103
Catalysts and Enzymes
• The role of a catalyst is to lower the
amount of E. to push a reaction forward
• Catalysts may be biological or chemical
• Biological catalysts are termed enzymes
• Catalysts (and enzymes) thus lower the
Activation E.
• Text pg. 104
Enzymes
• Speed up reactions by bringing molecules together or
by putting stress on covalent bonds to break them
• Enzymes can speed up reactions thousands-millions
of times faster
CO2 + H2O --> H2CO3
• Enzyme for this reaction is carbonic anhydrase
How Enzymes Work to Speed
Up Reactions
• Substrate molecule binds to enzyme
active site…
• This forms an enzyme-substrate
complex
• Enzyme may now act on substrate to
induce a change…
• Text pg. 104
Factors Affecting Enzyme Activity
Temperature
pH
– Text pg. 112
Inhibitors
– Competitive
– Non-competitive
Competitive Inhibitors
• Compete with normal substrate molecule
for enzyme active site
• Text pg. 109
Noncompetitive Inhibitors
• Bind to a different site on enzyme and
change its conformation
• Text pg. 109
How do cells use the energy of
chemical bonds for work in the
cell?
By creating an energy-rich compound for use now or stored for later use…
ATP
• Chief energy currency of cells
• Plant photosynthesis results in this
compound being produced
• ATP powers many cell reactions
• A nucleotide composed of sugar,
adenine and 3 PO4
• Text pg. 101