Transcript Document

Energy and Metabolism
Flow of Energy
Energy: the capacity to do work
-kinetic energy: the energy of motion
-potential energy: stored energy
2
Energy forms are inter-convertible
mechanical
light
heat
electric
radioactivity
3
Flow of Energy
• Most forms of energy can be converted to heat energy.
• Thermodynamics = “heat changes”
• 3(2) laws of thermodynamics
• Heat energy is measured in kilocalories.
• One calorie = the amount of heat required to raise the
temp of 1 g of water by 1oC
• 1 kilocalorie (kcal) = 1000 calories
4
13 x 1023 calories/year
4 x 1013 calories/second
5
Flow of Energy
Potential energy stored in chemical bonds can be used to do work –
breaking bonds can release energy.
Potential energy stored in chemical bonds can also be converted to
other energy forms.
Bond Bond Energy (kcal/mol)
C–H 100
C–O 86
C–N 70
C–C 85
N–H 93
There is always a loss of heat energy in these reactions
6
13 x 1023 calories/year
4 x 1013 calories/second
7
Flow of Energy
Potential energy stored in chemical bonds
can be transferred from one molecule to
another by way of electrons.
oxidation: loss of electrons
reduction: gain of electrons
redox reactions are coupled to each other.
8
9
Laws of Thermodynamics
First Law of Thermodynamics
10
11
Laws of Thermodynamics
First Law of Thermodynamics – energy
cannot be created or destroyed…energy
can only be converted from one form to
another
For example:
sunlight energy
chemical energy
photosynthesis
12
Energy in universe
Energy in universe
Available to do work
Total amount of energy in universe remains constant,
but energy available to do work decreases as heat is lost
13
Laws of Thermodynamics
Second Law of Thermodynamics
14
Laws of Thermodynamics
Second Law of Thermodynamics: disorder
is more likely than order
entropy: disorder in the universe
The 2nd Law of Thermodynamics states that
entropy is always increasing.
15
16
Laws of Thermodynamics
• The British scientist and author C.P. Snow had an excellent way of
remembering these laws:
• You cannot win (that is, you cannot get something
for nothing, because matter and energy are
conserved).
• You cannot break even (you cannot return to the
same energy state, because there is always an
increase in disorder; entropy always increases).
17
Laws of Thermodynamics
Free energy: the energy available to do
work
-denoted by the symbol G (Gibb’s free
energy)
enthalpy: energy contained in a molecule’s
chemical bonds
free energy = enthalpy – (entropy x temp.)
G = H - TS
18
Laws of Thermodynamics
• Chemical reactions can create changes in
free energy:
 DG = DH - T DS
• When products contain more free energy
than reactants – DG is positive.
• When reactants contain more free energy
than products – DG is negative.
19
Laws of Thermodynamics
Chemical reactions can be described by the
transfer of energy that occurs:
endergonic reaction: a reaction requiring
an input of energy
- DG is positive
exergonic reaction: a reaction that
releases free energy
- DG is negative
20
21
ΔG and Spontaneous Processes
ΔG= ΔH - TΔS
• Note that ΔG is composite of both ΔH and ΔS
• A reaction is spontaneous if ΔG < 0. Such that:
•
If ΔH < 0 and ΔS > 0....spontaneous at any T
•
If ΔH > 0 and ΔS < 0....not spontaneous at any T
•
If ΔH < 0 and ΔS < 0....spontaneous at low T
•
If ΔH > 0 and ΔS > 0....spontaneous at high T
22
23
Laws of Thermodynamics
Most reactions require some energy to get
started.
activation energy: extra energy needed to
get a reaction started
-destabilizes existing chemical bonds
-required even for exergonic reactions
catalysts: substances that lower the
activation energy of a reaction
24
25
Energy Currency of Cells
ATP = adenosine triphosphate
-the energy “currency” of cells
ATP structure:
-ribose, a 5-carbon sugar
-adenine
-three phosphates
26
27
Energy Currency of Cells
ATP stores energy in the bonds between
phosphates.
Phosphates are highly negative, therefore:
-the phosphates repel each other
-much energy is required to keep the
phosphates bound to each other
-much energy is released when the bond
between two phosphates is broken
28
Energy Currency of Cells
When the bond between phosphates is
broken:
ATP
ADP + Pi
energy is released
ADP = adenosine diphosphate
Pi = inorganic phosphate
This reaction is reversible.
29
30
Energy Currency of Cells
The energy released when ATP is broken
down to ADP can be used to fuel
endergonic reactions.
The energy released from an exergonic
reaction can be used to fuel the production
of ATP from ADP + Pi.
31
Enzymes
Enzymes: molecules that catalyze reactions
in living cells
-most are proteins
-lower the activation energy required for a
reaction
-are not changed or consumed by the
reaction
32
Enzymes
Enzymes interact with substrates.
substrate: molecule that will undergo a
reaction
active site: region of the enzyme that binds
to the substrate
Binding of an enzyme to a substrate causes
the enzyme to change shape, producing a
better induced fit between the molecules.
33
34
35
Enzymes
Multienzyme complexes offer certain
advantages:
1. The product of one reaction can be
directly delivered to the next enzyme.
2. The possibility of unwanted side reactions
is eliminated.
3. All of the reactions can be controlled as a
unit.
36
Enzymes
Not all enzymes are proteins.
Certain reactions involving RNA molecules
are catalyzed by the RNA itself.
ribozymes: RNA with enzymatic abilities
For example, the ribosome is a ribozyme.
37
Enzymes
Enzyme function is affected by its
environment.
Factors that can change an enzyme’s 3dimensional shape can change its function.
-for example, pH, temperature, regulatory
molecules
38
Enzymes
Temperature
-enzyme activity may be increased with
increasing temp, up to the temp optimum
-temperatures too far above the temp
optimum can denature the enzyme,
destroying its function
pH – most enzymes prefer pH values from 6
to 8.
39
40
Enzymes
Inhibitors are molecules that bind to an
enzyme to decrease enzyme activity.
-competitive inhibitors compete with the
substrate for binding to the same active
site
-noncompetitive inhibitors bind to sites
other than the enzyme’s active site
41
Enzymes
Allosteric enzymes exist in either an active
or inactive state.
-possess an allosteric site where
molecules other than the substrate bind
-allosteric inhibitors bind to the allosteric
site to inactivate the enzyme
allosteric activators bind to the allosteric
site to activate the enzyme
42
43
Metabolism
Metabolism: all chemical reactions
occurring in an organism
Anabolism: chemical reactions that expend
energy to make new chemical bonds
Catabolism: chemical reactions that harvest
energy when bonds are broken
44
Metabolism
Some enzymes require additional molecules
for proper enzymatic activity.
These molecules could be:
-cofactors: usually metal ions, found in the
active site participating in catalysis
-coenzymes: nonprotein organic molecules,
often used as an electron donor or
acceptor in a redox reaction
45
Metabolism
Biochemical pathways are a series of
reactions in which the product of one
reaction becomes the substrate for the
next reaction.
Biochemical pathways are often regulated
by feedback inhibition in which the end
product of the pathway is an allosteric
inhibitor of an earlier enzyme in the
pathway.
46
47
48