Download How does ATP transfer energy?

Topic 4: Metabolism, Enzymes and
Homeostasis Ch.8
-Energy is the capacity to do work or to move matter
against opposing forces such as gravity and friction.
- There are many forms of energy: Electrical,
Mechanical, Chemical, Light and Heat.
- First Law of Thermodynamics - Energy can be
transferred and transformed, but it cannot be created or
destroyed.
Metabolism pp.142-160
- Metabolism - The processing of energy and
materials (by means of chemical reactions) to maintain
existing life and grow.
- There are two forms:
1. Catabolism - Destructive metabolism in which
complex molecules are broken down into simpler
ones, with the liberation of energy.
- Catabolic reactions are exergonic because
energy is released when the complex molecules
are broken down.
- E.g. Cellular respiration
Metabolism
2. Anabolism - Constructive metabolism in which
complex substances are synthesized from simpler
ones.
-Anabolic reactions are endergonic because
energy is consumed (required) to build
complicated molecules from simpler ones.
-E.g. Protein synthesis from amino acids.
How does ATP transfer energy?
- The triphosphate tail is the chemical equivalent to a
loaded spring (the close packing of the 3 negatively
charged phosphate groups are unstable).
Fig. 8.8
Metabolism
- Most life processes are endergonic and therefore
require energy.
- Where does this energy come from?
-ATP - Adenosine triphosphate
- The ATP/ADP cycle is an example of Anabolic
and Catabolic processes.
Fig. 8.8
How does ATP transfer energy?
-The cell taps this energy source by using
enzymes to transfer phosphate groups from ATP
to other compounds, which are then said to be
phosphorylated.
- Phosphorylation primes a molecule to undergo
some kind of change that performs work, and the
molecule of ATP loses its phosphate group in the
process.
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Cellular Respiration pp.167-181
- Cellular Respiration - The most prevalent and
efficient catabolic pathway for the production of
ATP, in which oxygen is consumed as a reactant
along with the organic fuel.
- Aerobic respiration - Respiration where oxygen is
the final electron acceptor.
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
Fig. 8.10
Cellular Respiration
-Anaerobic respiration - A form of respiration
that occurs without oxygen.
E.g. For bacteria, the final electron acceptors
are sulphate and nitrate not oxygen.
E.g. Fermentation in bacteria and yeast also
breaks down glucose, but produces carbon
dioxide and ethanol.
(ATP and Heat)
Cellular Respiration
- Cellular respiration is composed of three steps:
1. Glycolysis - Occurs in all living cells. May or may
not require oxygen. Occurs in the cytoplasm.
2. Kreb’s cycle - A chemical cycle that completes the
breakdown of glucose to carbon dioxide. Located
in the mitochrondria.
3. Electron transport chain - Electron-carrier
molecules located on the inner mitochrondrial
membrane move electrons along during reactions.
This releases energy used to make ATP.
Review of Cellular Respiration
Glycolysis
Glucose  2 Pyruvate + 2 NADH + 2 ATP
Kreb’s Cycle
2 Pyruvate (Acetyl CoA)  8 NADH + 2 FADH2 +
2 ATP + 6 CO2
Fig 9.6
Electron Transport Chain
NADH and FADH2 used to create a H+ gradient.
Energy released when H+ travels down this
gradient is used to make 26 ATP (Oxidative
phosphorylation).
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Diversity of Metabolic Pathways
- Some nutritional modes are unique to prokaryotes.
-Nutrition refers here to how an organism obtains two
resources for synthesizing organic compounds; energy
and carbon.
- Energy can come from two sources:
Fig. 9.16
1. Phototrophs - Use light as an energy source.
2. Chemotrophs – Use reactions with chemicals
taken from the environment as an energy source.
Diversity of Metabolic Pathways
Major Nutritional modes
- Carbon can come from two sources:
1. Autotroph – Carbon comes from an inorganic
source (i.e. CO2 ).
2. Heterotroph – Carbon comes from an organic
source (i.e. glucose).
Mode of
nutrition
Energy
source
Carbon
source
Examples
Photoautotroph
Light
CO2
Plants & cyanobacteria
Photoheterotroph
Light
Glucose
Some cyanobacteria
Chemoautotroph
Inorganic
molecules
CO2
Sulfur bacteria &
Chemoheterotroph
Glucose
Glucose
Nitrifying bacteria
Animals
Most bacteria
Enzymes pp.152-156
- Enzymes are proteins that are produced on
ribosomes.
- Enzymes function as catalysts, chemical agents that
change the rate of a reaction without being consumed
by the reaction.
Enzymes
- Enzymes work by lowering the activation energy
so that the reaction can happen even at moderate
temperatures.
- Activation energy – Energy
required for a reaction to
occur.
Fig. 8.13
Fig. 8.12
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The Specificity of Enzymes
-Enzymes are very specific.
-Only certain chemicals (substrates) can fit in the
active site.
-The enzyme binds to its substrate (or substrates) and
while the two are joined, the catalytic action of the
enzyme converts the substrate to the product of the
reaction.
Fig. 8.15
Factors Affecting Enzyme Activity
1. Temperature
2. pH
Factors Affecting Enzyme Activity
3. Enzyme inhibitors:
a) Competitive inhibitors bind to the active site
preventing binding of the regular substrate. E.g.
DDT
b) Noncompetitive inhibitors bind to another part
of the enzyme, changing the shape of the binding
site. Eg. Penicillin
Fig. 8.17
Fig. 8.16
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