Topic 9 How Does Life Use Energy?

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Topic 9How Does Life Use Energy?
Dr. George Lapennas Dept. of Biology
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Nature of science
Search for mechanistic explanations ones that
predict events based on underlying rules and
structures
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Quick review of special characteristics of living
things (organisms)
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1. Growth
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2. Development (changes other than growth during
individual lifetime)
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3. Reproduction (involves inheritance)
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4. Ordered, complex structure adaptation
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5. Movement (esp. animals)
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6. Sensitivity/Responsiveness
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7. Evolution (change over generations)
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8. Consciousness/Rationality
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9. Use of energy
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Can life also be understood mechanistically (vs
vitalistically)?
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An early mechanistic success Harveys partial
explanation of the pumping and circulation of the
blood
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Some 19th century steps from a vitalistic toward
a mechanistic understanding of life
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1. The cell theory
Living things are made up of large numbers of
tiny units called cells that come from previous
cells Prerequisite technical advance Invention
of the microscope (early 1600s)
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Structure of an animal cell
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Structure of a plant cell
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2. In vitro (in glass) synthesis of organic
molecules
Wohlers 1828 in vitro synthesis of urea,
etc. Eventually, chemists learned to synthesize
everything in vitro that organisms synthesize in
vivo. General conclusion There are no unique
laws of chemistry operating within living
organisms.
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3. The fermentation controversy
Fermentations chemical transformations that
had only been observed in association with living
things Buchner (1897) observed fermentation of
fruit juice by cell-free extract of yeast,
yielding alcohol and carbon dioxide
(CO2) Conclusion Living cells are not required
for fermentation only need some materials that
were present within the cells (now known to be
enzymes - proteins that act as catalysts to speed
up reactions).
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4. Cryptobiosis
Does life irreversibly end when life processes
cease? or Can life processes be stopped and
later re-started, so long as necessary structure
have been preserved? Can the clock of life be
stopped and then re-started?
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4. Cryptobiosis
Conclusion Life processes only depend upon the
presence of certain matter in a certain
structural arrangement. That matter and
structure can persist during drying or freezing
when all processes cease. Life processes can
resume upon restoration of water or thawing.
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Why did mechanistic explanations take so long to
develop in biology?
- Because living things are much more complex
than anything else that scientists study - Many
other discoveries had to be made before the
mechanisms of biological structures and processes
could be effectively investigated.
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Machinery of life 4 classes of organic
macro-molecules assembled from smaller
building blocks
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Machinery of life 4 classes of organic
macro-molecules assembled from building blocks
1. Proteins (structural catalytic enzymes) 2.
Nucleic acids (DNA, RNA instructions for
inheritance as the structure of proteins) 3.
Polysaccharides (energy storage structure) 4.
Complex lipids (energy storage cell membranes)
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Amino acids are the building blocks of Proteins
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Protein structure primary structure
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Protein structure secondary structure (local
folding patterns)
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Protein structure tertiary structure (overall
folding pattern)
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Protein function depends on form
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DNA (molecule of inheritance)
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Living matter seems to obey the same laws of
physics and chemistry as non-living matter
Conservation of mass Conservation of
momentum Gravitation Chemical properties of
elements Laws of thermodynamics
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Laws of thermodynamics
In any isolated system (no matter or energy can
enter or leave the system), including the entire
universe First Law the total amount of energy
is constant, though it can change form.
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Laws of thermodynamics
In any isolated system (no matter or energy can
enter or leave), including the entire
universe First Law total amount of energy is
constant, though it can change form. Second Law
Whenever anything actually happens, the entropy
(disorder) of the system increases.
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Laws of thermodynamics
In any isolated system (no matter or energy can
enter or leave), including the entire
universe First Law total amount of energy is
constant, though it can change form. Second Law
Whenever anything actually happens, the entropy
(disorder) of the isolated system increases. -
Times Arrow points in the direction of
increasing entropy (disorder) of the universe.
- Changes that would reduce the entropy of the
universe cannot occur
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Spontaneous changes changes that can happen
downhill changes
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Spontaneous processes can happen
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Two old hypotheses about animals use of food
1. Assimilation - food is added to the body for
growth or to replace material lost through wear
and tear
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Two old hypotheses about animals use of food
1. Assimilation - food is added to body for
growth or to replace material lost through wear
and tear 2. Combustion - food is somehow
burned within the body, like fuel in a fire,
generating heat, and being consumed in the process
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Reinterpretation of combustion and animal
respiration by Lavoisier
Lavoisier (late 1700s) - Overthrew phlogiston
theory and applied new knowledge of gases to
combustion - Flames and animals do not produce
phlogiston, - Both consume oxygen (O2) and
release carbon dioxide (CO2) and heat
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Lavoisier and Laplace observed quantitative
similarities between burning charcoal and the
respiration of a living animal.
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• Quantitative similarities between combustion and
  respiration
• Same/Similar ratios of
• heat produced / vol. of CO2 produced
• and
• vol. of O2 consumed / vol. of CO2 produced

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Slow combustion
Lavoisier and Laplace hypothesized that animals
carry out a slow combustion of fuel (process
now called cellular respiration). They believed
that the function of cellular respiration was to
make heat.
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What do we know now about the use of food by
animals?
- Cells both ASSIMILATE food and use it as FUEL
FOR CELLULAR RESPIRATION
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What do we know now about the use of food?
- Cells both ASSIMILATE food and use it as FUEL
FOR CELLULAR RESPIRATION - For most organisms,
heat is just a useless by-product of cellular
respiration, not the function of the process.
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What is the primary function of cellular
respiration?
Cellular respiration provides energy to do cell
work.
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What is the function of cellular respiration?
Cellular respiration provides energy to do cell
work. Cell work means uphill cellular
processes that would not be spontaneous (could
not occur) on their own, but can occur if
coupled to some other, highly spontaneous
process, such that the two processes occurring
together increase the entropy of the universe.
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3 Types of Cell Work-Active transport-Movement
-Bio-synthesis
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Digestion of macro-molecules
When we digest food macro-molecules, we break
them down into their building blocks Examples
proteins ? amino acids polysaccharide
s ? simple sugars Nucleic acids ?
nucleotides
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Digestion of macro-molecules
When we digest food macro-molecules, we break
them down into their building blocks. Blood
carries building block to the cells, where they
are taken up, and some are reassembled into new
macro-molecules.
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Digestion is downhill
Dismantling macro-molecules is a disordering
process that increases the entropy of the
universe. Macro-molecule ? building blocks
heat (ordered, non-random) (disordered)
(random energy)
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Assembly of macromolecules simply by reversing
digestion?
NO! Digestion is downhill (increases the entropy
of universe).
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Assembly by simply reversing digestion?
NO - Digestion is downhill (increases entropy of
universe) So the reverse process (assembly simply
by reversing digestion) would be uphill (reduce
entropy of the universe), and cant happen
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A spontaneous processes can happen the reverse
process cannot
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Question Then how can macro-molecule assembly
(and other types of cell work) occur?
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Answer By coupling cell work to some very
downhill process
A spontaneous process can be reversed by coupling
it to a MORE spontaneous process (represented by
a larger weight).
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Mechanical coupling
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A spontaneous process can be reversed by coupling
it to a MORE spontaneous process (such as a
larger weight). The COMBINED process is then
downhill, and increases the entropy of the
universe. We say The second, highly
spontaneous, process supplies energy to drive the
uphill process (which could not have occurred
alone).
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What highly spontaneous process drives cell work?
The highly spontaneous process that drives cell
work is splitting ATP
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ATP Adenosine Tri-Phosphate
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Splitting ATP
ATP ? ADP Phosphate
heat (one larger (two smaller
(random molecule)
molecules) energy)
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Splitting ATP
ATP ? ADP Phosphate
heat Splitting ATP is very downhill, and so can
drive uphill cell work.
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Example of coupling ATP-driven assembly of a
protein

spontaneous? 1) Amino acids
heat ? protein no 2)
ATP ? ADP Phosphate
heat YES --------------------------------------
-------------------------------------- (12)
Amino acids ATP ? protein ADP
yes
Phosphate heat
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ATP splitting also drives the other types of cell
work
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Regeneration of ATP
Human cells contain only enough ATP to last about
30 seconds.
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Regeneration of ATP
Human cells contain only enough ATP to last 30
seconds. We must constantly regenerate ATP by
putting 3rd phosphate back on ADP to make ATP
again ( ATP synthesis)
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What process is downhill enough to drive uphill
ATP synthesis?
Since ATP splitting is downhill, putting the
third phosphate back on must be uphill. How can
we drive ATP synthesis?
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What process is downhill enough to drive uphill
ATP synthesis?
Since ATP hydrolysis (splitting) is downhill,
putting the third Phosphate back on must be
uphill. How can we drive ATP synthesis? Couple it
to something even more downhill something
highly spontaneous - but what?
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What process is downhill enough to drive uphill
ATP synthesis?
Since ATP hydrolysis (splitting) is downhill,
putting the third Phosphate back on must be
uphill. How can we drive ATP synthesis? Couple it
to something even more downhill something
highly spontaneous - but what? The slow
combustion of food cellular respiration.
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Coupling cell respiration and ATP synthesis

spontaneous? ADP Phosphate
heat ? ATP no Food
O2 ? CO2 H20 heat
YES ------------------------------------------
---------------------------------- Food O2
ADP ? ATP CO2 heat yes
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Coupling cell respiration and ATP synthesis

spontaneous? ADP Phosphate
heat ? ATP no Food O2
? CO2 H20 heat
YES ----------------------------------------------
------------------------------ Food O2 ADP
? ATP CO2 yes The COMBINED
process makes ATP and increases the entropy of
the universe.
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The ATP Cycle
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Metabolic pathways
Metabolism all the chemical processes of
cells Metabolic pathway sequence of reactions
by which chemical changes such as cell
respiration are carried out in many small steps,
each catalyzed by an enzyme
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Metabolic pathways
Metabolism the chemical processes of
cells Metabolic Pathway sequence of reactions
by which chemical changes such as cell
respiration are carried out in many small
steps. Cellular respiration using the sugar
glucose as fuel takes place in three phases,
involving 20 separate reactions, and 20 different
enzymes.
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3 Stages of glucose burning
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The ten steps of Stage 1 (glycolysis)
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Stage 1 (glycolysis) occurs in the cytosol
(cell juice) Stages 2 3 in mitochondria
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Mitochondrion
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Enzymes protein catalysts
Enzymes are proteins that act as catalysts
enzymes speed up chemical reactions.
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Structure of an enzyme
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Where does the food come from that is used as
fuel in cellular respiration?
Animals eat plants
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Where does the food come from that is used as
fuel in cellular respiration?
Animals eat plants, or they eat animals that
have eaten plants.
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Where does the food come from that is used as
fuel in cellular respiration?
Animals eat plants, or they eat animals that have
eaten plants. Plants make their own food by
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Where does the food come from that is used as
fuel in cellular respiration?
Animals eat plants, or they eat animals that have
eaten plants. Plants make their own food by
photosynthesis
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Photosynthesis

spontaneous? CO2 H2O
? Glucose O2 no Photons
of light ? heat
YES (ordered energy) (random
energy) ------------------------------------------
------------------------------------ CO2 H2O
Photons ? Glucose O2 heat yes Light
supplies the energy to drive synthesis of glucose
in photosynthesis
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Where photosynthesis occurs
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NOTE WELL Plant cells use the food they make in
the same way that animal cells do - by cellular
respiration
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