What is Photosynthesis

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ENERGY IS THE ABILITY TO DO WORK
WHAT IS ENERGY?
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All Living Things Contain Capture And Transform
Energy

• Energy is required to fight entropy, the tendency
  for matter to move from an organized to a
  disorganized state
• If living things do not have a continuous input
  of energy, their cellular and atomic components
  will diffuse and disperse until equilibrium is
  established with their surroundings

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TOPICS WE WILL COVER

• What Is Energy?
• How Does Energy Flow in Chemical Reactions?
• How Is Cellular Energy Carried Between Coupled
  Reactions?
• How Do Cells Control Their Metabolic Reactions?

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What Is Energy?

• The Laws of Thermodynamics Describe the Basic
  Properties of Energy
• Living Things Use the Energy of Sunlight to
  Create the Low-Entropy Conditions Characteristic
  of Life

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The Laws of Thermodynamics Describe the Basic
Properties of Energy

• The Two Types of Energy
• Kinetic energy is the energy of movement
• e.g. light, heat, electricity, moving objects
• Potential energy is stored energy
• e.g. chemical energy in bonds, electrical charge
  in a battery, a rock at the top of a hill

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First Law of Thermodynamics

• The total amount of energy within a given system
  remains constant unless energy is added or
  removed from the system

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Second Law of Thermodynamics

• The amount of useful energy decreases when
  energy is converted from one form to another and
  entropy (disorder) increases.

Why is this mans skin warmer than his hair?
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Are any laws of thermodynamics being violated
here?
gas
25 units kinetic energy (motion)
75 units heat energy

100 units chemical energy (concentrated)
No, the first law is fine as energy is not being
created or destroyed, it is only changing form.
The second law is also fine as when the energy
changes form the amount of useful energy
decreases (and the rest is released as heat)
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Living Things Use the Energy of Sunlight to
Create the Low-Entropy Conditions Characteristic
of Life

• Living things must gain external energy in order
  to counteract the increase in their entropy
• Photosynthetic organisms use external solar
  energy to maintain orderly structure
• Non-photosynthetic life uses stored chemical
  energy in other living things to counter their
  increase in entropy

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How Does Energy Flow in Chemical Reactions?

• Exergonic Reactions Release Energy
• Endergonic Reactions Require an Input of Energy
• Coupled Reactions Link Exergonic and Endergonic
  Reactions

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The Nature of Chemical Reactions

• Chemical reactions are process that form or break
  chemical bonds between atoms
• Chemical reactions convert reactants to products
• Reactants Products

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Exergonic Reactions Release Energy

• Reactants contain more energy than products in
  exergonic reactions

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Exergonic Reactions Release Energy

• Example the burning of glucose
• Glucose 6O2 6CO2 6H2O released
  energy
• (reactants)
  (products)

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Endergonic Reactions Require an Input of Energy

• Products contain more energy than reactants in
  endergonic reactions

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Endergonic reactions are uphill reactions and
require energy input

• In photosynthesis the energy input is
  sunlight
• 6CO2 6H2O sunlight energy
  glucose 6O2
  
• (reactants)
  (products)

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Activation Energy

• All chemical reactions require an initial energy
  input (activation energy) to get started
• Molecules need to be moving with sufficient
  collision speed
• The electrons of an atom repels other atoms and
  inhibits bond formation

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Photosynthesis an endergonic reaction
high
glucose
activation energy from light captured by
photosynthesis
energy content of molecules
net energy captured by synthesizing glucose
CO2 H2O
low
progress of reaction
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Coupled Reactions Link Exergonic and Endergonic
Reactions

• Exergonic reactions drive endergonic reactions
• The product of an energy-yielding reaction fuels
  an energy-requiring reaction in a coupled reaction

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Exergonic reaction
100 units energy released
ADP
ATP
P
Endergonic reaction
20 units energy

contracted muslce
relaxed muscle
Coupled reaction




80 units energy released as heat
ADP
P
ATP
relaxed muscle
contracted muslce
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Coupled Reactions Link Exergonic and Endergonic
Reactions

• Energy provided by exergonic reaction must exceed
  that needed by endergonic reaction
• Some energy is lost as heat during the transfer
• Energy carrier molecules are used to transfer
  energy in cells

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How Is Cellular Energy Carried Between Coupled
Reactions?

• Energy Carrier Molecules
• ATP Is the Principal Energy Carrier in Cells
• Electron Carriers Also Transport Energy Within
  Cells

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Energy Carrier Molecules

• Food energy cannot be used directly to power
  energy-requiring reactions (e.g. muscle
  contraction)

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Energy Carrier Molecules

• Energy carrier molecules act as intermediates to
  carry energy between exergonic and endergonic
  reactions
• Energy carrier molecules are only used within
  cells because they are unstable

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ATP is the Principal Energy Carrier in Cells

• Adenosine triphosphate (ATP) is the most common
  energy carrying molecule
• ATP is composed of an adenosine molecule and
  three phosphates (see Figure 6-4, p. 104)

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Adenosine diphosphate (ADP)
Adenosine triphosphate (ATP)
NH2
NH2
2
"high-energy bond
adenine
"high-energy bonds
C
C
N
N
C
C
N
N
HC
HC
CH
CH
C
C
N
N
N
N
O
O
O
O
O
O
O

O
CH2
CH2
O
P
O
P
P
O
O
O
P
O
P
ribose
H
H
H
H
H
H
H
H
O
O
O
O
O
phosphate groups
phosphate groups
OH
OH
OH
OH
Shorthand representations
A
ATP
A
or
or
P
P
P
P
P
ADP
Energy content
low
high
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ATP is the Principal Energy Carrier in Cells

• Energy is stored in the high-energy bond
  extending to the last phosphate
• Heat is given off when ATP breaks into ADP
  (adenosine diphosphate) and P (phosphate)

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ATP is the Principal Energy Carrier in Cells

• The energy released when ATP-gtADP P is
  transferred to endergonic reactions through
  coupling

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Coupled reaction glucose breakdown and protein
synthesis
glucose
A
P
P
P
exergonic (glucose breakdown)
protein
endergonic (ATP synthesis)
exergonic (ATP breakdown)
endergonic (protein synthesis)
CO2 H2O heat
A
P
P
P
ADP
amino acids
heat
net exergonic "downhill" reaction
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Electron Carriers Also Transport Energy Within
Cells

• Energy can be transferred to electrons in glucose
  metabolism and photosynthesis
• Electron carriers transport high-energy electrons

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Electron Carriers Also Transport Energy Within
Cells

• Two common electron carriers
• Nicotinamide adenine dinucleotide (NAD) Flavin
  adenine dinucleotide (FAD)

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Electron carrier molecules transport energy
NADH
(energized carrier)
exergonic reaction
e_
e_
(depleted carrier)
endergonic reaction
NAD
H
net exergonic "downhill" reaction
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How Do Cells Control Their Metabolic Reactions?

• At Body Temperatures, Spontaneous Reactions
  Proceed Too Slowly to Sustain Life
• Catalysts Reduce Activation Energy
• Enzymes Are Biological Catalysts
• The Structure of Enzymes Allows Them to Catalyze
  Specific Reactions
• Cells Regulate the Amount and Activity of Their
  Enzymes
• The Activity of Enzymes Is Influenced by the
  Environment

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Overview of Metabolism

• The sum of all the chemical reactions inside a
  cell is its metabolism
• Many cellular reactions are linked through
  metabolic pathways

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Final products
Initial reactant
Intermediates
A
D
PATHWAY 1
C
B
E
enzyme 1
enzyme 2
enzyme 3
enzyme 4
PATHWAY 2
F
G
enzyme 6
enzyme 5
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Overview of Metabolism

• Metabolic pathways proceed smoothly for three
  reasons
• Chemical reactions are regulated through protein
  enzymes
• Endergonic reactions are coupled with exergonic
  reactions
• Energy-carrier molecules capture energy and
  transfer it between endergonic and exergonic
  reactions

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At Body Temperatures, Spontaneous Reactions
Proceed Too Slowly to Sustain Life

• Reaction speed is generally determined by the
  activation energy required
• Reactions with low activation energies proceed
  rapidly at body temperature
• Reactions with high activation energies (e.g.
  sugar breakdown) move very slowly at body
  temperature, even if exergonic overall

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At Body Temperatures, Spontaneous Reactions
Proceed Too Slowly to Sustain Life

• Enzyme molecules are employed to catalyze (speed
  up) chemical reactions in cells

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Catalysts Reduce Activation Energy

• Catalysts speed up the rate of a chemical
  reaction without themselves being used up

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Catalysts Reduce Activation Energy

• Catalytic converters in cars facilitate the
  conversion of carbon monoxide to carbon dioxide
• Octane oxygen carbon dioxide water
  energy carbon
  monoxide
• (poisonous)

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Catalysts Reduce Activation Energy

• Catalyst in catalytic converter speeds carbon
  monoxide conversion
• Carbon monoxide oxygen carbon dioxide
  energy

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Catalysts Reduce Activation Energy

• Catalysts only speed up spontaneous reactions by
  reducing activation energy

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high
activation energy without catalyst
activation energy with catalyst
energy content of molecules
reactants
products
low
progress of reaction
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Enzymes Are Biological Catalysts

• Enzymes orient, distort, and reconfigure
  molecules in the process of lowering activation
  energy

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Enzymes Are Biological Catalysts

• Enzymes (proteins) differ from non-biological
  catalysts because
• Enzymes are very specific for the molecules they
  catalyze
• Enzyme activity is often enhanced or suppressed
  by their reactants or products

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The Structure of Enzymes Allows Them to Catalyze
Specific Reactions

• Enzymes have a pocket called an active site
• Reactants (substrates) bind to the active site
• Distinctive shape of active site is complementary
  and specific to the substrate
• Active site amino acids bind to the substrate and
  distort bonds to facilitate a reaction

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The Structure of Enzymes Allows Them to Catalyze
Specific Reactions

• Three steps of enzyme catalysis (see Figure 6-9,
  p. 107)
• Substrates enter the active site in a specific
  orientation
• Upon binding, the substrates and enzyme changes
  shape to promote a reaction
• Products of the reaction leave the active site,
  leaving the enzyme ready for another catalysis

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substrates
active site of enzyme
enzyme
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Cells Regulate the Amount and Activity of Their
Enzymes

• Enzymes usually catalyze a single step in a chain
  of metabolic reactions

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Cells Regulate the Amount and Activity of Their
Enzymes

• Enzyme activity in pathways is controlled in
  several ways
• Control of enzyme production regulates
  availability
• Some enzymes are inactive when synthesized and
  must be turned on to be active
• Adequate amounts of formed product inhibit enzyme
  activity (feedback inhibition)

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CH3
CH3
CH2
H
OH
C
A
B
C
D
CH3
H
C
enzyme 1
enzyme 2
enzyme 3
enzyme 4
enzyme 5
C
NH3
H
C
NH3
H
COOH
COOH
Feedback inhibition Isoleucine inhibits enzyme 1
isoleucine (end-product amino acid)
threonine (substrate amino acid)
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Cells Regulate the Amount and Activity of Their
Enzymes

• Small organic molecules can bind to enzymes and
  enhance/inhibit activity (allosteric regulation)

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Enzyme structure
substrate
active site
enzyme
allosteric regulatory site
Allosteric inhibition
allosteric regulator molecule
Competitive inhibition
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The Activity of Enzymes Is Influenced by the
Environment

• Three-dimensional structure of an enzyme is
  sensitive to pH, salts, temperature, and presence
  of coenzymes

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The Activity of Enzymes Is Influenced by the
Environment

• Enzyme structure is distorted and function is
  destroyed when pH is too high or low
• Salts in an enzymes environment can also destroy
  function by altering structure

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The Activity of Enzymes Is Influenced by the
Environment

• Temperature also affects enzyme activity
• Low temperatures slow down molecular movement
• High temperatures cause enzyme shape to be
  altered, destroying function

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The Activity of Enzymes Is Influenced by the
Environment

• Some enzymes require helper coenzyme molecules to
  function (e.g. certain B vitamins)