Title: What is Photosynthesis
1 ENERGY IS THE ABILITY TO DO WORK
WHAT IS ENERGY?
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3All 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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5TOPICS 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?
6What 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
7The 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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9First Law of Thermodynamics
- The total amount of energy within a given system
remains constant unless energy is added or
removed from the system
10Second 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?
11Are 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)
12Living 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
13How Does Energy Flow in Chemical Reactions?
- Exergonic Reactions Release Energy
- Endergonic Reactions Require an Input of Energy
- Coupled Reactions Link Exergonic and Endergonic
Reactions
14The Nature of Chemical Reactions
- Chemical reactions are process that form or break
chemical bonds between atoms - Chemical reactions convert reactants to products
- Reactants Products
15Exergonic Reactions Release Energy
- Reactants contain more energy than products in
exergonic reactions
16Exergonic Reactions Release Energy
- Example the burning of glucose
- Glucose 6O2 6CO2 6H2O released
energy - (reactants)
(products)
17Endergonic Reactions Require an Input of Energy
- Products contain more energy than reactants in
endergonic reactions
18Endergonic reactions are uphill reactions and
require energy input
- In photosynthesis the energy input is
sunlight - 6CO2 6H2O sunlight energy
glucose 6O2
- (reactants)
(products) -
19Activation 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
20Photosynthesis 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
21Coupled 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
22Exergonic 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
23Coupled 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
24How 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
25Energy Carrier Molecules
- Food energy cannot be used directly to power
energy-requiring reactions (e.g. muscle
contraction)
26Energy 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
27ATP 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)
28Adenosine 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
29ATP 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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31ATP is the Principal Energy Carrier in Cells
- The energy released when ATP-gtADP P is
transferred to endergonic reactions through
coupling
32Coupled 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
33Electron Carriers Also Transport Energy Within
Cells
- Energy can be transferred to electrons in glucose
metabolism and photosynthesis - Electron carriers transport high-energy electrons
34Electron Carriers Also Transport Energy Within
Cells
- Two common electron carriers
- Nicotinamide adenine dinucleotide (NAD) Flavin
adenine dinucleotide (FAD)
35Electron carrier molecules transport energy
NADH
(energized carrier)
exergonic reaction
e_
e_
(depleted carrier)
endergonic reaction
NAD
H
net exergonic "downhill" reaction
36How 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
37Overview of Metabolism
- The sum of all the chemical reactions inside a
cell is its metabolism - Many cellular reactions are linked through
metabolic pathways
38Final 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
39Overview 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
40At 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
41At Body Temperatures, Spontaneous Reactions
Proceed Too Slowly to Sustain Life
- Enzyme molecules are employed to catalyze (speed
up) chemical reactions in cells
42Catalysts Reduce Activation Energy
- Catalysts speed up the rate of a chemical
reaction without themselves being used up
43Catalysts 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)
44Catalysts Reduce Activation Energy
- Catalyst in catalytic converter speeds carbon
monoxide conversion - Carbon monoxide oxygen carbon dioxide
energy
45Catalysts Reduce Activation Energy
- Catalysts only speed up spontaneous reactions by
reducing activation energy
46high
activation energy without catalyst
activation energy with catalyst
energy content of molecules
reactants
products
low
progress of reaction
47Enzymes Are Biological Catalysts
- Enzymes orient, distort, and reconfigure
molecules in the process of lowering activation
energy
48Enzymes 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
49The 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
50The 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
51substrates
active site of enzyme
enzyme
52Cells Regulate the Amount and Activity of Their
Enzymes
- Enzymes usually catalyze a single step in a chain
of metabolic reactions
53Cells 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)
54CH3
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)
55Cells Regulate the Amount and Activity of Their
Enzymes
- Small organic molecules can bind to enzymes and
enhance/inhibit activity (allosteric regulation)
56Enzyme structure
substrate
active site
enzyme
allosteric regulatory site
Allosteric inhibition
allosteric regulator molecule
Competitive inhibition
57The Activity of Enzymes Is Influenced by the
Environment
- Three-dimensional structure of an enzyme is
sensitive to pH, salts, temperature, and presence
of coenzymes
58The 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
59The 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
60The Activity of Enzymes Is Influenced by the
Environment
- Some enzymes require helper coenzyme molecules to
function (e.g. certain B vitamins)