Transcript Chapter 6 - IRSC Biology Department

Energy and Metabolism
Chapter 6
1
Section 6.1 Learning Objectives
– The Flow of Energy in Living Systems
• Differentiate between kinetic and potential
energy.
• Identify the source of energy for the
biosphere (Earth).
• Contrast oxidation and reduction
reactions.
2
Flow of Energy
•
Thermodynamics
–
Branch of chemistry concerned with energy
changes
Study of energy flow or transformations
–
•
•
•
Kinetic energy  potential energy
Potential energy  kinetic energy
Cells are governed by the laws of
physics and chemistry
3
What is Energy?
• Energy – capacity to do work
– 2 states
1. Kinetic – energy of motion
2. Potential – stored energy
– Many forms – mechanical, heat, sound,
electric current, light, or radioactivity
– Heat the most convenient way of measuring
energy
•
1 calorie = heat required to raise 1 gram of water 1ºC
•
calorie or Calorie?
–
Calorie (1000 calories) how food energy measured
4
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a. Potential energy
Stored energy based on her
position (also think of a
bolder on top of a hill)
b. Kinetic energy
Energy in motion (she is able
to slide down based on her
previous position)
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The Source of Energy on Earth
• Energy flows into the biological world from
the sun
• Photosynthetic organisms (plants/algae)
capture this energy
• Stored as potential energy in chemical
bonds (in sugars made from
photosynthesis)
cell respiration
photosynthesis
6
Redox reactions (how energy is
transferred at molecular level)
• Oxidation
– Atom or molecule loses an electron
• Reduction
– Atom or molecule gains an electron
– Higher level of energy than oxidized form
• Oxidation-reduction reactions (redox)
– Reactions always paired
– LEO says GER (leo is a lion)
• Loss of e- is oxidation
• Gain of e- is reduction
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To follow the energy, follow the
eLoss of electron (oxidation) LEO
e-
e–
A
A
+
B
A+
B
+
B–
Gain of electron (reduction) GER
Lower energy
Higher energy
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Question
Oxidation is the ____________ and reduction is the
________.
a. loss of electrons, gain of electrons
b. gain of protons, loss of protons
c. loss of protons, gain of protons
d. loss of electrons, gain of protons
Section 6.2 Learning Objectives
– The Laws of Thermodynamics and Free
Energy
• Explain the laws of thermodynamics.
• Relate free energy changes to the
outcome of chemical reactions.
• Contrast the course of a reaction with and
without an enzyme catalyst.
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Laws of thermodynamics
• First law of thermodynamics
– Energy cannot be created or destroyed
– Energy can only change from one form to
another
– Total amount of energy in the universe
remains constant
– During each conversion, some energy is lost
as heat
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• Second law of thermodynamics
– Entropy (disorder) is continuously
increasing
– Energy transformations proceed
spontaneously to convert matter from a more
ordered/less stable form to a less ordered/
more stable form
12
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Disorder happens
spontaneously
Organization
requires energy
© Jill Braaten
Free energy
• G = Energy available to do work
• G = H – TS
 H = enthalpy, energy in a molecule’s chemical
bonds
 T = absolute temperature
 S = entropy, unavailable energy
G
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ΔG = ΔH – TS
• ΔG = change in free energy
• Positive ΔG
– Products have more free energy than reactants
– Not spontaneous, requires input of energy
– Endergonic (photosynthesis)
• Negative ΔG
– Products have less free energy than reactants
– Spontaneous (may not be instantaneous)
– Exergonic (cell respiration)
15
Free Energy (G)
Energy Released Energy Supplied
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Endergonic
Products
Energy must
be supplied
 G > 0
0
Reactants
photosynthesis
Course of Reaction
Free Energy (G)
Energy Released Energy Supplied
a.
b.
Exergonic
cell respiration
Reactants
0
Energy is
released
Products
G<0
Course of Reaction
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Activation Energy: How to Start
a Reaction
• Extra energy required to destabilize existing
bonds and initiate a chemical reaction
• Exergonic reaction’s rate depends on the
activation energy required
– Larger activation energy proceeds more slowly
• Rate can be increased 2 ways
1. Increasing energy of reacting molecules (heating)
2. Lowering activation energy
17
Energy Released Energy Supplied
Free Energy (G)
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uncatalyzed
catalyzed
Activation
energy
Activation
energy
0
Reactant
ΔG
Product
Course of Reaction
18
Catalysts
• Substances that influence chemical bonds
in a way that lowers activation energy
• Cannot violate laws of thermodynamics
– Cannot make an endergonic reaction
spontaneous
• Do not alter the proportion of reactant
turned into product
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Energy Released Energy Supplied
Free Energy (G)
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uncatalyzed
catalyzed
Activation
energy
Activation
energy
0
Reactant
ΔG
Product
Course of Reaction
20
Question
The energy in a system that is able to do work is called
a. Enthalpy
b. Entropy
c. Free energy
d. Kinetic energy
e. Potential energy
Question
A reaction with a positive ∆G is –
a. Exergonic
b. Entropic
c. Endergonic
d. Enthalpic
e. Energertic
Question
A ball sitting atop a hill begins to roll down after
getting a slight tap. This is analogous to an
endergonic reaction.
a. This is true
b. This is false
Section 6.3-6.4 Learning
Objectives
•
•
•
•
•
– ATP: The Energy Currency of Cells
Describe the role of ATP in short-term energy
storage.
Distinguish which bonds in ATP are “high energy.”
– Enzymes: Biological Catalysts
Discuss the specificity of enzymes.
Explain how enzymes bind to their substrates.
List the factors that influence the rate of enzymecatalyzed reactions.
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ATP: Cell Energy
• Adenosine triphosphate
• Chief “currency” all cells use
• Composed of
– Ribose – 5 carbon sugar
– Adenine
– Chain of 3 phosphates
•
•
•
•
Key to energy storage
Bonds are unstable
ADP – 2 phosphates
AMP – 1 phosphate – lowest energy form
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ATP
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Triphosphate
group
O–
O
P
O–
ADP
O
O
P
a.
High-energy
bonds
O–
Adenine
N
AMP CORE
O
P
O
C
N
H C
N
O
C
NH2
C
C H
N
O
CH2
H
O
H
H
OH
OH
H
Ribose
b.
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ATP cycle
• ATP hydrolysis drives endergonic
reactions
– Coupled reaction results in net –ΔG
(exergonic and spontaneous)
• ATP not suitable for long-term energy
storage
– Fats and carbohydrates better
– Cells store only a few seconds worth of ATP
27
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Energy from
exergonic
cellular
reactions
cell respiration
ATP
+
ADP +
H2O
Pi
Energy for
endergonic
cellular
processes
photosynthesis
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Enzymes: Biological Catalysts
• Most enzymes are protein
– Some are RNA
• Shape of enzyme stabilizes a temporary
association between substrates
• Enzyme not changed or consumed in
reaction
• Carbonic anhydrase (enzyme used to maintain
blood pH)
– 200 molecules of carbonic acid per hour made
without enzyme
– 600,000 molecules formed per second with enzyme
29
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Active site
Substrate
Enzyme
a.
Enzyme–substrate complex
b.
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Active site
•
•
•
•
Pockets or clefts for substrate binding
Forms enzyme–substrate complex
Precise fit of substrate into active site
Applies stress to distort particular bond to
lower activation energy
– Induced fit
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3. The binding of the substrate and
enzyme places stress on the glucose–
fructose bond, and the bond breaks.
1. The substrate, sucrose,
consists of glucose and
fructose bonded together.
2. The substrate binds to the active site
of the enzyme, forming an enzyme–
substrate complex.
Bond
H2O
Glucose
Fructose
4. Products are
released, and
the enzyme is
free to bind other
substrates.
Active site
Enzyme
sucrase
32
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33
Nonprotein enzymes
• Ribozymes
• 1981 discovery that certain reactions
catalyzed in cells by RNA molecule itself
1. 2 kinds
1. Intramolecular catalysis – catalyze reaction
on RNA molecule itself
2. Intermolecular catalysis – RNA acts on
another molecule
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Enzyme function
• Small molecules can affect function
– Coenzymes
– Cofactors
• Rate of enzyme-catalyzed reaction
depends on concentrations of substrate
and enzyme
• Any chemical or physical condition that
affects the enzyme’s three-dimensional
shape can change rate
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Rate of Reaction
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Optimum temperature
for human enzyme
30
40
Optimum temperature for enzyme
from hotsprings prokaryote
50
60
70
80
Temperature of Reaction (˚C)
Rate of Reaction
a.
Optimum pH for pepsin
1
b.
2
3
Optimum pH for trypsin
4
5
6
pH of Reaction
7
8
9
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Inhibitors
• Inhibitor – substance that binds to enzyme
and decreases its activity
• Competitive inhibitor
– Competes with substrate for active site
• Noncompetitive inhibitor
– Binds to enzyme at a site other than active
site
– Causes shape change that makes enzyme
unable to bind substrate
37
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Substrate
Active
site
Substrate
Inhibitor
Enzyme
Active
site
Inhibitor
Enzyme
Allosteric site
Competitive inhibitor interferes
with active site of enzyme so
substrate cannot bind
a. Competitive inhibition
Allosteric inhibitor changes
shape of enzyme so it cannot
bind to substrate
b. Noncompetitive inhibition
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Allosteric Enzymes
• Allosteric enzymes – enzymes exist in
active and inactive forms
• Most noncompetitive inhibitors bind to
allosteric site – chemical on/off switch
• Allosteric inhibitor – binds to allosteric site
and reduces enzyme activity
• Allosteric activator – binds to allosteric site
and increases enzyme activity
39
Question
If inhibition is to be competitive, which of the following
must be true?
a. There must be more than one binding site
b. The substrate and the inhibitor must be similar
c. The reaction can not require a cofactor
d. The reaction must be endergonic
e. The allosteric and active sites must be near each
other
Question
Carbon monoxide (CO) binds to the hemoglobin protein
at the oxygen binding site. Once the CO binds, the
oxygen can no longer be transported. What does this
describe?
a. Non-competitive inhibition
b. Feedback inhibition
c. Substrate inhibition
d. Allosteric inhibition
e. Competitive inhibition
Question
Increasing the temperature increases the rate of an
enzyme-catalyzed reaction. Once a critical temperature
is reached, the reaction stops. Why does this happen?
a. The concentration of reactants drop
b. The enzymes have all been consumed in the
reaction
c. The increase in temperature alters the pH
d. The polypeptide chains in the enzyme denature
Section 6.5 Learning Objectives
– Metabolism: The Chemical Description of Cell
Function
• Explain the kinds of reactions that make
up metabolism.
• Discuss what is meant by a metabolic
pathway.
• Describe mechanisms to control a
metabolic pathway
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Metabolism
• Total of all chemical reactions carried out by an
organism
• Anabolic reactions/anabolism
– Expend energy to build up molecules
– Anabolic Steroids=build muscle
• Catabolic reactions/catabolism
– Harvest energy by breaking down molecules
– Starvation=breakdown muscle
Large
molecules
Small
molecules
44
Biochemical pathways
• Chemical reactions that create/store or
produce other chemical products for daily
function.
• Reactions occur in a sequence
• Product of one reaction is the substrate for
the next reaction
A
Enzyme 1
B
Enzyme 2
C
Enzyme 3
D
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Basic metabolic pathway chart
46
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Initial substrate
Enzyme1
Intermediate
substrate A
Enzyme2
Intermediate
substrate B
Enzyme3
Intermediate
substrate C
Enzyme4
End product
47
Feedback inhibition
• End-product of pathway binds to an
allosteric site on enzyme that catalyzes
first reaction in pathway
• Shuts down pathway so raw materials and
energy are not wasted
48
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Initial
substrate
Enzyme 1
Enzyme 2
Enzyme 3
a.
Initial
substrate
Enzyme 1
Intermediate
substrate A
Enzyme 2
Intermediate
substrate B
End product
Enzyme 3
End product
b.
49
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50
Question
Feedback inhibition occurs when the final product acts
as an inhibitor to the first enzyme in the pathway.
a. This is true
b. This is false
Question
Catabolic reactions expend energy to form or transform
chemical bonds.
a. This is true
b. This is false
Final Review
53
Question
The First Law of Thermodynamics states that energy
can be –
a. Created
b. Destroyed
c. Converted
d. Lost
e. None of the above
Question
Small organic molecules that assist in enzymatic
functions are –
a. Coprolites
b. Cofactors
c. Activators
d. Coenzymes
e. Intermediates
Question
Spending ATP involves hydrolyzing it into ADP and
inorganic P. The energy released can drive other
chemical reactions.
a. This is true
b. This is false
Question
Enzymes are consumed by reactions.
a. This is true
b. This is false
Question
A catalyst speeds up chemical reactions. How do
catalysts do this?
a. Decreasing entropy
b. Altering ∆G
c. Consuming reactants
d. Lowering activation energy
e. Making different products
Question
A muscle contraction is ________, but as the
muscle contracts heat is released which is
___________.
a. Exergonic, endergonic
b. Exergonic, exergonic
c. Endergonic, endergonic
d. Endergonic, exergonic
Question
Study this metabolic pathway:
A -E1  B -E2  C -E3  D.
Which of the following statements is NOT correct?
(E represents enzymes)
a. C is the substrate for enzyme E1 and D is the
product
b. A is the substrate for enzyme E1 and B is the
product
c. Enzyme E2 can catalyze the substrate B but
not A, C and D
d. B is the product formed by enzyme E1 but the
substrate for enzyme E2
Question
When muscles contract, chemical energy is
converted to mechanical energy with the loss of
heat. This conversion of energy is an example of
the ______ Law of Thermodynamics.
a. First
b. Second
c. Third
d. Fourth
Question
Which of the following is defined as the amount of heat
required to raise one gram of water one degree Celsius?
a. Tesla
b. Joule
c. Newton
d. Calorie
e. calorie