Title: Chapter%206%20Metabolism:%20Energy%20and%20Enzymes
1Chapter 6 Metabolism Energy and Enzymes
2Metabolism
- The totality of an organism's chemical reactions,
consisting of catabolic and anabolic pathways - Catabolic pathway A metabolic pathway that
releases energy by breaking down complex
molecules to simpler compounds. (process?) - Anabolic pathway A metabolic pathway that
synthesizes a complex molecule from simpler
compounds. (process?)
3Energy
- The capacity to do work Cells must continually
use energy to do biological work. - Types of energy
- Kinetic Energy The energy of motion, which is
directly related to the speed of that motion.
Moving matter does work by imparting motion to
other matter. - Potential Energy The energy stored by matter as
a result of its location or spatial arrangement.
4Transformations between kinetic and potential
energy.Â
5Energy as explained by the Laws of Thermodynamics
- First Law (conservation of energy)
- Energy cannot be created nor destroyed it can
only change from one from to another. - Energy is found in covalent bonds b/t atoms
- Second Law Every energy transfer or
transformation increases the entropy of the
universe. - Entropy A quantitative measure of disorder or
randomness of energy. - Energy cannot be changed from one form to another
with out a loss of usable energy (heat the most
random form of energy)
6- Chemical energy Energy stored in the chemical
bonds of molecules a form of potential energy. - Energy is trapped inside molecules the more
complex the - molecule the more energy it has, visa versa.
7QOD
- How does the second law of thermodynamics help
explain the diffusion of a substance across a
membrane?
8QOD answer
- The second law is the trend toward randomness.
Equal concentrations of a substance on both sides
of a membrane is a more random distribution than
unequal concentrations. - Diffusion of a substance to a region where it is
initially less concentrated increases entropy, as
mandated by the second law.
9Energy Transformations
- In a reaction
- A B ? C D
- A and B are the reactants
- C and D are the products
- Free Energy (G) The amount of energy that is
free to do work after a chemical reaction takes
place. - Change in Free Energy (DG)
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11Free Energy
- Exergonic Reaction the free energy of reactants
are greater than free energy of products (-DG)
happens spontaneously. - Endergonic Reaction the free energy of the
reactants are less than the free energy of
products (DG) requires input of energy.
12- Because systems at equilibrium are at a minimum
of G and can do no work, a cell that has reached
metabolic equilibrium is dead! The fact that
metabolism as a whole is never at equilibrium is
one of the defining features of life. - Cells use
the products from one reaction as the reactants
in a second reaction, which pulls the first
reaction in one direction. - Energy is utilized
more efficiently in small increments
13QOD
- Cellular respiration uses glucose (C6H12O6), and
releases CO2 and water. Is it exergonic or
endergonic? What happens to the energy released
from glucose?
14QOD Answer
- Cellular respiration is a spontaneous and
exergonic process. The energy released from
glucose is used to do work in the cell, or is
lost as heat.
15Coupling Reactions
- When the energy released by exergonic reactions
is used to drive an endergonic reaction. - ATP ? ADP P
- Highly Exergonic
- The breakdown of ATP is coupled to all of a cells
endergonic reactions
16ATP The Energy Currency of Cells
- When cells require energy they spend
(breakdown) ATP. - Cells are constantly producing ATP because it is
in high demand.
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18Function of ATP
19ATP is constantly recycled in cells (more
efficiency)
Respiration
Photosynthesis
206.3 Metabolic Pathways and Enzymes
21Reactions in cells are orderly
- Metabolic Pathways orderly sequence of chemical
reactions, where each one is catalyzed by a
specific enzyme. - Enzymes Proteins that act as catalysts that
speed up chemical reactions. - Not part of the reaction, they only aid in the
process. - Enzyme does not change itself only the reactants
of the reaction. - Specific to reaction (only catalyze one reaction)
- Substrate a reactant in an enzymatic reaction
22Energy of Activation (EA)
- The amount of free energy that must be added to
cause molecules to react - Heating
- Example
- AB CD ? AC BD
23- Enzymes speed up reactions by lowering the energy
of activation (EA)
24Enzyme-Substrate Complexes
- Enzymes lower the energy of activation by forming
a complex with their substrate. - Active Site small region on surface of enzyme
where substrate binds. - Induced-fit model when substrate binds to
enzyme, the active site changes shape to
facilitate the reaction.
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26Enzyme-Substrate Complexes
- Enzymes do not get used up in a reaction
(substrate does), so only a small amount of
enzyme is required. - Every cell reaction requires a specific enzyme
therefore enzymes are named after their
substrates by adding the ending ase.
27Speed of Enzyme Activity
- Four factors that affect enzyme activity.
- Substrate Concentration
- Temperature
- pH
- Enzyme Inhibition
28Substrate Concentration
- Enzyme activity increases as substrate
concentration increases. - Due to higher probability of collisions between
substrate molecules and enzyme. - As the enzymes active sites are filled the
enzyme activity levels off (reaches a max rate).
29Temperature and pH
- As temperature rises, enzyme activity increases
b/c there are more molecular collisions. - If temperature rises beyond a certain point, the
activity of the enzyme declines rapidly ( enzyme
protein is denatured ). - Each enzyme has an optimal pH that maintains its
normal shape. - A change in pH causes denaturation of enzyme
which decreases activity.
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31Enzyme Inhibition
- When an enzyme is prevented from binding with its
substrate. 2 types - Competitive Inhibition another similar molecule
competes with the substrate for the enzymes
active site. Decreases product formation - Noncompetitive Inhibition a molecule binds to
the Allosteric site which changes the shape of
the active site and thus its ability to bind to
substrate.
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33QOD
- Malonate is a competitive inhibitor of the enzyme
succinate dehydrogenase. Describe how malonate
would prevent the enzyme succinate dehydrogenase
from acting on its normal substrate succinate.
34QOD Answer
- As a competitive inhibitor, malonate binds to the
active site of succinate dehydrogenase and so
prevents the normal substrate, succinate, from
binding.
35Enzyme Inhibition
- Feedback Inhibition A method of metabolic
control in which the end product of a metabolic
pathway acts as an inhibitor of an enzyme within
that pathway. - Inhibitor can be either Competitive or
Noncompetitive - When product is abundant, there is more
inhibition and enzyme activity drops. - When product is used up, there is less inhibition
and enzyme activity increases.
36Fig 6.8
37An example of feed back inhibition that directs
different metabolic pathways.
What would happen if there was high levels of Q
in the cytoplasm? What would happen if there was
high levels of O in the cytoplasm?
38Metabolic Pathways Redox reactions
- Oxidation The loss of electrons from a substance
involved in a redox reaction. - Reduction The addition of electrons to a
substance involved in a redox reaction. - In oxidation-reduction reactions, electrons pass
from one molecule to another - Happens at the same time
- Photosynthesis and respiration are examples
- In living things H ions accompany e-, so
oxidation is a loss of H atoms and reduction is a
gain of H atoms
39Photosynthesis
- 6CO2 6H2O ? C6H12O6 6O2
- H atoms are transferred from water to carbon
dioxide. (water is oxidized, carbon dioxide is
reduced) - The coenzyme NADP is needed as an electron
acceptor to remove hydrogen from water - NADP 2e- H ? NADPH
40Respiration
- C6H12O6 6O2 ? 6CO2 6H2O
- Opposite of photosynthesis (glucose is oxidized
and oxygen is reduced) - Respiration requires the coenzyme NAD as the
electron acceptor to remove Hydrogen atoms from
glucose - NAD 2e- H ? NADH
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