An Introduction to Metabolism chapter 8

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An Introduction to Metabolismchapter 8
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Energy Matter

• Universe is composed of 2 things
• Energy
• Ability to do work
• Force on an object that causes it to move
• Matter
• Anything that has mass and occupies space
• Atoms/elements

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Metabolismtransforming matter and energy

• Metabolism -- totality of an organisms chemical
  reactions
• Arises from interactions between molecules within
  the cell

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Organization of the Chemistry of Life into
Metabolic Pathways

• A metabolic pathway begins with a specific
  molecule and ends with a product
• Each step is catalyzed by a specific enzyme

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Kinds of Pathways

• Catabolic pathways -- release energy
• break down complex molecules into simpler
  compounds
• Anabolic pathways -- consume energy
• build complex molecules from simpler ones
• Bioenergetics -- study of how organisms manage
  their energy resources

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Chemical Reactions

• Functionality
• Catabolic
• Anabolic
• Energy Requirements
• Endergonic
• Exergonic

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Chemical Reactions

• Reactions can be categorized as exergonic or
  endergonic based on energy gain or loss
• Chemical reactions require initial energy input
  (activation energy)
• Molecules need to be moving with sufficient
  collision speed
• The electrons of an atom repel other atoms and
  inhibit bond formation

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Energy

• The ability to do work
• Work -- force on an object that causes it to move
• Whats moving?
• Two kinds of energy
• Kinetic
• Potential can be positional

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What Is Energy?

• The two fundamental types
• Kinetic -- energy of movement
• Heat (thermal energy) -- random movement of atoms
  or molecules
• Potential -- stored energy (can be because of
  location!)
• Chemical energy -- available for release in a
  chemical reaction

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Overview The Energy of Life

• Living cell -- miniature chemical factory
• Energy transformed and stored
• Energy observed in many forms

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The Laws of Energy Transformation

• Thermodynamics -- study of energy transformations
• Describe availability usefulness of energy
• Closed system -- isolated from its surroundings
• Open system -- energy and matter can be
  transferred between the system and its
  surroundings

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Closed and open hydroelectric systems can serve
as analogies
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Laws of Thermodynamics

• First -- In any process, the total energy of the
  universe remains constant.
• Principle of conservation of energy
• Energy can be transferred and transformed
• Energy cannot be created or destroyed
• Second -- The entropy of an isolated system not
  in equilibrium will tend to increase over time,
  approaching a maximum value at equilibrium.
• During every energy transfer or transformation,
  energy is lost (the amount of useable energy
  decreases disorder increases)

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Thermodynamics
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Entropy

• Entropy randomness
• Energy conversions increase entropy in the
  universe
• Spontaneous processes increase entropy
• Explosions car rusting
• Non-spontaneous process energy input
• Rocks rolling uphill

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Enthalpy

• Enthalpy (H) total potential energy of system
• Total energy Usable Energy Unusable Energy
• Entropy (S) randomness or disorder (unusable
  energy)
• Free Energy (G) energy available to do work
• ?G -- change in free energy
• ?G ?Gfinal ?Ginitial
• A negative ?G spontaneous
• Note as entropy increases, free energy
  decreases

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Free Energy Stability
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Exergonic Reactions

• Exergonic reactions release energy
• Reactants contain more energy than products

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Exergonic Reactions

• Exergonic reactions release energy
• Reactants contain more energy than products

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Endergonic Reactions

• Endergonic reactions require an input of energy
• Products contain more energy than reactants

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Endergonic Reactions

• Endergonic reactions require an input of energy
• Products contain more energy than reactants

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Coupled Reactions

• Exergonic reactions drive endergonic reactions
• The product of an energy-yielding reaction fuels
  an energy-requiring reaction in a coupled
  reaction
• The parts of coupled reactions often occur at
  different places within the cell
• Energy-carrier molecules transfer the energy
  within cells

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ATP powers cellular work by coupling exergonic
reactions to endergonic reactions

• Cells do work
• Mechanical
• Transport
• Chemical
• Cells manage energy resources by energy coupling
  the use of an exergonic process to drive an
  endergonic one

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The Structure and Hydrolysis of ATP

• ATP (adenosine triphosphate) -- cells energy
  shuttle
• ATP provides energy for cellular functions

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Hydrolysis of ATP

• High energy phosphate bonds -- broken by
  hydrolysis
• Energy release -- chemical change to a state of
  lower free energy, not from the phosphate bonds
  themselves

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• Energy from ATP hydrolysis can be used to drive
  an endergonic reaction
• Overall, the coupled reactions are exergonic

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Phosphorylation
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The Regeneration of ATP

• ATP -- renewable resource
• regenerated by addition of a phosphate group to
  ADP
• The energy comes from catabolic reactions in the
  cell
• The potential energy stored in ATP drives most
  cellular work

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LE 8-12
ATP
Energy for cellular work (endergonic,
energy- consuming processes)
Energy from catabolism (exergonic,
energy- yielding processes)
P
ADP

i
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Exergonic Reactions

• Exergonic reactions release energy
• Spontaneous?

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The Activation Energy Barrier

• Chemical reactions -- bond breaking and bond
  forming
• The initial energy -- free energy of activation,
  or activation energy (EA)
• EA often supplied in the form of heat from the
  surroundings

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LE 8-14
A
B
C
D
Transition state
EA
A
B
Free energy
C
D
Reactants
A
B
DG lt O
C
D
Products
Progress of the reaction
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How Enzymes Catalyze Reactions

• Lowering Energy of Activation (EA)
• Enzymes do not affect the change in free-energy
• hasten reactions that would occur eventually
• Biological catalysts
• Specific for the molecules they catalyze
• Activity often enhanced or suppressed by their
  reactants or products

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LE 8-15
Course of reaction without enzyme
EA without enzyme
EA with enzyme is lower
Reactants
Free energy
Course of reaction with enzyme
DG is unaffected by enzyme
Products
Progress of the reaction
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Catalysts

• Catalyst -- chemical agent that speeds up a
  reaction without being consumed by the reaction
• Enzyme -- catalytic protein
• Example Hydrolysis of sucrose by sucrase

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Enzymes

• Enzymes are a type of protein that acts as a
  catalyst, speeding up chemical reactions

• Enzymes can perform their functions repeatedly,
  functioning as workhorses that carry out the
  processes of life

Substrate (sucrose)
Glucose
Enzyme (sucrose)
Fructose
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LE 8-17
Substrates enter active site enzyme changes
shape so its active site embraces the substrates
(induced fit).
Substrates held in active site by
weak interactions, such as hydrogen bonds
and ionic bonds.

• Active site (and R groups of
• its amino acids) can lower EA
• and speed up a reaction by
• acting as a template for
• substrate orientation,
• stressing the substrates
• and stabilizing the
• transition state,
• providing a favorable
• microenvironment,
• participating directly in the
• catalytic reaction.

Substrates
Enzyme-substrate complex
Active site is available for two
new substrate molecules.
Enzyme
Products are released.
Substrates are converted into products.
Products
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LE 8-18

• An enzymes activity can be affected by
• General environmental factors
• temperature
• pH
• Chemicals that specifically influence the enzyme

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LE 8-19

• Competitive -- bind to the active site of an
  enzyme
• Noncompetitive -- bind to another part of an
  enzyme
• changes shape
• makes active site less effective

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Regulation of enzyme activity helps control
metabolism

• Chemical chaos -- if cells metabolic pathways
  were not tightly regulated
• Cells switch genes on or off that encode specific
  enzymes

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Allosteric Regulation of Enzymes

• Enzymes -- active and inactive forms
• The binding of activator -- stabilizes the active
  form
• The binding of an inhibitor -- stabilizes the
  inactive form

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LE 8-20a
Allosteric regulation
function affected by binding of a regulatory
molecule at another site
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• Allosteric Regulation
• Cooperativity -- can amplify enzyme activity

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Feedback Inhibition
Isoleucine used up by cell
Intermediate A

• End product of a metabolic pathway shuts down the
  pathway

Feedback inhibition
Active site of enzyme 1 cant bind theonine pathwa
y off
Intermediate B
Intermediate C
Isoleucine binds to allosteric site
Intermediate D
End product (isoleucine)