Chapter%206:%20Metabolism%20 - PowerPoint PPT Presentation

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Chapter%206:%20Metabolism%20

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Chapter 6: Metabolism Energy and Enzymes (Outline) Forms of Energy Two Laws of Thermodynamics Cells and Entropy Metabolic Reactions ATP Energy for Cells – PowerPoint PPT presentation

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Title: Chapter%206:%20Metabolism%20


1
Chapter 6 Metabolism Energy and Enzymes
(Outline)
  • Forms of Energy
  • Two Laws of Thermodynamics
  • Cells and Entropy
  • Metabolic Reactions
  • ATP Energy for Cells
  • Metabolic Pathways and Enzymes
  • Energy of Activation
  • Enzyme-Substrate Complex
  • Redox reactions

2
Forms of Energy
  • The capability to do work or produce an effect
    and is divided into two types
  • Kinetic- the energy of motion, such as waves,
    electrons, atoms, molecules, substances and
    objects
  • Mechanical energy of motion
  • Electrical (e.g. lightning)
  • Thermal (i.e. geothermal energy)
  • Radiant (e.g. visible light, x-rays, gamma rays
    and radio waves)

3
Forms of Energy
  • Potential
  • Stored energy or energy that is "waiting to
    happen"
  • Chemical - energy stored in the bonds of atoms
    and molecules
  • Nuclear energy stored in the nucleus of an atom
    (the energy that holds the nucleus together)
  • Stored mechanical energy (e.g. compressed springs)

4
Laws of Thermodynamics
  • First law
  • Law of conservation of energy
  • Energy cannot be created or destroyed, but
  • Energy CAN be changed from one form to another

5
Laws of Thermodynamics
  • Second law
  • Energy cannot be changed from one form to another
    without a loss of usable energy
  • Therefore, no process requiring a conversion of
    energy is ever 100 efficient

Carbohydrate Metabolism
Carbohydrate Synthesis
6
Cells and Entropy
  • Law of entropy
  • The spontaneous movement from order to disorder
    (randomness)
  • Waste energy goes to increase disorder
  • Entropy a measure of the degree of a systems
    disorder which increases over time
  • Cars rust, dead trees
    decay, buildings
    collapse all these
    are examples of
    entropy
    in action

7
Cells and Entropy
8
Energy Flow in Living Things
9
Metabolic Reactions andEnergy Transformations
  • Metabolism
  • Sum of cellular chemical reactions in a cell
  • Reactants participate in a reaction
  • Products form as result of a reaction
  • Free energy the amount of energy available to
    perform work
  • Concept of free energy was developed by Gibbs
  • For a reaction to occur spontaneously free energy
    must decrease - the products must have less free
    energy than the reactants

10
Metabolic Reactions Energy Transformations
  • Energy Changes in Metabolic Reactions
  • Exergonic Reactions - products have less free
    energy than reactants (i.e. spontaneous and
    releases energy)
  • Example ATP breakdown
  • Endergonic Reactions - products have more free
    energy than reactants (i.e. not spontaneous and
    requires energy)
  • Example
    Muscle contraction

11
ATP Energy for Cells
  • Adenosine triphosphate (ATP)
  • High energy compound used to drive metabolic
    reactions
  • Constantly being generated from adenosine
    diphosphate (ADP) and a molecule of inorganic
    phosphate
  • Composed of
  • Adenine, ribose (C5 sugar), and 3 phosphate
    groups
  • Biological advantages to the use of ATP
  • It provides a common energy currency used in many
    types of reactions
  • When ATP becomes ADP ? the amount of energy
    released is sufficient for biological function
    with little waste of energy ( 7.3 kcal per
    molecule)
  • ATP breakdown can be coupled to endergonic
    reactions that prevents energy waste

12
The ATP Cycle
13
ATP and Coupled Reactions
  • Coupled reactions
  • Energy released by an exergonic reaction is
    captured in ATP
  • That ATP is used to drive an endergonic reaction
  • Occur in the same place, at the same time, why?
  • Because the energy released by the hydrolysis of
    ATP is higher than the energy consumed by the
    endergonic reaction

14
Coupled Reactions
  • A cell has two ways to couple ATP hydrolysis
  • ATP is used to energize a reactant
  • ATP is used change the shape of a reactant
  • Both can be achieved by transferring ? to the
    reactant so that the product is phosphorylated
  • Example
  • Ion movement across the plasma membrane of a cell
    through carrier proteins
  • Attachment of amino acids to a growing
    polypeptide chain

15
Coupled Reactions Muscle Contraction
16
Enzymes
  • Protein molecules that function as catalysts,
    however ribozymes are made of RNA not proteins
  • The reactants of an enzymatically accelerated
    reaction are called substrates
  • Each enzyme accelerates a specific reaction
  • Each reaction in a metabolic pathway requires a
    unique and specific enzyme
  • End product will not appear unless ALL enzymes
    are present and functional

E1 E2 E3 E4 E5 E6 A ? B ? C ? D ? E
? F ? G
17
Metabolic Pathways
  • Reactions usually occur in a sequence
  • Products of an earlier reaction become reactants
    of a later reaction
  • Such linked reactions form a metabolic pathway
  • Begins with a particular reactant,
  • Proceeds through several intermediates, and
  • Terminates with a particular end product

18
Energy of Activation
  • Reactants are often reluctant to participate in
    the reaction
  • Energy must be added to at least one reactant to
    initiate the reaction
  • Energy of activation - minimum amount of energy
    required to trigger a chemical reaction
  • Enzyme Operation
  • Enzymes operate by lowering the energy of
    activation
  • Accomplished by bringing the substrates into
    contact with one another under mild conditions
  • Does not get consumed by the reaction nor does it
    alter the equilibrium of the reaction, thus it
    remains intact

19
Energy of activation (Ea)
20
Enzyme-Substrate Complex
  • The lock and key model of enzyme activity
  • The active site is made up of amino acids and has
    a very specific shape
  • The enzyme and substrate slot together to form a
    complex, as a key slots into a lock
  • This complex reduces the activation energy for
    the reaction
  • Then the products no longer fit into the active
    site and are released allowing another substrate
    in

21
Enzyme-Substrate Complex
  • Induced fit model
  • The active site complexes with the substrates by
    weak interactions, such as hydrogen bonds, etc
  • Causes active site to change shape
  • Shape change forces substrates together,
    initiating bond
  • Some enzymes participate in the reaction (e.g.
    Trypsin active site contains 3 amino acids with
    R groups interacting with the peptide bond (to
    break the bond and introduce H2O

22
Synthesis vs. Degradation
  • Synthesis
  • Enzyme complexes with two substrate molecules
  • Substrates are joined together and released as
    single product molecule
  • Degradation
  • Enzyme complexes with a single substrate molecule
  • Substrate is broken apart into two product
    molecules

23
Enzymatic action
24
Naming enzymes
  • Enzyme names usually end in ase
  • Many enzyme names have 3 parts (substrate
    name) (type of reaction) (ase)

Substrate Enzyme
Lipid Lipase
Urea Urease
Maltose Maltase
Cellulose Cellulase
Lactose Lactase
Sucrose Sucrase
25
Factors Affecting Enzyme Activity
  • Substrate concentration
  • Enzyme activity increases with substrate
    concentration
  • More collisions between substrate molecules and
    the enzyme
  • When the active sites of the enzyme are filled,
    with increasing substrate,
    the enzymes rate of activity
    cannot
    increase any more
  • Amount of active enzyme
    can also increase or limit the
    rate of an
    enzymatic reaction

26
Factors Affecting Enzyme Activity
  • Temperature
  • Enzyme activity increases with temperature
  • Warmer temperatures cause more effective
    collisions between enzyme and substrate
  • However, hot temperatures destroy enzymes, how?
  • Denaturation enzymes shape changes and it can
    no longer bind its substrate efficiently
  • However, there are exceptions such as
  • Some prokaryotes living in hot springs
  • Coat color pattern in Siamese cats

27
Factors Affecting Enzyme Activity
  • Optimal pH
  • Most enzymes are optimized for a particular pH
  • Changes in pH can make and break intra- and
    intermolecular bonds, and/or hydrogen bonds thus
    changing the globular shape of the enzyme
  • pH change can alter the ionization of R side
    chains
  • Under extreme conditions of pH, the enzyme
    becomes inactive (due to altered shape)
  • Example Pepsin (stomach) and trypsin (small
    intestine)

28
Effect of Temperature and pH
29
Enzyme Cofactors
  • Many enzymes require additional help in
    catalyzing their reaction from a coenzyme or
    cofactor
  • Cofactor is used to refer to inorganic metallic
    ions such as zinc, copper and iron, which is
    required by an enzyme
  • Coenzyme is a non-protein organic molecule
  • Many of the coenzymes are derived from vitamins
  • Enzyme activity decreases if vitamin is not
    available (i.e. vitamin-deficient disorder)
  • Niacin deficiency results in skin disease
    (pellagra), while riboflavin deficiency results
    in cracks at the corner of mouth

30
Enzyme Inhibition
  • Competitive inhibition
  • Substrate and the inhibitor are both able to bind
    to the active site
  • If a similar molecule is present, it will compete
    with the real substrate for the active sites
  • Product will form only when the substrate, not
    the inhibitor, is at the active site
  • This will regulate the amount of product

31
Enzyme Inhibition
  • Noncompetitive inhibition
  • Noncompetitive inhibitors are considered to be
    substances which when added to the enzyme change
    the enzyme in a way that it cannot accept the
    substrate
  • The inhibitor binds to another location
    (allosteric site) on the enzyme and inactivates
    the enzyme molecule
  • Both competitive and noncompetitive inhibition
    are examples of feedback inhibition

32
Competitive and Noncompetitive Inhibitors
33
Feedback Inhibition
  • The end product of a pathway inhibits the
    pathways first enzyme
  • The metabolic pathway is shut down when the end
    product of the pathway is bound to an allosteric
    site on the first enzyme of the pathway
  • Normally, enzyme inhibition is reversible and the
    enzyme is not damaged

34
Oxidation and Reduction
  • Oxidation
  • The loss of one or more electrons
  • Reduction
  • The gain of one or more electrons
  • Reduction-oxidation (redox) reactions
  • Simultaneous reaction in which one molecule is
    oxidized and another is reduced
  • Redox reactions occur during photosynthesis and
    cellular respiration

35
Electron Transfer in Redox Reactions
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