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Why dieting does not work. Ch 6. Metabolism - ch.8. Energy. = capacity to do work ( potential vs. kinetic ) 2 laws of thermodynamics 1) energy can be transformed but not created/destroyed 2) every energy transfer makes the world more unordered ( entropy )

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Why dieting does not work

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Ch 6



  • = capacity to do work (potential vs. kinetic)
  • 2 laws of thermodynamics

1) energy can be transformed but not created/destroyed

2) every energy transfer makes the world more unordered (entropy)

      • heat is energy is released
metabolism balance of all chemical reactions
Metabolism= balance of all chemical reactions
  • Catabolism - break down, release energy
  • Anabolism - build compounds, requires energy
  • reactions are often coupled = energy released from a catabolic rxn drives an anabolic one, ex. Na+/K+ pumps
  • Bioenergetics- study of management of one’s energy
free energy
Free energy
  • (G) available energy to do work→


  • ΔG = change in free energy

H= enthalpy(total energy)


S=change in entropy

  • Indicates if a reaction will or won't occur
    • If ΔG < 0, you can get spontaneous rxns
Exergonic rxn = spontaneous, - ΔG
  • Endergonic rxn = non-spontaneous, requires energy, ΔG is +

In a spontaneous change• The free energy of the system decreases (G 0)• The system becomes more stable• The released free energy can be harnessed to do work

ATP (Adenine + ribose + P-P-P)
  • Reactions when coupled allow cellular work, ex. ATP, *p.149 ΔG = -7.3 kcal/mol
energy is released from breaking the bond because the products (ADP + Pi) have less free energy than the reactants (ATP)
  • p.150
  • Proteins that speed chemical rxns without being used up in the rxn (catalysts)
  • lower the activation energy = energy needed to start the reaction, p.152
almost allrxns in the body require enzymes
  • very specific, only work for a specific substrate, dependant on the 3-D shape (structure/function)
  • animation
substrate = substance enzyme reacts with
  • active site = region on the enzyme where the substrate binds
  • shape of active site is altered during the rxn, this speeds rxn and lowers activation energy, lock and key
  • more substrate = faster rxn ?
    • only to a point, saturation point
several things affect enzyme rxns
Several things affect enzyme rxns
  • temp. increases rate to an extent (why?)
  • cofactors – nonproteins that help enzymes work, ex. Vitamins
  • inhibitors- bind someplace on the enzyme, p.156 reversible and irreversible
    • competitive - compete for active site
    • noncompetitive – binds at allosteric site, alters it, ex. DDT
control of metabolism other than gene regulation of enzymes too much enzyme action would be chaos
Control of Metabolism: other than gene regulation of enzymes, too much enzyme action would be chaos
  • allosteric site – receptor site (on enzyme) away from the active site, alters shape, p.157 ex. activators/inhibitors

2. feedback inhibition– regulation because the quantity of products stops or enhances the pathway, ex. body temp, or inhibition of isoleucine synthesis

cooperativity – substrate binds, enhances reactivity, p.158
  • location of enzymes – where they are stored, or can go
enzyme free response question
Enzyme free-response question

Enzymes are biological catalysts.

Relate the chemical structure of an enzyme to its specificity and catalytic activity.

Design a quantitative experiment to investigate the influence of pH or temperature on the activity of an enzyme.

Describe what information concerning the structure of an enzyme could be inferred from your experiments.


Free-Response Question from 2010 test: (complete in 22.5 minutes)

An experiment was conducted to measure the reaction rate of the human salivary enzyme α-amylase. Ten mL of a concentrated starch solution and 1.0 mL of α-amylase solution were placed in a test tube. The test tube was inverted several times to mix the solution and then incubated at 25°C. The amount of product (maltose) present was measured every 10 minutes for an hour. The results are given in the table below.

(a) Graph the data on the axes provided and calculate the rate of the reaction for the time period 0 to 30 minutes.

(b) Explain why a change in the reaction rate was observed after 30 minutes.

(c) Draw and label another line on the graph to predict the results if the concentration of α-amylase was doubled. Explain your predicted results.

(d) Identify TWO environmental factors that can change the rate of an enzyme-mediated reaction. Discuss how each of those two factors would affect the reaction rate of an enzyme

review problems from text
Review problems from text

Do Figure 8.12, figure 8.16, p. 162 #7 Answers on following slides

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