Energy and Enzymes (metabolism)

1
Energy and Enzymes(metabolism)

• Chapter 8.1, 8.2, 8.4, 8.5

2

• metabolism is the process of breaking down and
  creating molecules necessary for life
• each step in this process is driven by an enzyme
  which directs the speed of the reaction (enzymes
  are proteins!)
• catabolic--breakdown molecules
• cellular respiration
• anabolic--build molecules
• protein synthesis

3

• energy is the capacity to cause change
• kinetic (heat) vs. potential (chemical)
• thermodynamics energy transformations
• 1st law (matter cannot be created or destroyed,
  only change form)
• 2nd law (energy transfer increases the entropy of
  the universe)
• spontaneous reactions vs. reactions that need
  energy

4

• free energy--identifies if a reaction requires
  energy to proceed
• higher free energy unstable
• does not require outside energy for the reaction
  to happen (spontaneous)
• exergonic reaction (negative delta G)
• does not imply that it happens fast!
• lower free energy stable
• requires outside energy for the reaction to
  proceed (nonspontaneous)
• endergonic reaction (positive delta G)

5
Enzymes

• Lower energy barriers for the reaction to happen
  at an increased rate (catalyst) not used up
  during the reaction
• activation energy (energy required to get
  reaction going)
• based on how difficult it is to break the
  chemical bonds
• speed up reactions that would occur anyway

6
How enzymes work...(induced-fit model)

• substrate (reactant an enzyme acts on)
• enzyme binds to substrate, forming
  enzyme-substrate complex
• each enzyme has a specific substrate (results
  from unique sequence of amino acids)
• active site (region of enzyme where substrate
  binds)
• when this occurs, the shape of the enzyme changes
  which enhances the reaction

7

• Rate in which enzyme converts substrate to
  product is determined by...
• the initial concentration of the substrate (or
  enzyme)
• more substrate molecules that are available the
  more frequently they access active site.
• limited by the enzyme concentration (saturated
  when rate of reaction is determined by how often
  substrate can move into active site)
• general environmental factors
• temperature, pH, and other chemicals
• each enzyme has optimal environment depending on
  the organism and where it needs to work

8
Enzyme Inhibition and Regulation

• competitive inhibition
• reduce the productivity of enzymes by blocking
  substrate from entering active site
• overcome by increasing concentration of substrate
• noncompetitive inhibition
• impede reactions by binding to another part of
  the enzyme, thus changing the shape of the active
  site and making it less effective
• often pesticides, antibiotics, and toxins are
  inhibitors

9

• enzymes need to be told when and where to be
  active so only necessary reactions are occurring
• Allosteric regulation
• protein function changed by binding of another
  molecule
• has active (activator binds) and inactive
  (inhibitor binds) forms
• Chemical on/off switch
• feedback inhibition
• end product of reaction binds to enzyme causing
  inhibition, thus slowing the reaction down