An Introduction to Metabolism

1
An Introduction to Metabolism

• Chapter 8

2
Metabolism

• What is metabolism?
• The sum total of all chemical reactions in an
  organism
• How do catabolic and anabolic pathways differ?
• Catabolism - breaks down complex molecules
• Anabolism - builds complex molecules

3
Energy

• Energy is the capacity to cause change or do work
• Kinetic Energy
• Associated with the relative motion of objects
• Heat or thermal energy is kinetic energy
  associated with the random movement of atoms
• Potential Energy
• Chemical energy is potential energy available for
  release in a chemical reaction

4
The Laws of Thermodynamics

• The first Law Energy can be transformed, but is
  never lost, or created
• The second law With every energy transfer,
  entropy is increased
• Entropy is a measure of disorder

5

• How does a cell maintain its high level of order
  if with every energy transfer entropy is
  increased?
• Life demands a constant input of energy

6
What is free energy?

• Free energy is the portion of a systems energy
  that is available to perform work
• The term free does not mean that there is no cost
  to using this energy
• It means that the energy is available

7
How Do Reactions Occur?

• Spontaneous reactions may occur very slowly
• All reactions require free energy of activation
  (EA)
• Uphill portion represents the EA required to
  start the reaction
• Downhill portion represents the loss of free
  energy by the molecules in the reaction
• DG is the difference in free energy of products
  and reactants

8
Exergonic and Endergonic Reactions

• Exergonic

• Endergonic

• Less free energy in products than reactants
• Energetically downhill
• DG is negative

• More free energy in products than reactants
• Energetically uphill
• DG is positive

Give an example of the coupling of exergonic and
endergonic reactions in living organisms
9
Is this reaction exergonic or endergonic?
10
How can the EA barrier be overcome?

• Temperature
• Temperatures that are too high denature organic
  molecules, so what else is there?
• ENZYMES
• Enzymes lower the EA barrier so that reactions
  can occur at lower temperatures

11
(No Transcript)
12
What are Enzymes?

• Catalysts change the rate of the reaction without
  being altered themselves
• Enzymes are biological catalysts
• Enzymes are proteins, whose three dimensional
  shape allows for their ability to react
  specifically

13
Enzyme / Substrate Relationship

• What is the substrate?
• It is the reactant upon which an enzyme reacts
• Enzymes are substrate specific
• Only the active site of the enzyme actually binds
  the substrate

14
(No Transcript)
15
The Active Site

• The active site is where the enzyme-substrate
  interaction occurs
• Most enzyme-substrate interactions are the result
  of weak bonds
• The active site may cause the enzyme to hold onto
  the substrate in a very specific way
• The active site may provide a micro-environment
  (e.g. low pH) which enhances a reaction

16
Enzyme Activity

• Temperature
• pH
• Enzyme Concentration
• Substrate Concentration

17
Cofactors

• Non-protein molecules that help enzymes function
• Bind to active site to enhance enzymatic
  reactions
• Cofactors may be inorganic metals such as zinc,
  iron, or copper
• Coenzymes are organic cofactors (e.g. vitamins)

18
Enzyme Inhibition

• Competitive inhibitors - mimic the substrate and
  compete for the active site
• Non-competitive inhibitors bind to the enzyme
  away from the active site, and indirectly cause a
  change in the active site

19
Competitive and Noncompetitive Inhibition
20
Allosteric Regulation

• Regulatory molecules that bind to the enzymes
  allosteric site changing the shape of the enzyme
• Allosterically regulated enzymes have a
  quaternary protein structure
• Each subunit of the enzyme has an active site and
  an allosteric site
• Allosteric activators stabilizes the active site
• Allosteric inhibitors deactivates the active site

21
(No Transcript)
22
Feedback Inhibition
23
Cooperativity