Metabolism

1
Metabolism
2
Metabolism

• Metabolism
• Entirety of chemical reactions in living matter
• Intermediary metabolism
• All reactions involved in storage and generation
  of metabolic energy
• Two major categories
• Anabolism - assembly of complex molecules
• Catabolism - breakdown of complex molecules

3
Oxidation

• Oxygen rich environment
• Cells obtain most energy by oxidation
• Most biological oxidations due to removal of
  hydrogen
• Combustion and biological oxidation release same
  energy
• Combustion 100 energy given off as heat
• Biological oxidation 40 energy (free energy)
  used to drive synthesis of adenosine triphosphate
  (ATP)

From Stryer LS (1988) Biochemistry (3rd Ed.) New
York WH Freeman Co p 316.
4
Oxidation

• Potential energy stored in substrate bonds
  released in small increments
• Coupled oxidation-reduction reactions transfer
  electrons from hydrogen to intermediate carriers
  (eg NAD) and finally to oxygen
• CO2 and H2O formed
• Oxidation more controlled and less energy lost as
  heat

5
Oxidation

• The more highly reduced a substrate the more it
  can be oxidised and the more energy can be
  obtained
• Glucose yields 16 kJg-1
• Palmitic acid yields 39 kJg-1
• Palmitic acid contains more protons and electrons
  to combine with oxygen on path to CO2 and H2O

From Elliott, WH. Elliott, DC. (1997)
Biochemistry and Molecular Biology. Oxford
Oxford University Press. p65
From Stryer LS (1988) Biochemistry (3rd Ed.) New
York WH Freeman Co p 285.
6
Energy transductions

• Free energy captured in bonds of ATP
• Chemical energy in ATP converted to other forms
• energy transduction
• ATP has 2 high energy anhydride bonds
• Hydrolysis yields 30.5 kJmol-1 from each bond

7
Metabolism

• Metabolism can be roughly divided into 3 stages
• Conversion of polymers to monomers
• polysaccharides to monosaccharides
• Lipids to fatty acids and glycerol
• Proteins to amino acids
• Conversion of monomers to metabolic intermediates
• Final degradation to CO2, H2O and NH3

From Summerlin, LR (1981) Chemistry for the Life
Sciences. New York Random House p541.
8
Enzyme juxtaposition

• Cytoplasm of cell highly structured
• Enzymes in metabolic pathways juxtaposed to
  reduce opportunities for diffusion of substrate
  and/or product
• Keeps mean cellular concentration low
• Keeps concentrations at active site high
• Reduces transit time for pathway

9
Metabolism - major control mechanisms

• Cells use variety of mechanisms to regulate
  metabolism
• Enzyme levels
• Enzyme activity
• Compartmentation
• transporter molecules regulate substrate entry
  and product exit from different compartments
• Hormonal control
• Hormones affect all of above