Metabolism
Metabolism
Metabolism
Entirety of chemical reactions in living matter All reactions involved in storage and generation of metabolic energy
Anabolism - assembly of complex molecules Catabolism - breakdown of complex molecules
Intermediary metabolism
Two major categories:
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.
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
Oxidation
The more highly reduced a substrate the more it can be oxidised and the more energy can be obtained
From: Elliott, WH. Elliott, DC. (1997) Biochemistry and Molecular Biology. Oxford: Oxford University Press. p65
Glucose yields ~16 kJ·g-1 Palmitic acid yields ~39 kJ·g-1
Palmitic acid contains more protons and electrons to combine with oxygen on path to CO2 and H2O
From: Stryer LS (1988) Biochemistry (3rd Ed.) New York: WH Freeman & Co p 285.
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 kJ·mol-1 from each bond
From: Stryer LS (1988) Biochemistry (3rd Ed.) New York: WH Freeman & Co p316.
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.
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
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