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The Evolution of Endothermy: Role for Membranes and Molecular Activity By Paul L. Else, N. Turner and A.J. Hulbert Endothermy in Vertebrates: A Defining Property Characteristics (Compared to Ectotherms) High Rate of Metabolism/Oxygen Consumption

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the evolution of endothermy role for membranes and molecular activity

The Evolution of Endothermy:Role for Membranes and Molecular Activity

By

Paul L. Else, N. Turner and A.J. Hulbert

endothermy in vertebrates a defining property
Endothermy in Vertebrates:A Defining Property

Characteristics

(Compared to Ectotherms)

  • High Rate of Metabolism/Oxygen Consumption
  • Tissues have high levels of aerobic enzyme activity
  • Large mitochondrial volume and membrane densities (Table 1)
  • Internal organs are larger
  • Organisms with a “high cost of living” which impact every aspect of their life.
why is there a higher rate of metabolism o2 consumption

Why is there a higher rate of metabolism/O2 consumption???

There are differences in the overall rates of cellular processes when comparing endotherms to ectotherms.

(ex. Sodium pump / Protein synthesis

three models of metabolism show recurring themes
Three Models of Metabolism Show Recurring Themes
  • Compared body temp between ectotherms and endotherms (vertebrates) and mass-matched species.
  • Compared animals of varying body mass within a vertebrate class
  • Metabolic changes that occur during different phases of mammalian development
the three ideas of membrane pacemaker theory of metabolism
The Three Ideas of Membrane Pacemaker Theory of Metabolism
  • Only a few cellular processed consume most of the energy used by most organisms
    • Ex. Na+/K+ pump drives other processed (moves other ions across membranes)
  • What does this say????
    • No new or special processes acct for the differences in metabolism between species
pacemaker theory continued
Pacemaker Theory (continued)
  • Energy consuming processes acct for similar proportions/% of metabolism in animals with very different rates of metabolism
    • What does this say???
    • The amt of energy associated with a process may be different among species, but as a percentage of metabolic rate, it is similar.
pacemaker theory cont
Pacemaker Theory (cont.)
  • Most processes are directly or indirectly linked to membranes.
    • (examples – maintenance of ion gradients, protein synthesis, etc.
  • What does this mean…
    • The variations in animal metabolism is due to MEMBRANES setting the pace of a small number of Energy consuming processes.
testing the theory
Testing the Theory
  • “The Sodium Pump” A ubiquitous protein in the cells and tissues of all animals
  • Endotherms vs. Ectotherms tissues
  • There are no differences in the number or density of sodium pumps
  • There are differences in the rate of enzyme activity/ molecular activity.
  • (Figure 1)
sodium pump study more findings
Sodium Pump Study More Findings…
  • Changes in the Pump molecular activity is common during development
study of the membrane environment
Study of the Membrane Environment
  • Ectotherms have more monounsaturated membranes and fatty acids with only one C=C.
  • Endotherms compared to Ectotherms, Smaller compared with Larger –sized mammals and birds, and adult compared with young mammals tend to have higher molecular activities and fatty acids with more C=C double bonds.
membrane crossover experiments
Membrane “Crossover” Experiments
  • Used tissues from rat (with high mol. Activity)
    • Brain and Kidney
  • Used same tissues from toad (low molecular activity.
  • METHOD- detergent to lower activity to similar levels between the two, heat to destroy pump while fatty acid comp remained same.
cross over
Cross Over
  • Enzyme activity was reconstituted with same species membrane
    • Mol activ. Back to normal level
  • Membrane reconstituted with membrane of another species.
    • Mol activ. Shifts to the added membranes orig.activity.
    • Ex. Toad added to rat…reduced Mol. Act.
  • Other CO exper- During Development
    • Similar Findings
possible mechanisms
Possible Mechanisms
  • The use for polyunsaturates suggests an improvement in the activity of membrane proteins.
  • Looked at differences in acyl composition of membrane which suggests an altering of the electrical fields within the bilayer
    • It is still unknown how they influence lipid protein interactions.
mechanisms continued
Mechanisms (continued)
  • Experiments on Physical Properties of Membrane Lipids and influence on Molecular activity
    • Shows increasing molecular activity with increasing area occupied by lipids.
  • What does this say???
    • MA and area lipids correlate to polyunsaturation and
    • Electrical field strengths are dispersed by the “kinked” carbon chains of the unsaturated lipids
summing it up
Summing it up
  • During evolution, as body mass increased, there was a need for animals to reduce their mass-specific met rates.
    • (too little surface area to get rid of their heat)
  • Membrane lipid composition becomes important.
  • If, during evolution, increased polyunsaturated membranes occurred, then an increase in Molecular activity would occur
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