REVIEW: Metabolism & ~P Homeostasis

The Measurement of Metabolism

We obviously cannot exactly measure the sum of all chemical reactions in the body!

All methods used to measure metabolism involve assumptions -- in a way it is like measuring the economy and no one measure is perfect.

We will estimate metabolism analogously to the way that economists estimate the gross domestic product or ecologists estimate trophic level energy flow.

What Are the Means Used to Estimate Steady-State Metabolism?

The Krebs CycleTake Home:

• Occurs in the mitochondrial matrix

• Rate is very dependent on the ratio of oxidized to reduced coenzyme

• Feed ins -- 2 C frags.. from carbohydrate and fat metabolism;

• Amino acid frags in other places

Energy Schematic of the ETS

Take Home

• In inner membrane

• Will maintain a favorable steady-state ratio of oxidized to reduced coenzyme if sufficient O2 is present to accept each electron produced in the Krebs and other reactions.

• Oxidized and reduced in terms of coenzymes?

Mitochondrial Overall Energy Schematic

Glycolysis EnergySchematic

Aerobic Glycolysis Overview

Energetics of Aerobic Glycolysis

The overall reaction (path does not matter):

A distinct stoichiometry exists between all members of this process.

This means that if we know carbohydrate is the fuel, then if we measure the change in one component of this reaction, we know the changes in all others.

How About Lipids?

Once again, if we know that lipid (palmitic acid) is the fuel, we can measure one factor in the reaction and find all the others.

How do we know what fuel is being used?

You cannot tell simply from what the animal eats.

There is a certain ratio of CO2 production to O2 consumption exists for different fuels.

For carbs:

Ratio is 1:1

The Ratio is Different In Palmitic Acid

16/23 = 0.7

The Respiratory Quotient (RQ)

How the Table Values For Energy EquivalenceWere Obtained – An example

Problem

Suppose the following:

What is the metabolic power (P)?

What Happens in Non-Steady-States?

Phosphagen Cycle -- Phosphagen Buffer During High Demand

This process is controlled by the amount of enzyme present (CK) and thermodynamically (amts. of reactants/products)

Replenishment of Phosphagen

Anaerobic Metabolism & Reactions that Maintain Redox

Efficiency of Anaerobic Metabolism

Review: Control of Metabolism

[ATP] regulation is a problem given that demand can, especially in muscles, increase dramatically in a short period of time.

The concept of pathway flux (overall rate -- mols/(product time)

Equibrial and non-equilibrial reactions and control of flux

PFK and glycogen phosphorylase as examples of non-equilibrial reactions.

Inhibition and de-inhibition; activation.

Association/Dissociation Constants as Physiological Organizers

The concept of Kd

What should be the relative values of Kd for AMP and ATP on the regulatory sites of PFK?

Where should the Kd for AMP and ATP be compared to normal “resting” concentrations of these substances?