cellresp4

Control of cellular respiration

o feedback inhibition and allosteric enzymes are the main features

o in glycolysis, for example, a key allosteric enzyme in the third reaction, phosphofructokinase, is

activated by high concentrations of ADP and AMP

o the same enzyme is inhibited by high concentrations of ATP

o control occurs at two irreversible steps in glycolysis

Glycolysis and the Krebs cycle may be synchronized since high levels of

citrate will also inhibit phosphofructokinase (CONTRARY TO WHAT YOUR
TEXTBOOK SAYS). As glycolysis slows down, so will the Krebs cycle, since the

supply of acetyl CoA declines.

Cells are thrifty, expedient, and responsive in their metabolism

(Campbell,Reese, Mitchell : Biology 5th Ed. p. 166)

All macromolecules are able to be oxidized through glycolysis and/or

the Krebs cycle. Many of the intermediates of these pathways may

serve as building blocks for anabolic processes.

Carbohydrates are the preferred fuel but need to be broken down into

simple monosaccharides by digestive enzymes before they can be

oxidized in the cell.

Proteins are broken down into their constituent amino acids. These

serve as building blocks for the organism's own protein requirements.

If necessary, the body can manufacture amino acids to meet demand, if

not met through nutrition. About half of the amino acids made in our

bodies are made from Krebs cycle intermediates. To serve as a fuel

molecule, the amino functional group must be cut off and excreted as

ammonia, urea, or uric acid. The remainder can then be converted to

intermediates of the glycolytic pathway or Krebs cycle.

Fats yield glycerol and fatty acids when digested. The glycerol can be

converted to G3P and enter halfway through glycolysis. The fatty acids

can be broken down into 2C fragments that can be picked up by

coenzyme A and fed into the Krebs cycle.

Summary of metabolism

Metabolism includes all catabolic and anabolic pathways. The oxidation

of food molecules drives ATP synthesis and ATP hydrolysis provides the

energy required to drive anabolic processes. The pathways of

metabolism are interconnected and interdependent.