Bioenergetics and Integrated Metabolism

Metabolism

Sum of all process by which living organisms acquire and utilize energy.

Ultimate source, sun. Light energy is harvested from photographic organisms which convert it to carbohydrates using CO2 and H2O liberating O2 in the process - photosynthesis.

Chemotrophic organisms

Obtain their energy from biomolecules: carbohydrates, lipids and protein.

Primary source of energy

Carbohydrates.

Energy sources are interconvertible, preference dependent on metabolic state of organism

Regulation of pathways

Reactions that generate energy are coupled with those that use energy.

Done using a rate limiting step

Catabolic reactions

Generate energy. Large molecules are broken down into smaller ones

Anabolic reactions

Use energy. Small molecules are assembled into larger molecules

Rate limiting step

Control flux through each pathway. Regulated via:

1. Other cellular molecules acting on enzyme catalyzing the reaction.

2. Increasing or decreasing the amount of enzyme

3. Cellular compartmentalization using cellular organelles

Metabolic pathways

Are located in different cell organelles this each organelle is defined by specific metabolic activities that take place within it.

Dietary carbohydrates

Alpha amylase and pancreatic juice.

Alpha amylase hydrolyzes alpha 1-4 glycosidic bonds in amylose and amylopectin = maltotriose, maltose, glucose and alpha dextrin. In the small intestines, maltase, disaccharides and alpha-dextrinase complete the digestive process. Maltase hydrolyses maltose to glucose and alpha-dextrinase hydrolyses alpha 1-6 glycosidic bonds in dextrin. Monosaccharides take up epithelial cells and translocated to blood for transport to various tissue cells. Liver acts as a buffer because liver cells are permeable to glucose, not controlled by insulin

Glycolysis

Glucose broken down into 2 pyruvate molecules.

1st step serves to trap glucose because phosphorylated molecules cannot leave a cell.

Occurs in cytoplasm and does not require oxygen.

Step 1

Glucose is phosphorylated by hexokinase and ATP to form Glucose 6-phosphate and ADP

Step 2

Glucose 6-phosphate is isomerized by glucose 6-phosphate isomerise to form fructose 6-phosphate

Step 3

Phosphofructokinase transfers a second phosphoryl group from ATP to fructose 6-phosphate to form Fructose 1,6-bisphosphate and ADP

Step 4

Aldolase cleaves C3 and C4 of fructose 1,6-bisphosphate to form Dihydroxyacetone phosphate and Glyceraldehyde 3-phosphate

Step 5

Triose phosphate isomerase rapidly converts dihydroxyacetone phosphate to glyceraldehyde 3 phosphate

Step 6

Glyceraldehyde 3 phosphate dehydrogenase oxidates and phosphorylates both Glyceraldehyde molecules giving 1,3 Bisphosphoglycerate

Step 7

Phosphoglycerate kinase transfers high energy phosphoryl group to ADP yielding ATP and 3-phosphoglycerate

Step 8

Phosphoglycerate mutase transfers phosphoryl group (C3 to C2) forming 2-phosphoglycerate

Step 9

Enolase dehydrates 2-Phosphoglycerate into phosphoenolpyruvate

Step 10

Pyruvate kinase transfers high energy phosphoryl group to ADP to phosphoenol pyruvate yielding ATP and pyruvate