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Peter Fuerst
GLYCOLYSIS
This session introduces the study of metabolism. Metabolism includes the processes by which the body stores and converts ingested food into energy and the many essential chemical building blocks of cells and tissues.
Metabolism also includes how substances are broken down into chemical components that are recycled or excreted. Although much of the material describes detailed enzymatic steps of biochemical conversion of key compounds, it will be equally important for you to recognize and understand a larger picture. The logic and function of the metabolic pathways can be applied to understanding how dysfunction of these pathways could contribute to common chronic diseases.
Glycolysis Learning Objectives and Brief Synopsis:
SLO1. Describe the digestion and absorption of common dietary carbohydrates.
SLO1 and 2 Quiz 1 SL01 and 2 Quiz 2
Definitions:
Metabolism refers to the biochemical processes that occur within a living organism to maintain life.
Catabolism is the breakdown of complex molecules into elementary building blocks.
Anabolism is the synthesis of cellular components like RNA, DNA, proteins, lipids, and carbohydrates from elementary building blocks.
Redox reactions interconvert paired molecules (NAD+ <-> NADH and NADP+ <-> NADPH and FADH+ <-> FADH2) by reduction (gain of electrons) or oxidation (loss of electrons). Note: when NAD+ is reduced to NADH it receives two electrons. You will sometimes see this written as NADH +H, for example in figure 8. This is how NADH is able to pass two electrons when it is oxidized at the onset of the electron transport chain.
Overview of metabolism
The breakdown (catabolism) and synthesis (anabolism) of biochemical compounds occur through separate enzymatic routes engaging a sequence of enzymes that is called a metabolic pathway.
Catabolism produces cellular energy in the form of ATP and reducing power in the form of NADH, FADH2 or NADPH. Anabolism consumes reducing power and ATP. In the body, there is continual switching between the breakdown pathways and the biosynthetic pathways to maintain homeostasis.
A key element of this switching is a reciprocal regulation of metabolic pathways that catalyze opposed processes. For example, if glucose breakdown (glycolysis) is up-regulated, the opposite pathway of de novo glucose synthesis (gluconeogenesis) will be down-regulated, a reciprocal control mechanism that prevents what are called “futile cycles.”
Energy metabolism: The main energy currency of cells is ATP, mostly generated by glucose and fat metabolism. ATP can be produced by glycolysis, and, under oxygen-rich conditions, additional ATP is produced by subsequent oxidative phosphorylation of ADP via the electron transport chain (ETC).
Products of glucose and fat metabolism enter the TCA cycle (tricarboxylic acid cycle, also called the Krebs cycle or the citric acid cycle) that generates reducing power that drives oxidative phosphorylation of ADP via the electron transport chain.
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