Cell Energetics 2 Glycolysis

Overview of metabolism Usable energy is released as reactions break down carbon compounds, such as glucose. The released energy is used to drive an electron transport chain which drives ATP production. Cells use ATP to meet their energy needs.

Complete Glucose Metabolism The overall equation for glucose metabolism can be written as: C6H12O6 + 6 O2 6CO2 + 6 H2O

Glycolysis Literally, glycolysis means “sweet breaking.” In glycolysis, glucose is split into two 3-carbon chains. The process of glycolysis requires 2 ATP molecules and produces 4, for a net gain of 2 ATPs from each molecule of glucose. Glycolysis does not require oxygen.

Glucose Metabolism: Overview

Glycolysis: overview

Glycolysis: Energy Investment Glycolysis takes place in the cytoplasm. First step is “energy investment”: ATP is used to split glucose and make 2 3-carbon molecules. Each molecule is phosphorylated (phosphorus added).

Glycolysis: Energy Payoff Next is the “energy payoff” phase. The 3-carbon molecule gives up phosphorus, which is used to make 4 ATPs. NADH, an electron carrier, is also produced. The result are 2 3-carbon chains called pyruvate.

Without oxygen... In anaerobic conditions, hydrogen ions and electrons freed in glycolysis can accumulate. NAD+ accepts free electrons and hydrogen ions to become NADH as usual, but NADH then accumulates. This could bring glycolysis to a halt.

Anaerobic fermentation Fermentation deals with accumulated NADH. Pyruvate becomes the final electron and hydrogen ion acceptor. Pyruvate is converted into either lactate (lactic acid) or ethanol, depending on the organism.

Anaerobic Fermentation In the absence of oxygen, yeast can make some ATP from glucose. Alcohol is the waste product.

Anaerobic Fermentation During hard exercise, muscles may be deprived of oxygen. The muscles extract some energy from glucose, and produce lactic acid, which is later broken down when oxygen is available.

Summary Glycolysis is the process of splitting 6- carbon glucose into two 3-carbon chains (pyruvate). Two ATP molecules are generated. However, there is still a lot of potential energy in the bonds in pyruvate. Next: Into the mitochondria.