The Glycolysis Process in Humans and in Yeast - Essay Example

The Glycolysis Process in Humans and in Yeast Glycolysis is the reactive process that splits glucose into 2 molecules of pyruvate yielding 2 molecules of ATP for energy storage and 2 molecules of the NADH electron carrier known as nicotinamide adenine dinucleotide (Audesirk, Audesirk, & Byers 2006 p.101). The process is broken into two groups known as the energy investment phase and the energy generation phase (McMurray & Castellion 2003 p.670). In the first five investment steps, the body expends 2 ATPs to convert the glucose into 2 molecules of glyceraldehyde 3-phosphate that will process in the generation phase separately.

These two molecules will each yield 2 ATPs and 1 NADH during the 5-step payoff stage for a net gain of 2 ATPs and 1 NADH (Audesirk, Audesirk, & Byers 2006 p.102). These bonus ATP molecules will be used by the body's muscles as glycolysis converts glucose to energy. The investment stage begins its 5-step process by converting the glucose to a charged phosphate, which is then trapped inside the cell wall, which is impenetrable to ions (Campbell & Reese 2002 p.162). From this point on the process in non-reversible.

The reaction in the initial stage expends the first ATP. Step 3 expends the second ATP as fructose 6-phosphate is converted into fructose 1,6-bisphosphate (Audesirk, Audesirk, & Byers 2006 p.102). Step 4 will split this molecule into two carbon intermediaries to be processed separately by the generation phase (McMurry & Castillion 2003 p.670). Step 6 oxidizes by the transfer of NAD+ to the sugar from step 5. During step 6-7 of the generation phase the process yields 1 NADH and 1 ATP respectively (Audesirk, Audesirk, & Byers 2006 p.102). Since there were 2 molecules produced by the generation phase, the output is actually doubled.

At this point the glycolysis reaction is at a break even point. It has invested 2 ATPs and yielded 2 ATPs. Step 10 creates another ATP molecule by transferring the phosphoenolpyruvate from step 9 to ATP and pyruvate (McMurry & Castillion 2003 p.163). Additional energy was stored in step 6 in the form of NADH.In environments where oxygen is missing such as in sediments, deep beneath the earth's surface, or in animal intestines, cells are able to survive without oxygen by metabolizing glucose through the process of fermentation (Audesirk, Audesirk, & Byers 2006 p.106). Oxidation requires that an electron is lost to an electron receptor, but it does not need to be oxygen.

In fermentation the oxidizing agent for glycolysis is not oxygen but NAD+ and can continue the process and produce ATP as long as there is a supply of NAD+ (Campbell & Reese 2002 p.170). In a normal body with sufficient oxygen the pyruvate produced by glycolysis is converted to Acetyl -S coenzyme A. However, in the absence of oxygen it is converted to lactate. In an anaerobic condition in the presence of yeast, the yeast converts the pyruvate to ethanol (Audesirk, Audesirk, & Byers 2006 p.106).

ReferencesAudesirk, T., Audesirk, G., & Byers, B. E. (2006). Life on earth (4th ed.).San Francisco: Benjamin Cummings.Campbell, N. A., & Reese, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.McMurry, J., & Castillion, M. E. (2003). General, organic, and biological chemistry (4th ed.). Upper Saddle River, NJ: Pearson Education.