GLYCOLYSIS “Breaking glucose”

Overview Glycolysis = the process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid and releasing energy But how does this happen?

Step 1 1) First the cell starts with a molecule of glucose. 2) But the cell needs to use a little energy to get started. So it uses 2 ATP molecules to get things going. 3) TWO Phosphates are attached to Glucose, forming a NEW Six-Carbon Compound.  The Phosphate Groups came From TWO ATP, which were converted to ADP.

Step 2 The glucose molecule (which had 6 carbons) breaks into two 3-carbon molecules (called PGAL)

*Remember: adding phosphates stores energy Step 3 The PGAL then is reacted with NAD+, producing NADH and two new 3 carbon molecules with additional phosphates. *Remember: adding phosphates stores energy

Step 4 The Phosphate Groups added in Step 1 and Step 3 are Removed from the Three-Carbon Compounds.  This reaction produces Two molecules of Pyruvic Acid.  2) Each Phosphate Group is combined with a molecule of ADP to make a molecule of ATP.  Because a total of Four Phosphate Groups were Added, FOUR MOLECULES OF ATP ARE PRODUCED. 4 ADP + 4 P = 4 ATP

4 ATP – 2 ATP = 2 ATP So how much energy is produced by glycolysis? Net gain of energy Made in step 4 Used in step 1

The problem: When a cell makes a lot of ATP from glycolysis, it soon uses up all of it’s available NAD+ molecules with electrons. Without NAD+, the cell can’t keep glycolysis going and ATP production stops. So what does the cell do now?

OXYGEN If there is oxygen present = aerobic respiration The pyruvic acid made in gycolysis goes to the Krebs Cycle If there is no oxygen present = anaerobic respiration The pyruvic acid made in glycolysis goes to the fermentation pathway

FERMENTATION Cells convert NADH to NAD+ by passing the electrons back to pyruvic acid. This converts NADH back to NAD+, allowing glycolysis to continue making ATP. 2 TYPES: Alcoholic- used by yeast and some other microorganisms Lactic Acid- used by prokaryotes and your muscles during exercise

ALCOHOLIC FERMENTATION Pyruvic acid + NADH alcohol + CO2 + NAD+ From glycolysis Ethyl alcohol and carbon dioxide are produced when the electrons carried by NADH are transferred back to the pyruvic acid Alcoholic fermentation is what causes bread dough to rise. The yeast runs out of oxygen, starts to ferment, and gives off bubbles of CO2 that form the air spaces you see in a slice of bread.

LACTIC ACID FERMENTATION pyruvic acid + NADH lactic acid + NAD+ From glycolysis When you exercise vigorously by running or riding a bike, the large muscles in your arms and legs soon run out of oxygen. The muscle cells begin to produce ATP by lactic acid fermentation. The buildup of lactic acid causes a painful, burning feeling. Think of the saying: “Can you feel the burn?” Many foods are made by lactic acid fermentation: cheese, yogurt, sour cream, pickles, sauerkraut, and kimchi.

THE BIG PICTURE

How efficient is glycolysis? Glycolysis only has an efficiency of 3.5% meaning it only harnesses 3.5% of the energy available in one molecule of glucose Let’s do the calculation! Conclusion: Glycolysis is an inefficient process