Fermentation and Metabolic Pathways

Fermentation and
Metabolic Pathways

Metabolic pathways are series of chemical reactions in your cellsThe basic structural and functional units of life. that release energyThe capacity to do work or cause change. and harness it into ATPThe energy currency of cells used for muscle contraction..  Pathways can be thought of in many ways: is oxygen required? Where do the reactions happen? What reactants are required? What products are made? 

We’ve thoroughly discussed cellular respirationThe process of gas exchange, including ventilation, external and internal respiration. in this module, but fermentationprocess of regenerating NAD with either an inorganic or organic compound serving as the final elect is a pathway of making ATP important to many organisms.  Fermentation is sometimes called anaerobicprocess that does not use oxygen respiration in that no oxygen is required for the process to happen.  So, you can imagine that some mud-dwelling bacteria can do this to make ATP if no oxygen is present.  This process begins much like glycolysisprocess of breaking glucose into two three-carbon molecules with the production of ATP and NADH, the first step of cellular respiration, and happens in the cytoplasmThe gel-like substance within a cell that contains organelles and cytosol. with enzymesProteins that speed up chemical reactions in the body., but what it produces is very different.

Lactic acid Fermentation

The first type of fermentation is lactic acidA substance that releases hydrogen ions (H⁺) in solution. fermentation, which can be done by your muscle cells.  Ever work a double shift?  Yeah, and you don’t really eat enough between shifts, and then hallway through the second shift you just hit the wall.  That’s what we call it, right? Hitting the wall.  You are demanding so much ATP from your muscles and they just can’t make it happen with the glucoseA simple sugar that is the main source of energy for cells. that’s available.  Long story short, machinery in the cell gets confused and ATP is made, but through this pathway that looks like glycolysis with a bad ending.  Recognize the glucose breaking down into pyruvatethree-carbon sugar that can be decarboxylated and oxidized to make acetyl CoA, which enters the citr, with ATP and NADH, our electron taxi, being made in the process.  However, an additional step uses and recycles our NADH, instead of sending it to the mitochondria, and we end up with two lactate moleculesGroups of atoms bonded together., which are acidicA solution with a pH below 7, having a higher concentration of H⁺ ions..

Lactic acid, although is can denatureThe process in which a protein loses its shape and function due to heat or pH changes. muscle protein, can also denature lots of other yummy foods to make things like pickles, kim chi, root beer, sour cream, yogurt, beer, champagne.  As humans, we usually harness bacteria to do this fermentation, but we can use fungus as well.

Yeast

I just want to take a moment to introduce an organisms here called yeast.  This is actually a fungus, although a misconception is that it is a bacteria.  It’s Latin or scientific name is Sacchromycetes cerevisiae.  As a fungus, this organismA living individual made up of cells. is a eukaryotic organism with complex cells with organellestructures within a cell that perform specialized functions..  You can buy dried yeast in a packet.  Once you give it some sugar, waterThe universal solvent essential for life., and warmth, it will start to reproduce, called budding, which you can see yeast here in the microscopic picture on the left.  As the yeast grows it does cellular respiration and emits carbon dioxide, which forms the holes in the bread as it rises.

Facultative Anaerobe

Yeast is what we know as a facultative anaerobe.  The word facultative means “sometimes.”  it’s like an on-again-off-again relationship.  Oh, sometimes.  Do you know a couple like that.  I do.  But a facultative anaerobe can use oxygen, when it is present, for cellular respiration and make carbon dioxide as the byproduct.  When oxygen is absent, yeast can do fermentation, which produces alcohol, in this case, not lactic acid. 

Alcohol Fermentation

The first thing students do when they see this slide is they click back to look at the other slide of fermentation where lactate is produce.  Very similar isn’t it?  We have the breakdown of glucose to pyruvate, with the production of ATP and NADH in the process.  We also have that second step where the NADH is used and recycled back to the first step, but this time, carbon dioxide is released as a waste product.  Instead of lactate, we are left with ethanol, or alcohol.  So, we’d have an alcoholic, bubbly, liquid usually called beer, wine, champagne, or hard cider, or any of those new varieties of alcoholic beverages I see coming out these days.  Interesting industry wine and beer has become.  And yes, these beverages are basically the waste product of yeast, or you could say yeast pee.

Review your biological molecules

Take a moment here to review the biological modules from module 3.  Remember that your body will break down carbs first, because they are easy to break down, but they also only have 4 calories per gram.  Lipids, or fats, have more than twice that at 9 calories per gram, and are great storage molecules, like on this fat little bird here ready to fly south for the winter.  Well, it looks like, from the snow, that he missed his chance.  But, he stocked up on the lightest, and most densely packed with energy molecules as he could.  We have proteinsLarge molecules made of amino acids with various functions in the body. that are those complex molecules that carry, like carbs, four calories per gram.  Proteins have an incredible variety of uses in the human body, as we previously discussed.  And we have our nucleic acid which impart no energy, but are used to make our own DNA when replicating cells.

Where do you enter the process?

This is a map of cellular respiration along the bottom with the three significant groups of biological molecules listed up top. Check out how each group enters into the cellular respiration pathway.  We’ve been talking about glucose entering at the first step of glycolysis, but you can see that lipidsOrganic molecules including fats, oils, and steroids. and proteins enter at other points in the pathway.  Say that you ingest triglycerides when you eat peanuts, which you do.  Those triglycerides are broken up, the glycerol headRounded proximal end that fits into the acetabulum of the hip bone. from the three fatty acid tails.  The glycerol head is converted to be able to enter into glycolysis while the fatty acids enter into the citric acid cycleseries of enzyme-catalyzed chemical reactions of central importance in all living cells for extracti.  Check our the many pathways of proteins, and the remaining amino groups that are needed to make your own proteins in anabolismThe metabolic process that builds complex molecules from simpler ones, requiring energy..  This is essentially a question of what foods you are eating and where they enter the process.  Your body may want foods to enter at a certain point for efficiency.  Are you giving your body those foods?  Diet is so complex, and it is very difficult to listen to which foods are the best for you.  Tracking is a great way to find out.  Although time consuming at first, many people find that the act of tracking diet and energy levels is an easy way to see what does and doesn’t work for their body and their pathway.