Biology,3:14. Glycolysis and Fermentation.

Aerobic

Using oxygen; when applied to organisms, cell, tissue, it means they use oxygen as part of the process of obtaining energy from glucose.

In cellular respiration

oxygen is consumed and carbon dioxide and water are released.

Inside a cell, cellular respiration takes place in three main stages: Glycolysis, the Krebs cycle, and the electron transport chain.

1:Glycolysis-Glycolysis takes place in the cytosol of a cell. Glucose molecules move into the cytosol, where a series of chemical reactions take place to produce molecules of pyruvic acid. | 2:Krebs Cycle-The Krebs cycle takes place in the matrix of the mitochondria. Through a series of chemical reactions, the energy in pyruvic acid is transferred to molecules of NADH and FADH2 . | 3:Electron Transport Chain-The electron transport chain takes place in the folded inner membrane of the mitochondria. Through a series of chemical reactions, the energy in the NADH and FADH2 is transferred to molecules of ATP.

Krebs Cycle

A cyclical set of reactions in which pyruvic acid is metabolized and ATP, NADH, and FADHS are formed

Glucose

A monosaccharide with the chemical formula c6h12o6 used by cells for energy Glucose is the critical molecule in the generation of energy that cells can use. It is important to understand that glucose, and only glucose, is the starting point of a complex process that ends in the production of ATP ( adenosine triphosphate )—a form of energy that your cells can use. Glycolysis takes place in several stages. Again, you don't have to remember every step in glycolysis, but you do need to know how glycolysis fits into the process that produces usable energy for cells. The main end product of glycolysis is 2 molecules of pyruvic acid. At the end, 2 ATP molecules are used and 2 NADH molecules are made, meaning that during glycolysis, some energy is used and some electrons are gained. Study the diagram on page 58 in your reference book, and then explore the process online.

The process of cellular respiration begins with glycolysis

A series of chemical reactions take place during cellular respiration to transfer the energy stored in the chemical bonds of glucose to the energy stored in the chemical bonds of ATP. This lesson will lead you step by step through the first stage of cellular respiration— glycolysis . What is glycolysis? Whenever you see the suffix -lysis in biology, it means something is being split or broken into smaller pieces. Glycolysis is the splitting of glucose molecules, and it takes place in the cytosol of cells. Turn to page 58 of your reference book for an overview of glycolysis.

ATP;

ATP is the end product of cellular respiration, but ATP also powers certain processes during cellular respiration. When ATP loses a phosphate group, energy is released and ATP becomes ADP. Every part of your body needs the energy carried in ATP to work properly. You just blinked—that required ATP. You just scratched your head—that required ATP. Besides fueling obvious activities like blinking and scratching your head, ATP also provides energy for cells to conduct internal functions such as growth, repair and maintenance, and reproduction. Cells do not share ATP, and ATP does not leave a cell once it is produced. Each cell, therefore, must produce its own ATP. ATP carries energy and releases energy when it becomes ADP ( adenosine diphosphate ). Click the arrow to see how ATP becomes ADP and releases energy. As you look at the steps of cellular respiration, you will notice several parts that involve ATP. Different organisms need different amounts of ATP to fuel their energy needs.

Adenosine Triphosphate

ATP; the molecule that delivers usable chemical energy for almost all processes and reactions that a cell must undergo to survive.

Energy:

Energy is most readily available in the chemical bonds of carbohydrates. The enzymes in your digestive system break down starch, which is made of carbohydrates, into molecules of glucose . Your body also has the ability to break down proteins and fats when not enough carbohydrates are available. In such a case, proteins and fats will be metabolized into glucose via complex chemical pathways

Chart

GLUCOLYSIS | breaks down | ______ GLUCOSE / into | PYRUVIC ACID -- with a net gain of--- 2 ATP \ MOLECULES \ \ Which may then enter into on way of two _________pathways________ / \ CELLULAR(aerobic) ANAEROBIC RESPRIATION RESPRIATION

Lactic acid fermentation sometimes takes place in muscle cells and produces lactic acid.

If you've ever watched people run marathons, you've seen the second kind of anaerobic respiration in action—lactic acid fermentation. When muscle cells run out of oxygen, they resort to lactic acid fermentation for a supply of energy. When lactic acid accumulates in muscles, it can cause soreness. Eventually, however, the blood carries the lactic acid away, which is why the soreness doesn't last. In lactic acid fermentation, pyruvic acid is converted into lactic acid. Again, NADH donates electrons and becomes NAD+, which is supplied back for another round of glycolysis. When muscle cells run out of oxygen, they resort to lactic acid fermentation for a supply of energy.

Electron carriers play a role in cellular respiration.

In this lesson, you will also see the molecules NADH and NAD+. In cellular respiration, NADH and NAD+ capture and transport chemical energy by donating or accepting electrons. Molecules like these are called electron carrier . It is not necessary that you understand how NADH and NAD+ donate and accept electrons, but as you look at the steps of cellular respiration, you will see that these molecules play an important role in transferring energy during chemical reactions. Electron Carrier-molecules such as FADHS and NADH that carry electrons from one part of a chemical process to another NADH is an electron carrier. When NADH donates electrons, it becomes NAD+. When NAD+ accepts electrons, it becomes NADH NADH is an electron carrier. When NADH donates electrons, it becomes NAD+

Electron Carrier

Molecules such as FADH2 and NADH that carry electrons from one part of a chemical process to another.

Electron carrier

Molecules such as FADH2, and NADH that carry electrons from one part of a chemical process to another.

Mitochondria

Organelles that are the sites cellular respiration

After glycolysis, the 2 molecules of pyruvic acid can take one of several energy-producing pathways.

So, a cell has just completed glycolysis, and has produced 2 molecules of pyruvic acid. Now what? Well, that depends. If the cell is part of a multicell organism and oxygen is present, the pyruvic acid may move into the mitochondria of the cell where the Krebs cycle and the electron transport chain produce lots of ATP. This process involves oxygen, and is called aerobic respiration. It is important to remember that glycolysis has a net gain of 2 ATP molecules. In other words, glycolysis generates a small amount of energy. Some organisms—and their energy needs—are so small that they do not need the large amounts of energy produced in aerobic respiration. For many simple organisms, the energy stored in those 2 molecules of ATP can fuel all of their needs to survive. In that case, rather than continuing on to the Krebs cycle, the pyruvic acid molecules may enter a different pathway called anaerobic respiration, or fermentation . Pyruvic acid takes this pathway when oxygen is not needed or is not present.

Fermentation

The break down of pyruvic acid in the absence of oxygen

Glycolysis

The first of cellular respiration in which glucose molecules are broken down to produce pyruvic acid.

Cellular respiration

The process of breaking down glucose for the production of ATP in the presence of oxygen Cellular respiration is the process by which cells transfer the energy in glucose to the energy in ATP. It is also called aerobic respiration because it takes place in the presence of oxygen.

Anaerobic respiration generates NAD+ for glycolysis to continue

When oxygen is not present or is not needed, the pyruvic acid molecules produced during glycolysis enter an anaerobic respiration pathway. This pathway is also called fermentation. There are two types of fermentation: alcoholic fermentation and lactic acid fermentation. The role of fermentation is to supply NAD+ molecules to the cell to keep the process of glycolysis going. It is a feedback loop. Fermentation uses the 2 pyruvic acid molecules and 2 NADH molecules to regenerate NAD+. The NAD+ then feeds back into another round of glycolysis. ALCOHOLIC FERMENTATION(DOESNT REQUIRE OXYGEN) LACTIC ACID FERMENTATION(DOESNT REQUIRE OXYGEN) KREBS CYCLE (REQUIRES OXYGEN)

Glycolysis begins and ends with specific molecules

While you don't need to memorize every step of glycolysis, you do need to know the beginning and ending molecules. For glycolysis to take place, these molecules must be present: 1 glucose molecule 2 ATP molecules 2 NAD* molecules Glycolysis produces these molecules: 2 pyruvic acid molecules 4atpe molecules(2net) 2 NADH molecules

pyruvic

\piy-ROO-vihk\

Adenosine Diphosphate

\uh-DEH-nuh-seen-diy-FAHS-fayt

Fermentation

does not use oxygen and does not break down glucose as completely as cellular respiration, and therefore it does not recover as much of the chemical energy in glucose.