Where Does Glycolysis Take Place In A Cell?

Glycolysis takes place in the cytoplasm of a cell as the first step in cellular respiration of the Kreb’s cycle. When glycolysis occurs, it breaks down glucose into pyruvic acids in the cytoplasm.

There are many different kinds of pathways and processes that occur in our bodies. There are things that are primarily in humans and there are processes that are nearly universal in almost all cells. Those processes are usually very old and highly conserved because they play such an important role in biological systems. One of those things is, of course, DNA, which stores everything that makes us who we are (within certain parameters) and is seen in all living organisms.

But first, glycolysis takes place in the cytoplasm of a cell.

Where does the Kreb’s cycle take place? It occurs both within the mitochondrial matrix of eukaryotic cells and also in the cytoplasm of prokaryotic cells.

Processes like photosynthesis are also highly conserved throughout time and are similar in many different plants and cyanobacteria. These processes play crucial roles in our survival and so they are favored by evolutionary pathways to survive. Among those old and highly conserved processes is glycolysis. The pathway of glycolysis took almost 100 years to decipher because the pathway includes many steps that were discovered in pieces from about 1850 to 1940s.

GlycolysisInteresting Facts
Anaerobic conditionsThe process is called fermentation
Discovered byGustav Embden, Otto Meyerhof, and Jakub Karol Parnas
LocationCytoplasm of prokaryotes and  cytosol of eukaryotes
Number of combined reactions10
Two phasesPreparatory phase and the energy generation phase
WhoGlycolysis occurs in plant, animal, and microbe cells

Many scientists, like Louis Pasteur and Eduard Buchner, uncovered some of the steps in glycolysis but never connected those steps with the entire pathway. In the 1930s, Gustav Embden finally puts together all the other steps that were found and created the pathway of glycolysis in full. In the 1940s and onwards, scientists continued to refine the pathway and add in more details until it became what we had today. Glycolysis is a metabolic pathway that takes place in the cytosol and creates the energy that cells use for things like respiration.

What Is The Cytosol?

The cytosol, or cytoplasmic matrix, is the liquid that makes up the bulk of a cell and is the place where many different organelles sit. It is the hub of metabolic activity for many organisms and is essentially a large room where different offices are located, to put it into easily visualized terms. The cytosol is made up of mainly water with ions and proteins in it.

These compounds may be used for other processes and pathways or they may be traveling to different parts of the cell. The cytosol does not have any functions of its own except to hold the different organelles and be the space that is used by metabolic processes. In prokaryotes, like bacteria, metabolism happens primarily in the cytosol. In eukaryotes, like us, metabolism is split between the cytosol and organelles. Some of those metabolic pathways include things like protein biosynthesis, pentose phosphate pathway, gluconeogenesis, and glycolysis.

Diagram of an animal cell. Number 11 represents the cytosol. Image from Wikipedia

What Is Glycolysis?

Glycolysis is an energy conversion pathway that occurs in almost all cells and represents the breakdown of glucose into pyruvate in a series of 10 steps. These steps can be broken into three stages. Stage 1 is the capturing of glucose and destabilizing it to begin the breakdown. Step 2 is the creation of two interchangeable carbon molecules. Stage 3 is the final stage that leads to the creation of energy in the form of adenosine triphosphate (ATP). Cells that use cellular respiration uses glycolysis as the first step in this process. Glycolysis does not require oxygen and so can be used by anaerobic organisms for their own energy generation processes.

In the stage 1 and 2, glucose is converted into fructose-1,6-bisphosphate, a fructose sugar with two phosphates attached to it, using energy and a few enzymes to facilitate the process. This new fructose compound is turned into two interconvertible compounds. The two compounds eventually settle into one compound, glyceraldehyde-3-phosphate, and then goes into the final stage of energy generation. This stage uses enzymes and some energy to create pyruvate and ATP. This stage happens twice so the final product is 2 pyruvate and 4 ATP molecules. From here, the energy is used for other processes in the cells and even the pyruvate is used.

Illustration of where the products of glycolysis go. Image by R. Nave from hyperphysics.phy-astr.gsu.edu

If the organism is aerobic, like us, then the pyruvate will enter the citric acid cycle (CAC), which is also known as the TCA cycle. This cycle is the release of stored energy in compounds like carbohydrates, fats, and proteins. This all creates things like ATP. If the organism is anaerobic, when there is no oxygen, then the pyruvate is sent into process like fermentation to create more energy for the cells. While this is a glucose-based pathway, other sugars can be used. Galactose and fructose can be used instead of glucose because they can be turned into the modified fructose product that is the result of stage 1. Lactose can also be used because it can be turned into glucose and galactose using lactase enzyme.

Like all things in our cells, glycolysis is a regulated process because sometimes we need more or less energy and the process must be slowed or increased. The cell controls this using systems that affect the synthesis of the enzymes used in glycolysis. While glycolysis is a very important part of our function, and therefore more protected against problems like mutations and disease, problems do occur.

One such problem is pyruvate kinase deficiency, which is the an inherited disorder that results in reduced pyruvate kinase, the enzyme responsible for turning the final carbon compound in glycolysis into pyruvate and ATP. This primarily affects red blood cells and can lead to things like anemia, fatigue, jaundice, and gallstones. Most people do not need treatment because the body can manage and counteract the problem. Those that do need treatment can get blood transfusions or bone marrow transfers. There is no cure and treatments only reduce the symptoms.

Glycolysis is affected in many cancers as tumor cells show a higher rate of glycolysis, leading to increased energy production. This is understandable because cancers grow at such high rates and need a lot of energy to sustain themselves. Hopefully, with more research into the relationship between glycolysis and cancer, we may be able to develop diagnosis and treatment options for individuals with cancer cells. We are still developing our knowledge about glycolysis and overtime, we may even be able to add to it as scientists in the past did.

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