Cellular Respiration Breakdown and Macros

by Erik Tremblay

Cellular Respiration is a critical and magical event that occurs in every cell in the body to produce energy. Without undergoing cellular respiration, we as humans and animals would be non-existent due to the fact that our organs would have zero energy to carry out any of their functions. The exact reason we ingest food and break it down is to supply our bodies with the macromolecules (protein, fats, carbohydrates) to undergo respiration and produce useable forms of energy for cells in the form of the molecule ATP (Adenine Tri-Phosphate). Our body utilizes this molecule as an energy source due to its unique structure of containing three phosphate molecules on one end (hence where tri-phosphate comes from). The last phosphate group has a weak bond; this is due to the shape of the molecule where a positive charge is located on the ribose sugar and pulls the electrons towards it. Since the last phosphate group is farthest from the sugar, the attraction is much weaker and allows the last phosphate group to easily break its bond, which releases energy and allows the phosphate to from a stronger bond. ATP is seen as the basis of all life and how we make it is critically important, especially to those looking to improve their athletic performance. Without the correct source sources and amounts of energy, your body will conserve fuel from physical performance to use for vital actions such as breathing, thinking, and critical metabolic pathways. Proper nutrition to fuel maximum cellular respiration will allow you to train at a top level and push yourself to new levels feeling energized and driven.

Types of Cellular Respiration

There are two different types of cellular respiration pathways utilized by our bodies; aerobic and anaerobic. Oxygen gas (O2) is so critical to our bodies because it is the main reactant in the aerobic pathway as it allows for several oxidation reactions to occur as it acts as a universal electron acceptor that is utilized in the final step. The anaerobic pathway is used when O2 gas is not present; this is where anaerobic exercise gets it’s name. When physical activity is too intense for O2 gas to be supplied abundantly to cells as your respiration rate (breathing rate, not to be confused with cellular respiration) cannot keep up with the energy demand, the anaerobic pathway is turned on and relies on other electron acceptors for the final step,these include molecules such as; s sulfate (SO42−), nitrate (NO3−), sulphur (S), or fumarate. While these molecules are also electron acceptors, they have much smaller reduction potential (less of an ability to grab electrons) making anaerobic respiration less efficient and less preferred by the body.While the ultimate goal is the same and the processes are similar, they do produce different byproducts in different steps which affects the body differently.Aerobic goes through three full steps-glycolysis, Kreb’s Cycle, Electron Transport Chain- while anaerobic respiration only goes through 2- glycolysis and fermentation. The Below we will discuss the processes of cellular respiration and how that plays into what macros you should be consuming prior to a workout.

The Three Steps of Cellular Respiration


The body’s most preferred macromolecule to use for energy as it is the only one that can be used to initiate glycolysis is glucose. Glycolysis occurs in the cytoplasm of the cell when a molecule of glucose(chain of 6 carbons) undergoes a series of 10 chemical reactions which essentially break the molecule in half, generating two 3 carbon “pyruvate: molecules. The term glycolysis derived from the latin meanings “glyco”= glucose and “lysis”= to break/burst and the overall chemical reaction can be seen below:

This is the first step in respiration and occurs whether your cells are undergoing aerobic or anaerobic respiration. Depending on whether oxygen is present or not will determine what the outcome of this step will be. With oxygen not present the pyruvate moves into a step of fermentation that is much less efficient than the aerobic pathway. Here, lactic acid fermentation occurs to regenerate the NAD+ molecule from NADH needed to keep glycolysis going. This happens as NADH transfers its hydrogen molecule directly to pyruvate to form the byproduct lactate (eventually metabolized to lactic acid). However, if oxygen is present the pyruvate molecule moves into the second step of aerobic respiration, the Kreb’s cycle.

Kreb’s Cycle

When oxygen is present, the pyruvate molecule moves inside the mitochondria where it is oxidized to form acetyl-cozymeA by the enzyme pyruvate dehydrogenase complex (PDC) also forming another molecule of NADH and CO2. This Acetyl-CoA molecule can then begin what it is known as the Kreb’s Cycle. Here, the acetyl-CoA molecule is further oxidized to CO2 while any NAD+ is also reduced to NADH. This NADH is a major key as it is what’s used to power the next step, the electron transport chain. The cycle is an 8 step reaction that contains many intermediates we have talked about in previous posts. These intermediates can enter the cycle at the stage which they are normally present and be used to facilitate ATP, these intermediates include; α-ketoglutarate (5 carbons), succinyl-CoA, succinate, fumarate, malate, and, finally, oxaloacetate. The process can be seen below and generates 2 ATP molecules in addition to 6 NADH and 2 FADH2 from 1 glucose molecules. The NADH and FADH2 is then used for the final phase.

Source: http://r.search.yahoo.com/_ylt=AwrEwVon8Qtb3w8AURSjzbkF;_ylu=X3oDMTBtdXBkbHJyBHNlYwNmcC1hdHRyaWIEc2xrA3J1cmw-/RV=2/RE=1527538087/RO=11/RU=http%3a%2f%2fbiotrychemology.wordpress.com%2f2013%2f04%2f13%2ftca-cycle-krebs-cycle%2f/RK=2/RS=LWU_ayQ_ItHUf3vlCA4bNPtahbg-

Electron Transport Chain

The electron transport chain is the last step of the respiration process and produces the most amount ATP. It is a series of processes that relies on the transfer of electrons to electron acceptors, also transfering protons (H+) across the inner mitochondrial membrane. While FADH2 is used as an intermediate,NADH is directly oxidized along with succinate from the kreb’s cycle.

These are the main drivers that establish an electrochemical gradient between the inside and outside of the membrane, which allows H+ ions to move through the ATP synthase enzyme in the inner membrane to drive the phosphorylation of ADP to become ATP. This is the most important step in the chain as it can efficiently produce upward to 34 ATP. So glycolysis yields 2 ATP, kreb’s cycle yields 2 ATP, and the electron transport chain produces around 32-34.

The Electron Transport Chain:


What Does This Have To Do With Macros?

Well, in order for any of these processes to occur the right fuel must be provided. The body prefers simple carbs,glucose, as it’s energy source due to it’s ability to fully go through all three steps of respiration and fully generate the most ATP. This is why a simple carb source is absolutely critical before a workout. They can also be stored in muscle tissue as the form of glycogen to be broken down and provide ATP when needed, such as a workout. While other macromolecules are also used in these processes, or can be used, they are not your bodies preferred source. Use the table below to help keep you on track. Amino acids can be used but are much more preferred for building proteins inside the body. They must first be deaminated (it’s NH2 group removed) before it can enter the cycle as either pyruvate or Acetyl CoA, skipping glycolysis. Glycerol from fats is the only other macromolecule that can enter glycolysis so it is efficient in producing energy but glucose is still more preferred due to its limited storage capacity. Fats are most notably used for deriving Acetyl CoA to enter the citric acid cycle.


Why Are Carbohydrates important as a Pre-Workout?

Carbohydrates are your body’s preferred energy source due to the amount of cells that require the macromolecule, how efficient the process is to convert it to a useable energy source, and how much can be stored in your body.

Your body can easily store carbohydrates as it breaks them down into glucose (except cluster dextrin does not need to be broken down as it is already a simple carbohydrate) which is used to fuel the energy needs of the body. Glucose circulates in the blood and, through the use of insulin, the glucose enters cells where it is used for the cell to undergo cellular respiration and generate ATP to allow them to carry out their functions. When there is an excess of carbohydrates, your body stores them as glycogen in the liver and skeletal muscle tissue where they can be tapped into to generate ATP when the body is demanding more energy than is available in the current circulating glucose levels. However, the body can only store around 500g of glycogen before the storage is maxed out.This is one reason why your body prefers to use carbohydrates as an energy source over fats. Although fats carry a higher energy potential (about 9 calories a gram compared to carbohydrates that carry about 4 calories a gram), your body can store almost all the extra fat you consume in adipose tissue. So while you max out storage of carbohydrates at 500g, 98% of the fats you eat can be stored no matter how much you consume. Your body can convert excess carbohydrates into fat, but would then have to turn it back into carbohydrates to use it for energy, making it a less efficient process than prioritizing the consumption of carbohydrates as the initial energy source.

Also, your brain cells require the most energy out of any cells and it is more efficient for your body to use carbohydrates as the energy source. Fats have to be broken down which converts them into ketones to be used as energy in brain cells. Not to mention the central nervous system must have glucose to operate and cannot use energy from fats, so while ketones provide an energy source for most of the body, carbohydrates fuel the entire body.

The demand of glucose to provide energy for your entire body is why it is vital to include in your pre-workout. Having the glucose source dextrin in the cyclical shape allows the carb source to pass into the small intestines and absorbed within 20 minutes, making it a pre-workout secret ingredient. It offers a noticeable difference in delaying muscle fatigue and improving “pumps.”

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