Nutrition Lab #2

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Chemical Reactions in Nutrition

Chemical reactions are important to biological functions. Consider natural functions such as the breakdown of food in the digestive system, conversion of sunlight into oxygen and cellulose in plant leaves, or conversion of light energy into a biological signal that can be interpreted by the nervous system. Chemical reactions require two or more chemicals to interact in a way that modifies chemical bonds within each of the chemicals and result in the formation of new chemicals (reaction products). The chemicals that interact as inputs of a reaction are called reactants.

ReactantsReaction ProductsReactants→Reaction Products

Chemical reactions occur best under conditions that are optimized for each reaction. Optimization of the reaction can be influenced by several factors: (1) the interaction of a specific amount of each of the reactants (concentration); (2) the presence and concentration of an enzyme (a naturally-occurring protein that alters the rate of the reaction); (3) the temperature of the environment in which the reaction takes place; (4) salinity (saltiness due to dissolved ions) of the solution in which the reaction takes place; and (5) the pH of the solution in which the reaction takes place.

These five factors are commonly at play in the digestive system. We drink strong coffee (factor 1), consume whole, nutrient-dense foods as well as isolated extractions such as vitamins (factor 2), consume hot and cold foods (factor 3), enjoy a variety of seasonings including salt (factor 4), and use acidic condiments like vinegar and catsup (factor 5). Our digestive system must process macronutrients taken in under a variety of conditions and in a variety of forms. Protein enzymes have the task to digest foods and drinks to convert them into a form that the body can use. Specific digestive enzymes are needed to carry out catabolism which starts in the mouth and continues throughout the alimentary tract.

Distinct categories of digestive enzymes are specific to each type of macronutrient. Carbohydrates such as whole vegetables, whole fruits, and grains are processed (catabolized) by carbohydrases. (The ‘-ase’ at the end of the term signifies an enzyme.) Meat, nuts, beans, and other protein sources are catabolized with assistance from enzymes called proteinases. Examples of proteinases are pepsin, trypsin, and peptidase. Proteins can be further broken down by nucleases to yield the basic building blocks for DNA and RNA. Fatty foods like bacon, butter, cashew nuts, coconut, or mackerel are digested through activity of enzymes called lipases. Enzymatic activity is, therefore, the key to survival of all living organisms through the life-giving mechanism of nutrient metabolism.

Reactants−→−−−enzymeReaction ProductsReactants→enzymeReaction Products

Enzymes are proteins that fold into very specific shapes in order to interact with macromolecules like carbohydrates, proteins, and lipids (fats). Enzymes catalyze biochemical reactions which means that they assist in assuring that the reaction takes place in an energy-efficient manner.

Another term for reactants of a reaction in the life sciences is substrates. This term is specifically used for biological reactions that involve enzymes as catalysts, as shown in the image below. Recall that enzymes are proteins and, therefore, can be much larger than substrates which can be simple molecules.

An enzyme and substrate react to produce products.

Substrates could be complex macromolecules or simple molecules like oxygen. For example, the substrate disaccharide sucrose can be broken down enzymatically into the monosaccharides fructose and glucose.

Solutions and Concentration

Living organisms such as bacteria, fungi, squirrels, and humans are composed of water, and most biological reactions occur in the aqueous solution of our cells. As noted above, the concentration of enzymes and substrates can influence the rate and efficiency of a chemical reaction.

Solutions consist of two constituents: Solute and solvent. The solute represents substances present in lesser amount dissolved in a solvent which is present in a greater amount. The ratio of these amounts is directly related to the concentration of a solution. By definition, the concentration of a solution can be regarded as the amount of solute in a solution.

Concentration =# particles of solutevolume of solventConcentration =# particles of solutevolume of solvent

Concentration can be measured in any units that convey information about the ratio of the solutes to the entire solution. Unit examples are: Molarity, molality, normality, mass percent, volume percent, or parts per thousand/million/billion (ppt/ppm/ppb).

We are most familiar with the unit of percent but the other unit options to be used in this laboratory experiment are straightforward to understand. For example, 1% is 1/100 whereas 1 ppt is 1/1,000. We can also convert from one unit to another. Since 1/100 is ten times more than 1/1,000, then 1% converted to ppt is 10 ppt.

Rate of Reaction in Biology

As noted above, reactions are influenced by several factors. For example, enzyme concentration and substrate concentration both affect the amount of reaction products created in a given amount of time.

What is a Rate?

Reaction rate can be understood as the change in amount over time. Higher rate means greater change per unit time.

rate=changetime intervalrate=changetime interval

Which solution shown below is likely to result in the most reaction product in a given amount of time? Which solution shown below is likely to result in the highest production rate of reaction product (recall factor 1 mentioned above)?

Substrate concentration affects reaction rate, namely, higher concentrations of substrate lead to higher reaction rates.

Solutions with a high concentration of substrate will produce more reaction product in the presence of ample amounts of enzyme and they will produce reaction product at a higher rate.

Likewise, consider the impact of different enzyme concentrations (factor 2) as shown in the solutions below. Which solution shown below is likely to result in the most reaction product in a given amount of time?

Enzyme concentration affects reaction rate, namely, higher concentrations of enzyme lead to higher reaction rates.

Solutions with a high enzyme concentration will produce more reaction product in a given amount of time than solutions with a low enzyme concentration.

Other factors that affect enzyme reaction rate (enzyme activity)

In most chemical reactions, increases in temperature (factor 3) lead to increases in the reaction rate. An increase in temperature raises the speed of the reactants in solution and that increases the likelihood of reactants being close enough to react and also that they will have enough energy for the reaction to occur. Connection: Why do we refrigerate milk?

Reactions involving enzymes behave in a similar manner. However, enzymes (and all proteins) are sensitive to high temperatures and can lose their shape and functionality. This process is called denaturation. Connection: Why do egg whites change when cooked?

Likewise, enzymes are affected by the pH of the solution (factor 5) and by any other ions present in the solution. Just as high temperatures can affect the shape and functionality of an enzyme, so too can the concentration of charged ions in solution (pH of a solution is related to its H+ ion concentration). Most enzymes function properly only within a narrow range of pH. For example, gastric enzymes released by cells in the acidic environment of the stomach (pH = 2.0) do not function optimally in the physiological pH environment (pH = 7.4) of the small intestine (ileum).1

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