The Functions of Carbohydrates in the Body

The Functions of Carbohydrates in the Body - Carbohydrates function as the primary cellular energy source. They have an empirical formula of [C(H2O)]n/sub>. The main types of carbohydrates are monosaccharides, disaccharides, and polysaccharides.

Function of Carbohydrates

Carbohydrates are not just those things that you try to avoid when you are on a diet. All living things (plants, animals, fungi, and microorganisms) contain and utilize carbohydrates for their primary) source of energy. In addition, carbohydrates also serve a structural function in all living things. For example, plants are supported structurally by a carbohydrate called cellulose, which exists in their cell walls. Both plants and animals store reserves of excess carbohydrates, as either starch (in plants) or glycogen (animal starch). Carbohydrates fall into three major categories: monosaccharides, disaccharides, and polysaccharides.

An empirical formula is one that indicates the type and number of atoms within a molecule. When we compare the empirical formulas of most carbohydrates, we find carbon, hydrogen, and oxygen. Carbohydrates are literally watered (or hydrated) carbons C(H2O) as the name carbohydrate suggests, and their generalized empirical formula is [C(H2O)]n. The n designates the number of carbohydrate units in the molecule. The category to which a specific carbohydrate belongs depends on the number of units it possesses. (Source: Avila, Vernon L. Biology : Investigating Life On Earth Jones and Bartlett/Bookmark Series in Biology Page 55)

Chemical Reactions in Biological Terms

Chemical Reactions in Biological Terms - During hydrolysis macromolecules are cleaved into their smaller subunits by adding water. Dehydration synthesis is the linking of smaller subunits by removing water to form larger molecules.

Chemical

Let us see how some of these types of reactions affect my meal. Earlier I said that my meal actually consisted of large molecules (often called macromolecules or polymers) of proteins, carbohydrates, and lipids. To change those macromolecules into the types of proteins, carbohydrates, and lipids that my body can use, a set of paired reactions occurs in my cells: hydrolysis and dehydration synthesis (Figure 3.2). Both of these reactions are mediated by enzymes.

The first type of reaction is a degradation reaction called hydrolysis, a term that means water

 splitting. In hydrolysis, water molecules are enzymatically added to macromolecules, splitting them into their component subunits. Such small molecules are called monomers.

The second type of reaction is a synthesis reaction called dehydration synthesis. This step recycles the monomers by removing the water used in hydrolysis. The monomers are then joined to form polymers, such as the proteins, carbohydrates, and lipids that my body needs. Hence the name of the process, which means synthesis (or putting together) by dehydration (the removal of water).

So I benefit from my breakfast because of a pair of reactions that are the reverse of each other. One reaction adds water to a macromolecule to degrade it into monomers, and the other process removes water from monomers to form macromolecules. At present I am hydrolyzing, or breaking down, my meal into its component parts, its monomers. Once these simple molecules get into my cells, they will be utilized as sources of energy or as the raw materials used to synthesize the macromolecules that make up me.

So through these two paired reactions, monomers are synthesized into macromolecules that are of biological importance. What are the properties of these biological compounds, and what are their functions? Let us discuss them.

There are four groups of biological compounds that are important in living things: carbohydrates, lipids, proteins, and nucleic acids. Each group is divided into smaller subgroups that play an important role in the chemical activities of living things. (Source: Avila, Vernon L. Biology : Investigating Life On Earth Jones and Bartlett/Bookmark Series in Biology Page 53-54)

Displacement Reactions

Displacement Reactions  - In displacement reactions, there is an exchange of atoms (or groups of atoms) between molecules. There are two types of displacement reactions, single and double displacement. In a single displacement reaction, such as A + BC « AC + B, one element shifts position. In living systems, for example, hemoglobin (an iron-containing molecule) can combine with CO2 from the cells to form carbamino hemoglobin. When this carbamino hemoglobin is transported by the blood to the lungs, the carbon dioxide is displaced by O2. This single displacement reaction can be represented as follows:

In a double displacement, as in AB + CD « AC + BD, two elements shift position. A double displacement reaction occurs when silver nitrate reacts with hydrochloric acid to form silver chloride and nitric acid.

All four types of reactions take place during the various life processes in living things, such as the utilization of my breakfast. Often the reactions occur in pairs something is taken apart (degraded) in order to be put together (synthesized) in another arrangement. Such an arrangement is called a paired reaction. It is rather like cutting apart several types of board in order to build a bookcase. You have the same wood when you have finished that you had when you started, but the structure and arrangement are different. Paired reactions are an essential characteristic of chemical reactions in living things. In other words, if you put things together, you can usually break them apart. In fact, most chemical reactions are reversible. Chemists use a pair of arrows to indicate a reversible reaction:

Collision Theory

Collision Theory - The collision theory states that chemical reactions occur when molecules collide. The energy required to start a reaction is called the minimum energy of activation. There are four general types of chemical reactions: rearrangement, synthesis, degradation, and displacement.

Collision Theory

Today is a very exciting time in chemistry, since scientists can actually move atoms and also image the progress of chemical reactions. But, what are chemical reactions?

Simply stated, chemical reactions involve breaking and reforming chemical bonds. In order to do this, energy is required, and the amount of energy available in the system determines whether or not a reaction will occur. For example, if you assume that all atoms, ions, and molecules are constantly moving, then a chemical reaction can occur when they collide with one another. This is what happens when two atoms of hydrogen unite with a molecule of oxygen to form water (H2O). Chemists call this explanation the collision theory.

For example, when you played with your old chemistry set you learned that if you simply mixed two chemicals together, it usually took a long time for a chemical reaction to occur. However, if you heated the mixture (which is one way to put energy into a system), the reaction proceeded much more quickly. Basically, according to the collision theory, the addition of heat increased the speed at which the atoms and molecules were moving, and thus increased the likelihood that they would collide and react. (There are other ways to add energy to a material by shaking or increasing pressure, for instance but heat is the one that is most common, especially in biological processes.)

Adding just a little heat will not necessarily get results. Before a reaction can occur, a certain minimum amount of energy must be added, which chemists call the minimum energy of activation. What is more, the level of the minimum energy of activation depends on the substances involved. For instance, if you light a match and toss it into a small pan of gasoline, you provide enough energy (in the form of heat) to combine the gasoline and oxygen to form carbon dioxide, water, and a tremendous amount of liberated energy (in other words, the explosion will be something to see). However, if you fill the pan with another liquid, such as plain water, the lighted match will have no effect. (Source: Avila, Vernon L. Biology : Investigating Life On Earth Jones and Bartlett/Bookmark Series in Biology Page 52)

Chemical Reactions and the Molecules of Life

Chemical Reactions and the Molecules of Life - I just finished eating breakfast, which today consisted of a glass of low-fat milk and French toast covered with peanut butter and syrup. (I happen to like peanut butter on my pancakes and French toast you should try it.) How do we as living things break this meal down into its constituent parts and reconstitute or assimilate the chemical components into ourselves?

Chemical Reaction (source: http://www2.estrellamountain.edu/faculty/farabee/BIOBK/atweights.gif)

Although my breakfast consisted of the things I just mentioned, to the biological system that is my body, my meal consisted of carbohydrates, lipids, and proteins, the large molecular constructions that are found in all foods. It also contained water, minerals, and nucleic acids. The cells of my body and of other living things do not distinguish between a meal of insects or of steak. Protein is protein, and it will be broken down into the amino acids that make up that protein. The amino acids will eventually enter my cells and be reunited into new amino acid sequences that form the protein in my cells. 

How does nature degrade, or break down, large molecules into their component subunits? And how does nature take these component subunits and reunite them to form other complex molecules?

To begin with, all these activities are chemical reactions; so in order to answer our questions, we must first understand how chemical reactions take place.

Cohesiveness and Tensile Strength

Cohesiveness and Tensile Strength  - You have all heard of adhesion (the holding together of unlike substances). For example, the adhesion of adhesive tape holds you and the tape together. There is another way of "holding together," called cohesion, or the holding together of like substances. All of you have seen evidence of the cohesiveness of water molecules at one time or another. As you try to sleep, and finally locate the dripping faucet that has been keeping you awake, you notice that for a few moments before it falls, the trickle of water clings to the faucet as it forms a drop. Others have seen water striders run across the surface of a pond. All these phenomena are due to the surface tension of water. The water moisture in our lungs also exerts a surface tension that we must counteract to avoid the collapse of the air sacs in our lungs. Surface tension is a result of the hydrogen bonds that have formed because of the electronegative and electropositive qualities of water molecules.

Cohesiveness and Tensile strenght (www.gordonengland.co.uk/img/img00003.jpg)

Because of these cohesive properties, water also has a remarkable tensile strength in other words it resists being pulled apart. As a matter of fact, under certain conditions the tensile strength of

water exceeds that of steel wire. The cohesiveness and tensile strength of water help to explain how water can rise hundreds of feet from roots to the needles of a giant redwood tree.

What is ionization? Definition and Meaning

What is ionization? definition and meaning - With a predictable frequency, water itself can ionize into a hydrogen ion (H+) and hydroxide ion (OH-),thus providing the ions required in many fundamental reactions essential to the continuation of life. In addition, other molecules containing H+ and OH- groups dissociate in water. A substance that releases hydrogen ions (H+) is called an acid. Substances that release hydroxide ions (OH-) in water are called bases. (This is not a complete definition of an acid or base, but it will serve our purposes.) 

Ionization Energy

We use a scale called pH, which runs from 0 to 14, to indicate the relationship between these two ions in solutions. In pure water, the numbers of hydrogen ions (H+) and hydroxide ions (OH-) are equal; hence the water is said to have a neutral pH, or a pH of 7. When the number of H+ exceeds the number of OH-, the solution is said to be acidic, and has a pH of less than 7. Conversely, when the number of OH- exceeds the number of H+, the solution is said to be basic or alkaline; it has a pH between 7 and 14 (Figure 2.15). The scale is based on powers of 10, so that the difference of just one indicates a change ten times as great. For example, stomach acid has an acidity level around 2. Apples have a pH of about 5. That means that stomach acid is 1000 times as acidic as apples.

Chemical reactions of living organisms usually occur at a pH range of 6.9 to 7.5, a range that is called "neutral." (There are exceptions, such as the highly acidic environment inside your stomach.) However, many of the chemical reactions that occur in aqueous solutions either release or utilize hydrogen, which affects the pH. How does the cell prevent pH shifts away from neutrality? The maintenance of the internal pH of all cells is primarily due to buffers, chemical substances that play one of two roles. When there are too many hydrogen ions (when the solution is acidic), buffers combine with excess hydrogen ions to bring the solution to a neutral state. When there are too many hydroxide ions (when the solution is basic), buffers combine with hydroxide ions to bring the solution to a neutral state. Hence neutrality is maintained.

Carbonic acid is one of the major buffering substances of blood. Carbonic acid when present in water dissociates into bicarbonate and hydrogen ions. When chemical reactions in the body cause a high concentration of hydrogen ions in the blood, they combine with the bicarbonate to form carbonic acid, thus removing the hydrogen ions from the blood. When there is an excess of hydroxide ions, they combine with the hydrogen ions to form water. (Source: Avila, Vernon L. Biology : Investigating Life On Earth Jones and Bartlett/Bookmark Series in Biology Page 46-48)