Carbohydrates are composed entirely of atoms of carbon, hydrogen, and oxygen. All four of these classes of molecules are composed of basic units of structure. The basic unit of structure of carbohydrates is the monosaccharide or simple sugar. Simple sugars combine in a condensation reaction to produce a disaccharide or double sugar. Since one water molecule is extracted during this process, it is also known as dehydration synthesis. Glucose (blood sugar) and fructose (sugar in many fruits) are examples of simple sugars and sucrose (cane sugar) is an example of a double sugar. Complex carbohydrates such as starch and cellulose (found in plant cell walls) result from many simple sugars that link together like a chain. Carbohydrates are quick energy sources and the simpler the form, the faster the energy is provided since less digestion is required. The following diagrams represent structural formulas that show the geometry (shape) of the molecules and the kinds of atoms that make up the molecule as well as the number of each kind of atom. Where lines of the hexagon or pentagon meet, if no element is shown, assume that it is a carbon atom. Note that where three or more monosaccharides are joined together, the generic name is a polysaccharide and an example is starch. (No one ever said that biology lacked a large vocabulary!)
Credit to:dinamicscience.com.a
In the above condensation reaction also called dehydration synthesis reaction because a molecule of water is removed (see the HOH above), two simple sugars (monosaccharides) join to form a double sugar (disaccharide). The following three diagrams represent condensation reactions of glucose + glucose, glucose + galactose, and glucose + fructose respectively.
Note from the diagram below that glucose, fructose, and galactose all have the same chemical formula but are different sugars with slightly different but unique characteristics. Thus, they are known as isomers (of each other).
Question: What then accounts for their individual differences?
Answer: at the end of the essay
Remember that all of the above reactions are anabolic and endergonic reactions and are formed by plants; the reverse reactions occur when disaccharides or polysaccharides are broken down during digestion in animals bodies to the monosaccharides that comprised them with the addition of one molecule of water. Each reaction requires a particular enzyme to makethereaction occur. The enzyme that catalyzes the formation of sucrose is sucrase, the one for the formation of lactose is lactase and the one for maltose is maltase. As you can guess these reactions are both catabolic and exergonic.
Question: Why?
Question: What suffix probably indicates a sugar? An enzyme?
Proteins are called the “stuff of life” since they are necessary for growth and repair of the body. They are formed by long chains of amino acids (the basic unit of structure) which again results from a dehydration synthesis reaction. Ribosomes in the cell assemble the amino acids into polypeptides on the longer chained proteins. Proteins are grouped according to their function. For example, there are those that protect the body (antibodies), those for support and movement (i.e. ligaments, tendons, and muscles), those for speeding up chemical reactions (enzymes), and more. Below is a diagram of the four levels of protein structure and below that some examples of the 20 common amino acids that make up proteins.
Credit to: proteopedia
Credit to: biosiva.50webs.org
Credit to: Study.com
Note that this is again a condensation reaction where, in this case, the amino (NH2+) group of the glycine molecule on the right joins the carboxyl (COOH-) group on the left with the removal of one water molecule.
The third group, lipids, includes fats, oils, and wax. Since they are impervious to water, they are often used in waterproofing. Fat is, of course, long term energy storage material and also provides thermal insulation and cushions and protects vital body organs such as the eyes and kidneys. The basic unit of structure of lipids includes a glycerol molecule and three fatty acids. The typical fat or oil molecule consists of a long hydrocarbon chain which is hydrophobic (water fearing) and hydrophilic (water loving) head. This means that the head end dissolves in water and the hydrophobic tail doesn’t. Cell membranes are primarily composed of two layers of lipid. Likewise, lipids are formed by dehydration synthesis in which three water molecules are removed.
Credit to: dic.dcccd.edu
Credit to Columbia University
The fourth group of organic molecules discussed here are nucleic acids which include DNA and the many RNA’s. We all are aware of one of DNA’s central roles-it contains the hereditary code of life and transmits that code from generation to generation. However, its other function is less well known. It directs the synthesis (in most cases) of that other class of compounds, proteins. Those two functions put DNA right at the head of the class. By the way, the basic unit of structure of nucleic acids is a nucleotide. A nucleotide of DNA consists of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, guanine, cytocine, or thymine). The DNA molecule is a long double stranded molecule that is twisted into a double helix. There are many kinds of RNA but they all differ from DNA in that the sugar is ribose (with one more oxygen atom), uracil is substituted for thymine, and it is a single stranded molecule that may fold over upon itself in various shapes. Messenger RNA (mRNA, transcribes DNA’s code from the cell’s nucleus to the cytoplasm and specifies which particular amino acid is to be assembly by rRNA (a ribosome). Each amino acid is attached to a particular tRNA (transfer RNA) molecule). I always told my students that it is as if the mRNA says to the tRNA “I’ll meet you at the ribosome and we’ll make a protein.”
Credit to: Aidan balbach
The three major types of RNA structures include:
Credit to:quora.com
rRNA, mRNA, and rRNA
Credit to: Lumen Learning
Now that we’ve learned a little bit about each class of biologically important compounds, let’s focus in on one of those groups, the nucleic acids. A hundred years ago no one knew what molecule carried the genetic material. During the first half of the twentieth century a great debate raged among biologists about whether DNA or proteins carried that information. Many biologists favored proteins and their reasoning went something like this. If you think of the code like letters in an alphabet, proteins with their twenty letter alphabet (20 amino acids) could spell more words (greater genetic variability) than could DNA with its four letter alphabet (four kinds of nucleotides based on the four kinds of nitrogen bases). Space limits further discussion here but a series of brilliant experiments that culminated in 1953 with the iconic Watson and Crick model verified that DNA, indeed, is the universal carrier of genetic traits. (I would recommend that for further investigation of the other brilliant experiments, consult any AP or college biology text book)
The ramifications of this discovery are, of course, immense. As pointed out in a previous essay, virtually every scientific discovery raises more questions than it answers. One of those questions is a which came first the chicken or the egg question. Until 1982, all known enzymes were thought to be proteins. Rbonucleic acid (RNA) was thought to play a supporting role to DNA (deoxyribonucleic acid). It (RNA) simply passed genetic information from DNA to proteins, which carry out the work of the cell. A group lead by Sidney Altman and Thomas Cech discovered ”ribozymes”–RNA enzymes. This changed biologist’s view of the cell’s operations and their view of the origins of the first cells- how they view life’s origins.
Which substance did life acquire first– DNA or proteins? Proteins can perform many biological functions but they can’t propagate themselves. DNA can propagate (replicate) itself but can’t perform any biological tasks. On the other hand, RNA can transmit and store genetic information and can perform biological work based on the discovery of catalytic RNA (ribozymes) Thus, it is entirely possible that it preceded both proteins and DNA. The RNA molecule has a genotype which is the linear sequence of nucleotides along the RNA molecule. The genotype can record and make small changes in heritable information. It also has a phenotype which results from the ribozyme having an active site that can catalyze a chemical reaction.
Did RNA predate DNA and should RNA be elevated to a higher status than DNA? We will take up that question in the next essay.
Answers to questions
Their structural formulas (geometry)
Larger molecules are broken down into smaller ones (breaking down process with a release in energy). There is less energy in the products than in the reactants.
-ose
-ase
