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- 10/13/2021

Bio-Chemistry Review – Carbohydrates, Lipids & Proteins

Chimica Oggi-Chemistry Today

Carbohydrates are important to living organisms in these ways:
• store and/or transport of energy (i.e., glycogen)
• structural support (chitin in both fungi and arthropods)
• play major roles for a proper functionin immune system,
  human fertilization & development, blood clotting and more

Carbohydrates are made of the elements Carbon, Hydrogen & Oxygen, where hydrogen and oxygen atoms are often present in a ratio 2:1. The basic building block of a carbohydrate is a simple sugar with a typical molecular formula of C6H12O6, C12H22O11, C5H10O5 or others. These are mono- or disaccharides with the names usually ending in –ose; thus not to be confused with enzymes, which usually end in –ase (e.g. lipase). Using our mnemonic device, carbohydrates can be considered as CHO compounds. True lipids & fats are also comprised of CHO compounds, but the ratio of hydrogen to oxygen atoms is much different! The three main carbohydrates groups are sugars, cellulose & starches.

• Monosaccharides: Glucose, fructose and galactose are examples of these simple sugars. Monosaccharides are the major source of fuel for metabolism (Stoffwechsel) being used both as an energy source and in biosynthesis. Monosaccharides have a typical molecular formula of C6H12O6
• Disaccharides: Two joined monosaccharides are called disaccharides. Maltose, sucrose (most abundant) and lactose are some examples of these compounds.
• Oligosaccharides vs. Polysaccharides: The distinction between these two sugar groups is based upon the number of monosaccharide units present in the chain:
• Oligosaccharides typically contain between 3-9 monosaccharides
• Polysaccharides contain >10 monosaccharides

Cellulose: As for these polysaccharides, they represent an important class of biological polymers, where in plants they usually provide structure; however, for humans, cellulose is indigestible.
– Chitin (pronounced Ky-tin), a special form of cellulose: In terms of chemical structure, chitin may be compared to cellulose, yet provides structural support for cell walls in fungi such as mushrooms, yeasts & molds. Chitin also provides an external or exo-skeleton (vs. internal, endo-skeleton) for the Arthropods, aka the ‘jointed-legged animals’ such as: Crustaceans (lobster, shrimp, crabs), Insects (ants, wasps, moths), Arachnids (spiders).

Starches – Humans depend on plant-derived starches for nutritional purposes. Starches can be found in various grains and some examples are rice, wheat, barley, corn, etc. As you’d expect, potatoes as well as finished products such as pastas or breads are starches. Glycogen is the term for stored starch in humans. Thus, glycogen, which is stored sugar in the human liver, can be quickly metabolized, which suits the active lives of humans as well as other animals.



A broad group of naturally-occurring molecules which includes fats, waxes, sterols (such as cholesterol), fat-soluble vitamins (such as vitamins; A, D, E, K), mono-/di-glycerides, phospholipids & others.

The main biological functions of lipids include:
• energy storage, signaling molecules
• structural components of cell membranes, neuron’s myelin sheath

Lipids may be broadly defined as hydrophobic, and are made up of Carbon, Hydrogen & Oxygen (CHO) with the ratio of H:O >2:1. Although the term lipid is sometimes used as a synonym for fats, fats are a subgroup of lipids called triglycerides, which are solid at room temperature (temp.).

– Saturated fats (solid at Rm. temp.): found in various processed meats, butter/lard, snack foods, pastries baked with these fats. The chemical structure of a saturated fat is fully saturated with hydrogen atoms, and does not contain double bonds between carbon atoms. Saturated fats are not heart healthy, since they are most known for raising your LDL cholesterol (“bad” cholesterol).
– Unsaturated fats (liquid at Rm. temp.): found in foods such as nuts, avocados & olives. They are liquid at room temperature and differ from saturated fats in that their chemical structure contains double bonds. Additionally, studies have shown that unsaturated fats are also heart-healthy fats, having the ability to lower LDL cholesterol and raise HDL cholesterol (“good” cholesterol).


Considered the ‘building blocks of life’, they are organic compounds made of amino acids (i.e. Glycine, Leucine, etc.) arranged in a linear chain. Proteins are made up of contain the element in addition to Carbon, Hydrogen, Oxygen & Nitrogen (CHON).

However, many proteins also contain Sulphur (S). A protein molecule is composed of amino acids using information encoded in genetic material.

Each amino acid has an amino group at one end with a carboxyl group at the other end. Examples of proteins include Hemoglobin, Keratin, which makes up hair, & nails, digestive enzymes as well as some hormones such as insulin. 

Source: ‘Biological Science’, Prof. William T. Keeton, Cornell University, NY, USA