Review of 4 major types of biomolecules and their functions.

Contents:

1. 4 types of biomolecules and their functions
2. Chemical structure of biomolecules
3. Basic functional groups of biological macromolecules
4. Building blocks of biomolecules

Carbon atoms attaching to each other can form straight or branched chains and ringed structures of organic compounds.

Today millions of different organic compounds are known.

Structures of organic compounds form natural polymers and act as the backbones of different types of biological molecules. 

All 4 types of biomolecules or the biomolecules of life are carbon based.

Some examples of important biological molecules include vitamins, enzymes, polyphenols, and plenty of others.

While the most of carbon-containing molecules are organic compounds, there are a few exceptions.

Such compounds as carbides, carbonates, simple oxides of carbon (CO₂), allotropes of carbon and cyanides are considered to be inorganic.

4 types of biomolecules and their functions

Each of 4 major types of biomolecules is an important cell component and performs a wide variety of functions.

4 major classes of biological molecules include:

1. Carbohydrates (monosaccharides, oligosaccharides, polysaccharides)
2. Lipids (triglycerides, phospholipids, steroids)
3. Proteins
4. Nucleic Acids (DNA, RNA)

Besides their specific roles, carbohydrates, lipids, and proteins can serve as a source of energy, while nucleic acids are the most important macromolecules for the continuity of life.

Biological function of carbohydrates

Plants and algae produce millions of tons of carbohydrates each year through photosynthesis.

The main function of carbohydrates is to provide energy, particularly through glucose.

During cellular respiration, glucose is broken down and oxidized within cells. This process is used to synthesize adenosine triphosphate (ATP) – the source of energy for cellular reactions.

When the quantity of adenosine triphosphate are sufficient, simple carbohydrates are converted to carbohydrate polymers (glycogen or starch) or fat and stored.

Carbohydrates also have other important functions in all living organisms.

For example, they serve as building materials within the plant cells and perform cell-to-cell identification when attached to the external surfaces of the cytoplasmic membrane.

Lipids function

Lipids include a diverse group of biomolecules. They are insoluble in water and include mostly nonpolar carbon–carbon or carbon–hydrogen bonds.

The primary function of lipids is to serve as the energy-storing molecule for long-term use.

Excess carbohydrates are converted into fat for later usage.

1 g of fat is equal to 38 kJ or 9 kcal (versus 17 kJ or 4 kcal for carbohydrates and proteins).

Lipids perform many different functions in a cell.

For example, plants and animals use fat as insulation from the environment. Lipids are an important part of all cellular membranes and many hormones.

Biological role of proteins

Proteins are the most diverse group of 4 major types of biomolecules. Their macromolecular structures and functions vary greatly.

Each living cell contains thousands of proteins each performing a unique function. They can act as structural building blocks and functional molecules, involved in almost every task of the cell.

All enzymes are proteins.

This class of macromolecules is all polymers of 20 amino acids.

Function of nucleic acids in cells

The main function of nucleic acids is to store and carry the hereditary information for the functioning of the cell.

The nucleic acids include two major classes of biological molecules, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), and consist of nucleotides.

Protein and nucleic acid enzymes catalyze biochemical reactions in both catabolism and anabolism of macromolecules.

Catabolism - the breakdown of biomolecules in living organisms.

Anabolism - the synthesis of complex biological macromolecules.

Chemical structure of biomolecules

One of the basic qualities of organic compounds - to possess a variety of properties, depends, in particular, on their ability to form different structures or isomers.

Isomers are macromolecules with the same molecular formula but different chemical structures.

There are two main types of structures of organic compounds:

1. Structural isomers
2. Stereoisomers

Structural isomers of macromolecules differ in the placement of their covalent bonds.

Examples of structural isomers is biological molecules of carbohydrates - glucose and fructose. Because of their different structures, they have different properties and are metabolized differently.

Stereoisomers have similar placements of their covalent bonds but differ in how these bonds are made to the surrounding atoms. Stereoisomers can be geometrical or optical.

Geometrical isomers can have different physical, but similar chemical properties.

Examples of geometrical isomers are glucose and galactose.

Optical isomers (enantiomers) usually have similar chemical and physical properties, but enzymes can distinguish one biomolecule from another.

Typically, one optical isomer is biologically active, and the other is inactive.

Basic functional groups of 4 types of biomolecules: carbohydrates, lipids, proteins, and nucleic acids

When one biological molecules react with other biomolecules, generally just the functional groups are involved. Therefore, each functional group of biomolecule has a specific role in cell metabolism.

Functional groups of different types of biomolecules are specific groups (moieties) of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.

The basic functional groups of biomolecules include such groups as hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, and phosphate groups.

Many biomolecules have more than one functional group.

Each functional group is able to modify the chemical properties of the macromolecules to which it bonds.

Hydroxyl functional group

Hydroxyl functional group is the group of alcohols. It adds polarity to biological molecules.

One example of alcohols is glycerol, also commonly known as glycerine. Glycerol is a polyalcohol and an important part of triglycerides and phospholipids.

Carbonyl functional group

Carbonyl functional groups of aldehydes and ketones generally also increase polarity and reactivity of biological molecules.

Biomolecules containing carbonyls tend to be volatile and stimulate senses with both pleasant and unpleasant odors.

Carboxyl functional group

A carboxyl functional functional group of carboxylic acids contains both a carbonyl functional group and a hydroxyl functional group, bonded to the same carbon atom.

Biological macromolecules containing carboxyl groups are often highly polar and reactive. Common biomolecules, containing the carboxyl functional groups, are fatty acids and amino acids.

Amino functional group

Amino functional groups also increase polarity and reactivity of a biological macromolecule. They readily form hydrogen bonds with other polar molecules and water. Amines are weakly basic.

Amino and carboxyl functional groups of amino acids react to each other to form peptide bonds of proteins.

Phosphate functional group

Phosphate functional groups are highly acidic and reactive. Phosphates are essential to the metabolic processes of photosynthesis and cellular respiration.

A transfer of a phosphate group from one molecule to another delivers energy to chemical reactions.

Sulfhydryl functional group

The sulfhydryl functional  group (–SH) is essential to protein stabilization.  

Amino acids with sulfhydryl functional groups form bonds called disulfide bridges (S–S bonds) that help protein molecules to take on and maintain a specific shape.

Building blocks of biomolecules – monomers and their corresponding natural polymers

The most of 4 types of biomolecules are made from single subunits, or building blocks, called monomers.

The monomers combine with each other using covalent bonds to form larger macromolecules known as polymers.

Polymers can be divided into two groups:

1. natural polymers (different types of biomolecules),
2. synthetic polymers.

Two main type of reactions involved in synthesis and degradation of biological molecules are hydrolysis and dehydration.

Polymers are broken down into monomers in a process known as hydrolysis, which means “to split water,” a reaction in which a water molecule is used during the breakdown.

Dehydration reactions involve the formation of new bonds, requiring energy, while hydrolysis reactions break bonds and release energy.

In a dehydration reaction, the hydrogen of one monomer combines with the hydroxyl group of another monomer, releasing a molecule of water and forming a polymer.

Dehydration and hydrolysis reactions are catalyzed by specific enzymes made up of proteins.

Each type of the natural polymer or the molecule of life is formed from specific to it smaller building blocks.

4 types of biomolecules and their monomers

References & further readings:

Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. The Molecular Composition of Cells.