Biomolecules are organic compounds produced by living organisms, fundamental for all biological processes. They form cellular structural components and participate in life-sustaining functions. Primarily composed of carbon, hydrogen, oxygen, and nitrogen, they may also contain phosphorus and sulfur. Their specific arrangements dictate their roles within living systems.
Carbohydrates
Carbohydrates serve as a primary energy source and contribute to structural support in cells. They are classified into three main types based on their structural complexity, all derived from basic sugar units called saccharides. Monosaccharides, such as glucose, fructose, and galactose, are the simplest forms, consisting of a single sugar unit and providing immediate energy for cellular activities. Glucose is a universal energy source, used to produce adenosine triphosphate (ATP) through cellular respiration.
Disaccharides form when two monosaccharides link together, such as sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose). They are important for sugar transport and storage in plants. Polysaccharides are complex carbohydrates made from long chains of many monosaccharide units. Examples include starch and glycogen, which function as energy storage in plants and animals respectively, and cellulose, which provides structural support in plant cell walls.
Lipids
Lipids are a diverse group of biomolecules defined by their insolubility in water. This characteristic arises from their primarily nonpolar composition, which includes many carbon-carbon and carbon-hydrogen bonds. Lipids play diverse roles, including long-term energy storage, forming essential components of cell membranes, and acting as signaling molecules. They also provide insulation and help absorb fat-soluble vitamins.
Main types of lipids include triglycerides, phospholipids, and steroids. Triglycerides, also known as fats, are the primary form of energy storage in both humans and plants, composed of a glycerol molecule and three fatty acid chains. Phospholipids are fundamental to cell membrane structure, forming a bilayer that regulates what enters and exits the cell due to their unique hydrophilic and hydrophobic properties. Steroids, such as cholesterol and certain hormones like testosterone, feature a distinctive four-ring structure and function in cell membrane stability and as chemical messengers.
Proteins
Proteins are versatile biomolecules that participate in nearly all cellular processes. They are polymers constructed from smaller units called amino acids, linked together in long chains. The specific sequence and three-dimensional folding of these amino acid chains determine each protein’s unique function. Proteins serve various roles, acting as enzymes that accelerate biochemical reactions within the body, such as pepsin, a digestive enzyme that breaks down food proteins in the stomach.
Many proteins provide structural support, forming components of tissues like collagen in bones and skin, or keratin in hair and nails. They also function as transport molecules, exemplified by hemoglobin, which carries oxygen in the blood. Other proteins act as messengers, with some hormones, like insulin, being protein-based to regulate bodily functions such as blood sugar levels. Proteins also play a role in immune defense as antibodies, which identify and neutralize foreign invaders.
Nucleic Acids
Nucleic acids, primarily deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are biomolecules responsible for storing and transmitting genetic information. These complex molecules are polymers made up of repeating units called nucleotides. Each nucleotide consists of three components: a nitrogenous base, a five-carbon sugar, and a phosphate group.
DNA contains the sugar deoxyribose and the nitrogenous bases adenine (A), guanine (G), cytosine (C), and thymine (T). It forms a double helix structure, carrying the complete set of genetic instructions. RNA contains the sugar ribose and the bases adenine (A), guanine (G), cytosine (C), and uracil (U) instead of thymine. RNA is typically single-stranded and plays a central role in expressing genetic information from DNA, including messenger RNA (mRNA) carrying instructions for protein synthesis, ribosomal RNA (rRNA) forming part of ribosomes, and transfer RNA (tRNA) bringing amino acids to the ribosome.