Organic compounds are the building blocks of life. Carbohydrates, lipids, proteins, and nucleic acids play crucial roles in energy storage, cell structure, and genetic information. These molecules form the foundation of biochemistry and are essential for all living organisms.

Understanding these compounds is key to grasping how life works at the molecular level. From glucose powering our cells to DNA storing our genetic code, these molecules are the basis for all biological processes and structures in living things.

Carbohydrates

Monosaccharides and Polysaccharides

• Carbohydrates consist of carbon, hydrogen, and oxygen atoms, usually in a 1:2:1 ratio (CH2O)n
• Monosaccharides are simple sugars that serve as the building blocks of carbohydrates (glucose, fructose, galactose)
• Monosaccharides can be linked together by glycosidic bonds to form disaccharides (sucrose, lactose, maltose) and polysaccharides
• Polysaccharides are complex carbohydrates composed of long chains of monosaccharides
  • Polysaccharides can serve as energy storage molecules (starch in plants, glycogen in animals) or structural components (cellulose in plant cell walls, chitin in insect exoskeletons)

Functions and Importance of Carbohydrates

• Carbohydrates are the primary source of energy for living organisms
  • Glucose is the most common monosaccharide used for energy production through cellular respiration
• Carbohydrates play a crucial role in various biological processes, such as cell signaling, cell recognition, and immune system function
• Carbohydrates are essential components of nucleic acids (DNA and RNA), where they form the backbone of the molecule (deoxyribose in DNA, ribose in RNA)

Lipids

Structure and Types of Lipids

• Lipids are a diverse group of hydrophobic organic molecules that are insoluble in water but soluble in nonpolar solvents
• Fatty acids are long hydrocarbon chains with a carboxyl group (COOH) at one end, serving as the building blocks of many lipids
  • Fatty acids can be saturated (single bonds between carbon atoms) or unsaturated (one or more double bonds between carbon atoms)
• Triglycerides are the most common type of lipid, consisting of three fatty acid molecules attached to a glycerol backbone
  • Triglycerides serve as energy storage molecules in animals (fat) and plants (oils)
• Phospholipids are composed of two fatty acid molecules and a phosphate group attached to a glycerol backbone
  • Phospholipids are the primary components of cell membranes, forming a bilayer structure with their hydrophobic tails facing inward and hydrophilic heads facing outward

Functions and Importance of Lipids

• Lipids play a vital role in energy storage, providing a highly concentrated source of energy (9 kcal/g compared to 4 kcal/g for carbohydrates and proteins)
• Lipids are essential components of cell membranes, regulating the movement of molecules in and out of cells and maintaining cell structure and integrity
• Lipids serve as signaling molecules (hormones like steroids and eicosanoids) and are involved in various physiological processes (inflammation, blood clotting, immune response)
• Some lipids, such as cholesterol, are precursors for the synthesis of steroid hormones (testosterone, estrogen) and bile acids

Proteins

Amino Acids and Peptide Bonds

• Proteins are large, complex molecules composed of one or more chains of amino acids
• Amino acids are the building blocks of proteins, consisting of a central carbon atom (α-carbon) bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and a variable side chain (R group)
  • There are 20 different amino acids found in proteins, each with a unique R group that determines its chemical properties and interactions
• Amino acids are linked together by peptide bonds, which are covalent bonds formed between the carboxyl group of one amino acid and the amino group of another
  • Peptide bonds have a partial double bond character, resulting in a planar and rigid structure that contributes to the secondary structure of proteins (α-helices and β-sheets)

Protein Structure and Function

• Proteins have four levels of structure: primary (amino acid sequence), secondary (local folding patterns like α-helices and β-sheets), tertiary (overall 3D shape), and quaternary (multiple polypeptide chains)
  • The unique sequence of amino acids and the resulting structure determine a protein's specific function
• Proteins perform a wide variety of functions in living organisms, including:
  • Enzymes that catalyze biochemical reactions (digestive enzymes, metabolic enzymes)
  • Structural proteins that provide support and shape to cells and tissues (collagen, keratin)
  • Transport proteins that move molecules within and between cells (hemoglobin, ion channels)
  • Signaling proteins that transmit messages between cells (hormones, neurotransmitters)
  • Defensive proteins that protect against pathogens (antibodies, complement proteins)

Nucleic Acids

Nucleotides and Nucleic Acid Structure

• Nucleic acids are large biomolecules that store and transmit genetic information in living organisms
• Nucleotides are the building blocks of nucleic acids, consisting of three components: a nitrogenous base, a pentose sugar (deoxyribose in DNA, ribose in RNA), and a phosphate group
  • There are five nitrogenous bases found in nucleic acids: adenine (A), guanine (G), cytosine (C), thymine (T) in DNA, and uracil (U) in RNA
• Nucleotides are linked together by phosphodiester bonds between the phosphate group of one nucleotide and the sugar of another, forming a long polynucleotide chain
  • The sequence of nucleotides in a nucleic acid molecule determines the genetic information it encodes

DNA and RNA Structure and Function

• DNA (deoxyribonucleic acid) is a double-stranded molecule that stores genetic information in the form of a double helix
  • The two strands of DNA are held together by hydrogen bonds between complementary base pairs: A with T and G with C
  • DNA replication occurs during cell division, ensuring that each daughter cell receives an identical copy of the genetic material
• RNA (ribonucleic acid) is a single-stranded molecule that plays a crucial role in gene expression and protein synthesis
  • There are three main types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)
  • mRNA carries the genetic information from DNA to ribosomes, where it is translated into a protein sequence
  • tRNA molecules transport amino acids to the ribosomes and recognize the corresponding codons on the mRNA
  • rRNA is a component of ribosomes, the cellular machinery responsible for protein synthesis