Biology: Functional Groups and Molecules

Functional Groups

• Functional groups are chemical groups that affect molecular function, either by influencing shape or directly participating in chemical reactions.
• The seven most important functional groups in biology are: hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl.

Chemical Building Blocks of Life

• There are four major types of biological molecules: lipids, nucleic acids, proteins, and carbohydrates.
• Lipids, particularly phospholipids, are essential for cell membranes due to their amphipathic nature.
• Nucleic acids are polymers of nucleotides that exist as either DNA or RNA.
• Carbohydrates are polymers of sugars and serve as both structural components and energy sources.
• Proteins are polymers of amino acids and play vital roles in structure and enzymatic activity.

Polymers

• Polymers are large molecules composed of repeating units called monomers.
• Polymerization occurs through dehydration synthesis (condensation), where monomers are linked together with the loss of a water molecule.
• The process is facilitated by enzymes.
• Polymers are broken down into monomers through hydrolysis, the addition of a water molecule to break the bond.

Carbohydrates

• Carbohydrates include sugars and polymers of sugars.
• Monosaccharides are simple sugars, disaccharides are formed by two monosaccharides joined by a glycosidic linkage, and polysaccharides consist of many sugar units.
• The general formula for carbohydrates is (CH2O)n.
• Examples of monosaccharides include glucose, galactose, and fructose.
• Examples of disaccharides include sucrose, lactose, and maltose.

Polysaccharides

• Polysaccharides are macromolecules comprised of hundreds to thousands of monosaccharides linked by glycosidic linkages.
• Their function depends on the type of sugar monomers and the position of the glycosidic linkages.
• Storage polysaccharides include starch (plants) and glycogen (animals), both polymers of glucose.
• Structural polysaccharides like cellulose provide strong building material in plants.
• Humans lack enzymes to break down cellulose, making it a source of insoluble fiber.

Lipids

• Lipids are hydrophobic organic molecules composed primarily of carbon, hydrogen, and oxygen.
• They are less oxidized than carbohydrates, leading to higher caloric content per gram.
• The five main types of lipids in humans are: fatty acids, triglycerides, phospholipids, eicosanoids, and steroids.
• Fatty acids can be saturated (no double bonds) or unsaturated (one or more double bonds).
• Triglycerides consist of three fatty acids bound to a glycerol molecule.
• Phospholipids are similar to triglycerides but with a phosphate group replacing one fatty acid, giving them amphipathic properties.
• Eicosanoids are hormone-like signaling molecules between cells.

Proteins

• Proteins are composed of polypeptides, which are chains of amino acids linked together.
• Each amino acid has an amine group, a carboxyl group, and a unique side chain.
• Amino acids are linked together by peptide bonds formed via dehydration reactions.
• The structure of a protein can be categorized into four levels:
  • Primary: The linear sequence of amino acids.
  • Secondary: Local twists and turns in the polypeptide chain, such as alpha helices and beta pleated sheets.
  • Tertiary: The overall three-dimensional shape of a polypeptide, determined by interactions between side chains.
  • Quaternary: The arrangement of multiple polypeptide chains in a protein complex.
• Denaturation refers to the unfolding of a protein, often due to unfavorable environmental conditions, leading to loss of function.
• Chaperonins are proteins that assist in proper protein folding.

Nucleic Acids: DNA & RNA

• DNA is the genetic material passed from parents to offspring, organized into genes located on chromosomes.
• Genes contain the instructions for all cellular activities.
• RNA is synthesized from DNA and carries genetic information to ribosomes for protein synthesis.
• The process of DNA to RNA to protein is known as gene expression.

Nucleic Acid Structure

• Nucleic acids are polymers of nucleotides.
• Each nucleotide consists of a sugar (ribose or deoxyribose), a phosphate group, and a nitrogenous base.
• The nitrogenous bases include adenine (A), guanine (G), cytosine (C), thymine (T) (in DNA), and uracil (U) (in RNA).
• RNA is single-stranded, while DNA is double-stranded.
• The two DNA strands are antiparallel, running in opposite 5' to 3' directions, and held together by hydrogen bonds between complementary bases (A with T, G with C).
• The structure of DNA is a double helix, with sugar-phosphate backbones on the outside and bases towards the interior.