Disaccharides and Glycosidic Linkages Quiz

Life and Chemistry: Large Molecules

• Large biological molecules are called macromolecules
• These large molecules are present in all living things, in similar proportions
• Macromolecules are giant polymers
• Polymers are formed by covalent linkages of smaller units called monomers
• Molecules with molecular weights greater than 1,000 Daltons (1 kDa = 1000 Daltons) are usually classified as macromolecules
• The functions of macromolecules are related to their shape and the chemical properties of their monomers
• Some functions of macromolecules include: energy storage, structural support, transport, protection and defense, regulation of metabolic activities, means for movement, growth, and development, Heredity

Macromolecules: Condensation and Hydrolysis

• Macromolecules are made from smaller monomers by dehydration (condensation) reaction.
• In a condensation/dehydration reaction, an OH from one monomer links to an H from another monomer.
• A water molecule is released in this reaction (H₂O)
• The reverse reaction, where polymers are broken into monomers, is called a hydrolysis reaction.
• Energy is required to make or break polymers

Biological Macromolecules

• There are four major types of biological macromolecules: proteins, nucleic acids, carbohydrates, and lipids
• Of the four, only three are polymers: proteins, nucleic acids, and carbohydrates.

1. Proteins

• Proteins are polymers of amino acids. They are molecules with diverse structures and functions
• Each type of protein has a characteristic amino acid composition and order.
• Proteins range in size from a few amino acids to thousands
• Protein folding is crucial to function and is influenced largely by the amino acid sequence
• An amino acid has four groups attached to a central carbon atom: a hydrogen atom, an amino group (NH₃⁺), a carboxyl group (COO⁻), and a variable side chain (R group.)
• Differences in amino acids come from the side chains or R groups.
• There are twenty different amino acids found in cells
• Amino acids are linked by peptide bonds.
• A condensation reaction links the carboxyl group of one amino acid to the amino group of the next, releasing a water molecule
• Polypeptides have an amino-terminal (N-terminus) end and a carboxyl-terminal (C-terminus) end.
• The polypeptide backbone is relatively inflexible.
• Various interactions between the R groups cause the polypeptide to fold into a specific 3D shape, crucial to their function.
• Proteins can be classified into four levels of structure: primary, secondary, tertiary, and quaternary
• The primary structure of a protein is its amino acid sequence.
• The precise sequence of amino acids is called primary protein structure
• Secondary structure describes local folded structures like a-helices and ß-sheets
• Tertiary structure describes the overall, 3D folded structure of a single polypeptide chain.
• Quaternary structure describes how multiple polypeptide chains (subunits) interact to form a functional protein.

2. Nucleic Acids

• Nucleic acids are polymers of nucleotide monomers
• Nucleotides are composed of a phosphate group, a sugar (ribose in RNA and deoxyribose in DNA), and a nitrogenous base (purines or pyrimidines).
• There are two groups of nitrogenous bases: purines (adenine and guanine), and pyrimidines (cytosine, uracil, and thymine)
• Uracil is found only in RNA, and thymine is found only in DNA
• Nucleic acid strands are formed by a phosphodiester linkage (phosphodiester bond)
• The phosphodiester linkage is formed between the phosphate group of one nucleotide and the 3' hydroxyl group of an adjacent nucleotide.
• The sugar-phosphate backbone is directional, running 5' → 3'
• DNA has a double helix, with two antiparallel strands held together by complementary base pairing. The hydrophilic sugar-phosphate backbone is facing the outside, while nitrogenous bases are inside the structure.
• DNA has complementary base pairing of purines and pyrimidines; adenine pairs with thymine, and guanine pairs with cytosine
• The base-pairs are held together by hydrogen bonds.
• DNA strands are antiparallel. The structure of DNA is a double helix.
• The information necessary to maintain hereditary information is encoded in the DNA base sequences.
• Closely related species have more similar base sequences.

3. Carbohydrates

• Carbohydrate polymers are called glycans
• Carbohydrates serve as fuel and building material
• Carbohydrates include both sugars and their polymers
• Monosaccharides are the simplest sugars. They can be used for fuel and converted into other organic molecules and combined into polymers.
• Examples include glucose, galactose, fructose.
• Disaccharides are two monosaccharides joined by a glycosidic linkage. Examples include sucrose (glucose + fructose) and maltose (glucose + glucose).
• Polysaccharides are polymers of monosaccharides. Polysaccharides include: -Storage polysaccharides (starch and glycogen): -Starch is the main storage polysaccharide of plants, consisting entirely of α-glucose monomers; and used as energy storage in plants -Glycogen is the major storage polysaccharide in animals, also composed of α-glucose monomers, used as energy storage in animals -Structural polysaccharides (cellulose, chitin): -Cellulose is an unbranched polymer of β-glucose; forms plant cell wall structures -Chitin is a structural polymer present in fungal cell walls and the exoskeletons of arthropods
• Glycoproteins (proteins with covalently bound carbohydrates) are part of the cell’s surface, used for cell-cell recognition

4. Lipids

• Lipids are a diverse group of hydrophobic molecules
• Lipids are not polymers
• Lipids include a variety of molecules, including fats, phospholipids, steroids, and carotenoids
• Lipids share the common feature of being hydrophobic
• Fats (triglycerides): Composed of glycerol and three fatty acid chains. They store energy. Saturated fats have no double bonds and are solid at room temperature, and unsaturated fats have one or more double bonds and are liquid at room temperature.
• Phospholipids: Structure includes two fatty acid chains bound to glycerol, and a phosphate modified group. Part of cell membranes, they are amphipathic with hydrophobic tails and hydrophilic heads.
• Steroids: Have a four-ring carbon skeleton. Important signaling molecules in hormones and part of cell membranes. Cholesterol is an example, important in cell membranes and the precursor to other steroids.
• Carotenoids: Light-absorbing pigments. Examples include beta-carotene (a plant-based pigment that converts to vitamin A in animals)
• Additional Roles for lipids: energy storage, insulation, cushioning, part of cell membranes, capture of light energy, components of hormones and vitamins, thermal insulation, electrical insulation of nerves, water repellence

Test your knowledge on disaccharides, their composition, and glycosidic linkages. This quiz covers the key reactions and structural aspects of disaccharides like maltose, including the formation and characteristics of glycosidic bonds. Challenge yourself with questions about glucose linking and structural features!