Science

• The most important large molecules found in all living things can be sorted into four main classes: carbohydrates, lipids, proteins, and nucleic acids
• Members of three of these classes—carbohydrates, proteins, and nucleic acids—are huge and are therefore called macromolecules.
• A polymer (from the Greek polys, many, and meros, part) is a long molecule consisting of many similar or identical building blocks linked by covalent bonds
• The repeating units that serve as the building blocks of a polymer are smaller molecules called monomers (from the Greek monos, single).
• Polymerization is a synthesis of polymers that is connecting monomers through dehydration reaction
• Each monomer contributes part of the water molecule that is released during the reaction: One monomer provides a hydroxyl group (OH), while the other provides a hydrogen (H).
• •Polymers are disassembled to monomers by hydrolysis
• Hydrolysis means water breakage (from the Greek hydro, water, and lysis, break).
• The bond between monomers is broken by the addition of a water molecule, with a hydrogen from water attaching to one monomer and the hydroxyl group attaching to the other.
• Monosaccharides: the simplest carbohydrates or simple sugars; monomers
• Polysaccharides: carbohydrate macromolecules are polymers composed of many sugar building blocks.
• Disaccharides: are double sugars, consisting of two monosaccharides joined by a covalent bond.
• Monosaccharides, its molecular formulas: some multiple of the unit CH2O
• Glucose (C6H12O6) is of central importance in the chemistry of life
• Monosaccharides - Location of the carbonyl group:

  Aldose: Carbonyl group at end of carbon skeleton (aldehyde sugar)

  Ketose: Carbonyl group within carbon skeleton (ketose sugar)
• Monosaccharides - Size of the carbon skeleton (ranges from three to seven carbons long):

  Hexoses:  sugars that have six carbons (glucose, fructose)

  Trioses (three-carbon sugars) and pentoses (five-carbon sugars)
• Disaccharides is consists of two monosaccharides and joined by a glycosidic linkage, a covalent bond formed between two monosaccharides by a dehydration reaction (glyco refers to carbohydrate)
• Disaccharides examples:

  
  

  Maltose or malt sugar: two glucose molecule

  Sucrose or table sugar: glucose and fructose

  Lactose in milk: glucose and galactose
• Polysaccharides has a polymers with a few hundred to a few thousand monosaccharides and joined by a glycosidic linkages
• Polysaccharides some serve as storage material, hydrolyzed as needed to provide sugar for cells and some serve as building material for structures that protect the cell or the whole organism.
• Plants: store starch, a polymer of glucose monomers and within cellular structures known as plastids.
• Polymerization through dehydration reaction enables the plant to stockpile surplus glucose
• Hydrolysis: sugar can later be withdrawn by the plant from this carbohydrate “bank”. Breaks the bonds between the glucose monomers
• Animals: store a polysaccharide called glycogen
• Animals: Hydrolysis of glycogen in these cells releases glucose when the demand for sugar increases
• Cellulose a major component of the tough walls that enclose plant cells (cell wall) and most abundant organic compound on Earth.
• On food packages, “insoluble fiber” refers mainly to cellulose.
• Chitin: carbohydrate used by arthropods (insects, spiders, crustaceans, and related animals) to build their exoskeletons.
• Chitin is also found in fungi, which use this polysaccharide rather than cellulose as the building material for their cell walls
• Lipids: does not include true polymers, and they are generally not big enough to be considered macromolecules. It consist mostly of hydrocarbon regions (fats, phospholipids, and steroids)
• Fats: not polymers; large molecules assembled from smaller molecules by dehydration reactions
• Fats is constructed from two kinds of smaller molecules:

  glycerol = each of its three carbons bears a hydroxyl group

  fatty acids = a long carbon skeleton, usually 16 or 18 carbon atoms in length
• Fats has a three fatty acid molecules are each joined to glycerol by an ester linkage and bond formed by a dehydration reaction between a hydroxyl group and a carboxyl group.
• Fats: also called a triacylglycerol, thus consists of three fatty acids linked to one glycerol molecule (triglyceride)
• Fats saturated: refer to the structure of the hydrocarbon chains of the fatty acids, no double bonds between carbon atoms composing a chain.
• Fats unsaturated: has one or more double bonds, with one fewer hydrogen atom on each double-bonded carbon
• Steroids: lipids characterized by a carbon skeleton consisting of four fused rings. Different steroids are distinguished by the particular chemical groups attached to this ensemble of rings.
• Phospholipids: major components of cell membranes and has only two fatty acids attached to glycerol.
• The ends of phospholipids show different behaviors with respect to water:

  hydrocarbon tail: polar, hydrophobic and are excluded from water

  hydrophilic head: nonpolar, has an affinity for water
• Proteins: comes from the Greek word proteios, meaning “first,” or “primary." and account for more than 50% of the dry mass of most cells.