CARBS

CARBS

Made up of carbon, hydrogen and oxygen only.
1. The chains group into monomers, dimers and polymers.
  1. Monosaccharides - e.g. glucose.
    1. most important mono is glucose - C6H12O6
      1. Formula (CH2O)n, n can be 3-7. 6 carbon sugar.
        alpha glucose - used to make starch and glycogen. OH branches at the bottom of carbon 1.
        beta glucose - used to make cellulose. OH branches at top of carbon 1
        isomers of glucose, same formula (C6H12O6), different structural formulae. These isomers include fructose and galactose.
    2. Common five-carbon, (where n = 5, C5H10O5) include ribose and deoxyribose (found in nucleic acids and ATP) and ribulose (which occurs in photosynthesis).
  2. Disaccharides - e.g. sucrose.
    1. when 2 monosaccharides are joined by a glycosidic bond through a condensation reaction, forming a molecule of water
      1. reverse process, when bonds are broken by the addition of water (e.g. in digestion), is called a hydrolysis reaction.
    2. examples are maltose, formed on digestion of starch by amylase. its glucose 1-4 glucose. to break this down enzyme maltase is required.
    3. sucrose is glucose 1-2 fructose. common in plants as less reactive than glucose, their main transport sugar. more commonly known as table sugar. breakdown requires sucrase.
    4. lactose, galactose 1-4 glucose. found only in mammalian milk, main source of energy for infant mammals.
  3. Polysaccharides - starch.
    1. long chains of many monosaccharides joined by glycosidic bonds
    2. starch - plant storage, insoluble. doesn't cause water movement by osmosis. big SA:Vol ratio. mixture of amylose and amylopeptin
      1. amylose poly-(1-4) glucose. straight chain and coils up into a helix.
      2. amylopeptin is poly-(1-4) glucose with (1-6) branches. due to having more ends it can be broken down quicker by amylase. both are broken down by amylase but at different rates
    3. glycogen is similar to amylopeptin, poly-(1-4) glucose with more (1-6) branches. animals storage molecule. found mainly in muscle and liver. highly branched > broken down to glucose rapidly for energy (mobilised)
    4. cellulose only found in plants (cell walls). poly-(1-4) glucose but different isomer of glucose. contains beta glucose so can chain alternately.
      1. Tiny difference makes a huge difference in structure and properties. While the a 1-4 glucose polymer in starch coils up to form granules, the b14 glucose polymer in cellulose forms straight chains. Hundreds of these chains are linked together by hydrogen bonds to form cellulose microfibrils. These microfibrils are very strong and rigid, and give strength to plant cells, and therefore to young plants and also to materials such as paper, cotton and sellotape.
      2. to break beta glucose gylcosidic bond requires cellulase enzyme.
    5. Other polysaccharides include: Chitin, found in fungal cell walls and the exoskeletons of insects. Pectin, found in plant cell walls. Agar, found in algae and used to make agar plates. Murein, found in bacterial cell walls. Lignin, found in the walls of xylem cells, main component of wood.

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	Created by Mary-Louise Grundy over 10 years ago