Carbohydrates

Carbohydrates

• Primary energy source of body, mostly obtained from plants.
  → Photosynthesis: 6CO₂ +6H₂O → C₆H₁₂O₆ + 6O₂

• Basic empirical formula is CH₂O in a 1:2:1 ratio.

• They can exist singly or as a polymer with 2 or more monomers.

• “—ose” = a type of sugar.
  → Ex: glucose, ribose, lactose, amylose, etc.

• They are polar molecules → They CAN dissolve in water → They are hydrophilic (water-loving).

• Fats are non-polar molecules → They CANNOT dissolve in water → They hydrophobic (water-fearing).

Monosaccharide

• Sugars formed of a single monomer.

• Most biologically important have ring structures.

• Isomers: molecules with the same formula but different spatial arrangements (shapes)

  • Have different chemical properties because they have different functional groups.

  • Ex: Fructose tastes much sweeter than glucose even though they have the same chemical formula.

Disaccharides

• 2 monosaccharides bonded together:

  • sucrose = glucose + fructose

  • maltose = glucose + glucose

  • lactose = glucose + galactose

• Dehydration synthesis: a chemical reaction which results in a polymer being formed as a water molecule is removed.

Polysaccharides

• Many monosaccharide units.

• Starch: produced by plants, composed of 1000’s glucose bonded together.
  → Ex: G - G - G - G - G - G x 1000

• Glycogen: produced by animals cells to store glucose (function)

  • Stored in liver and muscle cells as reserve energy for blood sugar drops (homeostasis mechanism).

  • Has a more branched structure than starch, but all glucose are still “right side up”.

• Cellulose (aka fibre): a major component of plant cell walls

  • Chains of glucose but every 2^nd one is “upside down”

  • Humans are unable to break this type of bond so it passes through body undigested (“corn poo”)

  • Cellulose tends to form in layers to form “sheets” of cellulose due to H-bonding between layers.