L3 - carbohydrates

• Carbohydrates:

  -organic compounds made of carbon, hydrogen and oxygen

  -hydrate of carbon; hydrogen and oxygen are present in the same proportion as in water

  -an energy source (glucose)

  -an energy source (glycogen)

  -a structural support (cellulose)
• Carbohydrate monomers are called monosaccharide. Polymers are called polysaccharides. A pair of monomers is called a disaccharide
• In carbs, the basic monomer is sugar - otherwise know as a saccharide
• Monosaccharide are sweet tasting, soluble substances with the general formula Cn(H2O)n where ‘n’ can be any number between one and seven. Examples include glucose, galactose and fructose
• A triose sugar has three carbons, tetrose four, pentose five, hexose six, heptose seven
• Monosaccharides:

  -‘single sugars’

  -white crystalline solids

  -dissolve in water to form sweet tasting solutions
• Glucose isomers:

  -isomers are molecules with the same molecular formula as each other, but with atoms connected to each other in a different way

  -glucose has two isomers; alpha glucose and beta glucose
• Alpha glucose:

  
• Beta glucose:

  
• Glucose, galactose and fructose are all hexose sugars. This means they all have the same formula but they are structural isomers as they all have different atomic structures
• Disaccharides:

  -monosaccharide pairs (joined by condensation reaction, forming a glycosidic bond)

  -maltose (double glucose)

  -sucrose (glucose+fructose)

  -lactose (glucose+galactose)
• The glycosidic bonds of disaccharides form between carbons 1 to 4
• Maltose:

  -when two glucose molecules join they create maltose

  -formed in germinating seeds as an energy source
• Sucrose:

  -when glucose and fructose combine they form sucrose

  -known as cane sugar

  -plants transport carbohydrates in this form as an energy source
• Lactose:

  -when glucose and galactose combine they form lactose

  -energy source commonly found in milk and milk products
• Hydrolysis reactions:

  -polymers and disaccharides can be broken down into monomers by hydrolysis reaction (breaking the chemical bond using a water molecules)
• Starch:

  -a polymer of alpha glucose

  -insoluble due to its structure

  -therefore the main plant storage carbohydrate
• Starch molecules are made of two different types of chains:

  -a simpler linear polymer called amylose

  -a more complex branched form called amylopectin
• Amylose:

  -linear polysaccharide chain that is made up of glucose monomers joined by a (1,4) glycosidic linkage

  -makes up to 30% of the total starch molecule

  -all glucose monomers are in the same orientation, causing an overall bending/twisting effect in the shape of the molecule

  -helical structure is good for storage (compact)
• Amylopectin:

  -a highly branched polymer made up of glucose subunits

  -made up of linear chains of glucose units that are linked by a (1,4) glycosidic linkage with a number of side chains that branch the structure by a (1,6) glycosidic linkages

  -side chains stop it curling so much and creates a more messy branched look

  -makes up to 70% of the starch molecule

  -insoluble in water
• Glycogen:

  -an alpha glucose polysaccharide

  -referred to as “animal starch” as it’s the main storage molecule in animals

  -made up of many glucose molecules joined together by 1,4 and 1,6 glycosidic bonds

  -highly branched structure
• Glycogen:

  -typically stored in the liver

  -when energy is required, glycogen is broken down into glucose. glucose utilised by cells during cellular respiration in order to release energy

  -has a structure adapted for storage and fast breakdown

  -more branches than amylopectin and can therefore be easily broken down
• Cellulose:

  -a polymer of beta glucose

  -each alternate glucose monomer is rotated 180 degrees. this mean it forms a straight shape allowing for structural conformity

  -microfibrils are strong fibres that are made of many cellulose chains that are held together by hydrogen bonds

  -provides structural support in cell walls

  -insoluble

  -(1,4) glycosidic bonds