Carbohydrates

• what is a monomer?

  single molecule (small basic molecular units)

  e.g. monosaccharides, amino acids, nucleotides
• What is a polymer?

  large complex molecules made of long chains of monomers joined together

  most carbs are polymers

  
• what atoms do carbs include ?

  1. carbon
  2. oxygen
  3. hydrogen
  4. (there is twice as many hydrogens atoms compared to oxygen (CnH2nOn))
• What are monosaccharides?

  single sugars
• What are examples of monosaccharides ?

  1. glucose
  2. fructose
  3. galactose (all have 6 carbons )
• What is a disaccharide?

  carb that contains 2 sugar molecules joined together in a condensation reaction by a glycosidic bond
• Whats examples of disaccharides?

  1. sucrose
  2. maltose
  3. lactose
• What's a polysaccharide?

  carb containing many sugar molecules joined together in a condensation reaction by glycosidic bonds
• Whats examples of polysaccharides?

  1. Starch
  2. glycogen
  3. Cellulose
• polar molecules have an ....

  uneven electron distribution
• nonpolar molecules have an.....

  even electron distribution
• what is polymerization?

  • monomers join together to form long polymer chains
  • each monomer is joined between a hydroxide (OH) on each monomer during a condensation reaction
• Whats a condensation reaction?


  When 2 molecules join together with the formation of a new chemical bond and H2O is released e.g. monosacharides -> disaccharides
• What is the condensation reaction between 2 monosaccharides?


  a glycosidic bond forms between 2 monosaccharides as a molecule of H2O is released -> a disaccharide is formed

  
• examples of disaccharides formed from condensation reactions (hint 3)

  1. Sucrose = alpha glucose + fructose
  2. Lactose = alpha glucose + galactose
  3. Maltose = alpha glucose + alpha glucose (1,4 glycosidic bonds)
• what is a hydrolysis reaction ?

  Polymers can be broken down into their monomers by a hydrolysis reaction -

  breaks down chemical bond between monomer using H2O molecule e.g. carbs can be broken down into monosaccharides

  
• What is a hexose sugar? (example)

  monosaccharide with 6 carbon atoms in each molecule

  e.g. glucose
• what are the 2 types of glucose ?

  1. alpha glucose
  2. beta glucose } isomers = variations of the same chemical compound
• What bond joins monosaccharides together ?

  Glycosidic bond - bond between 2 monosaccharides
• alpha glucose and beta glucose diagram :

  • in between atoms are covalent bonds

  
• What is the test for sugars ?

  Benedicts test
• Explain the Benedicts Test for reducing sugars (includes all monosaccharides and some disaccharides e.g. maltose and lactose) =

  1. Add Benedicts reagent (blue) to a sample and heat it in a water bath that has been brought to a boil
  2. If positive it will form a coloured precipitate
  3. Higher concentration of sugar ->further colour changes

  
• Explain the Benedicts test for non-reducing sugars

  1. if result of reducing sugar test is negative, test for non reducing e.g. sucrose (first you have to break them down into monosaccharides)
  2. get a new sample of solution
  3. Add dilute hydrochloric acids
  4. Heat in a water bath
  5. Neutralize with sodium hydrogen carbonate
  6. carry out the benedicts test
  7. coloured precipitate = contains non reducing sugar
  8. stays blue = doesn't contain ANY sugar
• how's a polysaccharide formed ?

  when more than two monosaccharides join together by condensation reactions

  
• Starch and glycogen are storage polysaccharides because they are:

  • Compact (so large quantities can be stored)
  • Insoluble - doesn't affect water potential - doesn't cause water to enter cells by osmosis - would make them swell and potentially burst
• What is Starch?

  plants store excess glucose as starch (polysaccharide of alpha glucose)
• What are the 2 polysaccharides of alpha glucose that make up starch ?

  1. amylose
  2. amylopectin
• What is amylose ?

  • long unbranched chain of alpha glucose
  • joined by 1,4 glycosidic bonds
  • bonds give it a coiled structure, making it compact ->good for storage

  
• What is amylopectin ?

  • long branched chain of alpha glucose
  • joined by 1,4 and 1,6 glycosidic bonds
  • Its many side branches allows the enzymes to access and break down the bonds easily/simultaneously, meaning the glucose can be released quickly (easily hydrolyzed)

  
• What's Glycogens function?

  what animals store excess glucose as (polysaccharide of alpha glucose)
• What is glycogens structure? (& how it relates to function)

  • similar structure to amylopectin but A LOT more side branches! (not coiled)
  • contains 1,4 & 1,6 glycosidic bonds
  • This means stored glucose can be released quickly as enzymes can act simultaneously on the branches (hydrolyzed quickly) - important for energy release in animals
  • Large but compact molecule - maximizing the amount off energy stored
  • Insoluble - wont affect the water potential of cells e.t.c.

  
• What are comparisons of starch (amylose &amylopectin) and Glycogen?

  =

  
• What is the test for Starch?

  • Iodine Test
  • add iodine dissolved in potassium iodide solution to the test sample
  • if starch is present the sample changes from browny-orange to a dark blue-black colour
• what is the structure of cellulose ?

  • composed of long unbranched polymer chains of beta glucose (polysaccharide) joined together by 1,4 glycosidic bonds
  • when beta glucose molecules bond they form straight cellulose chains
  • As β-glucose is an isomer of α-glucose to form the 1,4 glycosidic bonds consecutive β-glucose molecules must be rotated 180° to each other (inverted)
  • the cellulose chains are linked together by hydrogen bonds to form strong fibers called microfibrils

  
• Diagram of cellulose :

  =

  A) 1 cellulose molecule

  
• What is cellulose? (& its function)

  • major component of cell walls in plants
  • provides structural support for the cells (plant cell walls) - due to strong microfibrils
  • cellulose helps stop the cell wall from bursting under osmotic pressure - helps keep the cell turgid and rigid