1.2,3,4 - Carbohydrates

• What’s a monosaccharide and 2 characteristics ?

  The monomers from which larger carbohydrates are made - they are sweet tasting and soluble
• Give 3 monosaccharides ?


  Glucose, Galactose, and Fructose
• What bond forms when a condensation reaction occurs between 2 monosaccharides ?


  Glycosidic bond
• What are disaccharides ?


  Formed when a pair of monosaccharides are bonded in a condensation reaction
• What‘s maltose made up of ?


  2 glucose molecules
• What’s lactose made up of ?


  Glucose and galactose molecule
• What’s sucrose made from ?


  Glucose and fructose molecules
• What are the 2 isomers of glucose ?


  Alpha glucose and beta glucose
• Is the hydrogen atom on alpha glucose higher or lower than the OH on the 1st carbon ?


  Higher (alpha on top and hydrogen is high)
• Test for reducing sugars ?

  • add Benedict’s reagent (in excess)
  • heat in a water bath for 5 mins
  • A coloured precipitate will form as copper oxide is formed (green to brick-red)
• What’s the bond created when monosaccharides join to form a disaccharide ?

  Glycosidic bond
• What are polysaccharides ?


  Polymers formed from the condensation of many monosaccharide molecules
• Why are polysaccharides suitable for storage ?


  The longer chains are insoluble
• How to test for non-reducing sugars ?

  • failed reducing sugars test
  • Add dilute HCl to sample and boil in a water bath
  • Neutralise with sodium hydrogen carbonate and test with an indicator to show it’s neutral, carry out Benedict’s as normal
• What’s the test for starch ?


  add 2cm3 to a test tube and add 2 drops of iodine solution and stir, blue-black colour indicates the presence of starch
• 3 important polysaccharides ?


  Starch, glycogen, cellulose
• What 2 glycosidic bonds can starch have ?


  1-4 and 1-6 glycosidic bonds
• What’s starch made of ?


  Chains of alpha-glucose monosaccharides linked by glycosidic bonds that are formed by condensation reactions
• What shape does starch form and how is it held together ?


  Forms coils held by hydrogen bonds
• Can starch be branched and unbranched ?


  Yes
• What’s the main role of starch ?


  Energy storage in plants
• Is starch insoluble ?


  Yes
• Why is it useful that starch is insoluble ?


  It doesn’t affect water potential so water isn’t drawn into the cells by osmosis
• Why’s it useful that starch is compact ?


  A lot of it can be stored in a small space
• Why’s it useful that starch can be branched ?


  Has many ends so each can be acted upon by enzymes simultaneously meaning glucose monomers can be released rapidly
• Why’s it useful that starch is large and insoluble ?


  Means it can’t diffuse out of cells
• Why is the hydrolysis of starch useful ?


  Forms alpha-glucose which is easily transported and used in respiration
• Is starch found in animal and plant cells ?


  No, only found in plant cells (glycogen is the animal equivalent)
• What cells are glycogen found in ?


  Animal and bacterial (never plants)
• 2 ways the structure of glycogen is different to starch ?


  Shorter chains and more highly branched
• What’s glycogen made up of ?


  Short chains of alpha-glucose monomers bonded together by glycosidic bonds formed in condensation reactions
• 3 structural characteristics glycogen has that are the same as starch ?


  Insoluble, doesn’t diffuse out of cells, compact
• Why is glycogen more highly branched than starch ?


  More rapidly broken down into alpha-glucose monomers which are used in respiration, important in animals which have a higher metabolic rate and respiratory rate than plants as they’re more active
• What’s cellulose made up of ?


  It’s made of beta-glucose molecules bonded together rather than alpha
• What type of bonds does cellulose form ?


  Only forms 1-4 glycosidic bonds
• How are the chains arranged in cellulose ?


  Straight chains that run parallel to each other
• What does the structure of cellulose allow to form ?


  Hydrogen bonds form cross links between chains
• How do the hydrogen bonds impact the strength of the cellulose structure ?


  The individual bonds don’t add strength but it’s the sheer number of them that strengthens the cellulose
• What’s formed when cellulose molecules are grouped together ?


  Microfibrils which are arranged in parallel groups called fibres
• What’s the role of cellulose in plants ?


  Major component of plant cell walls and provides rigidity to the plant cell