3.1.2 Carbohydrates Flashcards

• Disaccharide


  formed when two monosaccharides join together by condensation reactions— A glycosidic bond forms between the 2 monosaccharides as a molecule of water is released

  
• Monosaccharides

  joined together by condensation reactions, forming a glycosidic bond and releasing a molecule of water
• The test sample and iodine dissolved in potassium iodide solution produce

  a browny-orange colourindicating no starch

  
• Dark, blue-black colour in the test sample indicates

  the presence of starch

  
• Sucrose


  is a disaccharide formed from a condensation reaction between : ●glucose ●fructose

  
• Lactose


  is a disaccharide formed from glucose + galactose

  
• Maltose


  is a disaccharide formed from alpha glucose + alpha glucose

  
• All carbohydrates contain the elements


  ●C ●H ●O
• Monosaccharides


  monomers that carbohydrates are made frome.g : ● Glucose● Fructose● Galactose
• Hexose Sugar


  a monosaccharide with six carbon atoms in each moleculee.g Glucose
• There are 2 types of glucose :

  ● alpha (a) ● beta (b) glucose — they’re isomers

  
• Isomers


  molecules with the same molecular formula as each other, but with the atoms connected in a different way e.g Alpha and Beta Glucose
• Glycogen and starch are formed

  by the condensation of a-glucose
• Cellulose


  formed by the condensation of b-glucose
• Polysaccharides


  are carbohydrates and are formed by the condensation of many glucose units

  
• Biochemical test for starch

  using iodine/ potassium iodide
• All sugars can be classified as

  reducing sugars or non-reducing sugars.
• Reducing sugars


  ● include all monosaccharides● some disaccharides e.g : maltose and lactose.
• Reducing sugars can be identified by

  ● heating a sample with Benedict’s reagent ● observing if a green, yellow, orange, or brick red precipitate forms
• The concentration of reducing sugar can be determined by

  comparing the colour change of the precipitate in different solutions
• To test for sugars

  ● the Benedict’s test is used● differs depending on the type of sugar being tested for

  
• A positive Benedict's test result


  indicated by a brick red colour

  
• A negative Benedict's test result

  indicated by a blue colour

  
• To test for non-reducing sugars

  e.g sucrose,1. sugars need to be broken down into monosaccharides by getting a new sample of the test solution,2. adding dilute hydrochloric acid, 3. heating it in a water bath that’s been brought to the boil
• Benedict's test for non-reducing sugars


  ● involves heating a sample with Benedict’s reagent● observing if a coloured precipitate forms
• Benedict's reagent is

  ● blue when no reducing sugar present● changes to green, yellow, orange, or brick red when there is
• A more accurate way of determining the concentration of reducing sugar is

  ● filter the solution● weigh the precipitateor ● to remove the precipitate ● use a colorimeter to measure the absorbance of the remaining Benedict’s reagent
• Uses of Starch

  ● Plants use starch as a way of storing excess glucose ● as it is too large to leave cells + insoluble ● Starch can be hydrolysed to release glucose for respiration
• Insoluble


  doesn’t dissolve in water— this also means it does not affect water potential
• Structure of Amylose

  ● long● unbranched chain of a-glucose ● with angles in the glycosidic bonds ● give it a coiled structure, making it compact for storage

  
• Amylose is good for storage as


  ● compact● can fit more into a small space

  
• Strucure of Amylopectin

  ● long● branched chain of a-glucose ( due to 1,6 glcosidic bonds )● with side branches that allow the enzymes that break down the molecule to get at the glycosidic bonds easily● means the glucose can be released quickly

  
• Animals store excess glucose as

  Glycogen
• Structure of Glycogen

  ● long● branched chain with lots of side branches (more than amylopectin)● glycosidic bonds are 1,6

  
• Properties of Glycogen

  ● Lots of branches — increase surface area for enzymes to hydrolyse glycosidic bonds allowing glucose to be released quickly● It is also a compact molecule so it is good for storage
• Uses of Glycogen

  ● Animals store excess glucose as glycogen in muscles and the liver● Glycogen is an energy store — can be hydrolysed to release glucose quickly when needed for respiration ● e.g during exercise​
• Structure of Cellulose


  ●major component of plant cell walls ●long ●unbranched straight chains of b-glucose ●1-4 glycosidic bonds

  
• Cellulose chains are linked together by hydrogen bonds to


  ●form strong fibres called microfibrils ●mean cellulose provides structural support for cells ●e.g. in plant cell walls

  
• Properties of Cellulose

  ●hydrogen bonds between the cellulose chains make the microfibrils very strong ●but still flexible ●allowing them to provide support
• Uses of Cellulose

  ●major structural component in the cell walls of plants ●it provides support ●allows cells to become turgid