Carbohydrates- AS Biology any exam board

a quick over view of the important carbohhydrates that you need to know about - hope it helps



Structure -

  • very other molecule of Beta Glucose it is made up of it flipped so you have bonding at the top and on the next pair the bottem
  • it bonds through a condensation reaction which forms one molecule of water - the reverse of this reaction is a hydrolisis reaction where you add water to split up the glucose
  • when you make cellulose chains they can be cross linked becuase you will have some hydrogens with OHs facing them inbetween the 2 chains in this way you get hydrogen bonding ( just in the way water does) and this makes cellulose strong - this thicker 'rope' if you will is called microfibrils and when some of these join in the same way you get a cellulose fibre
  • because of the location of the CH2OH on the glucose swapping the weight is balanced on each side and this means that you get straight chains of cellulose
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cellulose- properties

  • Permeable - as is is part of cell walls in plant cells it needs to allow water in and out for osmosis as well as ions, it also stops a plant cell from bursting when it is turgid as the cellulose is strong
  • hydrogen bonding makes it strong and stabilises it as it has cross links in  - it is straight formation (C1- C4 bonding)
  • some animals can digest it but they need special enzymes( celluase) in their stomachs which humans do not have 
  • not easy to break down
  • resists stretching and compression 
  • has a high tensile and compressive strength
  • it is a polysaccharide
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Starch - structure

  • it can come in two forms and they are often mixed with each starch having a different combonation
  • amylose- this is when you form chains tha will then form in to spirals because of the attraction of the Hs and OHs( hydrogen bonds) which forms some curvature formed for C1 and C4 bonding
  • amylopectin - this is where you have straight chains but also branches in the starch from the bonding of C1 and C6 between the glucose molecules
  • starch is made from Alpha glucose
  •  it is a polysaccharide
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uses for starch

  • it is used for storage in plants- good compact size( see the way it bonds on the other card)
  • in is insouble which is good when it comes to storage in plants because it means that it will  not upset the osmotic balance of the plant very much if at all 
  • easy to break down into glucose for respiration and when more sugar is needed
  • stays in one place when it is stored 
  • starch is granular and is used in plants 
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  • is used for storage in humans in the liver and in the muscles and is easily broken down in to glucose for respiration thanks to the branch like structure of the molecule - if we are ever in short supply of sugar like starch does in plants
  • highly branched structure with C1- C4 as well as C1-C6 bonding in the chain that is formed from the C1-C4 bonding there is no glucose that does not have a branch off it 
  • it has similar properties to starch ( see past card)
  • it is made from alpha glucose and is a polysaccharide
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this is similar to cellulose it terms of its structural and chemical properties but is used to form exoskeletons on insects and is found in the cell walls of some fungis it is light strong and waterproof.

it is formed from polysaccharide and an amino acid to form a mucopolysaccharide

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  • Glucose( an energy store which is used for respiration) ,fructose( and energy store which is found in fruit) and galactose( found in milk) are the ones you need to know 
  • Glucose comes in alpha and beta forms they are structural isomers because they have the same formula C6 H12 O6 but the OH on the right hand side of beta glucose is above the H ( alpha glucose has the H on top)
  • they form Disaccharides by a condensation reaction of and OH and an H which forms one molecule of water and joins the 2 molecules together the opposite of this is a hydrolysis reaction where water is added so you get the 2 monosaccharides ( hydrolysis is how starch) and glycogen are broken down
  • all monosaccharides are reducing sugars and will go a brick red when Benedict's solution is added to it and the mixture is heated for a minute or so 
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  • examples- maltose( is 2 glucoses)( found in malt and beers) , lactose ( glucose and galactose) ( found in milk and sucrose ( glucose and fructose)
  • far fewer of these are reducing sugars and will cause Benedict's solution to say blue when they are mixed and heated however if you heat your test sample with HCl and once it has boiled add sodium bicarbonate ( a base) it will be neutralised and then add the benedicts it will turn yellow ans slowly change to red( polysaccharides give weaker results in colour
  • the formula for hexose disaccahrides is C12 H22 O11 like the 3 above They are structural isomers ( because there are 2 sugars and you have lost one molecule of water through them joining
  • Pentose sugars have the formula C5 H10 O5 ( singularly) for example ribose and deoxyribose which are found in DNA and RNA ( so the rhyme about girls being made of sugar and spice is almost right but boys are too )
  • triose have the formula C3 H6 O39s singularly for example glyceraldhyde
  • the general formula for carbohydrates is Cx( H2O)y where X and Y are the number of carbons in the carbohydrate 
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Chloe Thorn


i have a quiz up on this topic too if that helps as well or if you want to test your revision 

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