Carbohydrates

• What is the formula of carbohydrates?(use _ for subscript)

  $C_x(H_20)_y$
• Monosaccharides are sweet tasting and soluble. They are used for energy and building blocks (polymers).
• What is the formula for monosaccharides?(use _ for subscript)

  $(CH_20)_n$ - n being any number from 3-7
• What are the three examples of monosaccharides?

  Glucose, galactose, fructose
• What is the mnemonic to remember the difference between alpha-glucose and beta-glucose?

  Alpha wears the Hat
• What do the lines in alpha-glucose and beta-glucose represent?

  Covalent bonds
• Isomers (+ example)

  Compounds with the same chemical formula but a different chemical structure e.g. alpha-glucose and beta-glucose
• A condensation reaction occurs between two monosaccharides to form a glycosidic bond and a disaccharide.
• What does a glycosidic bond look like?

  C-O-C

  
• What are the three types of disaccharides we need to know?

  Maltose = glucose + glucose

  Sucrose = glucose + fructose

  Lactose = glucose + galactose
• What type of glycosidic bond does alpha-glucose form?

  1,4 - between the 1st carbon and the 4th carbon
• How are polysaccharides formed?

  Via condensation reactions
• What are the three polysaccharides we need to know?

  Starch, glycogen and cellulose
• Where is starch found and what is it's function?

  In plant cells, and it is a store of glucose
• Starch is insoluble. This means it will not affect water potential, and consequently will prevent osmosis from occurring. Also, starch cannot diffuse out of cells because it is too large and insoluble.
• What are the two polysaccharides starch is made from?

  Amylose and amylopectin
• Amylose is an alpha-glucose with 1,4 glycosidic bonds. It has a spiral structure - this means it is compact. It is also unbranched.

  
• Amylopectin is an alpha-glucose with 1,4 and 1,6 glycosidic bonds. It also has a spiral structure but it is also branched. These branches speed up the release of glucose due to enzymes acting on the ends of the branches.
• How are hydrogen bonds formed in amylose? (only to help me understand)

  As the glucose chains in amylose curve into a coil, hydrogen bonds (shown in orange) hold them together like glue

  
• Where is glycogen found and what is its function?

  It is stored in the liver and it is our form of starch (store of glucose in animals). Only found in animal and bacteria cells.
• Starch is compact and forms grains whereas glycogen is compact and forms granules, which are stored in the liver and muscles.
• Glycogen is large and insoluble, meaning it can't diffuse out of cells and no osmosis will occur (as water potential is not affected)
• What does glycogen being highly branched mean?

  It speeds up the release of glucose which can be used in respiration in animals.
• Glycogen is made up of shorter (than starch) chains of alpha-glucose with 1,4 and 1,6 glycosidic bonds. It is more branched than starch.
• Where is cellulose found and what is its function?

  It is the main structural sugar in plants and is used (and found) in plant cell walls to provide support and rigidity.
• Cellulose is very strong, permeable to numerous substances and is the most common organic compound on Earth.
• Cellulose is made up of beta glucose with 1,4 glycosidic bonds.
• What keeps cellulose compact and strong?

  Straight and unbranched chains of cellulose are held together by hydrogen bonds. These bonds are usually weak, but when together as a collective, they're strong.
• Microfibril = several hundred cellulose chains

  Macrofibril = several hundred microfibrils.
• What is the flip-flop assemblage of beta-glucose molecules to make cellulose chains?

  Beta-glucose molecules that are adjacent (next) to one another are rotated by 180 degrees (flipped) and joined together.
• What are the two types of functions for carbohydrates?

  Energy storage (e.g. starch or glycogen) and structural (e.g. cellulose, chitin and peptidoglycan).
• Polymer

  A molecule made from a large number of monomers joined together
• Reducing sugars

  A sugar that can donate electrons to another chemical e.g. Benedict's reagent
• What are reducing sugars usually?

  All monosaccharides and SOME disaccharides
• Reduction

  Chemical reaction where electrons or hydrogen is gained
• Benedict's reagent

  An alkaline solution of copper (II) sulfate
• What is the test for reducing sugars?

  Add 2cm^3 of the food sample to be tested to a test tube. If the sample is not already in liquid form, first grind it up in water. Add an equal volume of Benedict's reagent to the test tube and heat the mixture in a gently boiling water bath (80 degrees Celsius) for 5 minutes. If a reducing sugar is present, an insoluble brick-red precipitate of copper (I) oxide will form.
• Benedict's test for reducing sugars is semi-quantitative, which means the different colours can be used to estimate the (approximate) amount of reducing sugars in a sample.
• What are non-reducing sugars usually and how do we detect them?

  Some disaccharides, e.g. sucrose. They must be hydrolysed into their monosaccharide components by hydrolysis to be detected.
• What are the steps in the test for non-reducing sugars?

  Heat the 2cm^3 liquid food sample with dilute hydrochloric acid. The dilute HCl will hydrolyse any disaccharides into monosaccharides. Add some sodium hydrogen carbonate solution to the solution to neutralise the HCl (this is because Benedict's doesn't work in acidic conditions). Check for pH with a suitable indicator e.g. litmus paper. Add equal volume of Benedict's reagent to the sample. Place the sample in a gently boiling water bath (80 degrees Celsius) for 5 minutes.