Biology - carbohydrates including cellulose

• Important uses of carbohydrates

  Source of energy, stores energy, adds strength and rigidity to cell wall
• What are carbohydrates made of?

  carbon, hydrogen, oxygen
• What are monosaccharides?

  simple sugars that are building blocks for more complex carbohydrates (glucose, fructose, galactose)
• What is the general formula for monosaccharides?


  (CH2O)n where n can be any number from 3 to 7
• What are fructose and galactose?

  hexose monosaccharides (6 carbons)
• What is glucose?


  hexose sugar
• What is the main source of energy in respiration?

  glucose
• What are the properties of glucose?

  Small so easily transported in and out of cells, soluble so easily transported around an organism and less reactive so must be catalysed by enzymes
• isomers of glucose

  alpha glucose and beta glucose
• How do the isomers of glucose differ?

  By the position of the hydroxyl (-OH) group
• What is ribose?

  Pentose (5 carbon) sugar found in RNA nucleotides
• Cellulose


  A substance (made of sugars) that is common in the cell walls of many organisms
• What do plants need to survive?

  Water and a cell wall made of cellulose in order to have a nice turgid, upright structure
• What are cellulose composed of?

  Beta glucose molecules bonded together with 1,4 glycosidic bonds
• How are 1,4 glycosidic bonds formed

  They are formed by the beta glucose molecules being inverted every other molecule by 180 degrees, so the chain keeps alternating every other molecule
• Cellulose chain inversions


  The inversions keep cellulose from coiling and resulting in a long,straight chain
• beta glucose

  OH on top, H on bottom - forms straight chain
• alpha glucose


  OH on bottom, H on top - forms a coiled chain as alpha glucose don't invert every other chain
• What happens when glucose bond together?

  They form a water molecule through a condensation reaction
• Amylose


  simplest form of starch - forms coiled chains made from alpha glucose
• Why are hydrogen bonds in cellulose important?

  For cellulose's overall integrity
• Why does hydrogen bonding occur in cellulose?

  The cellulose chains run parallel with other chains which leads to the hydroxyl (-OH) groups being in close proximity - hydrogen bonds form between the hydroxyl groups on opposite chains and water is produced
• Are hydrogen bonds weak or strong?

  They are weak but many of them are strong together - making cellulose overall strong which is what we need
• What forms fibres of cellulose?

  Cellulose chains which forms microfibril structures and many microfibrils make up a fibre called macrofibrils
• what do macrofibrils do?

  They wrap around plant cells in multiple layers at different angles - this is important because as the plant cell swells up with water it's going to need something strong around it to withstand it from bursting
• Is cellulose digestible?

  herbivores can digest cellulose, but most carnivores can't STARCH EASY DIGEST, CELLULOSE HARD DIGEST
• Why is cellulose not digestible?

  It is hard to break them down by hydrolysis - most animals lack the the cellulose enzyme needed to break the 1,4 glycosidic bonds
• Why is cellulose still important even though we can't digest them?

  Provides fibre needed to keep the digestive system healthy