Carbs

• Monosaccharides:

  • aldehydes or ketones with two or more hydroxyl groups (aldoses or ketoses)
  • Simplest monosaccharides have 3 carbons (trioses)
• Epimers: differ at only one of many asymmetric carbons (ex. D-glucose and D-mannose)
• Anomers: differ at a new asymmetric carbon formed on a ring closure
• Are axial or equatorial positions more favourable in rings?

  Axial substituents can sterically hinder each other if they are on the same side of the ring. Equatorial substituents tend to be more spread out.
• How does a hemiacetal form?

  Aldehyde and alcohol groups react with each other.

  
• How does a hemiketal form?

  Alcohol and ketone group reacts with each other.

  
• How is a glycosidic bond formed?

  It is a bond formed between the anomeric carbon of a monosaccharide and an alcohol (-OH)

  
• What types of sugars are reducing sugars?

  Sugars that can react with oxidizing agents because of their free aldehyde or ketone.
• Glycogen- storage of glucose

  • Polysaccharide
  • Homopolymer made solely of glucose units
  • Mostly α 1,4 glycosidic bonds but branches are formed by α 1,6 glycosidic bonds (⁓ every 10 glucose units)
• Starch- Storage of glucose

  • Homopolymer of glucose units
  • nutritional reservoir in plants
  • Two types of starch:

  1. Amylose- linear and only α-1,4 glycosidic bonds
  2. Amylopectin- branched. Has one α-1,6-glycosidic bond per 30 α-1,4-glycosidic bonds
• what are amylopectin, amylose, and glycogen all rapidly hydrolyzed by?

  α-amylase cleaves α-1,4-glycosidic bonds between glucose
• Cellulose: structural component in cell wall.

  • Linear
  • β-1,4-glycosidic bonds (thus cannot be digested by α-amylase)
• What is O-linked glycosylation?

  Carbs attached to the side chain hydroxyl oxygen of serine or threonine residues
• What is N-linked glycosylation?

  Carbs attached to the side chain amide nitrogen of asparagine
• How are carb attached to proteins (to make glycoproteins)?

  A glycosidic bond forms between the anomeric carbon and the side chain hydroxyl oxygen or amide nitrogen

  • This is process can be catalyzed by glycotransferases
• N-linked oligosaccharides can act as important chemical tags on proteins
• What features of carbs make them information rich molecules?


  • They vary in the identity and number of monosaccharides joined together
  • Different types of linkages (ex. α vs β)
  • O-linked glycosylation vs N-linked glycosylation
• How does glycosylation change the properties of a protein?

  Increases the amount of chemical information and functionality of the protein
• Classes of glycoproteins: Glycoproteins

  • have diverse roles
  • More protein than carb by weight
• Classes of glycoprotein: Proteoglycan

  • Structural and lubrication roles
  • Protein attaches to glycosaminoglycans
  • More carbs than protein by weight
• Classes of glycoproteins: mucins

  • Lubricants/barrier roles
  • Have VNTR (variable tandem repeats)
  • More carbs than protein by weight
• What are glycosaminoglycans?

  Polymers of repeating disaccharides with negatively charged carbohydrate or sulfate

  • binds to water due to being heavily charged
• What are lectins?

  Proteins that recognize and bind specific carbohydrates through non-covalent interactions

  • promote interactions by having at least two carbohydrate binding sites
• What are selectins?

  Class of lectins. They help recruit immune system cells to injured cells
• What type of reaction is used to put monosaccharides together to make polysaccharides?

  A dehydration reaction in which water molecules are removed from the monosaccharides.
• An aldopentose has 5 carbons and an aldehyde group on carbon number 1
• What atoms in aldohexoses are involved in the formation of a furanose ring structure?

  C1 and C4.
• Why is the β anomer more favoured in sugars?

  Because the the hydroxyl in the equatorial position which has less sterically hinderance than in the axial position of α anomers
• what does the fact that all organisms contain lectin suggest about the role of carbohydrates? (besides the fact that they are important)

  suggests that carbs are on the cell surface of all organisms to be able to be recognized readily by lectins.