Week 10 carbohydrates

• General info on carbs:

  • formula of monosaccharides = C6H12O6
  • simple carbs (sugars) and complex carbs
  • functions include
  • energy source and storage (glucose and starch)
  • structural component of cell walls (cellulose)
  • extracellular matrix (glycosamioglycans)
  • information carrier
  • can covalently link to proteins and lipids
• Monosaccharides:

  • simplest carbohydrates
  • contain between 3 and 7 carbons
  • 3C = triose
  • 4C = tetrose
  • 5C = pentose
  • 6C = hexose
  • 7C = heptose
  • contain carbonyl group
  • each carbon bound to a hydroxyl group
• Carbonyl group:

  A) aldehyde

  B) ketone

  
• Hydroxyl group:

  • contains an OH group

  
• Isomeric forms of monosaccharides:

  • isomers have the same molecular formula but differernt structures
  • constitutional isomers differ in the order of attachement of atoms
  • example being glyceraldehyde

  
• Stereoisomers:

  • atoms connected in the same order by differ in spatial arrangement
  • enantiomers = stereoisomers that are non-superimposable mirror images
  • diastereomers = stereoisomers that are not mirror images
• chiral carbon = carbon atom that has 4 different groups bonded to it
• Enantiomers of glyceraldehyde and dihydroxyacetone:

  • glyceraldehyde has enantiomers as it has a chiral carbon
  • dohydroxyacetone has no enantiomers as it has no chiral carbon

  
• Fischer projection:

  • 2 dimentional
  • horizontal bonds pointing towards you and vertical bonds pointing away from you
  • hydroxyl on left = L form
  • hydroxyl on right = D form
  • most sugars occur in the D form

  
• Diastereomers:

  • they are stereoisomers that aren't mirror images
  • they have different physical properties
  • example of water solubility with threose and erythrose
  • chiral carbon most distant from the carbonyldetermines if the sugar is in the L or D form

  
• Epimers:

  • they are 2 sugars that differ only in the configuration around one carbon atom

  
• 3C and 4C aldoses:
• 3C and 4C aldoses:

  
• 5C aldoses:

  
• 6C aldoses:

  
• 3C and 4C ketoses:

  
• 5C and 6C ketoses

  
• Cyclisation of glucose:

  • molecules form rings
  • pentoses and hexoses readily undergo intramolecular cyclisation
  • pink O bonds to the carbonyl carbon forming a ring
  • form 2 rings (alpha and beta like glucose rings)

  
• Pyranoses:

  • it is a 6 membered oxygen containing ring
  • can have 2 different forms
  • alpha form - means hydroxyl group is below the ring
  • beta form - means hydroxyl group is above the ring
  • formation of a cyclic molecule creates another diastereomeric form called an anomer

  
• Glucose conformations part 1:

  A) boat

  B) chair

  
• cyclisation of fructose:

  • it is a ketose thus the carbonyl group is in the middle not at the top
  • have slightly different structure
  • 5 membered ring

  
• Furanoses:

  • 5 membered oxygen containing ring

  
• Monosaccharide isomer:

  A) isomers

  B) stereoisomer

  C) enantiomer

  D) anomers

  E) epimers

  
• Glycosidic bonds:

  • form by monosaccharides attaching together
  • N-glycosidic bond = bond formed between the anomeric carbon atom an dthe nitrogen atom of an amino group
  • O-glycosidic bond = bond formed between anomeric carbon and the oxygen of a hydroxyl group

  A) N

  
• Disaccharides:

  • contain 2 monosaccharides linked by O-glycosidic bonds
  • common disaccharides include maltose, sucrose and lactose

  A) maltose

  B) lactose

  C) sucrose

  
• Simple and complex carbohydrates:

  • monosaccharides = simplest carbs
  • disaccharides = two monosaccharides
  • Oligosaccharides = few monosaccharides
  • polysaccharides = long chains of monosaccharides
• Polysaccharides:

  • unlike proteins and DNA, they don't have a defined molecular weight
  • important polysaccharides include
  • starch
  • glycogen
  • glycosaminoglycans
  • cellulose

  A) unbranched

  B) branched

  C) branched

  D) unbranched

  
• Starch:

  • is the main polysaccharide in plants
  • it is a mixture of two polysaccharides of glucose
  • amylose
  • is an unbranched polysaccharide of alpha-1,4-linked glucose residues
  • amylopectin
  • branched polysaccharide of glucose
  • glucose monomers form alpha-1,4-linked chains

  
• Glycogen:

  • main storage polysaccharide in humans and animals
  • present in all cells (most prevalent in skeletal muscle and liver)
  • it is a branched polysaccharide of glucose
  • glucose monomers form alpha-1,4- linked chains
  • Branch-points with alpha-1,6 linkers occur every 10 residues
  • glycogen molecules often form granules in cells

  
• Cellulose:

  • primary stuctural component in plant cell walls
  • one of the most abundant organic molecules on earth
  • it is a linear polysaccharide of glucose (beta-1,4 bonds)
  • humans and most animals can't digest cellulose
  • it is an important component of human diet (dietary fibre)
  • form hydrogen bonds between adjacent glucose monomers and also between chains

  
• Glycosaminoglycans (GAGs):

  • linear polysaccharide of repeating disaccharide units
  • one monosaccharide is always either acetylglucoseamine ot acetylgalactosamine
  • other monosaccharide is an acid in most cases
  • some GAGs contain sulfate groups
  • they are important components of of the extracellular matrix (cartilage, bone, cornea, tendons, ligaments, etc)

  
• Glycoconjugates:

  • carbs can be covalently joined to lipids and proteins
  • glycolipids
  • glycoproteins
  • glycoproteins (contains carbs and proteins)
  • proteoglycans
• Proteoglycans:

  • consist of a core proteins with one more GAG covalently attached
  • many are secreted into the extracellular matrix
  • some are membrane proteins
  • main components of the extracellular matrix
  • collagen
  • GAGs
  • Proteoglycans
• Glycoproteins:

  • contain one or more oligosaccharide chain (s)
  • some are present in the cytoplasm and the nucleus
  • most are either secreted or can be found on the outer face of the plasma membrane
  • protein glycosylation
  • takes place in the lumen of the endoplasmic reticulum and the golgi complex

  
• O-linked oligosaccharides

  • carbs can be attached to the oxygen atom of serine or threonine
  • or even the nitroge atom of asparagine

  
• N-linked oligosaccharides:

  • carbs can be attached to the oxygen atom of serine or threonine
  • or even the nitroge atom of asparagine

  
• The sugar code:

  • oligosaccharide chains are complex and diverse
  • different monosaccharides
  • branched and unbranched chains
  • alpha and beta bonds
  • linkages include (1-2), (1-3), (1-4), (1-6), (2-3), and (2-6)
  • some proteins can bind carbs with high specificity
  • carbs are important for protein-proteins or cell-cell communication

  
• Cell-cell communication (example/abstract)

  • a leukocyte in a capillary is slowed down through the interaction between a glycoproteins of the leukocyte plasma membrane and the carb-binding protein P-selectin in the plasma membrane of endothelial cells
  • Near the site of an inflammation the leukocyte stops because of the interaction between a glycoprotein of an endothelial cell and a carbohydrate-binding protein (integrin) of the leukocyte → the leukocyte moves through the capillary wall towards the site of the inflammation

  
• Viral receptors (example/abstract):

  • The influenza virus surface protein Hemagglutinin binds to a specific oligosaccharide chain of a plasma membrane protein → endocytosis → virus replication