Macromolecules Macromolecules: large molecules make up cells or carry out the cellular vital processes (~26% of bacterial cell mass) – Structural or functional.

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  • MacromoleculesMacromolecules: large molecules make up cells or carry out the cellular vital processes (~26% of bacterial cell mass) Structural or functional rolesMacromolecules fall into 4 groups, Carbohydrates Lipids Nucleic acids Proteins

    Fig. 2-26, Alberts et al. 2004(K. Gilmour lecture series)

  • Dynamically synthesized and replenishedMacromolecules are constructed by linking together similar or dissimilar subunits (monomers)Role in cell:Informational: order of monomeric units is not random and required for proper function ie. proteins and nucleic acids

    Structural/storage: a single repeating subunit or alternating subunits; order of subunits does not carry information e.g. polysaccharides (cellulose, starch, glycogen)


  • Macromolecules Recycling of mocromolecules is controlled enzymatically through biochemical pathways Are synthesized from monomers by dehydration reactions condensation of monomers by losing a water molecule) Degraded by hydrolysis reactions (addition of a water molecule)

  • Carbohydrates include simple sugars and polysaccharides.Monosaccharides (simple sugars) are the major nutrients of cells. The basic formula is (CH2O)nGlucose (C6H12O6) is especially important since it provides the principal source of cellular energyRibose and deoxyribose are five carbon sugars that are found in RNA and DNACarbohydrates

  • Monosaccharides(CH2O)n; n = 3 to 7, with n = 5 (pentose) or 6 (hexose) most commonAldose sugars (functional group is aldehyde -CHO)Ketose sugars (ketone C=O as functional group) Isomers: same formula but structurally differenteg. glucose, galactose (aldohexoses) and fructose (Ketohexose) all are C6H12O6 but are structurally differentMonosaccharidesKetoAldoIsomers (C6H12O6) Galactose (C6H12O6)

  • MonosaccharidesStereoisomerismEnantiomers: optical isomers, same folmula, same groups bonding with carbon skeleton, but groups on asymmetric carbon are mirror images of each other, eg in glyceraldehydeD-form (Dexter=right) the OH is facing to the right of backboneL-form (Laevus=left) the OH is facing to the left of backbone; D and L are mirror images and cannot be superimposedD-form is important for cells? Why?Click to see a 3D model

  • Glyceraldehyde and Dihydroxyacetone are the 3 carbon aldo- and keto-trioses that result from the breakdown of glucose in glycolytic pathwayMonosaccharides: Trioses

  • Linear vs Ring C5 and 6 carbone sugars exist in linear and ring formsPenultimate carbon and the C of aldehyde or Ketone

  • or configurational isomers may formDifferent with respect to the position of OH relative to plane of ringIn isomer -OH is below the planeIn the -OH is above the plane or isomers are important for polysaccharide formationLinear vs Ring

  • Formation of a glycosidic bondDehydration reaction joins two simple sugars by glycosidic bond 14 bond or 14 (C1 and C4) is commonMain polysaccharide backbone 16 (C1 and C6) causes branches in the chain

    Courtesy of K. Gilmour

  • PolysaccharidesSome polysaccharides are short term energy storage molecules.Plants store glucose as starchAnimals store glucose as Glycogen in liverSome have structural roleCellulose in plants Chitin in arthoropod exoskeleton

  • Polysaccharide: chemical compositionGlycogen and Starch: composed entirely of glucose molecules in the configuration


  • Polysaccharide: chemical composition Cellulose is the most abundant polysaccharide; plant cell wallUnbranched glucose polymer with 14 glycosidic bondH-bonding between many parallel polymers forms strong fibers

    Chitin: polymer of N-acetylglucoseamine with 14 linkage; is a polysaccharide that forms the exoskeleton of crabs, lobsters, and insects(14)

  • LipidsLipids: diverse group of macromolecules that are insoluble in waterIncludeFats and oils are well-known lipids used for energy storage and other purposesPhospholipids are components of the membranes that surround cellsGlycolipids consist of two hydrocarbon chains linked to polar head groups that contain carbohydrates Steroids, which have a different structure from most lipids, are used as hormones and for other purposes.

  • Lipids

    Lipids have three main roles:Energy storageMajor components of cell membranesImportant in cell signaling: as steroid hormones and messenger molecules

  • FatsFats and oils contain two subunits Glycerol is a polyalcohol with three polar OH groups Fatty acids long hydrocarbon chains (16 or 18 carbons) with a carboxyl group (COO) at one end


  • Triglycerides (Fats) TG: dehydration reaction adds fatty acids to the OH groups of glycerol and broken down by hydrolysis reactions

    insoluble in water; accumulate as fat droplets in the cytoplasm When required, break down for use in energy-yielding reactions produce twice as much energy as sugars per unit weightEster bond

  • PhospholipidsPhospholipids: principal components of cell membranesGlycerol phospholipids: 2 fatty acids are bound to carbon in glycerol. The third carbon of glycerol is bound to a phosphate groupMolecule is hydrophilic at phosphate end and hydrophobic at fatty acid tailsThis is called amphipathic property; important for formation of bilayer biological membranes

  • PhospholipidsOther polar groups is added to phosphate to make the molecule more polar, including,Ethanolamine (phosphatidyl ethanolamine)Choline (phosphatidyl choline)Serine (phosphatidyl serine)Inositol (phosphatidyl inositol)

  • GlycolipidsMany cell membranes also contain glycolipids and cholesterolGlycolipids are amphipathicConsist of 2 FA, serine instead of glycerol and one or more sugar instead of phosphateAlso function as cell surface markers used for cell recognition

  • Cholestrol and steroids Cholesterol: amphipathic four ringed hydrocarbonAbundant in eukaryotic membranesIncreases membrane fluidityCholesterol derivatives estrogens and testosterone Steroid hormonal messengers

  • Can you meet these objectives?Distinguish among monomers, polymers and macromolecules?Discuss the structure and function of carbohydrates?Briefly describe the types of lipids, and outline the basic structure and function of each?

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