Macromolecules Macromolecules: large molecules make up cells or carry out the cellular vital processes (~26% of bacterial cell mass) – Structural or functional roles Macromolecules fall into 4 groups, – Carbohydrates – Lipids – Nucleic acids – Proteins Fig. 2-26, Alberts et al (K. Gilmour lecture series)

Dynamically synthesized and replenished Macromolecules 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 (CH 2 O) n Glucose (C 6 H 12 O 6 ) is especially important since it provides the principal source of cellular energy Ribose and deoxyribose are five carbon sugars that are found in RNA and DNA Carbohydrates

Monosaccharides Monosaccharides – (CH 2 O) n ; n = 3 to 7, with n = 5 (pentose) or 6 (hexose) most common – Aldose sugars (functional group is aldehyde - CHO) – Ketose sugars (ketone C=O as functional group) Isomers: same formula but structurally different eg. glucose, galactose (aldohexoses) and fructose (Ketohexose) all are C 6 H 12 O 6 but are structurally different Monosaccharides Keto Aldo Isomers (C 6 H 12 O 6 ) Galactose (C 6 H 12 O 6 )

HO H Monosaccharides D-glyceraldehyde L-glyceraldehyde Stereoisomerism Enantiomers: optical isomers, same folmula, same groups bonding with carbon skeleton, but groups on asymmetric carbon are mirror images of each other, eg in glyceraldehyde Enantiomers – D-form (Dexter=right) the –OH is facing to the right of backbone – L-form (Laevus=left) the –OH is facing to the left of backbone; D and L are mirror images and cannot be superimposed – D-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 pathway Monosaccharides: Trioses

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

α or β configurational isomers may form Different with respect to the position of –OH relative to plane of ring In α isomer -OH is below the plane In β the -OH is above the plane α or β isomers are important for polysaccharide formation Linear vs Ring

Formation of a glycosidic bond Dehydration reaction joins two simple sugars by glycosidic bond α 1→4 bond or β1→4 (C1 and C4) is common Main polysaccharide backbone α 1→6 (C1 and C6) causes branches in the chain O +H2O+H2O O +H2O+H2O Courtesy of K. Gilmour

Polysaccharides Some polysaccharides are short term energy storage molecules. – Plants store glucose as starch – Animals store glucose as Glycogen in liver Some have structural role – Cellulose in plants – Chitin in arthoropod exoskeleton

Polysaccharide: chemical composition α Glycogen and Starch: composed entirely of glucose molecules in the α configuration (α1→6) (α1→4)

Polysaccharide: chemical composition Cellulose is the most abundant polysaccharide; plant cell wall Unbranched glucose polymer with β1→4 glycosidic bond H-bonding between many parallel polymers forms strong fibers Chitin: polymer of N-acetylglucoseamine with β1→4 linkage; is a polysaccharide that forms the exoskeleton of crabs, lobsters, and insects (β1→4) NH C=O CH 3 NH C=O CH 3 NH C=O CH 3 NH C=O CH 3 () (β1→4)

Lipids Lipids: diverse group of macromolecules that are insoluble in water Include – Fats and oils are well-known lipids used for energy storage and other purposes – Phospholipids are components of the membranes that surround cells – Glycolipids 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 storage – Major components of cell membranes – Important in cell signaling: as steroid hormones and messenger molecules

Fats Fats 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 Glycerol UnsaturatedSaturated

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 weight Ester bond

Phospholipids Phospholipids: principal components of cell membranes Glycerol phospholipids: 2 fatty acids are bound to carbon in glycerol. The third carbon of glycerol is bound to a phosphate group Molecule is hydrophilic at phosphate end and hydrophobic at fatty acid tails This is called amphipathic property; important for formation of bilayer biological membranes

Phospholipids Other 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)

Glycolipids Many cell membranes also contain glycolipids and cholesterol Glycolipids are amphipathic Consist of 2 FA, serine instead of glycerol and one or more sugar instead of phosphate Also function as cell surface markers used for cell recognition

Cholestrol and steroids Cholesterol: amphipathic four ringed hydrocarbon – Abundant in eukaryotic membranes – Increases membrane fluidity Cholesterol 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?