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. 2004(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
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)n
• Glucose (C6H12O6) 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
• MonosaccharidesMonosaccharides– (CH2O)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 differenteg. glucose, galactose (aldohexoses) and fructose (Ketohexose) all are C6H12O6 but are structurally different
MonosaccharidesKeto Aldo
Isomers (C6H12O6)
Galactose (C6H12O6)
HO H
Monosaccharides
D-glyceraldehyde L-glyceraldehyde
StereoisomerismStereoisomerism• 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– 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
O+
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
• Glycogen and Starch: composed entirely of glucose molecules in the αα configuration
((αα1→6)1→6)
((αα1→4)1→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
((ββ1→4)1→4)
NH
C=O
CH3
NH
C=O
CH3
NH
C=O
CH3
NH
C=O
CH3
((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
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
GlycerolUnsaturatedSaturated
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?