Lecture 4 Carbs+Lipids Flashcards
Carbs + lipids
Major sources of energy
Stored in the body in the form of energy reserves - glycogen and triglycerides (fat)
May be bound to proteins and have important structural and regulatory functions
Lipids
Small hydrophobic or amphiphilic molecules. Form structures like vesicles/liposomes, micelles or membranes in aqueous environments. Insoluble in water, soluble in organic solvents.
Carbohydrates
Simple sugars (lactose- milk, sucrose-table sugar). Hydrophilic. Complex and simple.
Complex sugars
Polymers (starch or cellulose). Form insoluble colloidal dispersions in water or are completely insoluble.
Polyhydroxy aldehydes or ketones
Simplest 3 carbon sugars. Trioses with with two hydroxyl groups. Glyceraldehyde = aldose (aldehyde group at one end (glucose))
Dihydroxyacetone = ketose (keto group usually at C-2 (fructose))
Reducing vs. non-reducing carbos
Reducing: free aldehyde or ketone group (must first tautomerize to aldose)
Non-reducing: cannot be easily oxidized, less reactive (e.g., sucrose)
Carb classification
Mono, oligo, polysaccharides
Monosaccharides
Trioses, tetroses, pentoses, hexoses (single simple sugars). Most are straight chain.
Oligosaccharides
Di, tri, tetra, penta up to 9 or 10 multiple sugars. Most important are disaccharides - sucrose, lactose
Sucrose
Glucose and fructose
Lactose
Galactose and glucose
Polysaccharides/glycans
Homopoly (homoglycans) - simple sugar, hetero (heteroglycans), complex carbs.
Human tissue carbs
Ribose (pentose in RNA and 2 deoxyribose (DNA)
Gluconic acid (oxidation of C-6)
Gluconic acid (oxidation at C-1)
Glucosamine (amino sugar - building block for varying molecules)
N-acetylgulucosamine (acetylated amino sugar). Present in oligosaccharides in gram - bacteria.
Glucose-6-phosphate (intermediate in glucose metabolism)
Sorbitol (reducing glucose - polyol)
Carb functions
Most abundant compound (cellulose in plant walls)
Serve as biosynth intermediates
They are the base structure for glycosides (sugar bound to something else), vitamins, antibiotics, etc.
Structural tissue in plants and microorgs (cellulose, lignin)
Participate in biological transport - cell-cell recognition - activationo fgrowth factors- modulation of the immune system.
Chirality
Numbering of carbons begins from end w/functional group (aldehyde or ketone). D or L assignment based on configuration around highest numbered assymetric enter (farthest from aldehyde or keto).
D and L
mirror images of each other - enantiomers. Other stereoisomers have unique names.
Stereoisomer number
2^n (n = number of asymetric centers).
Confirmation of sugars
Nearly all D. Out of eight D-aldohexases, only 3 are found in significant amounts in the body 1. glucose, 2. mannose, 3. galactose. Only the D-ketohexose fructose is present significantly.
Chiral variation properties
Physical: Crystalline form, solubility, rotational power
Chemical: Reactions (oxidations, reductions, condensations) - form larger macromolecules
Physiological: Nutritive value (human, bacterial), sweetness, absorption.
Hemiacetal
Alcohol with aldehyde
Hemiketal
Alcohol with ketone
Tautomerization
D-glucose can cyclize to form pyranose or furanose.
Cyclization
new asymmetric center at C1. Two stereoisomers (anomers - alpha and beta). Anomeric C1: alpha (OH below ring), Beta (OH above ring).
Glucose
Exists largely in nonreactive inert cyclic hemiacetal. Can be easily oxidized otherwise. Of all D-sugars, D-glucose exists to greatest extent, least oxidizable and least reactive.
The relative chemical inertness of glucose is the reason for its evolutionary selection as blood sugar.
Haworth
Cyclic representations. Ratio for glucose shifts as a function of temp, pH, salt, concentration.
Chair
Stereochemical forms of alpha and beta forms of glucopyranose. To minimize sterics, best structure has hydroxyl groups in equatorial position.
Glycosidic bonds
Carbs couple to one another by glycosideic bonds to form disaccharides, tri, oligo, poly. Anomeric hydroxyl and a hydroxyl of another sugar covalently bind, liberating H20.
Glycosidic bond anomeric linkage diff.
Define differences in biochemistry and nutrition, solubility, structure. EX: Amylose is an alpha 1-4 linked linear glucan (D-glucose). Similar structure: cellulose is beta 1-4 linkage.
Cellulose
Fibrous, not soluble in H20, not digestible.
Starch (amylose)
Pasty, soluble, digestible.
Sucrose
Sucrose - glucose and fructose, from sugar cane or beet. Maltose - partial hydrolysis due to amylase (saliva and pancreas). Used in fermentations and as a sweetener
Maltose
Maltose - partial hydrolysis due to amylase (saliva and pancreas). Used in fermentations and as a sweetener
Lactose
Glucose and galactose, extracted from whey.
Homoglycans and heteroglycans (polysaccharides) characteristics
POlymers (MW from 200000), white and amorphous (glassy), not sweet, non reducing, form colloidal solutions/suspensions.
Starch
Most common storage polysaccharide in plants. Glucose storage in polymeric form minimizes osmotic effects. Alpha amylose (10-30%) and amylopectin (70-90%). Starch is mainly this.
Starch and iodine
Stain blue. Amylose adopts a helical formation in water, iodine goes in helix.
Cellulose
beta 1-4 linked D-glucose units. Most abundant carb. Plant cell wall strength+rigidity, prevents osmotic swelling, wood is 50% cellulose. Does not react with iodine, held together with lignin in woody plants.
Glycogen
Animal equivalent of starch, in muscle and liver cells as granules. Glycogen + iodine = red-violet color. Hydrolyzed by amylases and glycogen phosphorlyase. Has more alpha 1-6 branches than starch. Permits rapid glucose release during exercise.
Chitin
2nd most abundant carb. Present in cell wall of fungi, crustacean/insect exoskeleton. Used in coatings, pharmaceuticals, medical products.
Dextrans
Transglucosidase products of glucose. Used in treatment of shock, used in gel filtration chromatography of proteins, components of dental plaques.
Pectins
Heteropolysaccharides, found in the pulp of fruits. Used as a gelling agent.
Gums
Widely used in food as suspending agents, gelling agents, thickening, emulsifiers, foam stabilizers, crystallization inhibitors, adhesives, binding agents.
Amino sugars
Amino substitutes for hydroxyl (may be acetylated). N-acetylglucosamine - common o-linked glycosylation of protein serine or threonine residues. Important for folding or binding events.
N-acetylneuraminic acid
Terminal residue of oligosaccharide chains of glycoproteins. Gives negative charge.
Peptidoglycan
Bacterial cell walls, polypeptide linked to polysaccharide. Different cross links and thickness on bacterial walls. Gram - and Gram +. May have teichoic acids phosphate or ribitol covalently linked.
Hyaluronate
Polysaccharide - glycosaminoglycan- repeating disaccharide of glucuronic acid and N-acetyl glucosamine. beta 1-3 and beta 1-4 glycosidic linkages. Widely throughout connective epithelial and neural tissues and component of bacterial capsules where it plays a role in virulance.
Glycosylated proteins
Usually post-translational, enzyme directed within rough ER. Proteins can contain either O-linked oligosaccharides (serine, threonine) or N-linked oligosaccharides. Required for proper folding. Confer stability. Can also be important in cell-cell adhesion.
Glycolipids
Cerebrosides, sulfatides, globosides, gangliosides.
Cerebrosides
One sugar molecule
Galactocerebroside – in neuronal membranes
Glucocerebrosides – elsewhere in the body
Sulfatides- sulfogalactocerebrosides
A sulfuric acid ester of galactocerebroside
Globosides - ceramide oligosaccharides
Lactosylceramide 2 sugars (e.g., lactose)
Gangliosides
Have a more complex oligosaccharide attached
Biological functions: cell-cell recognition; receptors for hormones
Lipopolysaccharides
Bacterial endotoxin. Core oligosaccharide Bacterial internalization, initiation of immune resistance Long O-antigen side chains Responsible for resistance to human serum, antibiotics, detergents Adhesin – Lipid A Interacts with host TLR4 to initiate inflammatory response Fever, hypotension, Gram-negative sepsis
Dental plaque
mass of bacteria and sugar polymers that shield the tooth from saliva and tongue, facilitating enamel decay. All forms of sugar can cause decay. Fermentable carbs as well as milks fruits and juices are carious. Artificial sugars are not cariogenic. Xylitol is cariostatic (sugar alcohol).
Viridans streptococci
Surface proteins bind salivary glycoproteins on teeth (pellicle)
Thrive on sucrose sticky glucan polymers
Amounts to 50% or more of bacteria in plaque
Ferment sugar to lactic acid (demineralizes enamel)
And they remain metabolically active at low pH
Sugar substitutes
Sucralose Chlorinated sucrose Aspartame Methyl ester of aspartic acid and phenylalanine Saccharine Sorbitol (sugar alcohol): natural; gums; candies Steviol Extracts of stevia leaf
