module 7 Flashcards
what do the physiological roles of carbohydrates include?
-sources of energy
-energy storage
-structural roles
-cellular interaction
-cellular identification
-information transfer (DNA and RNA)
-signaling
what are carbohydrates?
-hydrates of carbon
-have empirical formula of (CH2O)n where n > or = 3 (usually 3-6)
-for each carbon, there is a water molecule
what are the two major classes of carbohydrates?
-aldoses (which have aldehyde groups)
-ketoses (which have ketone group)
what do most monosaccharides have multiple of?
-asymmetric carbons
what determines whether a sugar is D or L?
-the designation of a sugar as either D or L is based on the configuration of the chiral carbon most distant from the carbonyl oxygen
-the designation of D or L is relative to the reference molecule D-glyceraldehyde
how do you determine how many stereoisomers a sugar as?
-molecules with n chiral centers will have 2^n stereoisomers
-ex: 4 chiral center= 16 stereoisomers
3 chiral centers=8 stereoisomers
what are the categories of isomers within carbohydrates?
what are epimers?
-are sugars that differ at a single chiral center
in solution, longer carbohydrates (5 carbons and up)tend to be _________
CYCLIZED
formation of cyclized structures is the reaction of ______________?
formation of these cyclized structures is the result of a reaction of an internal alcohol (hydroxyl group) with either:
cyclized carbohydrates can be found in two ring forms:
what is the cyclization of glucose to glucopyranose? what is an anomeric carbon?
-cyclization of glucose involves the C5 hydroxyl and the C1 aldehyde
-cyclization renders C1 chiral, producing two stereoisomers, a and b
-the carbon that becomes chiral as a result of cyclization is the anomeric carbon
-the a and b forms are anomers of each other
what are a and b configurations?
cyclization produces a new chiral carbon at the anomeric carbon, resulting in two new stereoisomers
-a- hydroxyl of anomeric carbon is below the plane of the sugar
-b- hydroxyl of anomeric carbon is above the plane of the sugar
what is mutarotation? what is glucoses?
-in solution, the a and b configurations interconvert by a process called mutarotation
-occurs through a linear intermediate
-represents a change in configuration (break bonds)
-in solution, glucose tends to be 2/3 b glucopyranose, 1/3 a-glucopyranose and less than 1% linear
what is the cyclization of D-fructose to fructofuranose?
-cyclization of fructose involves the C5 hydroxyl and C2 ketone
-cyclization renders C2 chiral (anomeric carbon), producing a and b stereoisomers
what is the conversion of fructofuranose and fructopyranose?
-fructose exists in both pyran and furan rings
-b-fructopyranose, found in honey, is extremely sweet
-heating b-fructopyranose promotes its conversion to b-fructofuranose (which is less sweet)
-corn syrup, with high concentration of b-fructopyranose, is used to sweeten cold, but not hot drinks
what is the general about sugar derivatives?
-carbohydrates derivatives break from the empirical formula of (CH2O)n
-these derivatives can include nitrogen, phosphate, sulfur groups
-these modifications usually indicate specialized functions
what is myrosinase?
-some plants contain glucosinolate and the enzyme myrosinase
-myrosinase acts on glucosinolate to produce glucose and isothiocyanate (which has a sharp, bitter taste)
-myrosinase and glucosinolate are stored separately, but come together upon tissue damage (like being eaten)
-the bitter taste functions to discoourage herbivors from eating the plant
what are reducing agents of monosaccharides?
-linear forms of monosaccharides can be oxidized by mild oxidizing agents like iron and copper
-the carbonyl group is oxidized to a carboxyl group
-allows for quantifications of sugars present in blood and urine
-also defines the end of the sugar with the carboxyl carbon as being the reducing end
what is a glycosidic bond?
primary structural linkage in all polymers of monosaccharides (disaccharides)
-O-glycosidic bonds occur through oxygen
-N-glycosidic bonds occur through nitrogen
what is the nomenclature of a disaccharide specify?
-the monosaccharides involved in the disaccharide
-their ring types (puran, furan)
-their configurations (alpha or beta)
-their linkage (C1-C4)
what is the reducing end?
-the end of the chain with a anomeric carbon is called the reducing end of the polymer
what do monosaccharides have multiple of?
-monosaccharides have multiple hydroxyl groups mean that there are many different glycosidic linkages are possible
-three monosaccharides (glucose, galactose, mannose) can generate 12,000 different structures
how are higher order carbohydrate structures generated?
-higher order carbohydrate structures are generated through the action of glycotransferases
-glycotransferases use monosaccharides that are activated through linkage with UDP
what is the nomenclature of disaccharides?
- specify the configuration (alpha or beta) at the anomeric carbon of each monosaccharide
- specify the ring form (pyran or furan) of each monosaccharide
- the non-reducing sugar has the suffix “osyl”
- the reducing sugar has the suffix “ose”
- Indicate in parentheses the two carbon atom joined by the glycosidic bond with an arrow
what is lactose?
-disaccharide
what is lactose intolerance?
-individuals who have insufficient levels of enzyme (lactase) that catalyzes the hydrolysis of lactose into glucose and galactose
-consumption of lactose by them can led to bloating, cramps, flatulence, diarrhea and nausea
-most mammals cease to produce lactase after weaning but some human populations have developed lactase persistence
what are the biologicals functions of polysaccharides?
-energy storage
-structural
-specialized structural
-very diverse and complex
what are homo and heteropolysaccharides?
-homo: are polymers containing a single type of monosaccharide
-hetero: are polymers containing more than one type of monosaccharide
-both can either be unbranched or branched
what are the energy storage polysaccharides?
-glucose is stored intracellularly in polymeric forms in both plants (starch) and animals (glycogen)
starch:
-a mixture of two molecules, amylose (unbranched) and amylopectin (branched)
-found in plants and fungi
glucose:
-stored in liver and skeletal muscle of animals
what is amylose?
-a linear polymer of glucose residues through a(1-4) bonds
what is amylopectin?
-consists of a(1-4) linked glucose residues with a 1(1-6) branch every 24-30 residues
do amylose and amylopectin both have reducing and non-reducing ends?
-both have a single reducing end
-amylose has a single non-reducing end
-amylopectin has multiple non-reducing ends
is glycogen present in all cells in animals?
-present in all cells, but most prevalent in skeletal muscle and liver
how does the structure of glycogen differ from amylopectin?
-structurally identical to amylopectin
-consists of a(1-4) linked glucose residues with a(1-6) branch points but with a higher frequency of branch points (every 10 residues)
why is glycogen more branched?
-mobilized in times of need by glycogen phosphorylase which sequential cleaves glucose residues from non-reducing ends
-greater frequency of branching allows for rapid mobilization
what are the structural polysaccharides?
-cellulose: the primary component of plant cell walls (fiber), accounts for over half of the carbon in the biosphere
-chitin: the principal component of hard exoskeletons (insects, lobsters, etc)
what is the structure of cellulose?
-a linear, homopolysaccharide of glucose residues
-linear arrangement of b(1-4) glycosidic residues (these bonds cannot be cut my amylase)
what is the structure of chitin?
-a linear, homopolysaccharide of N-acetylglucosamine residues
what is the chemical difference between chitin and cellulose?
-the replacement of hydroxyl group C2 with acetylated amino group
what are a(1-4) linkages of starch and glycogen?
-form a hollow, helical structure
-this provides a compact, accessible storage structure of glucose
what are b(1-4) linkages of chitin and cellulose?
-allow formation of long straight chains
-fibrils are formed by parallel chains that are linked through hydrogen bonds
-these fibers generate a rigid supportive structure of high tensile strength
Sugar can also be _____________________ to form glycolipids?
covalently linked to a lipid molecule
what is a central function of glycolipids?
-the blood group antigens
-different patterns of sugars presented on the surface of cells by the glycolipids help the body to discriminate self from non-self
-differences in blood group antigens is critical for blood transfusions
what are glycoproteins?
-proteins with covalently attached sugars
-the protein constituent is the largest component by weight
-serve a variety of biological roles
what are proteoglycans?
-protein component is linked to a particular type of carbohydrate called a glycosaminoglycan
-the carbohydrate constituent is the largest component by weight
-often serve structural and lubricating functions
how are glycoproteins created?
-proteins undergo post-translational glycosylation (addition of sugar groups)
-about half of biological proteins are modified with sugar groups
-these modifications regulate the structure and function of the protein
-these modifications often involve complex, specific patterns of sugar attachment
what are sugars attached to in glycoproteins?
-the amide nitrogen of the side chain of an asparagine (N-linked)
-the hydroxyl oxygen of the side chain of serine or threonine (O-linked)
what is an example of a glycoprotein?
Erythropoietin (EPO)
-stimulates red blood cell production
-has three N-linked and an O-linked glycosylations
what is EPO used for?
-highly effective in the treatment of anemia (red blood cell deficiency)
-also exploited by endurance athletes to increase oxygen carrying capacity
-the patterns of glycosylation associated with the synthetic version of EPO differ from those of endogenous protein
what is the structure of proteoglycans? and functions?
-extracellular space in tissues contains a gel-like material, the extracellular matrix (ground substance)
-ground substance holds cells together, provides a porous pathway for diffusion of nutrients and waste products and serves as a cushioning function
-extracellular matrix is a meshwork of fibrous proteins and heteropolysaccharides called glycoaminoglycans
