Biochemistry – Carbohydrates Test Questions

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monosaccharide
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simple sugars
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disaccharide
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two monosaccharide units
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oligosaccharide
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short chains of saccharides connected by glycosidic bonds
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polysaccharide
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sugar polymers (>20 units)
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glycoconjugate
glycoconjugate
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carbohydrates COVALENTLY linked with other chemical species such as proteins, peptides, lipids and saccharides. Formed via glycosylation
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carbohydrate functions (3)
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energy source and energy storage structural component of cell walls and exoskeletons informational molecules in cell-cell signaling
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Aldose vs ketose
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aldose – aldehyde functionality (double-bonded O on last carbon in chain form) ketose – ketone functionality (double-bonded O on second-to-last carbon)
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Enantiomer
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Stereoisomers that are nonsuperimposable mirror images
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Diastereomer
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stereoisomers that are not mirror images different physical properties
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Epimers
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two sugars that differ only in the configuration around one carbon atom
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Ribose
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standard five-carbon sugar
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Glucose
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standard six-carbon sugar
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pyranoses
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Six-membered oxygen-containing rings
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furanoses
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Five-membered oxygen-containing rings
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What’s a reducing sugar? How is it reduced? Ex?
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any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group only linear chain the carbonyl group is oxidized (usually by Cu 2+) to a carboxyl group
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Colorimetric analysis (3)
Colorimetric analysis (3)
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The enzyme glucose oxidase catalyzes the conversion of glucose to glucono–lactone and hydrogen peroxide Hydrogen peroxide oxidizes organic molecules into highly colored compounds Concentrations of such compounds is measured colorimetrically
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Key structural features of sugars
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-aldose (carbonyl group at end) or ketose (carbonyl group in any other position) -sterchemistry of hydroxyl groups -number of chiral carbons -cyclic
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Significance of stereoisomers (w/r to enzymes)
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Enzymes that act on sugars prefer certain stereoisomers because of binding site specificity
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Ring form sugar (how? cis trans)
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carbonyl group forms covalent bond with hydroxyl oxygen creates new chiral center and therefore creates a more stereo-chemically complex molecule if anomeric hydroxyl group is trans to CH2OH group = alpha; cis = beta
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Open chain (structure, D and L)
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carbonyl group at one end hydroxyl group at other – if hydroxyl group furthest from carbonyl carbon is on left = L configuration; if right = D configuration
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# of stereoisomers equation
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= 2^(# of chiral centers)
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What configuration of isomer is hexose most found as?
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D isomers
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hemiacetal
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product of first addition of alcohol group to carbonyl carbon (aldehyde) alcohol group, hydrogen, r group, or group
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hemiketal
hemiketal
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product of first addition of alcohol group to carbonyl carbon (ketone) 2 r groups, or group, alcohol group
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acetal
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product of second addition of alcohol group to carbonyl carbon (aldehyde) two or groups, hydrogen, r group
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ketal (how formed, structure)
ketal (how formed, structure)
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product of second addition of alcohol group to carbonyl carbon (ketone) 2 r groups, 2 or groups
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mutarotation
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the process of decycilization and recycilization to switch alpha to beta or vice versa
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How are disaccharides joined? (O and N bond)
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O-glycosidic bond from anomeric carbon to hydroxyl group N-glycosyl bond from anomeric carbon to nitrogen atom in glycoproteins
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Non reducing sugar
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When anomeric carbon is in glycosidic bond (full acetal or ketal), the linear formation is prevented, making the carbonyl carbon unable to undergo reducing
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Functions of polysaccharides (homopolysaccharides & heteropolysaccharides)
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homo – storage forms of fuel (ex starch and glycogen) hetero – structural elements (ex chitin, cellulose, peptidoglycan)
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Structure and composition of Starch
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contains two types of glucose polymer, amylose and amylopectin hydrated (lots of hydroxyl groups)
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Amylose and Amylopectin
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Found in starch lose – consists of long, unbranched chains of D-glucose residues connected by (1 to 4) linkages pectin – highly branched. The glycosidic linkages joining glucose residues in amylopectin chains are (1 to 4); the branch points (occurring every 24 to 30 residues) (1 to 6)
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Glycogen
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polymer of (1 to 4)-linked subunits of glucose, with (1 to 6)-linked branches glycogen is more extensively branched (on average, every 8 to 12 residues) branches nonreducing
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Dextrans
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bacterial and yeast polysaccharides made up of (1 to 6)-linked poly-D-glucose have branches source of glucose for bacterial metabolism adhesive used by plaque bacteria
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Cellulose (structure, what sugar, orientation, why strong?)
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linear unbranched homopolysaccharide containing D- glucose In contrast with amylose: beta 1 to 4 linkages chairs 180 degrees relative to neighbor; all OH groups exposed for bonding with neighboring chains Very strong due to folding major component in tree trunks etc
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Chitin (linkage, type sugar, diff. cellulose, found?)
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linear homopolysaccharide composed of N-acetylglucosamine residues in (beta 1 to 4) linkage only chemical difference from cellulose is the replacement of the hydroxyl group at C-2 with an acetylated amino group found in exoskeletons
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Structure of polysaccharides. Ie glycogen and starch
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exposed hydroxyl groups participate in hydrogen bonding which create 3D structure limited by steric hindrance, broken down into angles glycogen and starch form coiled helices, 6 per turn with hydrogen bonds between the hydroxyl groups
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Test for amylose
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Iodine = blue I- fits into helix core
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Peptidoglycan
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heteropolymer N-acetylglucosamine and N-acetylmuramic acid linked by short peptide chains lysozyme hydrolyzes glycosidic bonds penicillin prevents peptide chains from forming which inhibits bacteria from stopping osmotic lysis
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Agar
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sulfated heteropolysaccharides made up of D-galactose and an L-galactose derivative ether-linked between C-3 and C-6
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Agarose
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the agar component with the fewest charged groups (sulfates, pyruvates) double helix
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Glycosaminoglycans
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linear polymers composed of repeating disaccharide units N-acetylglucosamine or N-acetylgalactosamine; the other is in most cases a uronic acid extended conformation due to negative charge provide viscosity, adhesiveness, and tensile strength to the extracellular matrix
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Functions of glycoconjugates
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communication between cells and their extracellular surroundings label proteins for transport to and localization in specific organelles recognition sites for extracellular signal molecules
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Proteoglycans (function, structure)
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tissue organizers, and they influence various cellular activities, such as growth factor activation and adhesion consists of a “core protein” with covalently attached glycosaminoglycan(s) -Ser-Gly-X-Gly- (where X = any amino acid)
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Glycoproteins (what, where, describe function procedure)
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one or several oligosaccharides of varying complexity joined covalently to a protein usually found on the outer face of the plasma membrane, in the extracellular matrix, in the blood, and in specific organelles highly specific sites for recognition and high affinity binding by carbohydrate-binding proteins called lectins
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Glycosphingolipids
Glycosphingolipids
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plasma membrane components in which the hydrophilic head groups are oligosaccharides oligosaccharides act as specific sites for recognition by lectins signal transduction in cells and nerve conduction
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Syndecan and Glypican
Syndecan and Glypican
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membrane heparan sulfate proteoglycans Syn – single transmembrane domain and an extracellular domain bearing three to five chains of heparan sulfate gly – attached to the membrane by a lipid anchor
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Proteoglycan aggregates
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enormous supramolecular assemblies of many core proteins all bound to a single molecule of hyaluronan
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Sugar code
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There is an enormous amount of information in each molecule due to the diversity of glycans. Read by proteins
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Lectins
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proteins that bind carbohydrates with high specificity and with moderate to high affinity cell-cell recognition, signaling, and adhesion processes and in intracellular targeting of newly synthesized proteins govern the rate of degradation of certain peptide hormones, circulating proteins, and blood cells
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Selectins
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a form of membrane bound lectin that mediate cell to cell recognition and adhesion selectin binds to oligosaccharide of the surface of glycoproteins on leukocytes
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Lectin binding (function, how function, increase binding how?)
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Binds with carbohydrate binding affinity is increased by multiple carbohydrate-binding domains for oligosaccharides polar side of sugar hydrogen bonds with lectin while less polar side interacts with non polar amino acid residues
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Mass spectrometry and high-resolution NMR spectroscopy
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yield essential information about sequence, configuration at anomeric and other carbons, and positions of glycosidic bonds
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Analysis of carbs structure
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specific enzymatic hydrolysis to determine stereochemistry at the glycosidic bond and to produce smaller fragments for further analysis; methylation to locate glycosidic bonds; and stepwise degradation to determine sequence and configuration of anomeric carbons
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methods of carbohydrate analysis
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Microarrays
Microarrays
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useful in determining the specificity and affinity of lectin binding to specific oligosaccharides.
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Solid-phase synthetic methods yield
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yield defined oligosaccharides that are of great value in exploring lectin-oligosaccharide interactions and may prove clinically useful.

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