Biochem Chapter 7 Study Questions

Galactosemia

A genetic disorder in which an enzyme required to metabolize galactose is missing; symptoms include liver damage, cataracts, and severe mental retardation.

Define the term reducing sugar. What structural feature does a reducing sugar have?

A reducing sugar reduces Cu(II) in Benedict's reagent. This reduction takes place because the hemiacetal portion of sugar can form an aldehyde functional group, which can be oxidized to a carboxylic acid.

Epimers

A subtype of diastereomers that differ in absolute configuration at exactly one chiral carbon.

Monosaccharides

A.k.a simple sugars Are polyhydroxy aldehydes or ketones

Oxidation of the aldehyde group of a sugar produces a(n) _____________ acid

Aldonic

_____________ are stereoisomers of sugars that differ only in the configuration at an acetal or ketal carbon.

Anomers

Glycosylation Reactions

Attach sugars or glycans (sugar polymers) to proteins or lipids.

In glycoproteins, what are the three amino acid residues to which carbohydrates are most frequently linked? To what functional group is the glycan linked in each case?

Carbohydrate moieties are most frequently linked to the amide nitrogen of asparagine and the hydroxyl oxygen of serine and threonine residues.

_____________ is the structural glucose-containing polysaccharide of plants.

Cellulose

D-Erythrose and D-threose are referred to as _____________ because their structures only differ in the configuration at one asymmetric carbon atom

Epimers

Esterification

Free OH groups of carbohydrates can be converted to esters by reactions with acids.

Why are individuals with type O blood at high risk for stomach ulcers?

Helicobacter pylori, the causative agent of gastritis and stomach ulcers, possesses several lectins that allow it to establish a chronic infection in the mucous lining of the stomach. Attachment of the organism to the stomach lining cells is mediated by the binding of bacteria lectins to oligosaccharides on cell surfaces. One of these lectins bind with high affinity to a portion of type O blood group determinant, an oligosaccharide. Individuals with type A or B blood are not immune to the infection; however, since he bacterium can also use other lectins to achieve adhesion.

Glycoside Formation

Hemiacetals and hemiketals react with alcohols to form the corresponding acetal and ketal

Polysaccharides that contain more than one type of monosaccharides are called _____________.

Heteroglycans

What is the difference between a heteroglycan and a homoglycan? Give examples.

Heteroglycans: are made up of more than one type of monosaccharide. Ex: hyaluronic acid Homoglycans: are made up of only one type. Ex: starch

What structural relationship is indicated by the term D-sugar? Why are (+) glucose (shifts polarized light to the right) and (−) fructose (shifts polarized light to the left) both classified as D-sugars?

In D-family sugars, the OH on the chiral carbon farthest from the carbonyl group is on the right side in a Fischer projection formula. So both (+) glucose and (-) fructose are D-sugars despite their rotation of plane-polarized light in opposite directions.

Why can aldoses and ketoses both behave as reducing sugars?

In aldoses, the sugar has a free aldehyde functional group and ketoses have a free carbonyl group present. Ketones can tautomerize in solution to form an aldehyde group which allows them to act as a reducing sugar.

_____________ are nonsuperimposable, non-mirror-image stereoisomers.

enantiomers

glycogen

energy storage molecule in animals composed of glucose residues linked by alpha(1,4) and alpha(1,6) linkages.

Glyceraldehyde structure

Pay attention to orientation of the hydroxyl group

Mutarotation

Produces an equilibrium mixture of a- and b-forms in both furanose and pyranose ring structures

Compare the structures of proteoglycans and glycoproteins. How are structural differences related to their functions?

Proteoglycans: large molecules that contain a large number of glycosaminoglycan chains linked to a core protein. Found primarily in extracellular fluids where their high carbohydrate content allows them to bind large amounts of water. When combined with proteins, like collagen, they form a gel that acts as a shock absorber in ligaments and tendons. glycoproteins: conjugated proteins in which the prosthetic groups are carbohydrate molecules. The carbohydrate groups stabilize the molecule via hydrogen bonding, protecting the molecule from denaturation, or shielding the protein from hydrolysis. The carbohydrate groups on the glycoproteins on the surface of cells play an important role in the variety of cell recognition phenomena.

glycolipid

a complex lipid molecule in which monosaccharide, disaccharide, or oligosaccharide is attached to a membrane lipid molecule through an O-glycosidic linkage.

maltose

a degradation product of starch hydrolysis; a disaccharide composed of two glucose molecules linked by an alpha(1,4) glycosidic bond/

Sugars that react with Benedict's reagent are called _____________.

Reducing Sugars

Review aldehyde and ketone mechanisms with alcohol

Refer to notes from Lecture 9/24

Lactose

a disaccharide found in milk; composed of one molecule of galactose linked in a beta(1,4)glycosidic bond to glucose.

The product of the reaction between an aldehyde or ketone and an amine is called a _____________ base.

Schiff

glycosaminoglycan

a long, unbranched heteropolysaccharide chain composed of dissaccharide repeating units.

heparan sulfate proteoglycans

a macromolecule containing large numbers of glycosaminoglycan chains with heparan sulfate components.

What structural differences characterize starch, cellulose, and glycogen?

Starch and glycogen are both homoglycans containing glucose monomers linked by alpha(1,4) glycosidic bonds, with branch points connected by alpha(1,6) glycosidic bonds. Glycogen has a lot more branches than starch though. Cellulose: is a linear polymer of glucose linked by beta(1,4) glycosidic bonds.

Epimer

a molecule that differs from the configuration of another isomer by one asymmetric center.

monosaccharide

a polyhydroxyl aldehyde or ketone containing at least 3 carbon atoms

Diastereoisomers

Stereoisomers that aren't mirror images of each other.

Haworth Structures

Structures that more accurately depict bond angle and length in ring structures than the original Fischer structures

Aldose

Sugars with aldehyde functional group

Ketose

Sugars with ketone functional group

Glycan

a polymer of monosaccharides; a polysaccharide

syndecan

a single-pass transmembrane core polypeptide that is linked to heparan sulfate and chondroitin sulfate GAG chains.

Amadori product

a stable ketoamine formed from the rearrangement of a Schiff base; an intermediate in glycation processed that produced advanced glycation end products.

GPI anchor

a sugar and phosphate containing molecules that links peripheral proteins to membranes; glycosylphosphatidylinositol.

Reducing sugar

a sugar that can be oxidized by weak oxidizing agents.

amylopectin

a type of plant starch; a branched polymer containing alpha(1,4) and alpha(1,6) glycosidic linkages.

amylose

a type of plant starch; an unbranched polymer of D-glucose residues linked with alpha(1,4) glycosidic linkages

The polymer chains of glycosaminoglycans are widely spread apart and bind large amounts of water. What are the two functional groups of the polymer that make the binding of water possible? What type of bonding is involved? (Refer to Online Book page 477 for figure).

They contain amino and sulfate groups, both of which have ionic charges that attract water molecules. Also, the large numbers of polar hydroxyl groups of glycoaminoglycans participate in hydrogen bonding with water molecules.

Glycation

The reaction of reducing sugars with nucleophilic nitrogen atoms in a non-enzymatic reaction

Optical isomers

The reference carbon is the asymmetric carbon farthest from the carbonyl carbon.

Epimerization

The transformation of glucose to mannose

Classify each of the following sugar pairs as enantiomers, diastereomers, epimers, or an aldose-ketose pair. a. D-erythrose and D-threose b. D-glucose and D-mannose c. D-ribose and L-ribose d. D-allose and D-galactose e. D-glyceraldehyde and dihydroxyacetone

a. D-erythose and D-threose are epimers b. D-glucose and D-mannose are epimers c. D- ribose and L-ribose are enantiomers d. D-allose and D-galactose are diastereomers e. D-glyceraldehyde and dihydroxyacetone are and aldose-ketose pair.

Which of the following carbohydrates are reducing and which are nonreducing? a. starch b. sucrose c. cellulose d. ribose e. fructose

a. starch - nonreducing b. sucrose - nonreducing c. cellulose - nonreducing d. ribose - nonreducing e. fructose - reducing

Oxidation of the aldehyde group of sugar produces a(n) _____________ acid.

alditol

heteroglycans

high-molecular-weight carbohydrate polymers that contain more than one type of monosaccharide.

homoglycans

high-molecular-weight carbohydrate polymers that contain only one type of monosaccharide.

Reactive Carbonyl-Containing Product

highly reactive molecules produced from Amadori products that cause protein cross-linkages and adduct formation; the dicarbonyl compound glyoxal (CHOCHO) is an example.

starch

homoglycan-containing glucose monomers linked by alpha(1,4) glycosidic bond with branch points connected by alpha(1,6) glycosidic bonds.

Glycoconjugate

molecule that possesses covalently bound carbohydrate group. Ex: glycoproteins and glycolipids

proteoglycan

large molecule containing large numbers of glycosaminoglycan chains linked to a core protein molecule.

Hemiacetal

one of the family of organic molecules with the general formula RCH(OR)OH that is formed by the reaction of a molecule of alcohol with aldehyde.

Hemiketal

one of the family of organic molecules with the general formula RRC(OR)OH that is formed by the reaction of a molecule of alcohol with a ketone.

Enterocyte

one of the numerous cells that line the small intestine; absorbs digested nutrients such as monosaccharides.

Anomer

one of two possible diastereomers that may form during the cyclization hemiacetal or hemiketal.

Reduction of the aldehyde group of a monosaccharide yields a _____________.

sorbitol

diastereomer

stereoisomer that is no an enantiomer (mirror-image isomer).

cellobiose

the disaccharide product of cellulose degradation; two molecules of glucose linked by beta(1,4) glycosidic bond

The more chiral carbon atoms present in a molecule....

the more enantiomers the molecule will have.

chitin

the principle structural component of the exoskeletons of arthropods and the cell walls of many fungi; a homoglycan composed of N-acetylglucosamide residues.

adduct

the product of an addition reaction

How many enantiomers of Glyceraldehyde?

two enantiomers is based on the presence of a chiral carbon atom.

Schiff base

an imine product of a reaction between a primary amino group and a carbonyl group.

anomer

an isomer of a cyclic sugar that differs from another in its configuration about the hemiacetal or acetal cabon.

O-glycan

an oligosaccharide linked to a protein via alpha-glycosidic bond to the hydroyl oxygen of serine or threonine residues; a mucin-type polysaccharide.

N-glycan

an oligosaccharide linked to a protein via beta-glycosidic bond between the core N-acetylglucosamine anomeric carbon and a side chain amide nitrogen of an asparagine residue.

Furan

an organic molecule with a five-sided ring containing one oxygen atom; furanoses are named in reference to furan.

Pyran

an organic molecule with a six-sided ring containing one oxygen atom; pyranoses are named in reference to pyran.

glycoprotein

carbohydrate-containing proteins; monosaccharides, disaccharides, and oligosaccharide that are covalently linked through N- or O- linkages.

Esterification and sugar

dramatically affects the physical and chemical properties of sugars.