BioChem chp 7 carbs and glycoconjugates of cell surfaces

carbs have what general formula

(CH2O)n

monosaccharides are what; broken down into

simple sugars

cannot be broken down into a simpler sugar under mild conditions

oligosaccharides are what

2-10 sugar residues

polysaccharides are

polymers of simple sugars

• hundreds to thousands of residues

what is an aldose

has an aldehyde functionality

what is a ketose

has a ketone functionality

something being an aldose or a ketose is based on what

location of the carbonyl carbon

number of carbons in a sugar and name

• Triose (3C)

• Tetrose (4C)

• Pentose (5C)

• Hexose (6C)

• Heptose (7C)

what are the main aldoses (6)

• glyceraldehyde

• D-erythrose

• D-ribose

• D-glucose

• D-mannose

• D-galactose

what are the main ketoses (3)

• dihydroxyacetone

• ribulose

• fructose

fisher projection and wedge-dash representation

• Fischer projections (top) are the most compact way to represent stereochemistry

• The wedge- dash representations of D- and L-glyceraldehyde are also shown

what are enantiomers

• Stereoisomers that are mirror images of each other but cannot be superimposed

• Stereoisomers that are non-superimposed mirror images of each other are enantiomers

• optimal isomer that are mirror images

D or L (how it works)

based on the location of the OH on the chiral carbon farther from the carbonyl carbon

D and L isomers of sugars are (relation to each other)

enantiomers

enantiomers have the same

chemical properties but diff physical properties and biological properties

most hexoses in living organisms are D or L

D

what are Diastereoisomers

Pairs of isomers that have opposite configurations at one or more chiral centers but are NOT mirror images

what are epimers

2 sugars that differ in configuration at only one chiral center

what happens to monosaccharides with 5C or more (usually)

form a ring structure in aqueous solution

Aldehyde and ketone carbons are

electrophillic

• They will accept electrons

• They will gain an oxygen (which has a partial negative charge) 

alcohol oxygen atom is

nucleophillic

• Donating electrons; tend to have a positive or partially positive charge

• Gain the hydrogen

when aldehyde is attacked by alcohols what forms

when ketone is attacked by alcohols what forms

hemiacetal

hemiketal

formation of hemiacetel, acetal, hemiketal, ketal

aldehyde or ketone—> hemi (one alcohol added) —> acetal or ketal (2nd alcohol added)

hemiacetal def

when only one alcohol has attacked the aldose

what a single ring sugar is

acetal def

when the 2nd alcohol has attacked

hemiacetal—> acetal

what forms when we have dissacharides

hemiketal def

when only one alcohol has attacked the ketose

ketal def

when the 2nd alcohol has attacked

hemiketal—> ketal

glucose is a (functional group)

aldose

glucose can cyclize into a

hemiacetal

fructose is a (functional group)

ketose

fructose can cyclize into a

hemiketal

When hemiacetals and hemiketals are formed, the carbonyl carbon atom becomes a

asymmetric center

what are anomers

Isomers of monosaccharides that differ only in their configuration about the asymmetric carbon

Cyclic form of glucose is a (anomer name)

pyranose

cyclic form of fructose is a

furanose

what readily undergoes intramolecular cyclization (2)

Pentose and hexoses

when a sugar has undergoes cyclization, what happens to the former carbonyl carbon

becomes a new chiral center

what is it now called

anomeric carbon—> the carbon that was a carbonyl group

what is anomeric carbon

the carbon that was a carbonyl group (C=O) in open structure

when a sugar has undergoes cyclization, what happens to the former carbonyl oxygen

becomes a hydroxyl group

what does the position of the hydroxyl group on annomeric carbon when cyclization has occur determine

if α or β

when is the sugar β or α

alpha when it is on the opposite side (trans) of the ring as the CH2OH

beta when it is on the same side (cis) of the ring as the CH2OH

D glucose formation of cyclic form (how, when does it turn beta and when alpha)

• If OH is on the left in fisher, it point up in hateworthy

• If the OH is on the right, then it points down in Haworth (except for anomeric C)

• α and β are anomers

• CH2OH is trans to OH on the anomeric C=α

• CH2OH is cis to OH on the anomeric C= β

when is a sugar alpha

• CH2OH is trans to OH on the anomeric C=α

alpha and beta are

anomers

when is a sugar beta

• CH2OH is cis to OH on the anomeric C= β

mutarotation

interconversion of α and β in solution

glucose can undergo (to do with the alpha and beta)

mutarotation

monosaccharides exist in what forms

cyclic, anomeric

what are the 4 most common hexoses

glucose (specific name, structure)

mannose (specific name and structure)

galactose (specific name and structure)

fructose (specific name and structure)

glucose and mannose are

epimers (2 sugars that differ in configuration at only one chiral center)

glucose and galactose are

also epimers

enantiomers

diastereomers

anomers

epimers

monosaccharide derivatives (8)

• Sugar acids

• Sugar alcohols

• Deoxy sugars- ribose and deoxyribose

• Sugar esters- like ATP, those with phosphates added

• Amino sugars

• Acetals, ketals, and glycosides

what are reducing sugars

 sugars with free anomeric carbons (they can react with other things)

• usually C1’

• They will reduce oxidizing agents such as peroxide, ferricyanide, and some metals (Cu2+ and Ag+)—> they themselves become oxidized

• These redox reactions oxidize the sugar to a sugar acid

is glucose a reducing sugar? used for what?

yes

• So these reactions are the basis for diagnostic tests for blood sugar—> HOW IT RELATES TO DIABETES

lactones and acids are produced by

oxidation of sugars (mainly their aldehyde group)

test for reducing sugars

fehlings and tolens

fehlings test

• Mild oxidation of aldose with alkaline Cu2+ (fehling's solution) produces aldonic acids as seen in visual "tests"

tolens test

(aldose reduce Ag+ to Ag0

Enzyme-catalyzed oxidation of monosaccharides

• gives other products

  • Uronic acids and glucuronic acid

    • Oxidation at C6

  • Important constituents of some polysaccharides

  • What is mainly used now with the finger prick test

hemoglobin glycation

• Hemoglobin becomes irreversibly glycated (Hb A1c)- no enzyme-

  • Measure of blood glucose control over RBC lifespan (around 3 months) so we get better idea of the glucose levels

  • Diabetes

    • When you eat you have glucose in the bloodstream

    • The glucose will attach to hemoglobin and then go into the RBC

    • However, diabetics have a higher percentage hemoglobin that has been glycation

• HbA1c can eventually form AGE’s (advanced glycated end products)--> not good

  • Form covalent cross-links with other molecules (proteins)

  • Can lead to damaged kidneys, retinas, CVD, etc.

so hemoglobin—→ HbA1C—> AGEs

glycation

 attaches glucose without an enzyme

glycosylation

attaches glucose using an enzyme

AGEs do what (advanced glycated end products)

• Form covalent cross-links with other molecules (proteins)

• Can lead to damaged kidneys, retinas, CVD, etc.

deoxy sugars

sugar esters

amino sugars

acetals, ketals, glycosides

• Deoxy sugars: constituents of DNA, etc.

• Sugar esters: phosphate esters like ATP are important

• Amino sugars contain an amino group in place of a hydroxyl group

• Acetals, ketals, and glycosides: basis for oligo and polysaccharides

sugar alcohols are what

• Sugar alcohols such as sorbitol, mannitol, and xylitol sweeten many “sugarless” gums and candies

deoxy sugars

• Deoxy sugars are monosaccharides with one or more hydroxyl groups replaced by hydrogens

  • 2-Deoxy-D-ribose is a constituent of DNA

  • Rhamnose is a component of ouabain, a toxic “cardiac glycoside”

  • Fucose is a component of some cell walls

sugar esters

• Phosphate esters of glucose, fructose, and other monosaccharides are important metabolic intermediates

• They have a phosphates groups added to them

• The ribose moiety of nucleotides such as ATP and GTP is phosphorylated at the 5’- position

amino sugars

 

• Sugars with an amino group at C-2 are amino sugars.

• They are found in many oligosaccharides and polysaccharides.

glycosides

• The pyranose and furanose forms of monosaccharides react with alcohols in dehydration synthesis reactions to form glycosides, with retention of the α- or β configuration at the C-1 carbon.

• The new bond formed is called a glycosidic bond.

• In the example, they have a methyl group added to replace the H of the alcohol group

so having a Non sugar group added through dehydration reaction

glycosidic bonds

the linkage between monosaccharides

disaccharides are what

simplest oligosaccharide

• linked by glycosidic bonds

each unit in the oligosaccharide is termed as a

residue

lactose glycosidic bond and residues

galactose and glucose

• beta 1→4 glycosidic bond

maltose glycosidic bond and residues

2 glucose

• alpha 1—>4 glycosidic bon

sucrose glycosidic bond and residues

glucose and fructose

• alpha, beta 1—> 2 glycosidic bond

what disaccharide is not a reducing sugar

sucrose

• does not have a free anomeric carbon

what is a mixed acetal

2 sugars with  one hydroxyl provided intramolecularly and one hydroxyl from the other monosaccharide

formation of glycosidic bond

• 2 sugar molecules can be joined covalently via a glycosidic bond

  • Between an anomeric carbon on the first monosaccharide and a hydroxyl group on the second monosaccharide

  • Condensation reaction (Water is eliminated)

reducing sugar with disaccharides

• Anomeric carbon on 2nd monosaccharide still free for additional reactions (reducing sugar)

• NOT SUCROSE

glycosidic bond is what type of bond

covalent

reaction that forms glycosidic bond

condensation (water is taken out)

nonreducing disaccharides occur when

• Two sugar molecules can be also joined via a glycosidic bond between two anomeric carbons

  • No free OH group on the anomeric carbon

  • There are no reducing ends, this is a nonreducing sugar

  • LIKE SUCROSE

what are the 2 nonreducing disaccharides

trehalose and sucrose

sucrose stability, function (2)

stable toward oxidation and makes it suitable as a storage and transport molecule for energy

• because is not easily oxidized and is not reducing sugar

is glycosidic bond reversible

not technically because it is a covalent bond. Would require an enzyme

oligosaccharides are commonly used for

antibiotics

functions of polysaccharides (3)

storage, structure, recognition

homopolysaccharide

 a polysaccharide that contains only one kind of monosaccharide

heteropolysaccharide

a polysaccharide made of several monosaccharides

which polys are storage molecules

starch and glycogen