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CMB-I Test 2 Pritchard


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What is the most aboundant of the four major classes of biological molecules?
- out of proteins, nucleic acids, lipids, and carbohydrates, carbs are the most numerous
Sugars are polyhydroxy ___________ or ___________. Biological sugars are in the _____ configuration, which is determined by ___________________________.
- aldehydes or ketones

- D

- the absolute configuration at its highest numbered asymmetric carbon
- stereoisomers
- enantiomers
- diastereomers
- stereoisomers: same chemical formula but differ in atomic arrangement
- enantiomers: stereoisomers that are mirror images of each other (have identical chemical and physical properties)
- diastereomers: stereoisomers which are NOT mirror images (different chemical and physical properties)
Most drugs today are resolved. What does this mean, and how is it done?
- resolved means that you have separated out the enantiomers to either D- or L-
- Racemic mixtures can be separated out by derivatizing the mixture with another chiral reagent and then separating the D- and L- forms
What is the Lobry de Bruyn-van Ekenstein reaction?
- C-2 epimerization of sugars occurs under alkaline conditions
- you will get interconversion of an aldose to a ketose if you put a sugar in base
Under physiological conditions, what types of sugars can be oxidized? What about under basic conditions?
- only aldoses (NOT ketoses) can be oxidized (-CHO to -COOH)
- under basic conditions and in the presence of Ag+ or Cu2+, both ketoses and aldoses are oxidized
What are some common mechanisms for oxidizing sugars?
- (-CHO)+Br2 and H20 will give (-COOH)
- dilute HNO3 will create an aldaric acid, where both ends of the sugar now have COOH
What are some common mechanisms for reducing sugars?
- using NaBH4, can get (-CHO) to reduce to an alditol (-CH2OH)
How are hemiacetals formed?

Why is this reaction important?
- an alcohol (ROH) attacks an aldehyde (R-COH) and forms a hemiacetal (R-COH-OR')
- a hemiacetal is a C with two O's attached

- this is how aldose sugars are cyclized
Looking at a Haworth projection formula, how can you tell if a cyclic sugar is in the alpha or beta form?
- alpha: the OH on C1 is on the opposite side of the CH2OH
- beta: the OH on C1 is on the same side as the CH2OH
A sugar with a 6-membered ring is called a ________ while a sugar with a 5-membered ring is called a _________. Two cyclic sugars that differ only in the configuration of the __________ are called __________.
- pyranose
- furanose
- anomeric carbon atom (either a hemiketal or hemiacetal)
- anomers
How are sugar hemiketals formed? How large is the ring?
- the C4 alcohol end of the sugar (ROH) attacks the ketone end of the sugar (R'-C-CH2OH) to form the hemiketal
- this results in a 5-C ring
Why does the optical rotation of a freshly prepared solution of D-glucose change?
- due to mutarotation
- a-D-glucose: +112 deg
- B-D-glucose: +19 deg
- The two anomers of D-glucose are diastereomers and have different chemical and physical properties
- this sugar will mutarotate between the alpha and beta configuration to reach an equilibrium of about +52.5 deg for the optical rotation
What are the total number of conformations of cyclic glucose?
- 2 chairs
- 4 boats
- 6 skews
- 12 half chairs
- total of 24 possible conformations
What are alditols?

What is the makeup of honey?
- sugars that have (-CH2OH) on either ends

- ~18% H20
- ~38% fructose (B-D-Fructopyranose)
- ~31% glucose
How do hemiacetals and hemiketals form acetals and ketals?

What are sugar acetals called? How can they be detected?
- each 'hemi' is attacked by another alcohol (R-OH) so that you now have two (-OR) groups attached to the carbon
- GLYCOSIDES: sugar acetals
- can detect them because the C1 carbon is now stable (has an extra R group attached) and will not mutarotate in solution
What two sugars are each of these common disaccharides made from?
- lactose
- sucrose
- maltose
- cellobiose
- isomaltose
- lactose: gal-B-1,4-glc
- sucrose: glc-a-1,2-fru
- maltose: glc-a-1,4-glc
- cellobiose: glc-B-1,4-glc
- isomaltose: glc-a-1,6-glc
What is unusual about sucrose in comparison to other disaccharides?
- it is an a-1,2 linkage (backwards) meaning that there is no free anomeric carbon
- it is a non reducing sugar
What is the reducing end of a sugar?

What are glycosidic bonds?
- the free anomeric carbon end

- when a hemiacetal or hemiketal joins to another R group, this is a glycosidic bond (between the C and the OR groups)
This sugar conjugate is found in bitter almonds, cherry kernels, peaches, and apricots.
- Amygdalin
What bean-derived acetal was claimed to be an anti-cancer agent?
- Laetrile
What sugar is a breakdown product of starch and is used in chromatographic separations?
- cycloheptaamylose
Why does stachyose give humans gas?
- humans can break down the sucrose portion of the sugar, but cannot break down the gal-a-1,6-gal linkages
- bacteria in the lower intestine can, which releases COâ‚‚
What is dextratriose a component of?
- sake and honeydew
What does human milk contain besides lactose? What role do these sugars play?
- contains a large number of oligosaccharides
- they don't serve any nutritional value, and it is thought that they help prevent bacterial adherence in babies (UTI prevention)
What donates sugars in glycoconjugate biosynthesis?
- glycosyl transferases steal a sugar from a nucleotide (base+sugar+POâ‚„)
What is the major nucleoside di- or monophosphate to donate sugars?
- UDP is attached to lots (glcNAc, galNAc, murNAc, gal, glc)
- GDP is attached to fucose and mannose
- CMP is attached to sialic acid (NeuNAc)
What are the two monomers of lactose synthase?

Which monomer only works in lactating mammary glands?
- B-D-galactosyl transferase and a-lactalbumin

- a-lactalbumin
What reaction does each monomer of lactose synthase catalyze?
- B-D-galactosyl transferase: UDP-gal + glcNAc-R to form B-D-gal-(1,4)-GlcNAc-R

- a-lactalbumin: UDP-Gal + Glc to form B-D-gal-(1,4)-glc [lactose]
What causes lactose intolerance?
- the enzyme B-galactosidase in the small intestine breaks down lactose to galactose and glucose
- as people get older, and if they aren't from a historically dairy-farming region of the world, this enzyme is lost
- lactose can't be broken down, and there is an influx of fluid into the small intestine
- lactose is broken down by the bacteria in the large intestine, causing gas (CO2 and H2)
What is the most abundant biological molecule on Earth?
- cellulose
Why can't humans eat wood?
- wood is made of cellulose
- linear glc-β(1,4)-glc
- human's can't digest this bond
- herbivores and termites have bacteria within their gut that produce cellulases that can degrade cellulose
After cellulose, what is the most abundant biological molecule on earth?
- chitin
- linear β(1,4) polymer of glcNAc
If a patient comes into the ER and has lost a lot of blood, what are they normally given before blood/plasma?
- dextran sulfate IV: causes fluid to come out of tissues and expands blood volume
- is a linear α(1,6) linked glucan that is water soluble
- produced by certain bacteria growing on sucrose
What is starch composed of?

What keeps it from being totally soluble in water?

Where is each portion digested in the body?
- α-amylose: linear α(1,4) glc polymer
- amylopectin: very large branched polymer of α(1,4)glc with α(1,6) branches every 24-30 residues
- amylopectin is insoluble in water

- amylopectin is in small intestine, while amylase is present in salivary secretions
What is often used to thicken jams and jellies?
- pectin, a "soluble fiber"
- heterogenous polymer of partially methylated α-D-galNAc
What polysaccharide is used in salad dressings because it has high viscosity at low shear but low viscosity at high shear?
Xanthan gum
What is guar gum used for?
- forms highly viscous solutions, and keeps water from leaching out of many foods
- found in hot dogs, cheese, ice cream, baked goods
True or false:

- Alginate is from red seaweed, and carrageenan is from brown seaweed.
- Alginate is used to make dental impressions.
- Alginate is used to thicken foods, milk, and toothpaste.
- FALSE: alginate=brown, carrageenan=red
- FALSE: carrageenan is used for these purposes. alginate is mainly used for low fat spreads, sauces, and pie fillings
What is a water-soluble derivative of cellulose, that is widely used in food products and pharmaceuticals?
- carboxymethylcellulose
What is the only glycosaminoglycan that is not covalently bound to the protein? Where is this found?
- Hyaluronan (hyaluronic acid)
- very important in ground substance, vitreous humor, synovial fluid
- forms very viscous solutions that are shear dependent
Which has a larger volume: hyaluronan or chondroitin-4-sulfate?
- hyaluronan
_______________________ is a major component of the proteoglycans of cartilage and other connective tissues. Where do people get this in their diet?
- chondroitin-4-sulfate

- from meat products (chicken skin, pigs feet, cartilage)
Which residue of chondroitin-4-sulfate is sulfated?

What other position can be sulfated?

What other glycosaminoglycan is similar to chondroitin?
- galNAc
- C6
- dermatan sulfate; difers by an inversion of the configuration at C5, and is commonly found in the skin
How is keratan sulfate linked to a protein?
- either through a ser/thr (O-linkage) or an asparagine (N-linkage)
Even though heparin and heparan sulfate are similar, they are found in different locations in the body. Where?

What makes these two GAGs unique?
- heparin: intracellular granules of mast cells
- heparan sulfate: basement membranes
- They both have N-sulfate groups on their glcNAc residues
What is the most highly negatively charged biological polymer known?

What biological activity does this enzyme possess?
- heparin

- enhances antithrombin III, which prevents thrombin from cleaving fibrinogen to fibrin (clot)
- its sulfate group is necessary for the tight binding to antithrombin III
All GAGs (except one) are covalently linked to proteins via what unique linkage?

What GAG differs in its linkage depending on what tissue it's in?
- gal-gal-xyl-O-(Ser/Thr)
- O-linked glycosylation

- keratan sulfate
- If in cartilage, linked via O-linkage to serine and galNAc
- If in cornea, linked via N-glycosidic linkage
Describe the keratan sulfate linkages.
- Cartilage: serine-O-GalNAc-(branches to keratan sulfate chain attached at C4; C5 has gal-NeuNAc attached); ser-O-GalNAc-Gal-NeuNAc
- cornea: asparagine-N-glcNAc-GlcNAc-Man-branches at C4 and C5 to join onto 2 other Man, each Man joins to a keratan sulfate chain
How is chondroitin sulfate sulfated?
- after the GalNAc residues have become part of the growing CS chain, a PAPS molecule donates a sulfate via a sulfotransferase
What are the four major groups of proteoglycans?
- hyalectans
- cell surface heparan sulfate-containing proteoglycans
- basement membrane proteoglycans
- small leucine-rich proteoglycans

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