Biochemistry CH4: Carbohydrate structure + function

Ketose sugars may have the ability to act as reducing sugars. Which process explains this? (A) Ketose sugars undergo tautomerization (B) the ketone group is oxidized directly (C) Ketose sugars undergo anomerization (D) the ketone group is reduced directly

(A) Ketose sugars undergo tautomerization Ketose sugars undergo tautomerization, a rearrangement of bonds to under ket-enos shifts. This forms an alcove, which then allows them to act as reducing sugars. A ketone group alone cannot be oxidized.

The most basic structural unit of carbs are ______ (A) Monosaccharides (B) Glucose (C) Polysaccharides (D) Galactose

(A) Monosaccharides

When converting from fischer to hawthorn projection everything on the right will be pointing ____ in the hawthorn project while everything on the left will be pointing ____ (A) down, up (B) up, down (C) right, left (D) right, down

(A) down, up

Which of the following best describes Tollens reagent? (A) its reduced to produce a silvery mirror when aldehydes are present (B) forms a red precipitate of CU2O (C) Both of these occur

(A) its reduced to produce a silvery mirror when aldehydes are present

Maltose is a very important disaccharide. Which of the following best characterizes the structure of maltose? (draw it for extra credit) (A) α-Glc1,4-Glc (B) β-Glc1,4-Gal (C) α-Gal1,4-Gal (D) β-Gal1,4-Glc

(A) α-Glc1,4-Glc α-Glc1,4-Glc is the structure of maltose.

You can determine the number of stereoisomers by which formula (A) 2n (B) 2^n (C) (2n+1) (D) (2n-1)

(B) 2^n # of stereoisomers= 2^n where n= the number of chiral centers in the molecule

All of the following are examples of aldohexoses except ____ (A) D-galactose (B) D-Fructose (C) D- Mannose (D D-Glucose

(B) D-Fructose D-Fructose is a ketohexose

Fill in the blanks: The simplest Aldose is ____________, whereas the simplest Ketose is ______________. (A) Glyceraldehyde, Ketohexose (B) Glyceraldehyde, Dihydroxyacetone (C) Aldopentose, Dihydroxyacetone (D) Aldopentose, Ketohexose

(B) Glyceraldehyde, Dihydroxyacetone The simplest Aldose is Glyceraldehyde, whereas the simplest Ketose is Dihydroxyacetone.

Which of the following statement(s) is true of a diastereomers? I. They have similar physical properties II. They have different physical properties III. They have similar chemical/biological properties IV. They have different chemical/biological properties

(B) II and IV Only Diastereomers are molecules that are different from each other in terms of their physical and chemical/biological properties.

Draw or visualize D-glucose versus D-galactose. These two compounds are considered: (A) diasteriomers (B) epimers (C) constitutional isomers (D) enantiomers

(B) epimers These two compounds are considered epimers because they have the opposite stereochemistry designation (R/S) at a single stereocenter.

Draw or visualize D-glucose versus D-mannose. These two compounds are considered: (A) diasteriomers (B) epimers (C) constitutional isomers (D) enantiomers

(B) epimers These two compounds are considered epimers because they have the opposite stereochemistry designation (R/S) at a single stereocenter.

Which type of bonds link sugars together? (A) peptide bond (B) glycosidic bond (C) hydrogen bond (D) amide bond

(B) glycosidic bond glycosidic bond forms between the hydroxyl groups of 2 monosaccharides

How many possible D-aldohexoses are there? (A) 4 (B) 6 (C) 8 (D) 16

(C) 8 An aldohexose has 4 chiral centers. You can calculate the possible number of configurations using the formula 2^n where n is the number of stereocenters. 2^4 is 16, so there are 16 possible aldohexoses (8 D-aldohexoses and 8 L-aldohexoses).

Based on the general structure of a Carbohydrate, you can expect lots of Oxygen-containing functional groups. Which of the following would you LEAST expect to see in a carbohydrate? (A) Carbonyl (B) Ether (C) Carboxylic Acid (D) Alcohol

(C) Carboxylic Acid Carbonyls, ethers, and alcohols are all commonly seen in carbohydrates.

Which of the following reagents are commonly used to test for reducing sugars? I. Lindlar's II. Tollen's III. Benedict's (A) I only (B) I and III only (C) II and III only (D) I, II and III

(C) II and III only Tollen's Reagent (Ag2O) and Benedict's Reagent (Cu2O) are both commonly used to test for reducing sugars.

The carbon that was attacked by the OH group is known as the ____________ carbon. (A) allosteric (B) epimeric (C) anomeric (D) episteric

(C) anomeric The carbon that was attacked by the OH group is known as the anomeric carbon.

Draw or visualize D-glucose versus D-fructose. These two compounds are considered: (A) diasteriomers (B) epimers (C) constitutional isomers (D) enantiomers

(C) constitutional isomers These two compounds are considered constitutional isomers because they have the same molecular formula with different connectivity. D-glucose is an aldose, while D-fructose is a ketose.

Aldonic acids are compounds that: (A) can be oxidized, and therefore act as reducing agents (B) can be reduced, and therefore act as reducing agents (C) have been oxidized and have acted as reducing agents (D) have been oxidized and have acted as oxidizing agents

(C) have been oxidized and have acted as reducing agents Aldonic acids form after the aldehyde group on a reducing sugar reduced another compound, becoming oxidized in the process

Fill in the blank: Monosaccharides contain hydroxyl group which acts as a _____ and a carbonyl group which acts as an _____ (A) acid, base (B) base, acid (C) nucleophile, electrophile (D) electrophile, nucleophile

(C) nucleophile, electrophile

Sucrose is a very important disaccharide that is often found in table sugar. Which of the following best characterizes the structure of sucrose? (draw it for extra credit) (A) β-Glc1,2-β-Fru (B) α-Glc1,4-β-Fru (C) α-Glc1,2-β-Fru (D) β-Glc1,4-α-Fru

(C) α-Glc1,2-β-Fru

What are epimers? (A) enantiomers that differentiations at 2 or more chiral centers (B) enantiomers that differ at 1 chiral center (C) diasteromers that differ at 2 or more chiral centers (D) diasteromers that differentiations at 1 chiral center

(D) diasteromers that differentiations at 1 chiral center

Draw or visualize D- versus L-glucose. These two compounds are considered: (A) diasteriomers (B) epimers (C) constitutional isomers (D) enantiomers

(D) enantiomers These two compounds are considered enantiomers because they have the opposite stereochemistry designation (R/S) at every stereocenter.

If a reaction occurs between a single OH group and a carbonyl group, a _______________ group will be generated. If a reaction occurs between two OH groups and a carbonyl group, a _______________ group will be generated. (A) acetal/ketal, acetal/ketal (B) acetal/ketal, hemiacetal/hemiketal (C) hemiacetal/hemiketal, hemiacetal/hemiketal (D) hemiacetal/hemiketal, acetal/ketal

(D) hemiacetal/hemiketal, acetal/ketal If a reaction occurs between a single OH group and a carbonyl group, a hemiacetal/hemiketal group will be generated. If a reaction occurs between two OH groups and a carbonyl group, a acetal/ketal group will be generated.

Lactose is a very important disaccharide found in milk. Which of the following best characterizes the structure of lactose? (draw it for extra credit) (A) α-Glc 1,4-Glc (B) β-Glc 1,4-Gal (C) α-Gal 1,4-Gal (D) β-Gal 1,4-Glc

(D) β-Gal 1,4-Glc β-Gal 1,4-Glc is the structure of lactose.

Benedict's reagent

-detects presence of reducing sugar -aldehyde group of an aldose is readily oxidized indicated by a red precipitate of Cu2O

Draw a D-ketohexose carbohydrate.

A ketohexose has 6 carbons, which gives it the suffix "hexose." It contains an ketone, which gives it the prefix "keto-". Lastly, the OH is located on the right of the last stereocenter carbon giving it a D configuration.

Why can a more powerful oxidizing agent NOT be used to test for reducing sugars?

A more powerful oxidizing agent would be able to oxidize both the aldehyde formed during mutaroatation AND the primary alcohols. If it reacts with primary alcohols, even non-reducing sugars would react!

Compare aldose and ketose

Aldoses contain an aldehyde in their structure while Ketoses contain a ketone

Compare Amylose and Amylopectin.

Amylose is a linear polysaccharide linked by α-1,4 linkages. Amylopectin is another polysaccharide, but along with the α-1,4 linkages, it also has branches with α-1,6 linkages

Compare the structure of amylose and glycogen.

Amylose is a polysaccharide composed of glucose with α-1,4 linkages. Glycogen is a polysaccharide composed of glucose with α-1,4 AND α-1,6 linkages. This is the storage form of glucose for our cells.

Draw a D-aldopentose carbohydrate.

An aldopentose has 5 carbons, which gives it the suffix "pentose." It contains an aldehyde functional group, which gives it the prefix "aldo-". Lastly, the OH is located on the right of the last stereocenter carbon giving it a D configuration.

The cyclic form of monosaccharides are: I. Hemiacetals II. Hemiketals III. acetals A) I only B) III only C) I and II only D) I,II and III

C) I and II only

Draw and compare D-Erythrose and D-threose

Both are aldotetroses that differ at 1 chiral center (on C2) therefore they are considered to be EPIMERS

How do you distinguish between D- and L-configuration?

D configuration has the hydroxyl (OH) group on the right of the highest number chiral center L configuration has the hydroxyl (OH) group on the left of the highest number chiral center

What are the 3 most important biological polysaccharides?

Cellulose Starch Glycogen

Compare the structure of cellulose and amylose (starch).

Cellulose is a polysaccharide composed of glucose with β-1,4 linkages. Amylose is a polysaccharide composed of glucose with α-1,4 linkages.

What are diasteriomers versus epimers?

Diastereomers are stereoisomers with a different configuration (R /S) at one or more (BUT NOT ALL) of the chiral carbons. Epimers are a type of diastereomers that differ at only one carbon configuration.

T/F cyclic sugar molecules are only stable in a pyranose ring

F cyclic sugar molecules are stable in both the pyranose and furganose ring form

T/F Cellulose can be digested by human enzymes

F cellulose contains B-1,4 linkages that cannot be digested by human enzymes

True or false? Any monosaccharide with an Acetal Ring is considered a Reducing Sugar.

False. Any monosaccharide with a Hemiacetal Ring is considered a Reducing Sugar.

Why can humans break down starches (like glycogen and amylose) and their α-1,4 glycosidic linkages for energy but cannot break down cellulose and its β-1,4 linkages?

Humans lack the enzyme necessary to cleave a β-1,4 linkage, so they cannot break down cellulose for energy! We do have enzymes to cleave α 1,4 linkages, which is why we can digest them and utilize them as energy.

Compare homopolysaccharides and heteropolysaccharides

Homopolysaccharides: made of one type of monosaccharides Heteropoysaccharides: made of multiple monosaccharides

Draw or visualize D-glucose α and β anomers as Haworth projections. What differentiates the α from the β anomer?

In the α form, the OH group at the anomeric carbon points in the same (think "sαme") direction (up/down) as the OH on C2, and the opposite direction of the CH2OH flag group. In the β form, the OH group at the anomeric carbon points in the same direction as the CH2OH flag group, and the opposite direction of the C2 hydroxyl.

Fill in the blank: Knowing that any specific Aldohexose has 4 chiral centers, it will have __________ enantiomer(s) and __________ diastereomer(s). (A) 2 , 5 (B) 2 , 14 (C) 1 , 6 (D) 1 , 14

Knowing that Aldohexoses have 4 chiral centers, they can have 1 enantiomer and 14 diastereomer(s). Note that any molecule can only have one Enantiomer, and that one of the 16 possible Aldohexoses is the original Aldohexose everything else is being compared to.

What is the difference between monosaccharides, disaccharides, and polysaccharides?

Monosaccharides consist of a single sugar monomer. Dissaccharides consist of two sugar monomers linked together. Polysaccharides consist of three or more sugar monomers linked

Describe the process of mutarotation.

Mutarotation is when the ring-form of the sugar opens up and then recloses again. This may cause the sugar to bounce back and forth between the α and β anomers.

What is the difference between trioses, tetroses, pentoses, and hexoses?

Trioses are sugar monomers made up of three carbons. Tetroses are sugar monomers made up of four carbons. Pentoses are sugar monomers made up of five carbons. Hexoses are sugar monomers made up of six carbons.

T/F Glycogen and amylopectin both contain alpha 1,6 branched linkages

True both glycogen and amylopectin contain alpha 1,6 branched linkages

True or false? Trioses are the simplest of all monosaccharides.

True. Trioses are the simplest of all monosaccharides.

Compare pyranose and furanose rings

Pyranose: a 6 membered ring Furanose: a 5 membered ring both ring structures minimize strain

Draw sucrose, lactose, maltose

Sucrose: (glucose -alpha-1,2-fructose) Lactose: (galactose-beta-1,4-glucose) Maltose (glucose-alpha-1,4-glucose)

T/F Glycogen serves as an energy storage unit for animals

T

T/F cellulose is the main structural components in plants

T

T/F cellulose, starch and glycogen are all composed of D-glucose

T

T/F enantiomers differ at every chiral center

T enantiomers a non superimposable mirror images. As a result, they must differ at every chiral center

What differs between cellulose, starch and glycogen?

They differ in the glycosidic bond linkage this leads to biological differences.

Draw or visualize D-glucose as a Fischer projection versus a Haworth diagram. Indicate which OH group attacks/attacked the carbonyl carbon in each.

The phrase "down right, up lefting" (which sounds like "downright uplifting") can help you remember that the groups on the right in the Fischer projection should point down in the Haworth diagram, and the groups on the left should point up.

Describe how the name "carbohydrate" relates to the structure of a carbohydrate.

The prefix "carbo-" and the suffix "hydrate" refers to the fact that carbohydrates contain carbon and water in general formula: Cn(H2O)n

Esterification

The reaction of an alcohol with a carboxylic acid to produce an ester and water.

Draw or visualize a D- versus L-glyceraldehyde. What makes a sugar monomer D versus L?

When drawn as Fischer projections, D sugar monomers have the OH group on the right for the final stereocenter.

glycoside formation of carbohydrates

When hemiacetals react with alcohols to form ACETALS

compare alpha and B-amylase

alpha-amylase cleaves amylose anywhere along the chain to yield short polysaccharides B-amylase: cleaves amylose at the NONREDUCING ENDS to yield maltose exclusively

How does branching affect solubility?

increased branching --> increased solubility because it decreases intermolecular forces

What is tautomerization?

rearrangement of bonds in a compound

Compare α and β anomers

α anomers: OH on C1 is trans to CH2OH β anomers: OH on C2 is cis to CH2OH

Which anomer is more stable?

β anomer (62%) is the most stable because it places all the large groups in the equatorial position in the chair conformation α anomer (38%) is less stable because the large groups are on the axial position (more steric strain)