Chapter 4: Carbohydrate Structure and Function Flashcards by Maria Tolosa

What is the basic structural unit of a carbohydrate?

monosaccharide

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What is the general formula for monosaccharides?

C_{n_{(H_{2_{O)_n}}}}

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What is the general formula for complex sugars?

C_{n_{(H_{2_{O)_m}}}}

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What is the simplest monosaccharide called and how many carbons does it have?

triose; 3 carbon atoms

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What are carbohydrates with four, five, and six carbon atoms?

tetroses, pentoses, and hexoses

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Carbohydrates that contain an aldehyde group as their most oxidized functional group are called ____________ and those with a ketone group as their most oxidized functional group are called ____________.

aldoses; ketoses

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What is a 6-carbon sugar with an aldehyde called?

aldhexose

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What is a 5-carbon sugar with a ketone called?

ketopentose

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The basic structure of a monosaccharide is illustrated by the simple sugar ________________, which is an aldose. Draw this structure.

glyceraldehyde

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How is a carbon atom in a monosaccharide numbered?

The carbonyl carbon is the most oxidized, and therefore will always have the lowest possible number

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In an aldose, the aldehyde carbon will always be carbon number ____. The aldehyde carbon can participate in ________________ linkages; sugars acting as substituents via this linkage are called ____________ residues.

one; glycosidic; glycosyl

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The simplest ketone sugar is ________________. Draw this structure.

dihydroxyacetone

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In dihydroxyacetone, the ____________ carbon is the most oxidized. In this case, the lowest number it will be assigned is carbon number ____. This is true for most ketoses on the MCAT.

carbonyl; two

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Ketoses can also participate in glycosidic bonds at the ________ carbon (#2).

carbonyl

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On every monosaccharide, every carbon other than the carbonyl carbon will carry a ____________ group.

hydroxyl

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Draw D-fructose

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Draw D-glucose

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Draw D-galactose

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Draw D-mannose

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Optical isomers, also called ________________, are compounds that have the same chemical formula; these molecules differ from one another only in terms of spatial arrangement of their component atoms.

stereoisomers

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A special type of isomerism exists between stereoisomers that are nonidentical, nonsuperimposable mirror images of each other. These are ____________.

enantiomers

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A chiral carbon is one that has ____ different groups attached to it.

chiral

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What characterizes an enantiomer?

Contains chiral carbons
No internal planes of symmetry

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While organic chemists use R and S to denote absolute configuration, biochemists use what?

D and L

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What is the general formula for number of stereoisomers with common backbone?

2ⁿ

The ____________ ____________ is a simple 2-D drawing of stereoisomers. Horizontal lines are ________, while vertical lines are ________.

Fischer projection; wedges; dashes

Using Fischer projections, all D-sugars have the hydroxide of their highest-numbered chiral center on the (right/left?) and all L-sugars have that hydroxide on the (right/left?)

right, left

Because D-glucose and L-glucose are enantiomers, *every* chiral center in D-glucose has the ________________ configuration of L-glcuose.

opposite

The same sugars, in different optical families, are ____________.

enantiomers

Two sugars that are in the same family (both are either ketoses or aldoses, and have the same number of carbons) that are not identical and are not mirror images of each other are ________________

diastereomers

A special subtype of diastereomers are those that differ in configuration at exactly one chiral center. These are defined as ____________.

epimers

Monosaccharrides contain both a ____________ group, which can serve as a nucleophila, and a ____________ group, which is the most common electrophile on the MCAT.

hydroxyl, carbonyl

The hydroxyl and carbonyl groups can undergo intramolecular reactions to form cyclic ____________ (from aldoses) and ____________ (from ketoses).

hemiacetals; hemiketals

Due to ring strain, the only cyclic molecule that are stable in solution are 6-membered ____________ rings or 5-membered ____________ rings.

pyranose; furanose

The hydroxyl group acts as the nucleophile during ring formation, so ____________ becomes part of the ring.

oxygen

Regardless of whether hemiacetal or hemikatal is formed, the carbonyl carbon becomes chiral in this process, and is referred to as the ____________ carbon.

anomeric

One of two ring forms can emerge during cyclization of a sugar molecule, either ____ or ____. Because they differ at the anomeric carbon, they are termed ____________

alpha or beta; anomers

In glucose, the ____-anomer has the -OH group of C-1 *trans* to the CH2OH substituent (axial and down), whereas the ____-anomer has the -OH group of C-1 *cis* to the -CH2OH substituent (equatorial and up).

alpha; beta

The Haworth projection is a useful method for describing what?

The 3D conformations of cyclic structures

How do Haworth projections depict cyclic sugars?

As 5 or 6-membered rings with top and bottom faces of the ring nearly perpendicular to the page.

Exposing hemiacetal rings to water will do what? What does this do and what is that called?

They cycle spontaneously between the open and closed form; since the C-1 and C-2 substituents can rotate freely, the alpha- or beta-anomer can be formed - this is **mutarotation**

Mutarotation results in a mixture that contains both alpha- and beta-anomers at ________________ concentrations.

equilibrium

Monosaccharides contain ________ and either ________________ or ________.

alcohols; aldehydes or ketones

The ____________ reaction of carbohydrates yields energy for the body.

oxidation

Just like aldehydes, hemiacetal rings can be oxidized to ________________ acids. These oxidized aldoses are called ____________ acids.

carboxylic; aldonic

Because aldoses can be oxidized, they are considered ____________ ________.

reducing agents

Any monosaccharide with a hemiacetal ring is considered a ____________ ____________.

reducing sugar

When an aldose is in a ring form, oxidation yields a ____________ instead - a cyclic ester with a carbonyl group persisting on the anomeric carbon.

lactone

Two standard reagents are used to detect the presence of reducing sugars. What are they?

1. Tollens' reagent 2. Benedict's reagent

Tollen's reagent must be freshly prepared, starting with ________ ________, which is mixed with ________ to produce ________ ________. Silver oxide is dissolved in ________________ to produce [Ag(NH3)2]+, the actual Tollens' reagent.

silver nitrate, NaOh, silver oxide ammonia

When Tollens' reagent is reduced, what does it produce when aldehydes are present?

A silvery mirror

When Benedict's reagent is used, the aldehyde group of an aldose is readily oxidized, indicated by what?

A red precipitate of Cu2O.

In addition to aldehydes, ________ ________ are also reducing sugars and give positive Tollens' and benedict's tests.

ketose sugars

Although ketones cannot be oxidized directly to carboyxlic acids, they can tautomerize to form aldoses under basic conditions, via ________-________ shifts.

keto-enol

________________ refers to the rearrangment of bonds in a compound, usually by moving a hydrogen and forming a double bond.

tautomerization

In tautomerization, the ketone group picks up a ____________ while the double bond is moved between 2 adjacent carbons, resulting in an ________: a compound with a double bond and an alcohol group.

enol

When the aldehyde group of an aldose is reduced to an alcohol, the compound is considered an ________. A ________ ________, on the other hand, contains a hydrogen that replaces a hydroxyl group on the sugar.

alditol, deoxy sugar

Esterification of carbohydrates forms a ____________ ________.

phosphate ester

Phosphorylation of glucose is a step in ____________ in which a phosphate group is transferred from ATP to glucose, which forms ________.

glycolysis; ADP

Hemiacetals react with alcohols to form ________.

acetals

What do disaccharides and polysaccharides form from?

glycosidic bonds between monosaccharides

Glycosides derived from furanose rings are referred to as ____________ and those derived from pyranose rings are called ____________.

furanosides; pyranosides

Glycoside formation is a ____________ reaction, thus breaking a glycosidic bond requires ____________.

dehydration; hydrolysis

A polysaccharide composed entirely of glucose is referred to as a ________________, while a polymer made up of more than one type of monosaccharide is considered a ________________.

homopolysaccharide; heteropolysaccharide

What are the 3 most important biological polysaccharides?

1. cellulose 2. starch 3. glycogen

Cellulose, starch, and glycogen are all made of ________________.

D-glucose

Polymer formation can be either ________ or ____________. Why?

linear or branched; because glycosidic bonding can occur at multiple hydroxyl groups in a monoaccharide

Polysaccharide branching occurs when what?

An internal monosaccharide in a polymer chain forms at least 2 glycosidic bonds

________ is the main component of plants.

cellulose

Can humans digest cellulose?

________ are polysaccharides that are more digestible by humans because they are linked alpha-D-glucose monomers.

starches

Plants predominantly store starch as ________, a linear glucose polymer linked via alpha-1,4 glucosidic bonds.

amylose

Another type of starch is ____________, which starts off with the same type of linkage that amylose exhibits but also contains branches via alpha-1,6-glycosidic bonds.

amylopectin

Starches like amylose and amylopectin are broken down by enzymes in the body and are used as a source of energy. Amylose is degraded by ____________ and ____________.

alpha-amylase, beta-amylase

____________ cleaves amylose at the **nonreducing** end of the polymer (the end with acetal) to yield ____________.

beta-amylase; maltose

____________ cleaves randomly along the chain to yield shorter polysaccharide chains: maltose and glucose.

alpha-amylase

________ is a carb storage unit in animals.

Glycogen

Glycogen has more ____________ bonds than starch.

alpha-1,6 glycosidic

Glycogen's branching optimizes its energy efficiency and makes it more ________, which allows more glucose to be stored in the body.

soluble

Glycogen's branching pattern also allows enzymes that cleave glucose from glycogen to do what?

Work on many sites within the molecule simultaneously

Glycogen phosphorylase functions by cleaving glucose from the nonreducing end of a glycogen branch and phosphorylating it, thereby producing ________ ____________, which plays an important role in metabolsim.

glucose 1-phosphate