Biochemistry Ch 7 Carbohydrates

What is the standard formula for carbohydrates?

Cn(H2O)n

How are carbohydrates produced? Products from what process?

Produced from CO2 and H2O via photosynthesis in plants

What’s the smallest sugar with a chiral carbon?

Glyceraldehyde

What’s are the major 3 functions of carbohydrates?

1. Energy source and energy storage

2. Structural component of cell walls and exoskeletons

3. Informational molecules in cell-cell signaling

Carbohydrates can be covalently linked to proteins forming products called what? (2 names)

Glycoproteins and proteoglycans

Carbohydrates typically have one or multiple chiral carbons?

Multiple

What are the monomers of carbohydrate polymers?

Monosaccharides

Does the way the monomer units are linked determine the sugar’s properties/function?

Yes

Storage of low molecular weight metabolites in the polymeric form avoids what effect that would occur from storing them as individual monomer?

High osmolarity, which would cause cells to swell and lyse due to entry of water via osmosis

Sequences of complex polysaccharides are determined by what?

Intrinsic properties of the biosynthetic enzymes that add each monomeric unit to the growing polymer

Is synthesis of polysaccharides a template dependent process?

No

Polysaccharides assume the 3D structure with the highest or lowest energy conformations?

Lowest

Is molecular complementarity central to function of carbohydrates?

Yes

What is the name of sugar-binding proteins?

Lectins

How are monosaccharides classified?

Number of carbons (triose - 3, tetraose - 4, pentose - 5)

How many carbons are in heptose?

7

Oligosaccharides are named based on what?

Number of monosaccharides (disaccharide - 2, trisaccharide - 3)

What are two categories polysaccharides are classified by?

• Homosaccharide (starch, glycogen)

• Heterosaccharide (semi-cellulose)

Do monosaccharides exhibit isomerism?

Yes

How do constitutional isomers and stereoisomers differ?

Constitutional isomer differs in the order of attachment of atoms

Stereoisomers are connected in the same order but differ in spatial arrangement

Enantiomers and diastereoisomers are both types of stereoisomers how do they differ?

Enantiomers are non-superimposable mirror images

Diastereoisomers are NOT mirror images

Epimers and anomers are different forms of which class of isomers?

Diastereoisomers

How do epimers and anomers differ as types of diastereoisomers?

Epimers differ at one of several asymmetric carbons

Anomers differ at a new asymmetric carbon atom formed from ring closure (alpha vs beta)

An aldose is a carbohydrate with what functional group?

Aldehyde

A ketose is a carbohydrate with what functional group?

Ketone

Aldoses and ketoses can be interconverted but in the process form what type of intermediate?

Enediol Intermediate

Can aldoses and ketoses be interconverted?

Yes

Glyceraldehyde and dihydroxy acetone are related how?

They are structural isomers. Both C3H6O3 but connected differently.

In sugars with many chiral centers which one designates the isomer as D (right) or L (left)?

The chiral carbon furthest from the carbonyl carbon.

D sugars and L sugars are what type of isomers?

Enantiomers (nonsuperimposable mirror images)

Most sugars in living organisms are D or L?

D

Do L- and D- glucose have the same water solubility?

Yes

What requirement must be met for a carbon to be considered chiral?

Four different groups attached to the carbon atom

What simple sugar occurs in the L form?

L-arabinose

How do optically active isomers affect light?

They rotate the plane of polarized light by a characteristic amount

Rotation of plane poralized light by chiral molecules can be split in two categories called what? And what direction do they rotate light?

Levorotatory (L) - left (counterclockwise)

Dextrorotatory (D) - right (clockwise)

Can chiral molecules rotate the plane of polarized light?

Yes

D and L conformations are determined when the aldehyde is positioned at the top or bottom relative to the determining chiral carbon?

Top

How many carbons and how many chiral centers are in Glyceraldehyde?

3 carbons and 1 chiral center

What is the reference carbon?

The anomeric carbon. I.e. the chiral center most distant from the carbonyl carbon

What is the relationship between these two isomers? Why?

They are diastereomers, specifically epimers, because they are not mirror images and they vary at only one chiral center.

Do diastereomers, including epimers and anomers, vary in their physical properties (i.e. water solubility and melting temp)?

Yes

What is the relationship between D-Mannose and D-Galactose in relationship to D-Glucose?

They are both epimers of D-Glucose

What carbon is the epimer between D-Mannose and D-Glucose?

C2

What carbon is the epimer between D-Galactose and D-Glucose?

C4

What is the relationship between chiral centers (n) and the number of stereoisomers?

A molecule with (n) chiral centers will have 2^n stereoisomers

4 chiral center = 16 stereoisomers (Aldohexoses)

How are fructose and glucose related?

Fructose is the ketose form of glucose which is an aldose

What is the standard five carbon sugar?

Ribose

What is the standard six carbon sugar?

Glucose

What five sugar structures do we need to memorize?

1. Ribose

2. Glucose

3. Galactose (epimer of glucose)

4. Mannose (epimer of glucose)

5. Fructose (ketose form of glucose)

What sugar is this?

D-Glucose

What sugar is this?

D-Mannose

What sugar is this?

D-Galactose

What sugar is this?

D-Fructose

What is this sugar?

Beta-D-Ribose

Do chiral molecules have a plane of symmetry?

No

A mirror image isomer of a chiral molecule is called what?

An enantiomer

A non-mirror-image isomer of a chiral molecule is called a what?

A diastereoisomer

In aldoses at what carbon is the aldehyde functional group located?

C1

In ketoses at which carbon is ketone functional group located?

C2

Are the carbons of aldehydes and ketones, nucleophilic or electrophilic?

Electrophilic

Can aldoses and ketoses react with alcohols?

Yes

The oxygen atom of an alcohol is nucleophilic or electrophilic?

Nucleophilic

When aldehydes are attacked by alcohols once they form what type of product?

Hemiacetal

When an aldehyde is reacted twice with an alcohol what type of product is formed?

Acetal

When a ketone is attacked one by an alcohol what type of product forms?

Hemiketal

When ketones are attacked twice by alcohols what type of product is formed?

A ketal

Why is the ability of ketones and aldehydes to react with alcohols important in carbohydrates?

It allows them to switch from the linear form to the cyclic form and back

How are cyclic sugars that only vary in their alpha vs beta configuration at the anomeric carbon related?

They are anomers

Where do anomers differ?

At the anomeric carbon

Do pentoses and hexoses readily undergo intramolecular cyclization?

Yes

When a monosaccharide is turned into the cyclic form which carbon becomes the anomeric carbon?

The carbon the previously bared the carbonyl

Which carbon determine alpha vs beta configuration?

Anomeric carbon

When is a cyclic sugar alpha?

When the OH group on the anomeric carbon is trans relative to the CH2OH group

When is a cyclic sugar beta?

When the OH group on the anomeric carbon is cis relative to the CH2OH group

Which carbon is the anomeric carbon in ketoses?

C2

Which carbon is the anomeric carbon in aldoses?

C1

Six membered oxygen containing rings are called what?

Pyranoses

Five-membered oxygen containing rings are called what?

Furanoses

The anomeric carbon is usually drawn on the left or right side?

Right

In the process of cyclization is the carbonyl carbon reduced or oxidized?

Reduced

Can alpha and beta forms be interconverted? Why?

Yes, because the orientation of the alcohol around the anomeric carbon is variable and transient

An attack between the C1 and C5 carbon will form what type of ring?

A pyranose (6 member O containing rings)

Formation of a hemiacetal will cause the carbohydrate to be in the linear or cyclic form?

Cyclic

Is pyranose and furanose a heterocyclic or homocyclic ring?

Heterocyclic

How does increasing temperature shift the equilibrium relative to the presence of pyranose and furanose

Shifts in the direction of the furanose form

Cyclization of glucose may take two different ways resulting in how many final configurations?

4 possible final configurations of glucose

What forms of ribose is the component of DNA and RNA backbone

Furanose form (specifically beta)

How are reducing sugars defined?

By the presence of a free anomeric carbon, not bound to another monosaccharide or larger.

What functional group can reduces Cu2+ to Cu+ via Fehling’s test?

Aldehydes

What functional group reduces Ag+ to Ag0 via Tollens’ test?

Aldehyde

What is the purpose of Fehling’s test and Tollen’s test?

Allows the detection of reducing sugars

Modern detection techniques for reducing sugars uses what two type of tests?

Colorimetric test and electrochemical test

Does the ring form of a sugar exist in equilibrium with the open-chain form?

Yes

The process of interconversion between the linear and cyclic conformations is known as what?

Mutarotation

Are monosaccharides reducing sugars?

Yes

What type of method is used to quantify reducing sugars?

Enzymatic methods

How does the enzyme glucose oxidase affect glucose?

Catalyzes its conversion to glucono-delta-lactone and hydrogen peroxide

How does hydrogen peroxide, a product of glucose oxidase reacting with glucose, affect organic compounds?

It oxidizes them into highly colored compounds. Concentrations of such compounds can then be measured colorimetrically.

Two sugar molecules can be joined via what type of bond?

Glycosidic bond