Carbohydrates

Carbohydrates

Polyhydroxyaldehydes or polyhydroxyketones or substances that give these compounds on hydrolysis

Functions of Carbohydrates

1) Energy source
2) Energy storage
3) Carbon source
4) Structure/Protection
5) Recognition or Signaling
6) Can be attached to other macromolecules

Classes of Carbohydrates

1) Monosaccharides
2) Disaccharides
3) Trisaccharides
4) Polysaccharides (oligosaccharides)

Polysaccharides

Long chains of monosaccharides bridged through oxygen atoms. Can be thousands long and can be branched.

Monosaccharide

A carbohydrate that cannot be hydrolyzed to a simpler carbohydrate

Monosaccharide

Building blocks of all carbohydrates

Monosaccharide

They have the general formula C(n)H(2n)O(n), where n varies from 3 to 8.

Aldose

A monosaccharide containing an aldehyde group

Ketose

A moosaccharide containing a ketone group

Monosaccharides

Classified by their number of carbon atoms

Trioses

Simplest carbohydrate monosaccharides

Glyceraldehyde

Contains a stereocenter and exists as a pair of enantiomers

D,L designation

Refers to the configuration of the highest-numbered asymmetric center

D and L

Refers the stereocenter of interest back to D- and L-glyceraldehyde

D-sugars

This configuration of sugars predominates in nature.

D and L

These do not specify the sign of rotation of plane-polarized light.

right, left

In the D-form, the hydroxyl group is at the ___ side, while in the L-form, the hydroxyl group is in the ___ side.

left, right

In the L-form, the hydroxyl group is at the ___ side, while in the D-form, the hydroxyl group is in the ___ side.

Reducing Sugar

A sugar that reduces an oxidizing agent.

True

(T or F) Oxidation of a cyclic hemiacetal form gives a lactone.

True

(T or F) When the oxidizing agent is Tollens solution, silver precipitates as a silver mirror.

negative

If anomeric carbons are involved in glycosidic linkage, there will be a (positive/negative) Tollens reagent test.

positive

If another anomeric carbon is not bonded and is free, there will be a (negative/positive) Tollens reagent test.

True

(T or F) The carbonyl group of a monosaccharide can be reduced to a hydroxyl group by a variety of reducing agents, such as NaBH4.

Phosphoric Esters

These are particularly important in the metabolism of sugars to provide energy.

Phosphoric Esters

These are frequently formed by transfer of a phosphate group from ATP.

Amino Derivatives

These are the replacement of a hydroxyl group by an amino group to form amino sugars.

Glycoside

A carbohydrate in which the -OH of the anomeric carbon is replaced by -OR.

O-Glycosides

This forms when carbohydrates are reacted with hydroxyl groups under anhydrous, mildly acidic conditions.

Glycosidic bond

This is the bond from the anomeric carbon to the -OR group.

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

Most abundant disaccharides

Maltose (glucose-alpha(1-4)-glucose)

An abundant disaccharide, which is a product from the hydrolytic breakdown of starch.

Cellobiose (glucose-beta(1-4)-glucose)

An abundant disaccharide, which is a hydrolysis product of cellulose.

Lactose (galactose-beta(1-4)-glucose)

An abundant disaccharide, which is a milk sugar found only in dairy products.

Lactose (galactose-beta(1-4)-glucose)

The hydrolysis of this milk sugar is catalyzed by the enzyme lactase (beta-galactosidase) to produce glucose and galactose.

Sucrose (glucose-alpha,beta(1-2)-fructose)

This abundant disaccharide's mono-units can not form an open chain that contains free aldehyde or ketone because both anomeric C are tied into glycosidic bonds

N-glycosides

This new link is formed when the N-H group of amines can substitute for hydroxyl groups and react at the anomeric carbon center

True

(T or F) Some antibiotics are oligosaccharides or contain oligosaccharide groups.

Amylose and Amylopectin

Two forms of starch

Amylose

A form of starch with continuous, unbranched chains of up to 4000 alpha-D-glucose units joined by alpha-1,4-glycosidic bonds

Amylopectin

A form of starch with a highly branched polymer consisting of 24-30 units of D-glucose joined by alpha-1,4-glycosidic bonds, and branches created by alpha-1,6-glycosidic bonds.

True

(T or F) Amylases catalyse hydrolysis of alpha-1,4-glycosidic bonds.

beta-amylase

This is an exoglycosidase and cleaves from the nonreducting end of the polymer.

alpha-amylase

This is an endoglycosidase that hydrolyzes glycosidic linkages anywhere along the chain to produce glucose and maltose.

poorly

Amylose is (highly, very, poorly) soluble in water. It forms micellar suspensions.

helical

When amylose is subjected to water, it forms micellar suspensions in which it is ____.

Iodine

What fits into the helices of amylose in water that produce a blue color?

Considering a phosphorylase reaction, phosphorylase releases glucose-1-P products from the amylose or amylopectin chains.

The more branches, the more sites for phosphorylase attack.

Branches provide a mechanism for quickly releasing (or strong) glucose units for (or from) metabolism.

Why branching in starch?

Glycogen

The glucose storage device in animals

10, 1-2

Glycogen constitutes up to __% of liver mass and __% of muscle mass.

Glycogen

What is stored energy for the organism?

number of branches

What is the only difference of glycogen and starch?

8-12

Alpha(1,6) branches in glycogen happen every ___ residues.

red-violet

What color does glycogen give with iodine (similar to amylopectin)?

Dextrans

A small but significant difference from starch and glycogen

Dextrans

If we change the main linkages between glucose from alpha(1,4) to alpha(1.6), we get a new family of is polysaccharide, which is ---.

(1,2), (1,3), or (1,4)

Branches in dextras can be --, --, or --.

Yeast and bacteria

Where can dextran be found?

Dextrans

This family of polysaccharides consists of glucose residues connected into a main chain via alpha(1,6) glycosidic linkage with occasional branches formed by alpha(1-2), alpha(1-3), alpha(1-4) glycosidic

Dextran

Bacteria growing in teeth produce ---, which is an important component of dental plaque.

Sephadex

Cross-linked dextrans are used as "---" gels in column chromatography.

alpha(1-6) & 1-2, 1-3, or 1-4

Dextran is a branched polymer of D-glucose units. The main chain linkage is ___ but ___, ___, or ___ branches can occur.

N-N'-methylene bisacrylamide

Sephacryl gels are formed by cross-linking of dextran polymers with ___.

epichlorohydrin

Sephadex gels are formed from dextran chains cross-linked with ___.

True

(T or F) The degree of cross-linking determines the chromatographic properties of Sephadex gels.

Inulin

This homopolymer of D-fructose connected by beta(2-1) glycosidic linkage is usually found in vegetables.

structural polysaccharides

This type of polysaccharide has composition similar to storage polysaccharides, but has small structural differences that greatly influence properties.

structural polysaccharides

This type of polysaccharides is synthesized inside the cells but extruded to the outside to provide a protective wall or lubricative coating to cells.

cellulose

This structural polysaccharide is the major structural component of plants, especially wood and plant fibers.

cellulose

This polysaccharide is linear polymer of approximately 2800 D-glucose units per molecule joined by beta-1,4-glycosidic bonds

cellulose

This polysaccharide has a fully extended conformation with alternating 180-degree flips of glucose units.

cellulose

This polysaccharide has extensive intra- and intermolecular hydrogen bonding between chains.

cellulose (beta-1,4-glycosidic linkages) vs. amylose (alpha-1.4-glycosidic linkages)

What is the difference between cellulose and amylose?

Chitin

This structural polysaccharide is the protective exoskeleton of invertebrates such as insects and crustaceans and the cell walls of fungi, algae, and yeasts.

Chitin

This is an unbranched, structural homopolysaccharide.

N-acetylglucosamine, beta(1-4)

The building block of chitin is the glucose derivative ___ linked by ___ glycosidic bonds.

C-2s are N-acetyl; cellulose strands are parallel, but chitins can either be parallel or antiparallel

What is the difference between chitin and celulose?

Mucopolysaccharide or glycosaminoglycans (GAGs)

These structural polysaccharides are found in connective tissue (cartilage and tendons) or extracellular matrix.

glycosaminoglycans

These polysaccharides provide a thin, viscous, jellylike coating to cells.

Hyaluronic acid

An example of GAG with alternating units of N-acetylglucosamine and G-glucuronic acid (C6 of glucose oxidized to COOH).

Hyaluronic acid

This GAG serves as lubricant in joints, and in vitreous humor of eye, and is found in extracellular matrix of connective tissues.

Glycosaminoglycans

These are polysaccharides based on a repeating disaccharide where one of the monomers is an amino sugar and the other has a negative charge due to a sulfate or carboxylate group.

Heparin, Hyaluronic acid, Chondroitin sulfate, and Keratan sulfate

These are examples of glycosaminoglycans.

Heparin

A natural anticoagulant GAG that helps prevent blood clots.

Hyaluronic acid

A GAG that is a component of the vitreous humor of the eye and the lubricating fluid of joints.

Chondroitin sulfate and Keratan sulfate

GAGs that are components of connective tissue

Chondroitin sulfate

A heteropolymer GAG composed of two alternating units of N-acetylgalactosamine sulfate and D-glucuronic acid.

Chondroitin sulfate

A GAG that is solid in large quantities as over-the-counter drugs for repair of frayed or damaged cartilage especially in knees.

Pectin

A polymer of D-galacturonic acid linked by alpha-1,4-glycosidic linkage.

Pectin

A C4 epimer of glucose which is another important polysaccharide in plant cell walls.

Pectin

The epimer of glucose that is used as a gelling agent in jams, jellies, yogurt, and fruit preserves.

bacterial cell wall

Unlike __, plant cell walls contain comparatively little peptide or protein.

Animal cell surfaces

___ contain an incredible diversity of glycoproteins and proteoglycans.

Cell surface polysaccharides

These polysaccharide structures regulate cell-cell recognition and interaction.

Cell surface polysaccharides

The uniqueness of the 'information' in these structures is determined by the enzymes that synthesize these polysaccharides.

Bacterial cell walls

This example of structural peptidoglycans is prokaryotic cell walls constructed on the framework of the repeating unit NAM-NAG joined by beta-1,4-glycosidic bonds.

peptidoglycan shell

Bacterial cell walls are composed of 1 or 2 bilayers and ___.

Gram-positive bacteria

This bacterial cell wall has one bilayer and thick peptidoglycan outer shell.

Gram-positive bacteria

This bacterial cell wall has pentaglycine bridge that connect tetrapeptides.

Gram-negative bacteria

This bacterial cell wall has two bilayers with thin peptidoglycan shell in between.