Chemistry and Functions of Carbohydrates

Carbohydrates

• Carbohydrates are polyhydroxy ketones or polyhydroxy aldehydes.
• Carbohydrates can be hydrolyzed to form polyhydroxy ketones or polyhydroxy aldehydes.

Chemistry of Carbohydrates

• Carbohydrates consist of carbon, hydrogen, and oxygen.
• Carbohydrates were thought to be carbon hydrates, represented by the general formula Cn(H2O)n, where "n" equals the number of carbon atoms, this formula is only applicable to monosaccharides.
• Carbohydrates are the most abundant biomolecule on Earth.
• Glucose is the most important carbohydrate for humans.

Functions of Carbohydrates

• Carbohydrates are the main source of metabolic fuel for the body.
• ATP is produced from glucose oxidation, powering various body processes.
• Some carbohydrates function as energy stores in the form of glycogen in animal tissues and starch in plants.
• Carbohydrates act as structural components in organisms, providing strength and protection.
• Cellulose is a component of plant cells, and peptidoglycans form bacterial cell walls.
• Ribose and deoxyribose (carbohydrates) are components of nucleic acids.
• Carbohydrates are components of blood group substances and are used as sweeteners.
• Dietary fibers aid nutrient absorption and bowel motility.
• Carbohydrates prevent proteins from being used as metabolic fuel.
• Carbohydrates are the primary energy source for the brain and red blood cells.
• Carbohydrates serve as precursors for synthesizing amino acids and fats

Classification of Carbohydrates

• Carbohydrates are categorized into four classes based on complexity:
• Monosaccharides: Consisting of one sugar unit.
• Disaccharides: Consisting of two sugar units.
• Oligosaccharides: Consisting of 3 to 10 sugar units.
• Polysaccharides: Consisting of more than 10 sugar units.

Monosaccharides

• Monosaccharides cannot be broken down into simpler carbohydrates.
• Monosaccharides taste sweet, are solid at room temperature, and are soluble in water.
• Monosaccharides are the monomer units for building other carbohydrate classes
• Monosaccharides are subdivided into aldoses (aldehyde group) and ketoses (ketone group), based on their functional groups.
• Monosaccharides are grouped by carbon atom count: trioses, tetroses, pentoses, hexoses, and heptoses.

Pentoses of Physiological Importance

• Examples of pentoses (5-carbon sugars).
• D-Ribose is found in nucleic acids and metabolic intermediates and is a structural component of ATP, NAD(P), and flavin coenzymes.
• D-Ribulose is a metabolic intermediate involved in the pentose phosphate pathway.
• D-Arabinose is a component of plant gums and glycoproteins.
• D-Xylose exists in plant gums, proteoglycans and glycosaminoglycans and is a constituent of glycoproteins.
• L-Xylulose exists as a metabolic intermediate, and is excreted in urine in essential pentosuria

Hexoses of Physiological Importance

• Examples of hexoses (6-carbon sugars).
• D-Glucose is extracted from fruit juices, starch, cane or beet sugar, maltose and lactose, its the main metabolic fuel for tissues ("blood sugar") and high glucose levels can indicate poorly controlled diabetes mellitus.
• D-Fructose is derived from fruit juices, honey, sucrose hydrolysis and glucose syrups and it is readily metabolized either via glucose or directly. Hereditary fructose intolerance leads to fructose accumulation and hypoglycemia.
• D-Galactose is created through hydrolysis of lactose, easily metabolized to glucose, it it synthesized in mammary glands for lactose production, and is found in glycolipids and glycoproteins. Malfunctioning metabolization can result in hereditary galactosemia resulting in cataracts.
• D-Mannose is extracted through Hydrolysis of plant mannan gums and is a Constituent of glycoproteins

Stereochemistry of Monosaccharides

• Monosaccharides have one or more chiral carbons (asymmetric or stereogenic carbons).
• A chiral carbon is connected to four different groups.
• Groups around each chiral carbon project in 3D space.
• Humans utilize monosaccharides with a specific spatial arrangement (stereochemistry).
• Most sugars in the human body are D-sugars.

Showing Sterochemistry of a Chiral Carbon

• Biochemists use wedges to show 3D structures on paper.
• A solid wedge denotes a bond coming toward the viewer.
• A dashed wedge denotes a bond going away from the viewer.
• Straight lines depict bonds in the same plane as the page.

Fischer Projection Formulas

• Emil Fischer created an easier way to write stereochemistry.
• Bonds to the central carbon are represented by vertical and horizontal lines.
• The chiral carbon atom is at the center of the crossed lines.
• Horizontal bonds project out, and vertical bonds project into the page.
• The most oxidized carbon is placed at the top (carbonyl carbon for aldehydes; carbon number 2 for ketones).

Isomerism in Monosaccharides

• Isomers share the same chemical formula but have different structural formulas.
• Monosaccharides exhibit different types of isomerism, including constitutional isomers and stereoisomers.

Constitutional Isomers

• Constitutional isomers have the same chemical formula but differ in the connectivity of atoms.
• The most common constitutional isomers among carbohydrates arise from differences in functional groups (ketone or aldehyde).
• Example of Glucose and Fructose, both having the formula C6H12O6, Glucose has an aldehyde group, but Fructose has a ketone group

Stereoisomers of Monosaccharides

• Stereoisomers have the same chemical formula and bond connectivity, but the difference lies in the spatial arrangement of atoms on the chiral carbon.
• Stereoisomers can be named using their configuration (D or L) relative to glyceraldehyde (reference molecule).
• For monosaccharides with multiple asymmetric carbons, the carbon furthest from the carbonyl group determines the configuration.

Stereoisomers Types

• Stereoisomers can be named by optical activity. Optical activity is the measure of how much a substance rotates plane-polarized light.
• Stereoisomers exhibit optical activity.
• Monosaccharides deflect a beam of plane-polarized light either left (levorotatory) or right (dextrorotatory).
• The total possible of stereoisomers is: 2n (n = number of chiral carbons; Van't Hoff's rule).
• Vertebrates predominantly contain D-sugars

Enantiomers

• Enantiomers are stereoisomers that are mirror images of one another and are non-superimposable.
• D-Erythrose and L-Erythrose are examples of enantiomers.

Diastereoisomers

• Diastereomers: Stereoisomers that are not mirror images of each other and are non-superimposable, like enantiomers.
• Example of D-Erythrose and L-Threose are diastereomers.

Epimers

• Epimers are diastereomers that differ in configuration at only one asymmetric carbon.
• Example: D-Glucose and D-Mannose, which differ only at carbon 2.
• Second example: D-Glucose and D-Galactose, which differ only at carbon 4.

Cyclization of Monosaccharides

• Monosaccharides with five or more carbon atoms form rings in solution.
• An alcohol reacts with an aldehyde to form a hemiacetal; an alcohol reacts with a ketone to form a hemiketal.
• Monosaccharides with five or more carbon atoms undergo intramolecular reactions to form 5- or 6-membered rings.

Haworth Projection Formulas

• These are used to depict ring forms of monosaccharides.
• Carbon atoms are not shown.
• Direction when writing Haworth projection formulas
• Groups to the right in a Fischer projection point downward in the Haworth projection.
• Groups to the left in a Fischer projection point upward in the Haworth projection.
• The ring is perpendicular to the page, with the heavy line projecting toward the viewer.

Anomerism

• Monosaccharide cyclization creates a new asymmetric carbon, leading to anomers (α- and β-forms).
• Hydroxyl groups (OH) that appear upwards on the anomeric carbon are known as beta-sugars. Conversely, hydroxyl groups shown pointing downwards on the anomeric carbon are known as alpha-sugars.
• Alpha and beta anomers can interconvert (mutarotation).
• A 5-membered ring is a furanose, while a 6-membered ring is a pyranose.

Modified Monosaccharides

• Monosaccharides are modified by reactions to form derived monosaccharides.
• Common sugar derivatives include:
• Sugar acids
• Sugar alcohols
• Deoxy sugars
• Sugar esters
• Amino sugars

Sugar Acids

• Sugar acids contain one or more carboxyl groups, this results from oxidation of carbonyl groups, terminal -OH groups or both carbonyl and terminal -OH groups.
• Carbonyl group oxidation creates aldonic acids (e.g., gluconic acid, ribonic acid): aldehydes convert to carboxyl groups.
• Terminal -OH group enzymatic oxidation creates uronic acids (e.g., D-glucuronic acid and L-iduronic acid).
• Simultaneous carbonyl and terminal -OH oxidation yields aldaric acids (e.g., glucaric acid).

Aldonic, Uronic and Aldaric Acids

• Aldonic acids exist in equilibrium with lactone structures.
• Oxidation of the terminal alcohol yields uronic acids (e.g. D-Glucuronic acid and L-Iduronic acid).
• Oxidation of both ends yields aldaric acids. (e.g. D-Glucaric acid).

Sugar Alcohols

• Sugar alcohols are prepared by gently reducing with NaBH4 monosaccharide carbonyl groups.
• Reducing an aldehyde results in an alditol.
• Alditols are linear molecules (not cyclized).
• Alditols taste sweet.
• Examples are sorbitol, mannitol, and xylitol and can be find in sugarless gum and mint.
• Sorbitol accumulation causes cataracts in diabetics.
• Ribitol is in flavin coenzymes.
• Glycerol and myo-inositol are lipid components.

Deoxy-Sugars

• Deoxy-sugars refer to a hydroxyl group being replaced by hydrogen.
• Example Deoxyribose where hydroxyl group at carbon 2 of ribose is replaced by hydrogen, a component of DNA.
• They are also components of glycoproteins and polysaccharides
• L -Fucose is a 6-Deoxy sugar within glycoproteins.
• -* L-Rhammose is also a 6-Deoxy sugar and is a component of ouabain, ouabain being a toxic cardiac glycoside.
• 2-deoxyglucose is used to inhibit glucose metabolism experimentally

Sugar Esters

• These are monosaccharides, commonly, with a phosphate group added to them.
• Phosphate esters of glucose, fructose, glyceraldehyde, and other monosaccharides are crucial metabolic intermediates.
• The ribose of nucleotides such as ATP and GTP are phosphorylated at the 5' position.

Amino Sugars (Hexosamines)

• Amino sugars are hexose sugars with the hydroxyl group (OH) replaced by amine group at C2.
• Glucosamine is an amino sugar, Galactosamine (chondrosamine) is an amino sugar, and Mannosamine is an amino sugar.

Glycosides

• Glycosides are formed of condensations between the hydroxyl group of an anomeric carbon of a monosaccharide and, a second compound.
• The second compound can also be another monosaccharide
• The second compound is an agylcone when it's not an other sugar, an aglycone is known as a non-sugar part of a glycoside.
• If the second molecule is a hydroxyl, its an O -glycosidic bond
• If the second molecule is an amine, its an N-glycosidic bond.
• Aglycones may be methanol, glycerol, a sterol, a phenol, or a nitrogenous base such adenine.
• Cardiac glycosides contain steroids as aglycone, and other medically important glycosides include streptomycin.

Naming Glycosides

• Here is how to name a glycoside that are made up of only monosaccharide units:
• The non-reducing end is indicated first (written to the left)
• The configuration (α or β) at the anomeric carbon
• Name the nonreducing residue (furano, pyrano inserts ring size).
• Indicate the glycosidic bond's carbon atoms (e.g., 1 → 4).
• Name the second residue, and abbreviate monosaccharides in polysaccharide descriptions.

Disaccharides

• Disaccharides consists of condensation of two sugar units via an O -glycosidic bond.
• Maltose, sucrose, and lactose are all disaccharides of physiological importance.
• Other types include trehalose, isomaltose, lactulose, and cellobiose.
• Disaccharides don't usually exist alone in nature, but mostly, as other prodcuts.

Maltose

• Maltose, a disaccharide, consists of two a -D-glucose residues (via O -glycosidicbond).
• Glycosidic linkage: á(1→4).
• The enzyme maltase catalyzes hydrolysis of maltose into glucose.
• It typically comes from enzymatic break down of starch and glycogen

Lactose

• Lactose, a disaccharide, consists of β -D-galactose with a O -glycosidic bond in a-D-glucose residue.
• Lactose's glycosidic linkage is β (1→4).
• The enzyme lactase breaks down the components monosaccharides in lactose.
• Betaglucosidase is a similar enzyme, but can be find, in bacteria!
• Lactose is the disaccharide of milk

Sucrose

• Sucrose is extracted in cane and beet sugars, also know as a table sugar.
• The monosaccharides that make up sucrose are a – D -glucose with and β – D -fructose.
• Linkage: a, β(1 → 2) forms the disaccharide sucrose.
• a- C1 carbon of glucose attaches to β- C2 carbon of fructose.
• Animals break down sucrose into metabolites used for energy

Cellobiose

• Obtained from cellulose hydrolysis, cellobiose is a disaccharide.
• Like, Maltose, Cellobiose uses to D-glucose residues.
• The glucose residues in cellobiose are connected β(1 → 4) like, cellulose, unlike maltose and Mammals can't digest it

Reactions of Carbohydrates

• Formation of hemiacetals and hemiketals.
• Reduction and oxidation of aldehydes especially produces aldonic, uronic and aldaric acids.
• Reduction of keto or aldehyde produces Sugar alcohols
• Reduction of the hydroxyl group can create deoxysugars-
• Esterification of phosphate esters most important, but also see sulfate esters.
• There is Addition of amino group and acetylation reactions
• We see the Formation of glycosides!

Other Carbohydrates reaction types

• Oxidation and reduction of monosaccharides yields carbon dioxide and water. Complete breakdown forms ATP
• Glycosylation consists of carbohydrate attached to macromolecules via enzymes.
• Glycation is a carbohydrate linked without to a micromolecule without control of enzymes.
• There is an equilibrium of ketone/aldehyde of monosaccharide to enol tautomers. These tautomers are constitutional isomers.

Polysaccharides (Glycans)

• Glycans are polymers with >10 monosaccharides (monomer units) and 0 - glycosidic bonds!
• Homopolysaccharides contain one type of monomer.
• Heteropolysaccharides contain two+ different monomers.
• Homopolysaccharides act as both storage in the form of starch and glycogen that act as fuels and serve a structural component in plant walls and animals exoskeletons such as chitin and cellulose.
• Heteropolysaccharides provide structural support for various other kingdom of organisms.

Starch

• Starch is a homopolymer of glucose residues which are known as glucosan or glucan and contain a-glycosidic linkages.
• Starch is the stored form of carbohydrates in plants
• Typically the two forms of starch are the following: Amylose at 10-30% and Amylopectin at 70-90%.
• Amylose is a joining linear polymer of glucose via alpha-linkages. 6 Residues per helical turn.
• Highly branched chain: branches every 12-30 residues and average branch length between 24 and 30 residues. Contains alpha 1-4 for linear linkages, linear linages for amylopectin and alpha 1-6 which functions as branch linkages

Glycogen

• The major storage of polysaccharides is in the liver and animal muscles, its called Glycogen
• Glycogen as a homopolymer made out of D molecules.
• A similarity between this homopolymer is that is has (1->4) glucose residues and is linked to main chains using alpha (1->6) glycosidic bonds.
• Glycogen can be hydrolyzed further using: Alpha and Beta, the results are glucose and matose respectively. Furthermore it can be hydrolyzed by glycogen phosphorylase in the body

Inulin

• Inulin is one of the special polysaccharides! Known as a fructosan it made from a fructose component.
• Components join by beta (2->1) glycosidic bonds.
• The inulin is extremely soluble when wet and can be used to the determined the rate of glomerular filtration.
• They have no useful benefits to the body.
• No hydrolase can break down inulin.

Cellulose

• The primary structural support or polysaccharide which can be found in plants.
• Since the chain is of the same composition it is considered to be homopolymer.
• Linkages are Beta 1->4, is NOT like amylose. It is also INSOLUABLE which means that in mammalian bodies can not digest the B chains.
• Cellulose are long, straight chains which are strengthened by cross-linked hydrogen bonds.

Pectin

• Pectin is an essential element of the of a plant's cell wall since it it another important polysaccharide compound.
• It a heteropolysaccharide mainly comprised beta- D and has monomers of galacturnic acid.
• Pectins stop syneresis when you want to make jams.
• Used commonly for thickening and stabilizing agents and can be find in: Foods, laxatives, in throat lozenges

Chitin

• Chitin is structural polypeptide.
• It is found heavily in insect exoskeletons (prominently found/ second most abundant) .
• Structure and function similar to glucose.
• Monomer for this polypeptide is through BETA-glycosydic and the monomers are linked this way.
• Can't be digested by humans.
• Acetyalated aminosuvar: Unlike glucose/ cellulose .

Agarose

• Agarose functions as a polysaccharide and generally originates through red seaweed
• It is also linear in nature because of the repeating properties it has and the "Argarobiose" and Argarobiose functions of disaccharide with "2 parts" being. D-Galactose and D-Alactose
• Separates DNA, proteins through "Electrophoresis."
• Can be related with agar

Agar

• Agar is extracted as a jelly-like substance from algae that is red.
• But instead of individual component, there are 2, agarose! and AgarOpectin.
• When Algea is boiling with Agar, it forms a supporting structure.
• It gives a culture for micro biology work, solid state .
• It has many components in one, such as:
• As a general additive;
• Laxatives.
• Vegetarian additive's (gelatin).
• Thickener

Peptidoglycan

• Peptidoglycan, being a component in bacteria bacterial cell walls function's as a structural ployscharide of the cell's composition.
• Typically there are linear properties that can be find for the chains and the combination of amino groups, NAM beta (1 to 4) glycosidic bonds.
• Peptide can be joined through muramic and there have short peptide that have (4 to 5). Peptide chain of said molecule is cross across.
• Peptidoglycan in general is very THICK/ STRONG for gram -positive bacteria due gram to negative.

Glycosaminoglycans (GAGs)

• Also labelled mucopolysaccharides but generally are made through complex carbs that are primarily in the extracellular metric
• Heleropolysaccarides are a part of "repeat" disaccharide unit composition
• These composition is also known as:
• acetylated amino sugars. Can act either N or N. Typically acetylated amino sugars or "acetylgalactosamine" Uronic acids is another example and generally consist or id or Glu. And you are able to acetylgalactosamine can be joined with protein (molecule's) and you are able to come out with PROTEOGLYCAN

Classes of Glycosaminoglycans

Here are some components found within in: Hyaluronuc Heparin. Heparan. Kerstan Dermatan Chon4 Chon6

Hyaluronic acid

• Component that has D amino acids and N aminos
• No sulfate on Hyal which mean does not attach to protein. Mainly functions to support things like:
• lubricant
• Give shock absorbant in the synovial.
• gives vitreous humor to Vertebrae

Hyal allows certain types of Bacteria called HYALURONIDASE which breaks HA (hyaluronic acid) Hyalronidase is degrades GEL for effective penetration (ovum)

Heparin

• Glygcosaminoglycan it is an intracellular.

• Antigoayulatns that binds and is the greatest density for all known for molecules! It binds the anti thrombin via interactions, that are electrical.

• ADDED to samples for blood (analyzed)

Heparan Sulfate

• A sugar which is the same Heparin, although there are components such as sulfate and amino groups that are changed and are found in extracellular space

Keratan sulfate

• Has D-Galactose and N

This has no acid that can be in. However their are things like: bones/cartilage tendons etc

• Horn hair nail and hoof keratin (for “horn" in Greek)

Dermatan sulfate

• L can contribute to a plIANT in blood and skin • Overall "shape" in our eye area

Chondroitin Sulfates

• This is with D glucuro and N amnio. The important part is also the fact is in AbunDANT (glyco.)

Two examples that can provide here:

1. chondroitin 4 2). chondroitin 6

• Support :Ligaments tendons (Cartilage.) • In cartilage helps collgan and fibers in very strong settings

Glycoconjugates

• Linkage with carbs of oligosaccharides and polysaccharides to molecules
• Glycoconjugates include: proteoglycans, glycoproteins, glycolipids, and lipopolysaccharides

Proteoglycans

• Proteoglycans have covalent bonds to proteins
• High carbohydrate content (glycosaminoglycans, for example)
• Main site of activity occurs through carbon region.
• Extra or on surfaces.

Glycoproteins

• Protein has to have carbs linked to them. – Has 1 0r 3 sugar chain link
• Carbs typically LESS (con) compared and in comparsion and can be more protein.

Classification of Glycoproteins

Glycoproteins possess 3 classes 1st the O-LINK class for covalent bonding and amino side chains. Typically serine + or threonine . 2nd= N linked which consist amide nitrogen that the components join here through As par a gene and etc.

• GIP IS TERMINAL AMIN
• Carbohydrates used via linking with the help of ethanol, to gluso.