Carbohydrates

• Carbohydrates are absorbed in the jejunum.
• A carbohydrate is a polyhydroxy aldehyde, a polyhydroxy ketone, or a compound yielding these upon hydrolysis.
• Carbohydrates contain only carbon (C), hydrogen (H), and oxygen (O), thus are hydrates of carbon.

Structure of Glucose

• Glucose's structure includes an aldehyde functional group and hydroxyl functional groups arrayed along a carbon chain.

Biological Importance

• Carbohydrates provide energy through oxidation.
• They supply carbon for cell component synthesis.
• They serve as a stored chemical energy form.
• They form structures of some cells and tissues.
• Carbohydrates, along with other compounds such as lipids and nucleic acids, are known as biomolecules because they are associated with living organisms.

Occurrence of Carbohydrates

• Carbohydrates are the most abundant class of bioorganic molecules.
• They constitute 75% of dry plant material mass.
• The ideal human diet consists of around ½ carbohydrate by mass.

Classes of Carbohydrates

• Carbohydrates undergo hydrolysis to produce monosaccharides.
• Monosaccharides are single-unit carbohydrates.
• Disaccharides are two monosaccharides.
• Oligosaccharides contain three to ten monosaccharides.
• Polysaccharides are long chains with potentially thousands of monosaccharides.

Monosaccharides

• They contain a single polyhydroxy aldehyde or ketone unit.
• They cannot be broken down into simpler units by hydrolysis reactions.

Disaccharides

• Disaccharides contain two monosaccharide units bonded covalently.
• Examples of disaccharides include sucrose or table sugar, and lactose which is milk sugar.

Oligosaccharides

• Oligosaccharides contain three to ten monosaccharide units bonded covalently.
• "Free" oligosaccharides are seldom encountered in biochemical systems.
• They are often found with proteins and lipids.

Polysaccharides

• Polysaccharides are polymeric carbohydrates with many monosaccharide units covalently bonded.
• They range from a few hundred to over 50,000 units.

Chirality

• Chiral molecules share the same relationship as left and right hands when reflected in a mirror.
• A chiral center is an atom in a molecule bonded to four different groups in a tetrahedral orientation, generating handedness.
• Nonsuperimposable mirror images are images where not all points coincide when overlaid.
• Achiral objects can be superimposed on their mirror images and do not possess handedness.
• Superimposable mirror images coincide at all points when overlaid.
• Any carbon atom connected to four different groups will be chiral and have two non-superimposable mirror images, acting a chiral carbon or center of chirality.
• If any two groups on the carbon are the same, the carbon atom cannot be chiral.
• Organic compounds, including carbohydrates, may contain more than one chiral carbon.

Stereochemistry of Carbohydrates

• Stereoisomers have the same molecular and structural formulas but differ in the orientation of atoms in space.
• Major features include the presence of a chiral center in a molecule and structural rigidity.

Enantiomers

• Enantiomers have structures that are non-superimposable mirror images of each other.

Diastereomers

• Diastereomers have structures that are not mirror images of each other.

Fischer Projections

• D and L systems are used to designate the handedness of glyceraldehyde enantiomers.
• Fischer projections are two-dimensional structural notations for showing the spatial arrangement of groups/chiral centers in molecules.
• A chiral center is represented as the intersection of vertical and horizontal lines.

Optical Activity

• An optically active compound rotates the plane of polarized light.
• Polarimeters are instruments used to measure the degree of plane-polarized light.
• A dextrorotatory compound rotates polarized light to the right or clockwise, such as D-glucose or (+)-glucose.
• A levorotatory compound rotates polarized light to the left or counterclockwise, for example, I-glucose or (-)-glucose.

Monosaccharide Classification

• Monosaccharides are the simplest carbohydrates with only one polyhydroxy aldehyde or ketone unit.
• They are classified by the number of carbon atoms they contain.
• The number of carbons determines class where: 3 = Triose, 4 = Tetrose, 5 = Pentose, and 6 = Hexose.
• The presence of an aldehyde (aldo-) or a ketone (keto-) is indicated by prefixes.
• Aldoses: Glucose, Ribose
• Ketoses: Fructose, Sedoheptulose

Physical Properties of Monosaccharides

• Most have a sweet taste, with fructose being the sweetest at 73% sweeter than sucrose.
• They are solids at room temperature.
• Monosaccharides are extremely soluble in water.

Biologically Important Monosaccharides

• D-Glucose (aldohexose) is the most abundant in nature and important for human nutrition.
• D-Fructose (ketohexose) is also important, known as fruit sugar, or levulose.

Haworth Projection Formula

• This is a two-dimensional structure notation specifying the three-dimensional structure of a cyclic form of monosaccharides.
• It was developed by Walter Norman Haworth.

Alpha & Beta Configuration

• The position of the -OH group on C1 relative to the CH2OH group determines the D or L series.
• The anomeric carbon is the hemiacetal carbon atom in a cyclic monosaccharide structure.
• Anomers are cyclic monosaccharides differing only in the substituents' position on the anomeric carbon atom.
• In beta configuration, both groups point in the same direction.
• in Alpha configuration, the two groups point in opposite directions.

Reactions of Monosaccharides

• Oxidation to acidic sugars
• Reduction of sugar alcohols
• Glycoside formation
• Phosphate ester formation
• Amino sugar formation

Oxidation to Acidic Sugars

• Monosaccharide redox chemistry is closely tied to their alcohol and aldehyde functional groups.
• Oxidation yields three different types of acidic sugars, depending on the oxidizing agent used.
• Aldehydes and ketones that have an -OH group on the carbon next to the carbonyl group react with a basic solution such as Benedict's reagent to create a brick-red percipitate.
• Sugars undergoing oxidation are reducing sugars, where all monosaccharides are considered reducing sugars.

Glycoside Formation

• Glycoside is the general name for monosaccharide acetals.
• It is an acetal formed from a cyclic monosaccharide via the replacement of the hemiacetal carbon -OH group with an -OR group.

Blood Types and Monosaccharides

• Blood types A, B, AB, and O's biochemical basis involves monosaccharides on plasma membranes of RBCs.
• The monosaccharides responsible for blood groups are D-galactose and its derivatives.
• Can also be knowns as Agglutination.

Phosphate Ester Formation

• The hydroxyl groups of monosaccharides react with inorganic oxyacids to form inorganic esters.
• Phosphate ester formation is stable in an aqueous solution and plays a role in carbohydrate metabolism.

Amino Sugar Formation

• In this formation, one hydroxyl group of a monosaccharide is replaced with an amino acid.
• Amino sugars and their N-acetyl derivatives are important building blocks of polysaccharides.

Disaccharide Formation

• Two monosaccharides can react to form a disaccharide.
• The bond that links two monosaccharides of a disaccharide is called a glycosidic linkage.

Cellobiose

• Cellobiose is produced as an intermediate in the hydrolysis of cellulose.
• This disaccharide contains two β-D-glucose monosaccharide units via a β(1-4) glycosidic linkage.
• It cannot be digested by humans.

Maltose

• Maltose is also known as malt sugar.
• Produced when starch, a polysaccharide, breaks down when seeds germinate and in the human digestion process.
• Composed of two D-glucose units, one of the must be α-D-glucose.

Lactose

• Lactose is mainly composed of B-D-glucose joined by α b(1-4) glycosidic linkage.
• A major sugar found in milk.
• Lactose Intolerance manifests when people lack the enzyme lactase, which is needed to hydrolyze lactose into galactose and glucose.
• Lactase hydrolyzes the in β(1-4) glycosidic linkages.
• Lactase deficiency can be caused by a genetic defect, physiological decline with age, or injuries to intestinal mucus.

Sucrose

• Sucrose is non-reducing table sugar.
• The most abundant disaccharide and found in plants.
• It is produced commercially from the juice of sugar cane and sugar beets.

Oligosaccharide Composition and Digestion

• Made up of 3 to 6 simple sugar units.
• Can be in peas and beans, and remains largely undigested until it reaches the large intestine, which releases gases.

Solanine

• A large multi-ring amine system to which a trisaccharide attaches.
• Raffinose (galactose-glucose-fructose).

Polysaccharides

• A large polymer containing many monosaccharide units bonded with glycosidic linkages.

Homopolysaccharide

• A polysaccharide in which only one type of monosaccharide monomer is present

Heteropolysaccharide

• A polysaccharide in which more than one type of monosaccharide monomer is present

Glycogen

• It is also known as "Animal starch".
• A polysaccharide containing only glucose units.
• Liver and muscle cells are storage sites for glycogen in humans.
• This polysaccharide is an ideal glucose storage form.
• Structurally contains both glycosidic linkages.
• It is highly branched, with branches occurring every 8-12 glucose units.
• Abundant in the liver and muscles; on hydrolysis; it forms glucose, which maintains normal blood sugar levels and provides energy.

Cellulose

• Is a linear homopolysaccharide featuring a β (1-4) glycosidic bond.
• Lacking the specific enzyme, the body cannot digest cellulose.
• Used as a dietary fiber ingredient which causes water to absorbed creating softer stools.

Acidic Polysaccharide

• A polysaccharide with a repeating disaccharide unit containing an amino sugar and a sugar with a negative charge due to a sulfate or carboxyl group.
• Structural polysaccharides in connective tissue associated with joints, cartilage, and synovial fluids in animals and humans.
• Ex. Hyaluronic acid and Heparin.

Hyaluronic Acid

• Alternating residues of N-acetyl-β-D-glucosamine, and D-glucuronic acid.
• It's highly viscous to serve as a lubricant in joints and part of the eye's vitreous humor.

Heparin

• An anticoagulant which prevents blood clots.

Glycolipids

• Lipids with one or more covalently bonded carbohydrates (or carbohydrate derivatives).

Glycoprotein

• Protein molecule with one or more carbohydrate units bonded to it.

Explore the structure, function, and classification of carbohydrates. Understand their roles in energy storage, plant structure, and optical activity. Review key concepts for biochemistry and biology studies.