Biochemistry: Carbohydrates Overview

Biochemistry

• Study of chemical substances in living organisms and their interactions
• Includes bioinorganic and bioorganic substances

Bioinorganic Substances

• Water (70% of mass)
• Inorganic salts (5% of mass)

Bioorganic Substances

• Proteins (15% of mass)
• Lipids (8% of mass)
• Carbohydrates (2% of mass)
• Nucleic acids (2% of mass)

Carbohydrates

• About 75% of the dry mass of plant material
• Important for energy production, storage, structure, and cell recognition

Carbohydrate Functions

• Oxidation provides energy
• Storage as glycogen provides a short energy reserve
• Supplies carbon atoms for other biomolecules
• Structural component of DNA and RNA
• Structural component of cell membranes
• Linked to protein function in cell-cell and cell-molecule recognition process

Carbohydrate Classification

• General formula: CnH2nOn or Cn(H2O)n
• Polyhydroxy aldehydes or ketones

Monosaccharide

• Single polyhydroxy aldehyde or ketone unit
• Cannot be broken down by hydrolysis
• Common examples: Glucose, fructose

Disaccharide

• Contains two monosaccharide units covalently bonded
• Common examples: Sucrose, lactose

Oligosaccharide

• Contains 3 to 10 monosaccharides
• Usually found associated with proteins and lipids
• Can be broken down into multiple monosaccharides via hydrolysis

Polysaccharide

• Polymeric carbohydrates with many monosaccharides
• Undergo hydrolysis under appropriate conditions
• Common examples: Cellulose and starch

Chirality

• Related to handedness of molecules
• Left-handedness and right-handedness are forms of isomerism

Mirror Images

• Reflection of an object in a mirror
• Superimposable mirror images coincide at all points when laid on top of each other
• Nonsuperimposable mirror images do not coincide at all points when laid on top of each other

Chirality in Molecules

• Presence of a carbon atom with four different groups bonded in a tetrahedral orientation
• Chiral center: carbon atom that generates handedness
• Chiral molecule: mirror images are not superimposable
• Achiral molecule: mirror images are superimposable

Stereoisomers

• Isomers with the same molecular and structural formula but differ in the orientation of atoms in space
• Two types: Enantiomers and diastereomers

Fischer Projection Formula

• Two-dimensional notation showing the spatial arrangement of groups around chiral centers in molecules

D, L System for Handedness

• Glyceraldehyde enantiomers are used as a reference to designate handedness
• Applied to monosaccharides with more than one chiral center in the lower manner

Haworth Projection Formula

• Two-dimensional notation specifying the three-dimensional structure of cyclic forms of monosaccharides

Enzymatic Oxidation Reaction

• Enzymes oxidize the primary alcohol end of an aldose, such as glucose
• Produces alduronic acid

Phosphate Ester Formation

• Hydroxyl groups of monosaccharides react with inorganic oxyacids to form inorganic esters

Reduction Reaction to Produce Sugar Alcohols

• Reduction of a monosaccharide results in a polyhydroxy alcohol
• Polyhydroxy alcohols are called sugar alcohols or alditols

Amino Sugar Formation

• Replacement of a hydroxyl group of a monosaccharide with an amino group

Glycoside Formation

• Hemiacetal reacts with alcohols in acid solution to produce acetals
• Glycoside: acetal form of a cyclic monosaccharide with the hemiacetal carbon –OH group replaced with an -OR group

Lipids

• Organic compounds found in living organisms that are insoluble (or sparingly soluble) in water, but soluble in nonpolar solvents
• Can be esters, amides, and alcohols (acyclic, cyclic, and polycyclic)
• Do not have a common structural feature that defines all lipids

Lipid Characteristics

• Mostly hydrophobic
• Made up of mostly C-H bonds
• Useful for long-term energy storage
• Make up the membranes of cells

Fatty Acids

• Carboxylic acids with a hydrocarbon chain
• Saturated: no double bonds in carbon chain (single bond)
• Unsaturated: one or more double bonds in carbon chain (double bonds)

Polyunsaturated Fatty Acids

• Fatty acids with two or more carbon-carbon double bonds in the carbon chain

Omega (ω)-6 Fatty Acids

• Unsaturated fatty acids with their endmost double bond six carbon atoms away from the methyl end

IUPAC Names for Fatty Acids

• Example: cis,cis-9,12-octadecadienoic acid indicates a double bond at carbons 9 and 12

Trans Unsaturated Fatty Acids

• The H atoms on the double bond are on opposite sides

Physical Properties of Fatty Acids

• Water solubility: directly related to carbon chain length; solubility decreases as chain length increases
• Short-chain fatty acids: slightly soluble
• Long-chain fatty acids: insoluble in water; nonpolar nature dominates solubility
• Melting point: strongly influenced by carbon chain length and degree of unsaturation
• Longer carbon chains have higher melting points
• Saturated fatty acids tend to be solid at room temperature
• Unsaturated fatty acids tend to be liquid at room temperature

Energy Storage Lipids: Triacylglycerols

• Human cells store small amounts of these materials
• Used as an energy source when energy demands are high

Triacylglycerols: Basic Structure

• Dehydration synthesis reaction
• Triacylglycerols are triesters (3 ester functional groups)
• Alcohol: glycerol
• Esterification reaction: one molecule of glycerol reacts with three fatty acids
• Acyl group: portion of a carboxylic acid remaining after the -OH group is removed from the carboxyl carbon atom

Triacylglycerols: Types

• Simple triacylglycerol: all three fatty acids are identical
• Mixed triacylglycerol: more than one kind of fatty acid is present

Types of Fatty Acids:

• Saturated Fatty Acids: Mostly solid at room temperature; commonly found in animal fats (butter, lard)
• Monounsaturated Fatty Acids (MUFA): "Good fats"; decrease heart disease and breast cancer risk; help reduce blood platelet stickiness and prevent blood clots; found in olive, avocado, and canola oils
• Polyunsaturated Fatty Acids (PUFA): "Good fats" and "bad fats"; found in many sources: vegetable oils, nuts, seeds
• Essential Fatty Acids: Required by the body but not produced by the body; include omega-3 and omega-6 fatty acids.

Recommended Fatty Acid Intake

• 15% of total fat intake should be MUFA
• 10% of total fat intake should be PUFA

Explore the essential biochemistry of carbohydrates, including their classification, functions, and significance in living organisms. This quiz covers the structures and roles of monosaccharides and their contributions to energy production, storage, and structural integrity in cells.