Introduction to Carbohydrates

Carbohydrate Introduction

• Carbohydrates can be defined as polyhydroxy-aldehydes or polyhydroxy-ketones or derivatives of polyhydroxy alcohols.
• They are composed of carbon, hydrogen, and oxygen.
• They are also referred to as saccharides.
• Carbohydrates are the main energy source for the body.

Classification of Carbohydrates

• Monosaccharides consist of a single polyhydroxy aldehyde or polyhydroxy ketone unit.
• Disaccharides are composed of two monosaccharide units linked by a glycosidic bond.
• Oligosaccharides have 3-10 monosaccharide units.
• Polysaccharides are polymers of more than 10 monosaccharides, which can be linear (e.g., cellulose) or branched (e.g., glycogen).

Monosaccharides

• Monosaccharides are classified based on the number of carbon atoms and the active group.
• Trioses (3 carbons) have either aldehyde or ketone groups.
• Tetroses (4 carbons) have either aldehyde or ketone groups.
• Pentoses (5 carbons) have either aldehyde or ketone groups.
• Hexoses (6 carbons) have either aldehyde or ketone groups.

Characteristics of Monosaccharides

• Isomers are compounds with the same formula but different arrangements in space.
• Stereoisomers are isomers that are non-superimposable mirror images.
• Aldo-keto isomers differ in functional groups (aldehyde vs. ketone).
• Epimers differ in the position of an OH group around one carbon.
• Enantiomers are mirror-image isomers.
• Anomers differ at the anomeric carbon, the new chiral center formed in the ring structure.

Disaccharides

• Maltose is composed of two glucose molecules linked by an α(1→4) glycosidic bond.
• Isomaltose is composed of two glucose molecules linked by an α(1→6) glycosidic bond.
• Cellobiose is composed of two glucose molecules linked by a β(1→4) glycosidic bond.
• Lactose is composed of galactose and glucose linked by a β(1→4) glycosidic bond.
• Sucrose is composed of glucose and fructose linked by an α,β(1→2) glycosidic bond.
• Lactulose is composed of galactose and fructose linked by a β(1→4) glycosidic bond.

Polysaccharides

• Glycogen, starch, and cellulose are important examples of polysaccharides.
• Glycogen is a branched polymer of glucose that serves as a storage form of glucose in animals.
• Starch is a storage polysaccharide in plants, composed of two components, amylose (linear) and amylopectin (branched).
• Cellulose is a structural polysaccharide in plants, composed of β-(1→4) linked glucose units.
• Hyaluronic acid is a component of connective tissues, composed of alternating N-acetyl glucosamine and glucuronic acid residues.
• Keratan sulfate is a glycoaminoglycan composed of N-acetylgalactosamine-4-sulfate and galactose.
• Heparin and heparin sulfate are anticoagulants found in mast cells, composed of glucosamine and glucuronic acid.

Chemical Properties of Carbohydrates

• Reducing properties: All monosaccharides are reducing sugars, due to the presence of an aldehyde or ketone group.
• Amino sugars: replacing an OH group with an amino group.
• Deoxy sugars: replacing an OH group with a hydrogen.
• Sugar acids: by oxidation.

Sugar alcohols

• Aldehyde/Ketone group in sugar can be reduced to alcohol.
• Examples are; sorbitol, mannitol and ribitol.

Carbohydrates: Optical Activity

• Optical activity of a solution arises from asymmetric carbon atoms.

• All monosaccharides (except dihydroxyacetone) are optically active.

• D- or L- enantiomers rotate plane-polarized light in opposite directions.

• α and β anomers rotate plane-polarized light in the same direction but at different angles.

•  Glycoconjugates are carbohydrates covalently linked to proteins or lipids.

• Proteoglycans are a type of glycoconjugate.

• Glycoproteins include proteins with covalently attached oligosaccharides.

• Glycolipids include membrane lipids with attached oligosaccharides.

Proteins Chemistry

• Proteins are polyamides made up of amino acid monomers connected by peptide bonds.
• Amino acids are the building blocks of proteins.
• Amino acids are classified based on their R-group properties and side chains
• Some amino acids (isoleucine, leucine, valine) are Branched-chain amino acids (BCAAs)
• Some amino acids contain Sulfur
• Proteins have four different structural levels.
• Primary structure: The linear sequence of amino acids in a polypeptide chain..
• Secondary structure: The folding of the polypeptide chain into repeating structural motifs such as α-helices or β-sheets.
• Tertiary structure: The three-dimensional arrangement of the entire polypeptide chain.
• Quaternary structure: The structure formed by the assembly of multiple polypeptide chains.

Protein Denaturation

• Denaturation is the loss of a protein's 3-dimensional structure and biological activity due to factors.
• Causes of Denaturation: Physical factors (e.g., high temperature, high pressure), chemical factors (e.g., strong acids or bases, urea).

Enzymes

• Enzymes are biological catalysts, increasing reaction rates without being consumed.
• Enzyme nomenclature utilizes both common names (e.g., sucrase) and systematic names (e.g., α-D-fructofuranosidase).
• Enzymes are classified into six major classes based on the type of reaction they catalyze.
• Enzyme activity is affected by temperature, pH, substrate concentration, and enzyme concentration.

Lipids

• Lipids are a diverse group of hydrophobic molecules with diverse structures and functions.
• They are classified into simple, complex, and derived lipids.
• Fatty acids are important components of lipids, with common classifications based on their chain length and the presence or absence of double bonds.
• Essential fatty acids are those that must be supplied in the diet because they cannot be synthesized in the body.
• Triglycerides are esters of glycerol and fatty acids and are the major form of energy storage in animals.
• Phospholipids are essential components of cell membranes, with a hydrophilic head and hydrophobic tails.
• Steroids are lipids with a four-ring structure.
• Cholesterol is a crucial steroid and the precursor for other steroid hormones.

Lipoproteins

• Lipoproteins are complexes of lipids and proteins that transport lipids in the blood.
• Four major classes of lipoproteins are chylomicrons, VLDL, LDL, and HDL..
• These lipoproteins differ in their lipid and protein composition, size, and function.

Biological Membrane Proteins

• Membranes are important biological structures that separate cells from their surroundings.
• Membranes are highly selective to control the flow of information.
• Membrane structure is characterized by a phospholipid bilayer and embedded proteins.

Metabolism

• Metabolism is the sum of all biochemical reactions inside living organisms.
• Catabolic reactions break down large molecules into smaller ones (releasing energy).
• Anabolic reactions build up large molecules from smaller ones (requiring energy).
• Amphibolic pathways are involved in both catabolic and anabolic reactions.
• Metabolic pathways are a series of chemical reactions that occur in a cell.
• Metabolic pathways can be regulated by controlling the activity or amount of enzymes.

This quiz covers the basics of carbohydrates, including their chemical structure and classification. Learn about monosaccharides, disaccharides, oligosaccharides, and polysaccharides, and understand their roles as energy sources in the body.