Cell Function - Carbohydrates

Cell Function - Carbohydrates

• Lecture Objectives: Define carbohydrate nomenclature, understand saccharide groups chemically and descriptively, understand carbohydrate classes, know glycosidic bonds, and understand the general role of carbohydrates.

Basic Concept of Carbohydrates

• Definition: Carbohydrates are composed of carbon, hydrogen, and oxygen, with the general formula (CH₂O)ₙ.

• Structure: Carbohydrates are diverse in structure, with a basic building block of monosaccharides. Monosaccharides link to form oligosaccharides, which further link to form polysaccharides.

Sources of Carbohydrates

• Various food sources contain carbohydrates, including vegetables, sugars, pulses, nuts, cereals, oil seeds, maize, potatoes, Jerusalem artichoke, leeks, burdock, and milk products like asparagus and artichoke.

Good vs. Bad Carbohydrates

• Complex Carbohydrates: These are also known as complex carbohydrates, and their chemical structure and fibers require more energy to digest and release energy over a longer period. Sources include whole-grain breads, cereals, and pastas.

• Simple Carbohydrates: These are smaller sugar molecules, digested quickly and stored as glycogen in cells. If not immediately utilized they are converted into fat. Sources include candy, desserts, sugared cereals, sodas, and sugary drinks.

Carbohydrate Nomenclature

• Basis: Nomenclature depends on the number of carbon chains, the functional group (aldehyde/ketone), and stereochemistry.

Glucose

• Formula: C₆H₁₂O₆

• Role: A crucial metabolite, significant in human blood circulation, and central to cellular energy metabolism.

Naming Monosaccharides

• Prefixes: The number of carbon atoms determines the prefix (e.g., triose, tetrose, pentose, hexose).

• Suffixes: The presence of an aldehyde group gives an "aldo" suffix, while a ketone group gives a "keto" suffix.

Monosaccharides (MS)

• Structure: Simple carbohydrate units composed of 3-9 carbon atoms with at least one aldehyde or ketone group and multiple hydroxyl groups.

• Types: Examples: Dihydroxyacetone, D-Glyceraldehyde, and L-Glyceraldehyde are discussed.

Stereoisomers

• Definition: Compounds with the same atomic order but differing spatial arrangements.

• Fischer Projections: Used to represent enantiomers; in these projections, chiral carbon atoms are at the intersection of vertical and horizontal lines, indicating bonds pointing toward/away from the observer.

Oligosaccharides

• Definition: Two or more monosaccharides linked by O-glycosidic bonds.

• Formation: Bonds form between hydroxyl groups on adjacent monosaccharides via reactions.

• Diversity: Multiple OH groups lead to various glycosidic linkages creating diverse structural carbohydrates.

Disaccharides

• Common forms: Sucrose, lactose, and maltose are common/abundant disaccharides.

• Dietary role: They serve as important components of the diet.

Sucrose

• Source: Sugar from cane or beet

• Composition: Formed from glucose and fructose.

Lactose

• Source: Milk

• Composition: Consists of galactose and glucose.

Maltose

• Formation: Formed from X + X.

• Reverse reaction: Maltose can be broken down into X + X.

Glycosidases

• Role: Enzymes that hydrolyze glycosidic bonds, breaking down oligosaccharides into monosaccharides.

Polysaccharides

• Structure: Large, complex oligosaccharides, including examples like amylose, amylopectin, glycogen, and cellulose.

Glycogen

• Function: Storage form of glucose.

Starch

• Structure: Glucose storage form in plants, including its unbranched (amylose) and branched (amylopectin) forms.

• Hydrolysis: Hydrolysed to glucose by α-amylase.

Cellulose

• Function: Major structural polymer in plants, consisting of linear glucose chains with β-1,4 glycosidic linkages.

Roles of Carbohydrates

• Energy: Carbohydrates function as energy stores and metabolic intermediates.

• Structure: Carbohydrates are components of RNA and DNA structures, and major components of plant cell walls.

• Signaling: Involved in cellular processes and signaling as carbohydrate molecules linked to proteins and lipids.

Glycoproteins/Glycolipids

• Structure: Carbohydrates attached to proteins or lipids.

• Process: Glycosylation process attaches carbohydrates to proteins/lipids.

Additional Information (from the presentation):

• There are different types of linkages, such as alpha and beta linkages that will influence the functionality of the molecule.