Function of Carbohydrates and Lipids

Carbohydrates contain the elements carbon (C), hydrogen (H), and oxygen (O).
Their main role is to provide energy through respiration, with glucose being the primary substrate.

Most basic units of carbohydrates with the general formula: $C<em>nH</em>{2n}O_n$
Hexoses (e.g., glucose, fructose, galactose) contain 6 carbon atoms.
Pentoses (e.g., ribose, deoxyribose) contain 5 carbon atoms.

Glucose is crucial due to the following properties:
- Can be completely broken down in aerobic respiration to generate a large number of ATP molecules.
- Main product of photosynthesis.
- Soluble in water, facilitating easy transport.
- Stable structure.

Alpha and beta glucose molecules differ in orientation of the hydroxyl group:
- In alpha glucose, the hydroxyl group at carbon 1 is downwards.
- In beta glucose, the hydroxyl group at carbon 1 is upwards.
This difference leads to distinct bonding formations and properties, resulting in different polysaccharides.
Enzymatic hydrolysis differs for alpha and beta glucose.

Formed by the union of two monosaccharides:
- Maltose: Two glucose molecules.
- Lactose: Glucose + galactose.
- Sucrose: Glucose + fructose.
Fructose has a pentagon shape in its ring form but is classified as a hexose sugar.

Glycosidic linkages connect monosaccharides, forming disaccharides and polysaccharides:
- Example: Two alpha glucose molecules join by a 1-4 glycosidic linkage between carbon 1 and carbon 4.
- Condensation Reaction: Two hydrogen atoms and one oxygen atom are released, forming a water molecule.
Hydrolysis Reaction: Water is added to break down maltose back into glucose units.

Storage carbohydrate in plants, composed of:
- Amylose (unbranched) and Amylopectin (branched).
- Both consist of alpha glucose linked by alpha-1,4 glycosidic linkages and branching via alpha-1,6 linkages.
- Starch is insoluble, making it ideal for storage.

Major storage carbohydrate in animals:
- Composed of highly branched alpha glucose.
- Has more branches compared to amylopectin for rapid glucose release.
- Utilizes alpha-1,6 glycosidic linkages for branching.

Structural carbohydrate in plants:
- Composed of beta glucose linked by beta-1,4 glycosidic linkages.
- Alternating rotations (180 degrees) create a straight chain.
- Forms extensive hydrogen bonds, resulting in strong fibril structures, providing strength to plant cell walls.

Lipids contain carbon (C), hydrogen (H), and oxygen (O), but proportionally, they have less oxygen than carbohydrates.
Generally insoluble in water, but soluble in organic solvents like ethanol.
Types of lipids include fats, oils, steroids, and waxes.

Composed of three fatty acids bound to a glycerol molecule.
- Fatty acids include a carboxyl group and a hydrocarbon chain.
- Hydrocarbon chains may be:
- Saturated: No double bonds.
- Monounsaturated: One double bond.
- Polyunsaturated: More than one double bond.
Formation involves ester bonds via condensation reactions, releasing three water molecules.
Energy storage, thermal insulation, protection of organs, and buoyancy in aquatic mammals.

Similar to triglycerides but one fatty acid is replaced by a phosphate group.
Characterized as amphipathic:
- Hydrophilic (water-loving) phosphate group.
- Hydrophobic (water-hating) fatty acid tails.
Important for cell membrane structure, with orientation in a bilayer (phosphate facing outwards, tails inwards).
Unsaturated fatty acids create more fluid membranes, which vary by environmental temperature.

A steroid with a distinct structure:
- Polar head group, fused ring structure, and flexible nonpolar tail.
Located within cell membranes:
- At higher temperatures, it decreases fluidity; at lower temperatures, it increases fluidity.
Serves as a precursor to steroid hormones (e.g., estradiol, testosterone) that can pass through cell membranes to reach target receptors.

Condensation reactions create larger molecules from smaller ones (e.g., polysaccharides from monosaccharides, triglycerides from fatty acids and glycerol).
Glycosidic linkages form in carbohydrates; ester bonds form in lipids.
Starch (plant storage) and glycogen (animal storage) are composed of α-glucose; both utilize α-1,6 linkages.
Cellulose, a structural carbohydrate, is made of β-glucose, with strength from extensive hydrogen bonding.
Phospholipids and cholesterol are amphipathic and crucial for cell membrane fluidity control, influenced by fatty acid saturation and cholesterol presence.