Lipids Bio

Elemental composition of lipids

Composed mainly of carbon ($C$) and hydrogen ($H$), with very few oxygen ($O$) atoms.

Monomer and polymer status of lipids

They do not form true monomers or polymers, unlike carbohydrates, proteins, and nucleic acids.

Primary biological functions of lipids

• Forming cell membranes

• Acting as chemical messengers/hormones

• Providing long-term energy storage

Closest monomer equivalent in lipids

Fatty acids

Saturated fatty acid

A fatty acid chain with no double bonds and the maximum possible number of hydrogen atoms; typically solid at room temperature (e.g., butter, lard).

Unsaturated fatty acid

A fatty acid chain containing one or more double bonds, which introduces kinks and lowers the melting point (e.g., olive oil).

Steroids

Lipids characterized by four fused carbon rings; act as hormones (such as testosterone and estrogen) and structural membrane components.

Triglyceride

A lipid molecule composed of one glycerol bonded to three fatty acids via three dehydration synthesis reactions; used for long-term energy storage.

Phospholipid structure

Consists of a polar, hydrophilic phosphate head and two nonpolar, hydrophobic fatty acid tails.

Phospholipid bilayer arrangement

The hydrophilic phosphate heads face towards the outer and inner cellular environments, while the hydrophobic fatty acid tails face inward away from water.

Cell membrane

A selectively permeable boundary composed of a phospholipid bilayer embedded with proteins and cholesterol; present in all cell types.

Vesicle

A small, spherical phospholipid bilayer structure in eukaryotes that transports materials into and out of the cell.

Vacuole

A large, membrane-bound organelle found in eukaryotes that stores water, nutrients, and dissolved solutes.

Turgor pressure

Internal hydrostatic pressure exerted by a vacuole against the plant cell wall to maintain plant rigidity.

Smooth endoplasmic reticulum (SER)

A eukaryotic network of membrane tubules without ribosomes that synthesizes lipids, modifies lipids, and detoxifies chemicals.