Biological Macromolecules: Lipids

Study Notes

Large group of nonpolar molecules, primarily composed of carbon, hydrogen, and oxygen.
Do not dissolve in water; soluble in organic solvents.

Fats (Triacylglycerols):
- Composed of glycerol linked to three fatty acids via ester bonds.
- Fatty acids consist of long hydrocarbon chains with a single carboxyl group.
- Saturated fats have no double bonds; unsaturated fats contain one or more double bonds.
Steroids:
- Characterized by complex ring structures with four hydrocarbon rings.
- Cholesterol is an essential component of animal cell membranes and a building block for steroid hormones.
Phospholipids:
- Made up of glycerol, two fatty acids, and a phosphate group, plus a head group.
- They are amphipathic, with a hydrophilic (water-attracting) end and a hydrophobic (water-repelling) end.
- Key components of cellular and organelle membranes.
Glycolipids:
- Similar to phospholipids but contain carbohydrate molecules.

Lipids can arrange into a bilayer form, with hydrophobic regions facing inward and hydrophilic regions on the exterior.

Include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
DNA serves as genetic material and directs cellular activities, coding for essential proteins.
RNA plays various roles, including protein synthesis and gene expression regulation; it also acts as genetic material in some viruses.
Composed of polymers of nucleotides.

Nucleotides consist of a nitrogenous base, a sugar, and a phosphate group.
DNA base pairing rules: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).
Hydrogen bonds between bases stabilize the double helix structure.
Nucleotides are joined via sugar-phosphate linkages, forming the sugar-phosphate backbone.

Cells obtain energy from the environment to create order, thus appearing to defy the second law of thermodynamics, which states that entropy increases in isolated systems.
Energy is used in cellular reactions, converting some into heat, which raises entropy outside the cells.

Cells perform millions of chemical reactions continuously.
Enzymes act as catalysts, facilitating reactions by lowering activation energy, making them occur at normal temperatures.

Enzymes cannot make energetically unfavorable reactions occur; they can only speed up favorable reactions (marked by negative change in Gibbs free energy, ΔG).
Cells couple reactions to harness energy from favorable reactions to drive unfavorable ones.
Standard free energy change (ΔG°) is used to predict reaction courses under standardized conditions.