BIOLOGICAL MOLECULES

Secondary structure refers to the regular, repeated local spatial conformations of the polypeptide backbone, stabilized by hydrogen bonds between backbone atoms. The primary structure is the sequence, tertiary is the overall 3D fold of one chain, and quaternary is multi-subunit assembly.

The fundamental function of an enzyme is to act as a biological catalyst, lowering the activation energy and speeding up a reaction while remaining unchanged at the end. Specificity is about substrate choice, sensitivity relates to environmental factors, and regulation refers to control of its activity.

A conjugated protein (holoprotein) consists of a protein part (apoprotein) and a non-protein part (prosthetic group). If the prosthetic group is a cofactor and the protein is an enzyme, its removal yields an inactive apoenzyme. The term specifically relates to the loss of the non-protein component.

The model proposes a dynamic, fluid phospholipid bilayer where individual lipid molecules can move laterally. Proteins are not just on the surface but are integral or peripheral, creating a "mosaic" pattern that floats within the fluid lipid sea.

Denaturation unfolds a protein by disrupting the non-covalent interactions (hydrogen bonds, ionic bonds, hydrophobic interactions) that stabilize secondary, tertiary, and quaternary structures. The primary structure's covalent peptide bonds usually remain intact.

Unsaturated fatty acids contain kinks due to double bonds, preventing tight packing of the hydrocarbon tails. This increased space between lipids makes the membrane more fluid and permeable compared to a membrane rich in straight-chained saturated fatty acids.

The active site is a 3D pocket formed by amino acid residues brought together via the protein's tertiary folding. It is complementary to the substrate's shape and chemistry, and models like "induced fit" show it is flexible, not rigid.

Carbohydrates, particularly monosaccharides like glucose, are the primary and immediate energy source broken down during cellular respiration. Proteins are mainly structural and catalytic, lipids are for long-term energy storage, and nucleic acids store genetic information.

The term "carbohydrate" literally means hydrated carbon, reflecting the general ratio of one carbon to two hydrogens to one oxygen atom. Proteins contain nitrogen, and nucleic acids contain phosphorus, distinguishing them from this basic formula.

Glucose and fructose both have the molecular formula C6H12O6. Glucose is an aldehyde sugar (aldose), while fructose is a ketone sugar (ketose). This difference in the carbonyl functional group makes them structural isomers, not identical molecules.

The formation of a disaccharide involves the removal of a water molecule (dehydration synthesis) to form a glycosidic linkage between two monosaccharides. A peptide bond links amino acids, and an ester bond links fatty acids to glycerol.

Lipids are defined by their hydrophobic nature, being soluble in non-polar organic solvents (like ether, chloroform) but insoluble in water. This contrasts with carbohydrates and proteins which are generally hydrophilic.