Chapter 3

Chapter 3
Macromolecules
Macromolecules
Four classes of cellular macromolecules:
Proteins-amino acids-polypeptides-protein
Nucleic acids-DNA and RNA
Lipids- fatty acids, fats, sterols, waxes,
Saccharides (carbohydrates)
Protein Structure
Lipids: Fats, Waxes, Steroids, Phospholipids
Saccharides

Weak bonds—such as hydrogen bonds van der Waals forces, and hydrophobic interactions—also affect macromolecular structure, but through more subtle atomic interactions.

A variety of functional groups containing carbon atoms are common in biomolecules and in the folding of complex biomolecules.

The bacterial cell is about 70% water, with over one-half of the dry portion being made up of protein and one-quarter being made up of nucleic acids.

Proteins are polymers of monomers called amino acids.

Nucleic acids are polymers of nucleotides and are found in the cell in two forms, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).

Lipids have both hydrophobic (nonpolar) and hydrophilic (polar) properties. They play crucial roles in membrane structure and as storage depots for excess carbon.

Polysaccharides are polymers of sugars and are present primarily in the cell wall.

The relatively simple structure of the polysaccharides and their derivatives makes them:
the most abundant natural polymer on Earth and
allows them to be used for metabolism, as a component of information transfer molecules, and for cellular structure.

Combine monomeric units (monosaccharides) into polymers (polysaccharides)

All with a carbon-water (carbohydrate) chemical composition approaching (CH2O)n.

The two different orientations of the glycosidic bonds that link sugar residues impart different properties to the resultant molecules. (isomers)

Polysaccharides can also contain other molecules such as proteins or lipids, forming complex polysaccharides.

Lipids
Lipids are amphipathic—they have both hydrophilic and hydrophobic components.

This property makes them ideal structural components for cytoplasmic membranes.

The fourth bond can be one of 21 common side groups, which may be ionic, polar, or nonpolar. It is the heterogeneity of these side groups that defines the properties of a peptide or protein.

Proteins: Primary and Secondary Structure
The sequence of covalently linked amino acids in a polypeptide is the primary structure.

When many amino acids are covalently linked via peptide bonds, they form a polypeptide.

Secondary structure
Hydrogen bonding that produces an alpha-helix ("corkscrew") or beta-sheet ("washboard") formation, or domain

Proteins may have an assortment of either or both domains.

Quaternary Structure
Association of several polypeptides results in quaternary structure

Protein Structure
The final orientation and folding dictates the usefulness of a protein.

Destruction of the folded structure by chemicals or environmental conditions is called denaturation