1. What is the difference between a nucleoside and a nucleotide? How are they linked together to form

nucleic acids?

- A nucleoside is a compound that consists of a nitrogenous base and a pentose sugar, while a nucleotide is a

nucleoside with one or more phosphate groups attached to the sugar. They are linked together by

phosphodiester bonds between the 3' hydroxyl group of one sugar and the 5' phosphate group of another

sugar to form nucleic acids.

2. What are the major types of lipids found in biological membranes? What are their roles and properties?

- The major types of lipids found in biological membranes are phospholipids, glycolipids, and cholesterol.

Phospholipids are amphipathic molecules that have a hydrophilic head and a hydrophobic tail, and they form

bilayers that act as barriers for the movement of polar molecules across the membrane. Glycolipids are

lipids with one or more sugar groups attached to the head, and they serve as recognition markers for cell-cell

interactions and signaling. Cholesterol is a steroid that modulates the fluidity and stability of the membrane

by inserting itself between the phospholipid tails.

3. What are the four levels of protein structure? How are they determined by the amino acid sequence and

interactions?

- The four levels of protein structure are primary, secondary, tertiary, and quaternary. The primary structure

is the linear sequence of amino acids in a polypeptide chain, which is determined by the genetic code. The

secondary structure is the local folding of the polypeptide chain into regular patterns such as alpha helices

and beta sheets, which are stabilized by hydrogen bonds between the backbone atoms. The tertiary structure

is the overall three-dimensional shape of the polypeptide chain, which is determined by the interactions

between the side chains of amino acids, such as hydrophobic interactions, ionic bonds, hydrogen bonds,

disulfide bridges, and van der Waals forces. The quaternary structure is the arrangement of two or more

polypeptide chains into a functional protein complex, which is determined by the same interactions as the

tertiary structure.

4. What are enzymes? How do they catalyze biochemical reactions?

- Enzymes are biological catalysts that speed up biochemical reactions by lowering their activation energy.

They do this by binding to specific substrates and forming an enzyme-substrate complex, which facilitates

the formation of transition states and products. Enzymes can also orient, strain, or stabilize substrates, or

provide alternative reaction pathways.

5. What are cofactors and coenzymes? How do they assist enzyme function?

- Cofactors and coenzymes are non-protein molecules that bind to enzymes and enhance their activity.

Cofactors are usually metal ions or inorganic molecules that act as electron donors or acceptors, or

participate in redox reactions. Coenzymes are organic molecules that act as carriers or transfer agents of