Question

1. what does the term \directionality\ refer to when discussing polynucleotides? 7. in reference to question 6, label the ends of the polynucleotide to the left. 8. what type of reaction occurs to covalently bond nucleotides? describe the reaction. 9. what is the name of the bond that holds nucleotides together? label these bonds on the polynucleotide to the left. 10. to which end would nucleotides be added in a growing polynucleotide? demonstrate this by drawing a nucleotide being added to the polynucleotide chain to the left (you may choose any appropriate nitrogenous base for the nucleotide).

Explanation:

1. Directionality in polynucleotides refers to the orientation of the 5' - phosphate and 3' - hydroxyl ends. Nucleic acid synthesis occurs in the 5' to 3' direction.
2. The top - most end is the 5' phosphate end and the bottom - most end is the 3' hydroxyl end as labeled in the given structure.
3. A condensation (dehydration synthesis) reaction occurs. In this reaction, the 3' hydroxyl group of one nucleotide reacts with the 5' phosphate group of another nucleotide, releasing a water molecule and forming a covalent bond.
4. The bond is a phosphodiester bond. It connects the 3' carbon of one sugar molecule to the 5' carbon of the next sugar molecule in the polynucleotide chain.
5. Nucleotides are added to the 3' end. In DNA and RNA synthesis, the incoming nucleotide's 5' - phosphate group forms a phosphodiester bond with the 3' - OH group of the growing polynucleotide chain.

Answer:

1. It refers to the 5' - 3' orientation of the polynucleotide, with synthesis occurring in the 5' to 3' direction.
2. The top end is 5' phosphate end and the bottom end is 3' hydroxyl end.
3. Condensation (dehydration synthesis) reaction. A water molecule is released when the 3' - OH of one nucleotide reacts with the 5' - phosphate of another.
4. Phosphodiester bond.
5. Nucleotides are added to the 3' end.