What is the difference between the 3′ end and the 5′ end of a polynucleotide?

Verified step by step guidance

1. Understand that a polynucleotide is a polymer consisting of many nucleotide monomers covalently bonded together.
2. Recognize that each nucleotide in a polynucleotide has a sugar, a phosphate group, and a nitrogenous base.
3. Identify that the 5′ end of a polynucleotide has a phosphate group attached to the fifth carbon of the sugar molecule.
4. Identify that the 3′ end of a polynucleotide has a hydroxyl group (-OH) attached to the third carbon of the sugar molecule.
5. Note that the directionality of a polynucleotide is important for processes like DNA replication and transcription, as enzymes typically work in a 5′ to 3′ direction.

Key Concepts

Polynucleotide Structure

Polynucleotides, such as DNA and RNA, are long chains of nucleotides linked by phosphodiester bonds. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base. The sequence and orientation of these nucleotides determine the polynucleotide's function and properties.

5′ and 3′ Ends

The 5′ end of a polynucleotide refers to the terminal end that has a free phosphate group attached to the fifth carbon of the sugar molecule. Conversely, the 3′ end has a free hydroxyl group attached to the third carbon. This directional difference is crucial for processes like DNA replication and transcription.

Directionality in Nucleic Acids

Directionality in nucleic acids refers to the orientation of the polynucleotide strand, which is always synthesized in the 5′ to 3′ direction. This means that new nucleotides are added to the 3′ end of the growing strand, influencing how enzymes interact with the DNA or RNA during replication and transcription.