5' end

5' end refers to the end of a DNA or RNA strand that has the fifth carbon in the sugar-ring of the deoxyribose or ribose at its terminus. It is a significant concept in molecular biology and genetics, playing a crucial role in the processes of DNA replication, transcription, and translation.

Overview

In the structure of nucleic acids, each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base. The sugar in the nucleotide is either ribose (in RNA) or deoxyribose (in DNA). These sugars are pentose, meaning they have five carbon atoms. The carbons are numbered 1' through 5' (the prime symbol is used to distinguish these carbon atoms from those in the base). The 5' end of a nucleic acid molecule is the end at which the 5' carbon of the sugar is not bonded to another nucleotide, making it an end or terminus of the chain.

Role in DNA Replication

During DNA replication, the 5' end of the new DNA strand is the starting point. The enzyme DNA polymerase can only add new nucleotides to the 3' end of the DNA strand, so replication proceeds in the 5' to 3' direction. This is a critical aspect of the semiconservative replication model of DNA replication.

Role in Transcription and Translation

In transcription, the 5' end of the RNA transcript corresponds to the start of the gene on the DNA template strand. During translation, the ribosome reads the mRNA in the 5' to 3' direction, starting at the 5' end.

Modifications

In eukaryotic cells, the 5' end of the mRNA molecule is often modified with a 5' cap, which is important for stability of the mRNA and for initiation of translation. In some cases, the 5' end of a DNA molecule can be marked by phosphorylation, which can be important for the regulation of replication and other processes.

See Also

• 3' end
• DNA replication
• Transcription
• Translation
• 5' cap
• Phosphorylation