A transcription bubble is a molecular structure that occurs during the transcription or replication of DNA when DNA helicase and DNA topoisomerase "unzip" the DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 double strand. DNA polymerase

DNA polymerase

A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....

 or RNA polymerase

RNA polymerase

RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...

 (Main Articles: DNA replication

DNA replication

DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...

, transcription

Transcription (genetics)

Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...

) may then bind to the exposed DNA and begin synthesizing a new strand of DNA or RNA. As DNA and/or RNA polymerase progresses down the DNA strand in the 3' to 5' direction, more of the DNA double strand is unwound, creating a replication or transcription bubble in the process that may be seen with specialized staining techniques and microscopy.
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See also:
Okazaki fragment

Okazaki fragment

Okazaki fragments are short molecules of single-stranded DNA that are formed on the lagging strand during DNA replication. They are between 1,000 to 2,000 nucleotides long in Escherichia coli and are between 100 to 200 nucleotides long in eukaryotes....

,
primase

Primase

DNA primase is an enzyme involved in the replication of DNA.Primase catalyzes the synthesis of a short RNA segment called a primer complementary to a ssDNA template...

,
transcription factors,
replication initiation complex,
transcription initiation