Transcription Process and Initiation

Transcription Process

• Transcription is the process of creating a complementary RNA copy from a DNA template.
• The transcriptase enzyme reads the DNA template and adds nucleotides to a growing RNA chain.
• In eukaryotic cells, transcription occurs in the nucleus, and the resulting RNA is called pre-mRNA.
• The pre-mRNA undergoes processing to become mature mRNA, which can then leave the nucleus and be translated into protein.

Initiation of Transcription

• The process of transcription begins with the binding of an enzyme called RNA polymerase to a specific DNA sequence called a promoter.
• The promoter acts as a binding site for RNA polymerase, allowing it to recognize where to start transcription.
• Each gene has its own promoter sequence, and some genes may have multiple promoters.

Elongation of Transcription

• Once RNA polymerase has bound to the promoter, it begins to unwind the DNA double helix and transcribe the template strand.
• The RNA polymerase reads the template strand in the 5' to 3' direction, adding nucleotides to the growing RNA chain.
• The process of transcription is similar to DNA replication, with the exception that RNA polymerase only adds nucleotides to the 3' end of the RNA chain.

Termination of Transcription

• Transcription is terminated when the RNA polymerase reaches a specific DNA sequence called a terminator.
• The terminator acts as a signal for the RNA polymerase to stop transcription.
• There are several ways in which the terminator can signal the RNA polymerase to stop, including the formation of a hairpin loop that prevents further transcription.

Processing of pre-mRNA

• In eukaryotic cells, the pre-mRNA undergoes processing to become mature mRNA.
• This processing involves the addition of a 5' cap and a poly-A tail to the pre-mRNA.
• The 5' cap is a modified guanine nucleotide that helps to protect the mRNA from degradation and aids in translation.
• The poly-A tail is a long sequence of adenine nucleotides that helps to stabilize the mRNA and promote translation.

Splicing of pre-mRNA

• In eukaryotic cells, the pre-mRNA may contain introns, which are sequences that do not code for protein.
• These introns are removed from the pre-mRNA through a process called splicing, leaving behind exons that are joined together to form the mature mRNA.
• The splicing process is carried out by a complex of enzymes called the spliceosome.

Final mRNA Product

• The final mRNA product is a mature, processed RNA molecule that is ready to be translated into protein.
• The mRNA molecule is composed of exons that are joined together, and is capped with a 5' cap and a poly-A tail.
• The mature mRNA is then transported out of the nucleus and into the cytoplasm, where it is translated into protein by the ribosome.

Transcription Process

• Transcription is the process of creating a complementary RNA copy from a DNA template.
• The transcriptase enzyme reads the DNA template and adds nucleotides to a growing RNA chain.

Initiation of Transcription

• The process of transcription begins with the binding of RNA polymerase to a specific DNA sequence called a promoter.
• The promoter acts as a binding site for RNA polymerase, allowing it to recognize where to start transcription.
• Each gene has its own promoter sequence, and some genes may have multiple promoters.

Elongation of Transcription

• RNA polymerase unwinds the DNA double helix and transcribes the template strand in the 5' to 3' direction.
• RNA polymerase adds nucleotides to the growing RNA chain, similar to DNA replication, but only adds nucleotides to the 3' end of the RNA chain.

Termination of Transcription

• Transcription is terminated when the RNA polymerase reaches a specific DNA sequence called a terminator.
• The terminator acts as a signal for the RNA polymerase to stop transcription.
• The terminator can signal the RNA polymerase to stop through the formation of a hairpin loop that prevents further transcription.

Processing of pre-mRNA

• In eukaryotic cells, the pre-mRNA undergoes processing to become mature mRNA.
• Processing involves the addition of a 5' cap and a poly-A tail to the pre-mRNA.
• The 5' cap is a modified guanine nucleotide that helps protect the mRNA from degradation and aids in translation.
• The poly-A tail is a long sequence of adenine nucleotides that helps stabilize the mRNA and promote translation.

Splicing of pre-mRNA

• In eukaryotic cells, the pre-mRNA may contain introns, which are sequences that do not code for protein.
• Introns are removed from the pre-mRNA through a process called splicing, leaving behind exons that are joined together to form the mature mRNA.
• The splicing process is carried out by a complex of enzymes called the spliceosome.

Final mRNA Product

• The final mRNA product is a mature, processed RNA molecule that is ready to be translated into protein.
• The mRNA molecule is composed of exons that are joined together, and is capped with a 5' cap and a poly-A tail.
• The mature mRNA is then transported out of the nucleus and into the cytoplasm, where it is translated into protein by the ribosome.