Week 7 - DNA Transcription Flashcards
What are genes
A specific sequence of nucleotides (part of DNA) which acts as instructions for discrete products:
- translated mRNA (which creates protein)
- non-translated RNA e.g. tRNA and rRNA
everything else is not transcribed from the genome (DNA)
What is the complementary strand of DNA
the strand of DNA which is the exact opposite of the other strand e.g. the complementary strand of ATGTAC is TACATG
What is the template strand
The DNA strand which is read by the enzyme during transcription and where a complementary strand is added to
What is the non-templated strand
the complementary strand tot he template strand, which is not directly involved in transcription. This strand has the same sequence as the RNA transcript instead the U is replaced by T
What is DNA transcription
Transcription is the process by which a segment of DNA is used as a template to synthesize a complementary RNA molecule. This process is essential for gene expression, where the genetic information encoded in DNA is converted into functional RNA molecules such as messenger RNA (mRNA)
What are the names of the 3 major steps of DNA transcription
- Initiation
- Elongation
- Termination
What are the 3 major steps of transcription
- Initiation
- Transcription begins with the binding of RNA polymerase and other proteins called transcription factors, to the promoter region of DNA.
- Once bound to the promoter, RNA polymerase unwinds a short stretch of the DNA double helix to form an open complex, exposing the template strand
2.Elongation
- RNA polymerase moves along the template DNA strand, synthesizing a complementary RNA molecule in the 5’ to 3’ (5 prime to 3 prime) direction
- It adds nucleotides to the growing RNA chain based on the sequence of the template DNA strand, following the base-pairing rules (A with U, and C with G)
- As RNA polymerase progresses it continues to unwind the DNA double helix ahead of the transcription bubble and rewinds it behind, allowing transcription to proceed
3.Termination
Transcription ends when RNA polymerase reaches a specific sequence on the DNA called the terminator
What is the regulation of Lac Operon
The Lac Operon is an regulatory system in bacteria such as E.coli (Escherichia coli, which controls the expression of genes involved in the metabolism of lactose.
The regulation of the lac operon is mainly controlled by the presence or absence of lactose and glucose in the environment
What is the regulation of Lac Operon when only Lactose is present
- When lactose is present it is converted into allolactose which binds to the lac repressor protein, removing it from the operator region
- this allows RNA polymerase to bind to the promoter and transcribe the structural genes
- cAMP binds to the CAP site which boosts the RNA polymerase - acting like a glove
What is the regulation of Lac Operon when glucose and lactose is present
-When lactose is present it is converted into allolactose which binds to the lac repressor protein, removing it from the operator region
- this allows RNA polymerase to bind to the promoter and transcribe the structural genes
- presence of glucose prevents the binding of the catabolite activator protein to the CAP site so the transcription is not boosted
What is the regulation of Lac Operon when just glucose is present
In the absence of lactose the lac repressor protein binds to the operator region of the lac operon, preventing RNA polymerase from transcribing the structural genes
There is no lac operon expression/ transcription
What is the regulation of Lac Operon when just glucose is present
No lac operon transcription
Describe the post transcription modifications and mature mRNA
- in eukaryotes after transcription the RNA molecule undergoes several modifications to become mature mRNA (messenger RNA)
- Exons are the region of the transcript which are translated
- Introns are the region of the transcription which are ‘spliced out’
- Alternative splicing is where exons can be spliced together in many potential orders
in what type of cell does post transcription modifications occur
eukaryotes
