Theme 2B Flashcards
What are the three steps of transcriptional regulation of gene expression?
- Initiation
- Elongation
- Termination
What does differential regulation of the genome give?
It gives rise to different cell types and tissues
What is an organisms phenotype dependant on?
Number of cells, type of cells, and the function of cells
Is every cell in an organism identical or different?
Every cell in an organism has an identical genome (DNA sequence)
What is transcriptional regulation?
Different genes are being turned on and off in different cell types and at different times in development
What is regenerative medicine?
Growing a desired tissue type by turning on/off the appropriate genes using molecular techniques
What are the components of a gene?
- The promoter
- Transcriptional unit
What is the promoter?
DNA sequence (including the TATA box) that specifies where transcription begins on the chromosome
- It is located upstream (5’) of the start point
- Found on the non-template/sense strand
- Recognized and bound by the transcriptional machinery (RNA polymerase, transcription factors) that initiate transcription
What is RNA polymerase?
- Synthesizes RNA transcript in the 5’-3’ (adds new ribonucleotides to 3’-OH)
- Reads DNA template in 3’-5’
- Does not need a primer for the initiation of RNA synthesis
- Unwinds and rewinds DNA helix during RNA synthesis (has helicase activity)
What are the three types of RNA polymerases?
- RNA polymerase 1: transcribes rRNA
- RNA polymerase 2: transcribes mRNA and microRNA
- RNA polymerase 3: transcribes tRNA
What is transcriptional initiation?
Mediated by direct interaction of DNA binding proteins to specific regulatory sequences of the gene (rate determining step, how much RNA made in a given time)
What are the two types of transcriptional initiation processes?
- General transcription factors: bind to promoter and recruit RNA polymerase 2 resulting in low level of transcription
- Transcriptional activator proteins: bind to enhancers (not part of the gene) regions distant from the promoter to cause DNA looping bringing mediator and RNA polymerase to the promoter resulting in lots of transcription
What are the steps of transcriptional elongation?
- RNA polymerase moves along the template DNA (3’-5’)
- DNA is unwound in front of moving RNA polymerase and reannealed behind the transcription bubble (contains DNA-RNA hybrid)
- Ribonucleotides added at the 3’ end of RNA transcript
- Synthesis continues in a 5’-3’
- Growing RNA transcript is displaced from DNA template strand to allow reannealing back into double stranded DNA
How does transcriptional termination occur in prokaryotes?
A 5’ termination sequence in DNA template causes termination after it is transcribed into RNA
What is Rho-independant termination?
Terminator sequence in mRNA base pairs with itself to form GC hairpin and causes RNA polymerase to stall and dissociate
What is Rho-dependant termination?
- Terminator sequence in mRNA is recognized and bound by the Rho helicase which unwinds the RNA from the template DNA and RNA polymerase
How does transcriptional termination occur in eukaryotes?
Poly-adenylation sequence in the DNA is transcribed into mRNA. It contains a cleavage site that signals the protein complex: CPSF to cleave the completed RNA transcript, which signals to the RNA polymerase to stop transcription
What are the components of post-transcriptional modifications? And what are post-transcriptional modifications?
it is the processing of mRNA molecules for stability and proper translation
1. 5’ capping
2. 3’ Polyadenylation
3. Splicing
Are the ends of prokaryotic and eukaryotic mRNAs translated?
NO. The 5’ and 3’ end have untranslated regions (UTRs). Both end UTRs regulate mRNA stability and translational efficiency
Were are ribosome binding sites (RBS) found and what are they?
5’ UTRs. These have part in translational initiation.
- Called Shine-Dalgaro sequence in prokaryotes
- Called Kozak (box) sequence in eukaryotes
What is an open reading frame (ORF)?
A region of mRNA that is translated and includes the start and the end codons at the borders (contains only exons).
What are some post-transcriptional modifications of eukaryotic pre-mRNA?
- 5’ cap: modified guanosine triphosphate is added to the 5’ end of the mRNA and acts as a ribosome binding site and protects mRNA from degradation
- Poly(A) tail: a long string of adenine nucleotides added to the 3’ end of mRNA by poly-A polymerase to protect mRNA from being degraded and increase translational efficiency
- Introns: are removed/spliced during pre-mRNA processing to produce translatable mRNA
What is newly transcribed mRNA?
Called pre-mRNA, undergoes processing in the nucleus to produce mature translatable mRNA
Describe pre-mRNA.
- Newly transcribed, not ready to be translated into a protein
- Needs to be converted to translatable mature mRNA
- Addition of the 5’cap and poly(A) tail
- Alternating exons and introns
- Once spliced, it is now mature mRNA and is exported from the nucleus into the cytoplasm to associate with ribosomes (translation)
