7.2 Transcription and Gene expression (HL) Flashcards
What are the 3 main parts of transcribed RNA?
Promoter
Coding sequence
Terminator
What is the function of the promoter?
Non-coding sequence responsible for initiation if transcription
What binds the the promoter?
RNA polymerase
What controls the binding of RNA polymerase to the promoter?
Transcription factors
What are the two types of transcription factors?
Proximal or distal
What is the function of the coding sequence?
To code for proteins
What is the function of the terminator?
To stop RNA polymerase from continuing to transcribe
Which strand is the antisense strand?
The strand that is transcribed into RNA
Which strand is the sense strand?
The strand that is not transcribed into RNA
What is another name for the antisense strand?
Template strand
In which direction is the sense strand?
It is gene specific as either strand could have a gene
What is transcription?
The process by which DNA sequence (gene) is copied into complementary RNA sequence
What enzyme carries out transcription?
RNA Polymerase
Describe the process of transcription
RNA pol covalently binds nucleotide triphosphates (releasing 2 phosphates)
The 5’ phosphate links to the 3’-end
In what direction does transcription occur?
5’ - 3’
What must happen to the RNA sequence post-transcriptionally in eukaryotes?
Modification to the RNA sequence
Define capping
Involves adding a methyl group to the 5’ end of RNA
Why does capping occur?
To protect against degradation by exonucleases
Also used for recognition
What are the 3 post-transcriptional events that occur to form mature mRNA?
Capping
Polyadenylation
Splicing
Define polyadenylation
Adding a long chain of adenine nucleotides (poly-A tail) to the 3’ end of the transcript
Why does polyadenylation occur?
Improves transcript stability and facilitates the export from the nucleus
Define splicing
The removal of introns from RNA
Why does splicing occur?
Introns do not code for proteins
Define alternative splicing
The removal of exons that will result in the formation of different polypeptides from a single gene sequence
What are the functions of the regulatory proteins?
Bind to DNA sequences outside of the promoter and interact with transcription factors
Where do activator proteins bind?
Enhancer site
What is the function of activator proteins?
Increase rates of transcription
Where do repressor proteins bind?
Silencer sequences
What is the function of repressor proteins?
Decrease rates of transcription
What can cause changes in gene expression?
A variety of external and internal factors such as chemical signals
What determines how tightly DNA is packaged?
The protruding tails on histone
What can make DNA coil less tightly on a histone?
Adding an acetyl group to the tail, neutralising the charge on the histone
Why would we want DNA to coil less tightly?
Ease of transcription
What can make DNA coil more tightly on a histone?
Adding a methyl group to the tail, maintaining the positive charge
Define heterochromatin
DNA which is supercoiled and not accessible for transcription
Define euchromatin
DNA which is loosely packed and therefore accessible to the transcription machinery
What effect will increased methylation have on gene expression?
Decrease gene expression (by preventing the binding of transcription factors)
Define epigenetics
The study of changes in phenotype as a result of variations in gene expression levels
What factors (other than genes) can effect epigenetics?
Environmental factors
E.g.:
Pathogens, diet, exposure
