lecture 16 - transcription & gene expression Flashcards
What does the central dogma of molecular biology state?
Information ‘flows’ from DNA to RNA to a protein, in process called gene expression.
What is gene expression?
A process in which info from a gene is used in the synthesis of a functional gene product (protein or non-coding RNA).
How many protein coding genes are there?
~20,000
What is a gene, in terms of DNA sequence?
A defined region/sequence of DNA that produces a type of RNA molecule that has a particular function.
What are the functions of genes?
Regulate RNA synthesis, produce RNA, process RNA
What is transcription?
Process taking double-stranded DNA molecule and producing a single stranded RNA molecule
What catalyses transcription?
Enzyme - RNA polymerase
What does RNA polymerase synthesise?
mRNA (messenger RNA)
How does RNA polymerase form mRNA?
By catalysing the formation of phsophodiester bonds between ribonucleotides.
What are the two complementary strands of DNA, in terms of transcription?
Coding and template strands
What strand is used as the template for mRNA synthesis?
the template strand
What is the direction (in terms of 3’ and 5’ groups) of the coding strand of DNA?
5’ to 3’
What is the direction (in terms of 3’ and 5’ groups) of the template strand of DNA?
3’ to 5’
What are the 3 stages of transcription?
Initiation, elongation, termination.
In transcription, what is initiation regulated by?
Specific DNA sequences, that code for the beginning of a gene.
Where do transcription factors bind in transcription?
the TATA box
What is the TATA box?
A nucleotide sequence containing TATA found 25 nucleotides upstream from the transcription start point.
What is the promoter in transcription?
A region that includes the start point and the TATA box, and all of the nucleotides in between.
When RNA polymerase II binds to the DNA molecule in transcription, what is formed?
A transcriptional initiation complex.
How is mRNA synthesised after RNA pol II binds to the template strand?
RNA pol II unwinds the DNA double helix and then elongation can begin.
What is the process elongation in transcription?
RNA pol III moves along the DNA template strand, untwisting it in 3’ to 5’ direction, inserting complementary ribonucleotides in the 5’ to 3’ direction. As RNA strand grows, it peels away from template strand, allowing the DNA double helix to reform.
What is the direction of transcription along the template strand in mRNA synthesis?
Nucleotides added from 5’ to 3’ direction of mRNA strand (3’ to 5’ on the original strand, as they are anti parallel)
What is a ‘coding sequence’?
A portion of gene’s DNA that is translated into protein.
What are UTRs in terms of transcription?
Untranslated regions - transcribed regions of DNA that sit adjacent to the coding sequence but are not translated. They contain regulatory elements (sequences) that influence on gene expression at the transcriptional or translational level.
