2.2 Gene expression Flashcards
What is gene expression?
The process of the information encoded in a gene is used to assemble a protein molecule
Why is gene expression regulated?
So the gene products are only produced if and when they are required by the cell
What are the three thing that must occur for a gene to be expressed?
Transcription, RNA processing and Translation
What are the sections before and after a gene called?
Upstream before the gene, downstream after the gene
What is a stop sequence?
A regional where encoding DNA ends for a gene
What is a start triplet sequence?
Region where encoding DNA begins
What is a promoter region?
Binding regions upstream of the gene where RNA polymerase can bind in order for transcription to occur
What are exons?
DNA regions within the gene that contain coding instructions
What are introns?
Non-coding segment of pre mRNA
What are the three steps of transcription?
Initiation, elongation and termination
Explain the initiation step of transcription
RNA polymerase attaches to the promoter region at the start of the gene and unwinds and unzips the DNA strand
How is DNA unzipped?
Through the use of the enzyme called helicase, which breaks the hydrogen bonds, exposing the nitrogenous bases
Explain the elongation phase of transcription
RNA polymerase moves along the template strand in a 3’ to 5’ direction. Complementary nucleotides bind to the template strand. This builds a strand called mRNA
What direction is mRNA made in?
5’ to 3’ direction, nucleotides being added to the 3’ end of the mRNA
What is the template strand?
The strand of DNA that nucleotides bind to to make mRNA
What is the coding strand?
The strand with the same base sequence as the mRNA strand, where Uracil replaces Thymine
Describe termination of the transcription phase
Transcription ends when the RNA polymerase reaches the termination site of the gene. (TAA, TAG OR TGA). The RNA polymerase detaches and the DNA reforms.
What strand does the RNA polymerase bind to?
Template strand
What strand is complementary to the growing mRNA strand?
The coding strand
What is the purpose of RNA processing?
To turn pre-mRNA into mature mRNA
What occurs during RNA processing?
A methyl cap is added to the 5’ end, a spliceosome removes the introns and some exons, a poly-A tail is added to the 3’ end
Where is a methyl cap added?
The 5’ end
What are introns?
Non coding sections of DNA
What are exons?
The coding sections of mRNA
Where is a poly-A tail added?
To the 3’ end of the mRNA molecule
What is the purpose of the methyl cap and poly-A tail?
To increase the mRNA’s stability and prevent it from degrading
Where does mature mRNA leave the cell?
Via the nuclear pore
