Gene Expression 1 (Genetics 5) Flashcards
Control elements
non-coding DNA segments that regulate transcription by binding transcription factors
Promoters
sequences of DNA bound by the first component
Enhancers
short nucleotide sequences that influence the rate of transcription, could be thousands of nucleotides away from the promoter, could also be bound by silencers/ repressor proteins
Introns
non-coding
Transcription
The process by which the information in a strand of DNA is copied into a new molecule of mRNA
Where does Transcription take place?
within the nucleus, Mature mRNA is exported to the cytoplasm for translation
What are the 4 steps of transcription
Initiation, Elongation, Termination and processing
Initiation
unwinding of DNA, RNA polymerase binds to the template strand
Elongation
RNA polymerase moves along the temperature strand, synthesising the pre-mRNA molecules
Termination
addition of additional adenine nucleotides at the 3’ of the RNA transcript (polyadenylation)
Processing
Introns are removed and the exons are spliced together to form a mature mRNA molecule consisting of a single protein-coding experience
What is the purpose of Chromatin remodelling?
Exposes the Promoter
Initiation: Recognition
Pre-initiation complex binds to
recognition sites within the promoter
» Control elements facilitate the binding
of the complex components
* Remember that distal control
elements can be far upstream but 3D
folding can bring them physically
closer
» Transcription occurs within a
transcription bubble opened by the
polymerase which has multiple
functions
Mediator Complex
Made up of many proteins in head, middle and tail regions, it interacts with transcription factors and RNA polymerase II
TATAA box
a recognition site within the
promoter with the nucleotide sequence TATAA.
PreInitiation Complex (PIC)
General Transcription Factors + RNA Polymerase
Anti-Sense Strand
non-coding DNA strand
Sense Strand
Coding strand, carries the translatable information
Pre-mRNA processing
both ends of pre mRNA are modified by the addition of chemical groups, introns are removed and exons are spliced together
What is capping
As RNA polymerase is elongating the
transcript, guanyltransferase attaches a
methylated GTP cap to the 5’ end of the
mRNA
What are the purposes of capping
- Regulation of nuclear export
- Prevention of degradation by exonucleases
- Promotion of translation
- Promotion of 5′ proximal intron excision.
Splicing
introns must be removed to get mature mRNA
How are introns removed?
a complex of RNAs and proteins called the spliceosome
Poly-A-Polymerase
Adds about 100-250 Adenine nucleotides to the cut end forming a Poly-A-Tail
