3.4 - DNA to protein Flashcards
transcription
production of messenger RNA using DNA template and ribonucleoside triphosphates as substrates
in which direction does RNA synthesis occur?
5’-3’
difference between DNA replication and transcription? (2)
- replication - identical copies of entire genome
- transcription - selective copies of certain parts of genome into RNA
role of RNA polymerase (3)
- DNA strands separate at active site of enzyme, polymerase transiently unwinds DNA base pairs
- ribonucleotides added to 3’ end of new RNA
- newly formed RNA forms RNA-DNA double helix (about 12 base pairs in length)
3 phases of transcription (3)
- initiation
- elongation
- termination
where does transcription occur?
the nucleus
promoters
RNA polymerase recognises and binds to promoters to start transcription
promoter in eukaryotes
TATA box (binding initiated by TATA-binding protein)
how is the first transcribed nucleotide numbered?
+1, regulatory sequences upstream have -ve numbers
terminator sequences (2)
- palindromic sequences that result in formation of hairpin, causing RNA polymerase to drop off DNA
- tell RNA polymerase where to stop
prokaryotic transcription (4)
- simpler production of mRNA molecules
- prokaryotic cells lack nucleus
3.transcription/translation/degradation take place in common compartment - translation of mRNA can begin before synthesis is completed
mRNA processing (eukaryotes) (3)
- adding 5’-cap of 7-methylguanosine (protects from degradation by nucleases)
- adding 3’-poly(A) tail
- splicing out introns and rejoining exons
what performs splicing reactions in the processing of pre-mRNA?
spliceosome
alternative splicing
- important means if generating protein diversity in eukaryotes
- different combinations of exons removed or retained in mature mRNA (can generate 2+ proteins from one gene)
what % of genetic diseases are caused by defects in splicing?
15%