lecture 24 Flashcards
transcription and intron processing
what is the central dogma?
DNA(genotype) -> mRNA(intermediate) -> protein(phenotype)
where does transcription occur in eukaryotic cells?
nucleus
when does transcription occur?
in waves either at G1/S or G2/M
what is the DNA strand that mRNA is built from?
template strand
what is the exact same sequence of nucleotides in the mRNA except T, i.e., the DNA strand that is not being transcribed?
coding strand
what direction does transcription occur in?
5’ to 3’
what end are nucleotides added to?
3’ growing tip
what form must DNA be in for transcription to occur?
euchromatin
how does DNA become euchromatin from a heterochromatic state?
the histone cores are de-acetylated thereby reducing the positive charge of the core and loosening the wrapped DNA
what occurs during the recognition step of transcription?
a large complex of proteins form at the TATA box(promotor region) including TATA binding protein
what occurs during the initiation step of transcription?
other transcription factors bind to promotor region at TATA box and a mediator complex including ATPase and helicase unwind DNA, forming transcription bubble; unphosphorylated RNA Polymerase II binds to template strand via active site
what occurs during the elongation step of transcription?
RNA Polymerase II is phosphorylated at its carboxyl end by the mediator complex, allowing it to traverse the template strand and make an RNA copy; reads 3’ to 5’
what occurs during the termination stage of transcription?
two protein complexes(CPSF and CSTF) recognize poly A signal; strand is cleaved
what are the function of the 5’ guanine cap?
- regulation of transport out of nucleus through pore
- allows for translation as it helps the ribosome recognize the message
- prevention of mRNA degradation in the cytoplasm
- intron splicing
when is the 5’ guanine cap added?
once the RNA transcript is ~30 nucleotides long
where does ribonuclease cleave the nascent RNA?
downstream of the conserved AAUAAA site
what are the functions of the 3’ poly A tail?
- enhances stability of RNA molecule
- regulates transport to the cytoplasm
what is he mechanism by
which introns are removed?
splicing
what is the protein/RNA complex that
directs and insures proper RNA splicing?
spliceosome
what is hnRNA?
aka pre-mRNA, immature single-stranded mRNA that is present in the nucleus that contains introns
what is snRNP?
small nuclear RNA molecules
associated with specific ribonuclear
proteins playing essential role in splicing
what removes introns in tRNA genes?
proteins
what type of intron catalyzes its own removal from mRNA, tRNA, and rRNA precursors using guanosine‐5’‐
triphosphate (GTP), or another nucleotide cofactor – Ribozymes?
self-splicing introns (group 1)
how do group 2 self-splicing introns differ from group 1?
group 2 does not require GTP to remove themselves like group 1 does, instead group 2 requires the assistance of proteins
what are the parts of an intron?
- GU nucleotide sequence at the 5’ splice site (donor site)
- AG nucleotide sequence at the 3’ splice site (acceptor site)
- Polypyrimidine Tract (PPT) just upstream of the 3’ splice site that promotes the assembly of the spliceosome
- ranch Point Sequence (UACUAAC) – binding site for snRNP‐U2
what is a regulated process that results in a single gene coding for multiple proteins?
alternative splicing
what type of factors involved in alternative splicing are usually proteins that control gene expression?
trans-acting factors
what type of factors involved in alternative splicing DNA sequences in the vicinity of a gene
required for gene expression?
cis-acting factors
where does transcription occur in plants?
mitochondria or chloroplasts
