DNA transcription Flashcards
what are the 3 RNA molecules called
mRNA, tRNA and rRNA
what does mRNA do
encodes the amino acid sequence specified by a segment of DNA
what does tRNA do
transfers amino acids to a growing chain by encoding the mRNA sequence
what is rRNA
a constituent of ribosomes where protein synthesis occurs
what is transcription
enzyme system converts genetic information contained in a segment of the DNA double helix into a complimentary single strand of RNA
how many phases of transcription are there
3
what are the 3 phases of transcription called
initiation, elongation and termination
what happens during initiation
transcription does not require a primer so begins when the RNA polymerase binds to specific DNA sequences called promoters
describe promoters
they direct the transcription of adjacent segments of DNA
what do transcription factors do
regulate transcription
can upregulate or downregulate transcription by binding to sites on DNA allied to the promoter sequence or by altering activity of RNA polymerase
describe the assembly of the transcription machinery
DNA helicases- unwind the double helix of DNA
the topological strain on the DNA molecule is reduced by topoisomerases
how many types of RNA polymerase is there
3
what are the names of the 3 different RNA polymerases
RNA polymerase 1
RNA polymerase 11
RNA polymerases 111
what does RNA polymerase 1 do
synthesizes pre-ribosomal RNA which contains the precursors for 18S, 5.8S and 28S rRNAs
what does RNA polymerase 11 do
synthesizes mRNAs
what does RNA polymerase 111 do
synthesises tRNAs and 5S rRNA
what do RNA polymerases do
adds new ribonucleotide units to the 3/-hydroxyl end of a growing strand of RNA
what happens during elongation
new ribonucleotide units being added continues until an entire gene is transcribed
what happens during termination
a termination sequence in DNA releases RNA polymerase from DNA and newly synthesized strand of RNA is released - primary transcript
DNA recoils
the primary transcript is inactive
how is the primary transcript activated
post-transcriptional processing
what is the 5/ cap
the first residue inserted into RNA retains itd triphosphate groups
a residue of 7-methylguanosine is linked to this 5/ terminal by a 5/, 5/-triphosphate linkage
what is the role of the 5/ cap
facilitates the binding of mature mRNA to the ribosome during translation
may also protect mRNA from enzymatic destruction
what is polyadenylation involved in
post-transcriptional processing
what does happens during post transcriptional processing
several 3/-nucleotides are removed by an endonuclease
adenylate residues added to the free 3/-hydroxyl group by polyadenylate polymerase
3/-tail of 20-250 adenosine monophosphates
