ch 17

rna polymerase

enzyme that catalyzes polymerazation of rna from ribunucleoside triphosphates (NTPs). energy for polymerization from exergonic cleagave of 2 phosphates from each ntp. synthesis 5’ to 3’ end. does not require a primer

bacterial transcription

rna polymerase has core enzyme that transcribes genes, sigma binds to start of gene.

promoter

sequence of dna where transcription starts. -10 (usually TATAAT) and -35 box in bacteria. These are base pairs upstream of start of transcription.

bacterial transcription

initiation: sigma binds to dna at promoter and splits the strands. elongation: sigma released, rna polymerase uses template strand is used to polymerize dna using ntps. termination: transcription of stop codon rna forms hairpin loop.

differences in eukaryotic transcription

1. multiple rna polymerases: I mades rRNA, II makes mRNA, III makes tRNA and small RNA

2. TATA box is primary promoter region, located -30 bs from start point

3. general transcription factors instead of sigma recognize promoter region

4. transcription and translation are separate

rna processing

introns removed from rna primary transcript (non-functional), exons kept. first step to form mature rna

rna splicing

next step to rna processing. removes introns from primary transcript.

1. snRNPs bind to ends of introns and adenine site near the 3’ and.

2. introns come together to form spliceosome

3. cut the 5’ end of the intron, and form a loop.

4. cut the 3’ end, which is released.

5. exons come together

final rna processing

5’ cap added, made of gtp.

polya tail, adding adenines at the 3’ end of the sequence, increasing stability. poly a signal tells to stop transcription and add poly adenylation sequence.

hoagland et al experiment

showed that trnas are needed to transfer amino acids onto protein for translation because radioactive leucine transfered from trna to peptides.

anticodon

sequence on trna that attaches to codon. atp used to attache amino acid to trna, catalyzes by aminoacyl trna synthase.

wobble hypothesis

40 diff trnas. only first 2 nucleotides are important for binding anticodon

ribosomes

made of a large and small subunit, encase mrna for translation. 3 binding sides APE

translation part one

initiation: 1. ribosome binding side binds complementary rna on small subunit with help from initation factors. 2. initiator trna attaches anti-codon to start codone. 3. large subunit binds and ribosome moves trna to p site.

translation part two

elongation:

1. new trna attaches to a site, anticodon binds to mrna

2. amino acids form a peptide bond

3. translocation: ribosome moves one codon down mrna sequence. trnas move from a site to p site. elongation factors facilitate using gtp.

translation part three

termination:

1. release factor binds to stop codon at a site and breaks bond linking trna in p site to the peptide

2. polypeptide and trnas are released

3. ribosome seperates and mrna is released