tRNA, rRNA structure and synthesis

CCA 3' end is added

post-transcriptionally after removal of intron, then leaves nucleus via nuclear pore added by nucleotidyltransferase

Inhibitors of RNA synthesis that bind to DNA

Actinomycin D intercalates DNA, blocks replication and transcription. Very toxic for both prokaryotic and eukaryotic cells.

tRNA anticodon site

Each tRNA has one binding site for a specific sequence of three nucleotides in mRNA

synthesis of tRNA

Eukaryotic cells contain multiple copies of each tRNA gene. RNA polymerase III transcribes the tRNA genes, recognizing a split promoter within the transcribed region of the gene.

Bacterial rRNA and tRNA transcripts

In prokaryotes, rRNA is produced as a single, long transcript that is cleaved to produce the 16S, 23S and 5S ribosomal RNAs. tRNA is also cleaved from a larger transcript. RNaseP, one of the cleavage enzymes, catalyzes the cleavage reaction.

synthesis of eukaryotic rRNA

Ribosomal RNA is transcribed as a large precursor molecule that is then modified and trimmed to form the mature species that participates in protein synthesis. RNA polymerase I transcribes the 45S ribosomal RNA precursor which is cleaved to produce the 18S, 28S and 5.8S rRNAs. The promoter consists of two sequences in the 5'-flanking region of the gene that differ from the promoters for RNA polymerases II and III. The 45S precursor is found in the nucleolar region of the nucleus, and methylated by S-adenosyl methionine (SAM) and cleaved to produce a 41S precursor, which undergoes further processing. During processing the rRNA precursors are associated with proteins. The 5S rRNA, produced by RNA polymerase III from genes located outside the nucleolus, migrates into the nucleolus and joins the ribonucleoprotein particles.

The nucleolus consists of 2 major regions that do what?

The nucleolus consists of a fibrous region in which the genes for rRNA are being transcribed and a granular region in which the precursors of rRNA, complexed with proteins, are being modified and trimmed.

structures of ribosomes in eukary. and prokary.

Three types of rRNA molecules, with sedimentation coefficients of 16, 23 and 5S are present in the ribosomes of prokaryotic cells. In eukaryotic cells there are four rRNA molecules of 18,28, 5 and 5.8S in ribosomes.

tRNA has a CCA 3' end where

amino acid attaches

40S and 60S ribosomal subunits are produced and

migrate through the nuclear pores to the cytoplasm where they combine, forming the 80S ribosomes which, complexed with mRNA, serve as the sites of protein synthesis

what is an operon? its components

operon is stretch of DNA found in bacteria. This operon controls gene regulation. there are typically three components of an operon: a promoter, operator, and structural gene. Promotor sequence- is where RNA polymerase binds. Operator sequence- is were a repressor binds and inhibits RNA polymerase from binding. Structural sequence- sequence that codes for the protein.

Inhibitors of RNA synthesis that bind to RNA polymerase

rifampicin prevents initiation of RNA synthesis, does not block elongation. Used as antibiotic. Streptolydigin prevents elongation of RNA chains. Used as antibiotic. alpha-Amanitin inhibits eukaryotic RNA polymerase (Pol II readily inhibited, Pol I is insensitive). Found in poisonous mushrooms

Structure and Synthesis of Eukaryotic Transfer RNA (tRNA)

tRNA molecules carry amino acids to ribosomes and ensure that the amino acids are incorporated into the appropriate positions in the growing polypeptide chain; they are adaptors. Cells contain at least 20 different tRNA molecules, one for each amino acid Many amino acids have more than one tRNA.

T or F, Although their base sequences differ, tRNA molecules all form a similar structure.

true

T or F, The genes for the 45S rRNA precursor are linked in tandem in the human genome

true