Chapter 9 Flashcards
What is initiation?
It is the beginning of transcription.
What happens in the initiation stage in transcription?
An enzyme called RNA polymerase attaches to a region of a gene, called the promoter, and signals to the DNA to unwind so that it can read the bases of one DNA strand.
What is elongation?
It is the addition of nucleotides to the mRNA strand.
What is termination?
The end of transcription.
When does termination happen?
When the RNA polymerase crosses a termination sequence in the gene.
What happens to eukaryotic pre-mRNAs after transcription?
They must undergo several processing steps before they can be translated.
What are the steps of eukaryotic pre-mRNA processing?
A cap is added to the 5′ end of the growing transcript by a phosphate linkage, an enzyme called poly-A polymerase adds a string of approximately 200 A residues, and eukaryotic genes are composed of exons and introns
What is the poly-A tail?
A string of approximately 200 A residues that the poly-A polymerase adds to the pre-mRNAs.
What happens to introns during processing?
They are removed from pre-mRNAs.
What is the process of removing introns and reconnection exons called?
It is called splicing.
What is another name for the translation process?
protein synthesis!
The process of translation involves the decoding of an mRNA message into ____?
a polypeptide product.
Amino acids are covalently strung together by ______?
interlinking peptide bonds.
When are polypeptides formed?
They are formed when an amino group of one amino acid forms an amide (i.e. peptide) bond with a carboxyl group of another amino acid.
in addition to the mRNA template, what other molecules and macromolecules contribute to the process of translation?
Ribosomes, tRNAs, and various enzymatic factors.
What are ribosomes?
A complex macromolecule composed of structural and catalytic rRNAs, and many distinct polypeptides.
What are tRNAs? what is their role in translation?
They are structural RNA molecules that were transcribed from genes by RNA polymerase III. They do the actual translation from RNA language into protein language.
tRNA molecules are linked to their correct acid by what?
A group of enzymes called aminoacyl tRNA synthetases.
At least one type of aminoacyl synthetase exists for each _______?
20 amino acids.
What do nucleotide triplets encode?
amino acids.
there are 64 mRNA codons, what do 3 of them do?
three of them are stop codons.
there are 64 possible mRNA codons, what do 61 do?
they specify the addition of amino acids to the polypeptide chain.
What are the three compartments in elongation?
A (aminoacyl) site, P (peptidyl) site, E (exit) site.
What does the aminoacyl site do?
it binds incoming aminoacyl tRNAs.
What does the peptidyl site do?
binds charged tRNAs carrying amino acids that have formed peptide bonds with the growing polypeptide chain but have not yet dissociated from their corresponding tRNA.
What does the exit site do?
it releases dissociated tRNAs so that they can be recharged with free amino acids.
