ch. 15 Flashcards
what is a 7-methylguanosine cap?
a modification added to the 5’ end of pre-mRNAs to protect mRNA from degradation and assist translation
what is aminoacytl tRNA synthase?
an enzyme that “charges” tRNA molecules by catalyzing a bond between the tRNA and a corresponding amino acid
what is an anticodon?
a three-nucleotide sequence in a tRNA molecule that corresponds to an mRNA codon
what is a CAAT box?
(GGCCAATCT) essential eukaryotic promoter sequence involved in binding transcription factors
what is the central dogma?
it states that genes specify the sequence of mRNAs which in turn specify the sequence of proteins
what is a codon?
three consecutive nucleotides in mRNA that specify the insertion of an amino acid or the release of a polypeptide chain during translation
what does colinear mean?
in terms of RNA and protein, three “units” of RNA (nucleotides) specify one “unit” of protein (amino acid) in a consecutive fashion
what is a consensus?
DNA sequence that is used by many species to perform the same or similar functions
what is a core enzyme?
prokaryotic RNA polymerase consisting of α, α, β, and β’ but missing σ; this complex performs elongation
what is degeneracy of the genetic code?
it describes that a given amino acid can be encoded by more than one nucleotide triplet; the code is degenerate, but not ambiguous
what does downstream mean?
nucleotides following the initiation site in the direction of mRNA transcription; in general sequences that are toward the 3’ end relative to a site on the mRNA
what is an exon?
sequence present in protein-coding mRNA after completion of pre-mRNA splicing
what is a FACT complex?
complex that “facilitates chromatin transcription” by disassembling nucleosides ahead of a transcribing RNA polymerase II and reassembling them after the polymerase passes by
what is a GC-rich box?
(GGCG) nonessential eukaryotic promoter sequence that binds cellular factors to increase the efficiency of transcription; may be present several times in a promoter
what is a hairpin structure?
a structure of RNA when it folds back on itself and forms intramolecular hydrogen bonds between complementary nucleotides
what is a holoenzyme?
prokaryotic RNA polymerase consisting of α, α, β,β’, and σ; this complex is responsible for transcription initiation
what is an information site?
a nucleotide from which mRNA synthesis proceeds in the 5’ to 3’ direction; denoted with a “+1”
what is initiator tRNA?
(in prokaryotes, called tRNA^Met f; in eukaryotes, called tRNAi) a tRNA that interacts with a start codon, binds directly to the ribosome P site, and links to a special methionine to begin a polypeptide chain
what is an intron?
non-protein-coding intervening sequences that are spliced from mRNA during processing
what are Kozak’s rules?
They determine the correct initiation Aug in a eukaryotic mRNA; the following consensus sequence must appear around the AUG; 5’-GCC(purine) CCAUGG-3’
what is a nonsense codon?
one of the three mRNA codons that specifies termination of translation
what is a nontemplate strand?
a strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA
what is an Octamer box?
(ATTGCAT) nonessential eukaryotic promoter sequence that binds cellular factors to increase the efficiency of transcription; may be present several times in a promoter
what is peptidyl transferase?
an RNA-based enzyme that is integrated into the 50S ribosomal subunit and catalyzes the formation of peptide bonds
what are 50S ribosomal subunits?
50S is the larger subunit of the 70S ribosome of prokaryotes, i.e. bacteria and archaea. It is the site of inhibition for antibiotics.
what is a plasmid?
extrachromosomal, covalently closed, circular DNA molecule that may only contain one or a few genes; common in prokaryotes
what is a poly-A tail?
a modification added to the 3’ end of pre-mRNAs to protect mRNA from degradation and assist mRNA export from the nucleus
what is a polysome?
an mRNA molecule simultaneously being translated by many ribosomes all going the same direction
what is a pre initiation complex?
a cluster of transcription factors and other proteins that recruit RNA polymerase II for transcription of a DNA template
what is a promoter?
a DNA sequence to which RNA polymerase and associated factors bind and initiate transcription
what is a reading frame?
sequence of triplet codons in mRNA that specify a particular protein; a ribosome shift of one or two nucleotides in either direction completely abolishes synthesis of that protein
what is rho-dependent termination?
in prokaryotes, termination of transcription by an interaction between RNA polymerase and the rho protein at a run of G nucleotides on the DNA template
what is rho-independent termination?
sequence-dependent termination of prokaryotic mRNA synthesis; caused by a hairpin formation in the mRNA that stalls the polymerase
what is RNA editing?
direct alteration of one or more nucleotides in an mRNA that has already been synthesized
what is the Shine-Dalgarno sequence?
(AGGAGG); initiates prokaryotic translation by interacting with rRNA molecules comprising the 30S ribosome
what is a signal sequence?
a short tail of amino acids that directs a protein to a specific cellular compartment
what are small nuclear RNA?
molecules synthesized by RNA polymerase III that have a variety of functions, including splicing pre-mRNAs and regulation transcription factors
what is splicing?
the process of removing introns and reconnecting exons in a pre-mRNA
what is the start codon?
AUG on an mRNA from which translation begins; always specifies methionine
what is a TATA box?
a conserved promoter sequence in eukaryotes and prokaryotes that helps to establish the initiation site for transcription
what is the template strand?
the strand of DNA that specifies the complementary mRNA molecule
what is the transcription bubble?
the region of locally unwound DNA that allows for transcription of mRNA
what does upstream mean?
nucleotides preceding the initiation site; in general, sequences toward the 5’ end relative to a site on the mRNA
