Chapter 12: Genetic Code and Transcription Flashcards
True or False. The code is unambiguous – each triplet specifies only a single amino acid
True
Enables the production of synthetic mRNAs.
Polynucleotide phosphorylase
Type of RNA that is composed of only one type of ribonucleotides.
RNA Homopolymers
Type of RNA with two or more different ribonucleoside diphosphates added in combination to form the synthetic mRNA.
RNA Heteropolymers
Almost all amino acids are specified by two, three, or four different codons.
Degeneracy
The first two letters of a codon coding for one amino acid are the same, with only the third differing.
Wobble hypothesis
Either U or C is often present in the second position of triplets that specify what type of amino acids, including valine and alanine, among others.
hydrophobic amino acids
A codon with either G or C in the second position always specifies what kind of amino acid?
hydrophilic amino acids
Significance of an “ordered” code?
It buffers the potential effect of mutation on protein function.
When the chemical constitution of genes and their encoded proteins, the linear sequence of triplet codons corresponds precisely with the linear sequence of amino acids in each protein. This phenomenon is called?
Colinearity
True or False. Codon UGA, normally specifying termination, encodes tryptophan during translation in yeast and human mitochondria.
True
True or False. In human mitochondria, AUA, which normally specifies isoleucine, directs the internal insertion of methionine.
True
There may be several points of initiation in one mRNA thus, creating several different reading frames within the same mRNA, and specifying more than one polypeptide. These mRNAs are called?
Overlapping genes
The process by which RNA molecules are synthesized on a DNA template.
Transcription
The enzyme that catalyzes the synthesis of RNA molecule has the same general substrate requirements as does DNA polymerase, the major exception being that the substrate nucleotides contain the ribose rather than the deoxyribose form of the sugar.
RNA polymerase
The active form of the RNA polymerase is made of subunits alpha, beta, beta prime, and sigma.
holoenzyme
Which subunits provide the catalytic basis and active site for transcription in RNA polymerase?
beta and beta prime
What molecule serves as the substrate for the RNA polymerase?
nucleoside trisphosphate (NTPs)
RNA polymerase converts nucleoside triphosphate
to what molecule as it is being added to the growing mRNA.
nucleoside monophosphate
Nucleotides are linked during synthesis by what kind of bond?
3′-to-5′ phosphodiester bonds
Which DNA is being transcribed during transcription?
template strand
The DNA strand that is not involved in the transcription
Partner strand
The site of this initial binding is established when the RNA polymerase sigma subunit recognizes specific DNA sequences called what?
Promoters
Point in the DNA sequence at which transcription actually begins.
Transcription Start Site
These sequences are similar (homologous) in different genes of the same organism or in one or more genes of related organisms. They usually exist as promoter sequences or as telomere sequences.
Consensus Sequences
This bacterial promoter is located 10 nucleotides (Pribnow Box) upstream from the site of initial transcription.
TATAAT sequence
This bacterial promoter is located 35 nucleotides upstream (the −35 region).
TTGACA sequence
Promoter sequence in eukaryotes.
TATA box
The insertion of the first 5′-ribonucleoside triphosphate, which is complementary to the first nucleotide at the start site of the DNA template strand.
Initiation
Subsequent ribonucleotide complements are inserted and linked by phosphodiester bonds as RNA polymerization proceeds. This process is called?
Elongation
The unique sequence of nucleotides in the termination region causes the newly formed transcript to fold back on itself, forming what is called?
hairpin secondary structure
A large hexameric protein that physically interacts with the growing RNA transcript and serves as termination region.
termination factor, R (rho)
A large mRNA is produced that encodes more than one protein. Products of genes transcribed in this fashion are usually all needed by the cell at the same time, so this is an efficient way to transcribe and subsequently translate the needed genetic information.
Polycistronic mRNA (found in bacteria)
What type of mRNA is occurring in eukaryotes?
Monocistronic mRNA
Alteration of the primary RNA transcript to produce mature eukaryotic mRNA. The initial processing step involves the addition of a 5′ cap and a 3′ tail to most transcripts destined to become mRNAs.
RNA processing
Such RNA molecules are of variable but large size and are complexed with proteins, forming heterogeneous nuclear ribonucleoprotein particles (hnRNPs). Immature RNA transcript.
Pre-RNA
Pre-RNA is part of a group of molecules found only in the nucleus referred to as?
Heterogeneous nuclear RNA (hnRNA)
Initiation of transcription of eukaryotic genes requires
that the compact chromatin fiber, characterized by
nucleosome coiling, must be uncoiled and the DNA made
accessible to RNA polymerase and other regulatory proteins. This tran sition is referred to as?
Chromatin Remodeling
Responsible for the transcription of a wide range of genes in eukaryotes
RNA polymerase II (RNAP II)
Determines where RNAP II binds to the DNA and where it begins copying the DNA into RNA.
Core-promoter (TATA box in eukaryotes)
o Located about 30 nucleotide pairs upstream (−30) from the start point of transcription. It is the cis-acting core-promoter element in Eukaryotic genes.
TATA Box (or the Goldberg-Hogness box)
Facilitate RNAP II binding and, therefore, the initiation of transcription.
Trans-acting factors (transcription factors)
This category of transcription factors is absolutely required for all RNAP II-mediated transcription.
General transcription factors (GTFs)
What general transcription factor (GTFs) is involved with human RNAP II binding?
TFIID (binds to TATA box)
Once the initial binding of TFIID to DNA occurs, the other general transcription factors, along with RNAP II, bind sequentially to TFIID, forming what structure?
Pre-initiation complex
These molecules influence the efficiency or the rate of RNAP II transcription initiation.
Transcriptional activators and repressors
Posttranscriptional modification of eukaryotic RNA transcripts destined to become mRNAs occurs at the 5′-end of these molecules, where a molecule cap is added. What molecule is being described?
7-methylguanosine (7-mG)
What posttranscriptional molecule is added after the 3′-end of the initial transcript is cleaved enzymatically at a position some 10 to 35 ribonucleotides from a highly conserved AAUAAA sequence?
poly-A tail
Nucleotide sequences that are not expressed in the amino acid sequence of the proteins they encode. These internal DNA sequences are represented in initial RNA transcripts, but they are removed before the mature mRNA is translated.
Intervening sequences (introns)
Part of pre-RNA that are retained and expressed.
Exons
These genes appear to be deprived of introns.
Genes coding for histones and interferon
True or False. In bacterial tRNA, a specific endonuclease recognizes the intron termini and excises the intervening sequences. Then RNA ligase seals the exon ends to complete each splicing.
True
Represented by introns that are part of the primary transcript of rRNAs, require no additional components for intron excision; the intron itself is the source of the enzymatic activity necessary for removal.
Group I introns
Type of RNAs that are capable of catalytic activity
Ribozymes
Primary RNA and tRNA transcript in mitochondria and chloroplasts where self-excision is also the case.
Group II introns
Mediates the splicing reactions in nuclear-derived pre-RNA.
Spliceosome
5’ end of the intron in nuclear-derived pre-RNA
Donor sequence
3’ end of the intron in nuclear-derived pre-RNA
Acceptor sequence
Loop of intron produced after spliceosome mediated splicing.
Lariat
Produced by a group of similar but nonidentical mRNAs resulting from a gene spliced in more than one way.
Isoforms
The nucleotide sequence of a pre-mRNA is actually changed prior to translation. This process is called?
RNA editing
An RNA editing process whereby nucleotides are added to or subtracted from the total number of bases.
Insertion/Deletion Editing
This molecule directs the insertion/deletion editing in Trypanosoma mitochondrial RNA.
guide RNA (gRNA)
In this editing method, identities of individual nucleotide bases are altered. This is also used in some nuclear-derived eukaryotic RNAs and is prevalent in mitochondrial and chloroplast RNAs transcribed in plants.
Substitution Editing
