ch 15
The mRNA message forms as the RNA complement to the _____.
DNA template strand
How has the one gene - one enzyme hypothesis been updated to fit with the latest biological information?
Eukaryotic genes contain introns and exons that can lead to alternative pathways of splicing so that one gene may encode multiple polypeptides.
All introns are exactly the same size (in nucleotide count) and consist of TATA sequences.
False
Each time DNA is copied to RNA, the gene is shortened by several hundred nucleotides.
False
In eukaryotes, transcription and translation occur in the nucleoplasm (inside the nuclear membrane).
False
In the Genetic Code, one codon specifies one amino acid, and every amino acid is specified by only one codon.
False
The monomer building blocks of mRNA are amino acids.
False
What is the role of the 5' cap in eukaryotic mRNA?
The cap is recognized by proteins in the nuclear membrane to facilitate exit into the cytosol and then to bind to a ribosome.
If a DNA template strand has a sequence of 3′ TACAATGTAGCC 5′, then the RNA produced from it will be which sequence?
5′AUGUUACAUCGG3'
Why is the rate of transcription faster in bacteria than in eukaryotic cells? -mRNA has to exit the nucleus in eukaryotes; prokaryotes don't have a nucleus. -Eukaryotic cytosol is thicker, more gelled than prokaryotic cytoplasm, so this creates friction and resistance that slow the movement of all molecules. THIS ONE IS WRONG-This statement is false; eukaryotes normally conduct transcription at double, triple, or even 10X the rate of prokaryotes. -Prokaryotes skip the mRNA step; their DNA is read directly by ribosomes.
mRNA has to exit the nucleus in eukaryotes; prokaryotes don't have a nucleus.
RNA polymerase is used to _____.
make mRNA from a DNA template
Sigma factor is important in binding to RNA polymerase and to the DNA template during the initiation stage of transcription in _____.
prokaryotes
What is a splicosome made of?
snRNPs
Anticodons are part of_____.
tRNA
In molecular genetics, the terminator is _____.
the DNA sequence that signals the end of transcription
A tRNA with the sequence UAG is expected to be carrying _____.
the amino acid isoleucine
What genes are transcribed but never translated?
transfer RNA and ribosomal RNA
The process of synthesizing a specific polypeptide on a ribosome based on a messenger RNA strand is called _____. -translation -replication -THIS ONE IS WRONG-transcription -methylation -termination
translation
The majority of the energy of most cells is used to translate mRNA into polypeptides.
true
Which part of a tRNA carries the amino acid? -The single-stranded region -One or both of the side stem loops -THIS ONE IS WRONG-The central area of the clover leaf, where RNA nucleotides are associated in complementary base pairs -At the tip of the middle stem loop, at the anti-codon site
The single-stranded region
What do codons code for, ultimately? THIS ONE IS WRONG-nucleotides that will go into building snRNPs -an RNA that will be part of the ribosome (rRNA) -an RNA that will be function as transfer RNA (tRNA) -an amino acid in a polypeptide
an amino acid in a polypeptide
Alternative splicing of mRNA results in _____.
an increase in the size of the proteome while minimizing the size of the genome
Intervening sequences that are transcribed, but not translated into protein are called _____.
introns
The Genetic Code includes one start codon and three stop codons.
True
The leading edge of a polypeptide chain being synthesized by a ribosome is the N-terminus and the ending point is the C-terminus, referring to the amino- group and the carboxyl group of the amino acid, respectively.
True
The mRNA of most bacterial species lacks a cap or tail. In the few bacteria that have been discovered to have mRNA with poly-A tails, the result on the stabilization of the mRNA strand seems to be the exact opposite of what occurs in eukaryotes.
True
tRNA and rRNA are self-splicing when it comes to removing intron sequences.
True
________ is to transcription as ________ is to translation.
RNA polymerase; ribosome
An RNA molecule that can catalyze a chemical reaction (acting as an enzyme) is called _____.
a ribozyme
In molecular genetics, what is a promoter?
a sequence of DNA that determines whether or not transcription will begin
What is the job of ribosomal RNAs? -THIS ONE IS WRONG-digests the bonds between the monomers of the mRNA chain, releasing them into the cytoplasm as translation at the ribosome is completed, so that recycling can occur -forms the complementary binding sites that connect the ribosome to mRNA -searches out amino acids, bind one or more, and bring them back to the ribosome for assembly into polypeptide chains -all of the listed choices are roles of rRNA
forms the complementary binding sites that connect the ribosome to mRNA
The process that produces mRNA from DNA is called _____.
transcription
What has happened when a gene as been "expressed" (as in gene expression)?
transcription and translation
The one gene / one protein hypothesis was proposed in the _____ time period.
1940s
What is the expected consequence of a change to a single nucleotide base (a point mutation) within the coding sequence of a gene? -There is no consequence - the same amino acid will be the result and the polypeptide will be unaffected. -A changed "stop codon" will result in an mRNA message that incorporates the information from two genes, plus all sorts of extra stuff from in between. This may be correctable through mRNA editing or post-translational modifications. -A different amino acid will be substituted in translation, and this may affect the way the polypeptide chain folds into its secondary and tertiary structure and therefore affect function. -A changed "start codon" will result in a gene that can no longer be expressed.
All of the listed choices are possible -There is no consequence - the same amino acid will be the result and the polypeptide will be unaffected. -A changed "stop codon" will result in an mRNA message that incorporates the information from two genes, plus all sorts of extra stuff from in between. This may be correctable through mRNA editing or post-translational modifications. -A different amino acid will be substituted in translation, and this may affect the way the polypeptide chain folds into its secondary and tertiary structure and therefore affect function. -A changed "start codon" will result in a gene that can no longer be expressed.
Which statement about aminoacyl-tRNA synthetases is true? -The anticodon region of the tRNA and possibly other base sequences in the tRNA are important to the ability of the synthetase to bind to its correct partner. -The cell makes 20 different types, with each synthetase recognizing just one of the 20 different amino acids. -The job of this enzyme is to catalyze the attachment of amino acids to tRNA molecules, utilizing ATP energy.
All of the listed choices are true. -The anticodon region of the tRNA and possibly other base sequences in the tRNA are important to the ability of the synthetase to bind to its correct partner. -The cell makes 20 different types, with each synthetase recognizing just one of the 20 different amino acids. -The job of this enzyme is to catalyze the attachment of amino acids to tRNA molecules, utilizing ATP energy.
Refer to a Genetic Code table (our textbook p. 243, or any source). What amino acid does the codon CCC specify?
Proline
How do the A, P, and E ribosomal sites contribute to polypeptide synthesis? -Three charged tRNA bind simultaneously to the A, P, and E sites. The ribosome facilitates covalent bonding of the triplet of amino acids, which are then passed to the termination complex to await the next triplet. -The tRNA enters carrying an amino acid at the A site, is shifted to the P site as it binds to the growing polypeptide chain, and is shifted again to the E site as this pattern repeats with newly arriving charged tRNAs at the A site. THIS ONE IS WRONG-The ribosome is full of A, P, and E sites. The maximum size of a polypeptide is determined by this limit. mRNA matches the first nucleotide of each codon to an A site, the second nucleotide to a P site, and the third nucleotide to an E site. Once the ribosome is maximally saturated with mRNA, then a conformational change attracts tRNA, which ribozymally create the amino acid chain in one almost simultaneous action, using a chain reaction of exergonic reactions. -Truly, nobody knows. This is one of the greatest mysteries of molecular biology.
The tRNA enters carrying an amino acid at the A site, is shifted to the P site as it binds to the growing polypeptide chain, and is shifted again to the E site as this pattern repeats with newly arriving charged tRNAs at the A site.
Which statement about translation is FALSE? -When translation is not occurring, the small and large ribosomal subunits exist separately. -The initiator tRNA binds to the start codon. In eukaryotes, the initiator tRNA carries methionine, and in prokaryotes the initiator tRNA is a methionine modified with a formyl group. -In eukaryotes, the genetic sequence around the start codon is important in order for the start codon to be recognized as a start codon. -To begin translation, mRNA "loads" by threading through the center of the ribosome poly-A tail first, stopping when when the mRNA cap binds to the large ribosomal subunit. THIS ONE IS WRONG-The rate of synthesis of a polypeptide chain, covalently binding one amino acid to another, is two to three times faster in prokaryotes compared to eukaryotes.
To begin translation, mRNA "loads" by threading through the center of the ribosome poly-A tail first, stopping when when the mRNA cap binds to the large ribosomal subunit.
Archaea, bacteria, and eukaryotes all share the basic process of DNA genetic code being converted to RNA messages which are then used to assemble specific proteins using ribosomal machinery.
True
Eukaryotic DNA typically contains introns, while prokaryotic DNA typically lacks introns.
True
Many proteins have structural or regulatory roles and do not function as enzyme.
True
Some genes encode RNA that does not become mRNA. Examples are tRNA and rRNA.
True
Some proteins are composted of two or more polypeptides.
True
When a regulatory protein binds to a regulatory sequence, the result is _____. -THIS ONE IS WRONG-an inhibition of transcription, slowing down the rate -an enhancement of transcription, speeding up the rate -either an enhancement or an inhibition, to speed up or slow down the rate of transcription
either an enhancement or an inhibition, to speed up or slow down the rate of transcription
If a cell is described as having an 80s ribosome, that cell is _____.
eukaryotic
Pre-mRNA and mature mRNA are terms associated with the discussion of _____.
eukaryotic transcription and post-transcriptional processes
Review of chemistry chapter: Polypeptides are proteins that are covalently bonded to polysaccharides.
false
How many nucleotides does it take to make one codon?
three