bio quiz
Which of the following statements about the genetic code is correct?(a) All codons specify more than one amino acid. (b) The genetic code is redundant.(c) All amino acids are specified by more than one codon. (d) All codons specify an amino acid.
(b) The genetic code is redundant. Most amino acids can be specified by more than one codon. Each codon specifies only one amino acid [choice (a)]. Tryptophan and methionine are encoded by only one codon [choice(c)]. Some codons specify translational stop signals [choice (d
The ribosome is important for catalyzing the formation of peptide bonds. Which of the following statements is true? a. Once the large and small subunits of the ribosome assemble, they will not separate from each other until degraded by the proteasome. b. The catalytic site for peptide bond formation is formed primarily from an rRNA. c. The large subunit of the ribosome is important for binding to the mRNA. d. The number of rRNA molecules that make up a ribosome greatly exceeds the number of protein molecules found in the ribosome.
The catalytic site for peptide bond formation is formed primarily from an rRNA.
What experimental result eliminated the dispersive model of DNA replication?
The dispersive model was ruled out by using heat to denature the DNA duplexes and then comparing the densities of the single-stranded DNA. If the dispersive model had been correct, individual strands should have had an intermediate density. However, this was not the case; only heavy strands and light strands were observed, which convincingly supported the semiconservative model for DNA replication.
The DNA duplex consists of two long covalent polymers wrapped around each other many times over their entire length. The separation of the DNA strands for replication causes the strands to be "overwound" in front of the replication fork. How does the cell relieve the torsional stress created along the DNA duplex during replication?
Topoisomerases break the covalent bonds of the backbone allowing the local unwinding of DNA ahead of the replication fork.
Indicate whether the following statements are true or false. If a statement is false, explain why it is false. (see next slide) Primase is needed to initiate DNA replication on both the leading strand and the lagging strand. The sliding clamp is loaded once on each DNA strand, where it remains associated until replication is complete. Telomerase is a DNA polymerase that carries its own RNA molecule to use as a primer at the end of the lagging strand. Primase requires a proofreading function that ensures there are no errors in the RNA primers used for DNA replication.
True. False. Although the sliding clamp is only loaded once on the leading strand, the lagging strand needs to unload the clamp once the polymerase reaches the RNA primer from the previous segment and then reload it where a new primer has been synthesized. True. False. Primase does not have a proofreading function, nor does it need one because the RNA primers are not a permanent part of the DNA. The primers are removed, and a DNA polymerase that does have a proofreading function fills in the remaining gaps.
Which of the following statements is false? A new RNA molecule can begin to be synthesized from a gene before the previous RNA molecule's synthesis is completed. If two genes are to be expressed in a cell, these two genes can be transcribed with different efficiencies. RNA polymerase is responsible for both unwinding the DNA helix and catalyzing the formation of the phosphodiester bonds between nucleotides. Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.
Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.
(1) continuous replication, (2) discontinuous replication, or (3) both modes of replication. ______ primase ______ single-strand binding protein ______ sliding clamp ______ RNA primers ______ leading strand ______ lagging strand ______ Okazaki fragments ______ DNA helicase ______ DNA ligase
___3___ primase ___2___ single-strand binding protein ___3___ sliding clamp ___3___ RNA primers ___1___ leading strand ___2___ lagging strand ___2___ Okazaki fragments ___3___ DNA helicase ___2___ DNA ligase
Which of the following statements about RNA splicing is false? (a) Conventional introns are not found in bacterial genes. (b) For a gene to function properly, every exon must be removed fromthe primary transcript in the same fashion on every mRNA moleculeproduced from the same gene. (c) Small RNA molecules in the nucleus perform the splicing reactionsnecessary for the removal of introns. (d) Splicing occurs after the 5′ cap has been added to the end of theprimary transcript.
For a gene to function properly, every exon must be removed fromthe primary transcript in the same fashion on every mRNA moleculeproduced from the same gene. The primary transcript of a gene can sometimes be spliced differently so that different exonscan be stitched together to produce distinct proteins in a process called alternative splicing.
Which of the following statements is true? (a) Phospholipids will spontaneously form liposomes in nonpolarsolvents. (b) In eukaryotes, all membrane-enclosed organelles are surroundedby one lipid bilayer. (c) Membrane lipids diffuse within the plane of the membrane (d) Membrane lipids frequently flip-flop between one monolayer andthe other.
Membrane lipids diffuse within the plane of the membrane (c) The remaining answers are false. Phospholipids form bilayers only in polar solvents. Nucleiand mitochondria are enclosed by two membranes. Membrane lipids rarely flip-flop betweenone monolayer and the other.
Transcription in bacteria differs from transcription in a eukaryotic cell because __________________________.
RNA polymerase (along with its sigma subunit) can initiate transcription on its own.
A molecule of bacterial DNA introduced into a yeast cell is imported into the nucleus but fails to replicate with the yeast DNA. Where do you think the block to replication arises? Choose the protein or protein complex below that is most probably responsible for the failure to replicate bacterial DNA. Give an explanation for your answer.
initiator proteins
RNA in cells differs from DNA in that ___________________
it is single-stranded and can fold up into a variety of structures.
What part of the DNA replication process would be most directly affected if a strain of bacteria lacking DNA ligase were used to make the cell extracts?
lagging-strand completion
After a short incubation, the beads are then extracted from the mixture. When you analyze the cellular nucleic acids that have stuck to the beads, which of the following is most abundant?
mRNA
If the polymerase is transcribing from this segment of DNA from left to right, which strand (top or bottom) is the template?
The bottom strand.
The ribosome is important for catalyzing the formation of peptide bonds. Which of the following statements is true? The number of rRNA molecules that make up a ribosome greatly exceeds the number of protein molecules found in the ribosome. The large subunit of the ribosome is important for binding to the mRNA. The catalytic site for peptide bond formation is formed primarily from an rRNA. Once the large and small subunits of the ribosome assemble, they will not separate from each other until degraded by the proteasome.
The catalytic site for peptide bond formation is formed primarily from an rRNA.
New membrane phospholipids are synthesized by enzymes bound to the _____________ side of the_________________ membrane. (a) cytosolic, mitochondrial (b) luminal, Golgi( c) cytosolic, endoplasmic reticulum (d) extracellular, plasma
cytosolic, endoplasmic reticulum
What do you predict would happen if you created a tRNA with an anticodon of 5′-UAC-3′ that is charged with methionine, and added this modified tRNA to a cell-free translation system that has all the normal components required for translating RNAs? a. methionine would be incorporated into proteins at some positions where tyrosine should be b. methionine would be incorporated into proteins at some positions where histidine should be c. methionine would be incorporated into proteins at some positions where valine should be d. translation would no longer be able to initiate
methionine would be incorporated into proteins at some positions where valine should be
Which type of lipids are the most abundant in the plasma membrane? (a) phospholipids (b) glycolipids (c) sterols (d) triacylglycerides
phospholipids
When grown at high temperatures, bacteria and yeast maintain an optimal membrane fluidity by: producing membrane lipids with tails that are longer and contain more double bonds. producing membrane lipids with tails that are shorter and contain more double bonds. producing membrane lipids with tails that are shorter and contain fewer double bonds. producing membrane lipids with tails that are longer and contain fewer double bonds.
producing membrane lipids with tails that are longer and contain fewer double bonds.
Which of the following statements is true? (a) Ribosomes are large RNA structures composed solely of rRNA. (b) Ribosomes are synthesized entirely in the cytoplasm. (c) rRNA contains the catalytic activity that joins amino acids together. (d) A ribosome binds one tRNA at a time.
rRNA contains the catalytic activity that joins amino acids together Ribosomes contain proteins as well as rRNA [choice (a)]. rRNA is synthesized in the nucleus, and ribosomes are partly assembled in the nucleus [choice (b)]. A ribosome must be able to bind two tRNAs at any one time [choice (d)].
The sigma subunit of bacterial RNA polymerase ___________________.
recognizes promoter sites in the DNA.
The plasma membrane serves many functions, many ofwhich depend on the presence of specialized membrane proteins. Which of the following roles of the plasma membrane could still occur if the bilayer were lacking these proteins? (a) intercellular communication (b) selective permeability (c) cellular movement (d) import/export of molecules
selective permeability
The classic experiments conducted by Meselson and Stahl demonstrated that DNA replication is accomplished by employing a ________________ mechanism.
semi-conservative
DNA polymerases are processive, which means that they remain tightly associated with the template strand while moving rapidly and adding nucleotides to the growing daughter strand. Which piece of the replication machinery accounts for this characteristic?
sliding clamp
A mutation in the anticodon sequence 5′-AUA-3′ of a tRNA results in the anticodon sequence 5′-AAA-3'. Which of the following aberrations in protein synthesis might this cause? substitution of tyrosine for phenylalanine substitution of phenylalanine for tyrosine substitution of lysine for isoleucine substitution of isoleucine for lysine
substitution of tyrosine for phenylalanine
Membrane lipids are capable of many different typesof movement. Which of these does not occur spontaneously in biological membranes? (a) switching between lipid layers (b) lateral movement (c) rotation (d) flexing of hydrocarbon chains
switching between lipid layers
The process of DNA replication requires that each of the parental DNA strands be used as a ___________________ to produce a duplicate of the opposing strand.
template
You know that the RNA transcribed from this segment contains the following sequence: 5′-GGACUAGACAAUAGGGACCUAGAGAUUCCGAAA-3′ Which of the following choices best describes how transcription occurs?
the bottom strand is the template strand; RNA polymerase moves along this strand from 3′ to 5′
Which of the following phenomena will be observedif a cell's membrane is pierced? (a) the membrane reseals (b) the membrane collapses (c) a tear is formed( d) the membrane expands
the membrane reseals
Post-translational control occurs between: the DNA and the RNA transcript. the RNA transcript and the mRNA. the mRNA and the protein. the protein and the inactive protein.
the protein and the inactive protein
Initiator proteins bind to replication origins and disrupt hydrogen bonds between the two DNA strands being copied. Which of the factors below does not contribute to the relative ease of strand separation by initiator proteins?
the reaction can occur at room temperature
Most animal fats form a solid at room temperature,while plant fats remain liquid at room temperature. Which of the following is a feature of lipids in plant membranes that best explains this difference? (a) unsaturated hydrocarbons (b) longer hydrocarbon tails (c) higher levels of sterols (d) larger head groups
unsaturated hydrocarbons
snRNAs ___________________. (a) are translated into snRNPs. (b) are important for producing mature mRNA transcripts in bacteria (c) are removed by the spliceosome during RNA splicing.(d) can bind to specific sequences at intron-exon boundaries through complementary base-pairing.
(d) can bind to specific sequences at intron-exon boundaries through complementary base-pairing. snRNAs are part of the snRNPs, which include proteins and RNA molecules. The proteinswithin the snRNPs are encoded by their own genes and not translated from snRNPs, which iswhy choice (a) is incorrect. Bacteria do not have introns, which is why choice (b) is incorrect.
Name three covalent modifications that can be made to an RNA molecule in eukaryotic cells before the RNA molecule becomes a mature mRNA.
1. A poly-A tail is added. 2. A 5′ cap is added. 3. Introns can be spliced out.
There are two properties of phospholipids that affecthow tightly they pack together: the length of thehydrocarbon chain and the number of double bonds. Thedegree of packing, in turn, influences the relative mobility ofthese molecules in the membrane. Which of the followingwould yield the most highly mobile phospholipid (listed asnumber of carbons and number of double bonds,respectively)? (a) 24 carbons with 1 double bond (b) 15 carbons with 2 double bonds (c) 20 carbons with 2 double bonds (d) 16 carbons with no double bonds
15 carbons with 2 double bonds
How many replication forks are formed when an origin of replication is opened?
2
What will be the sequence of that RNA (be sure to label the 5′ and 3′ ends of your RNA molecule)?
5′-AGUCUAGGCACUGA-3′
5′-ATAGGCATTCGATCCGGATAGCAT-3′ 3′-TATCCGTAAGCTAGGCCTATCGTA-5′ Which of the following RNA molecules could be transcribed from this piece of DNA?
5′-AUAGGCAUUCGAUCCGGAUAGCAU-3′
Which of the following molecules of RNA would you predict to be the most likely to fold into a specific structure as a result of intramolecular base-pairing?
5′-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3′
On a DNA strand that is being used as a template, where is the copying occurring relative to the replication origin—3′ of the origin, 5′, or both?
Both, as a result of the bidirectional nature of chromosomal replication.
T or F: "Since introns do not contain protein-coding information, they do nothave to be removed precisely (meaning, a nucleotide here and thereshould not matter) from the primary transcript during RNA splicing."
False. Although it is true that the sequences within the introns are mostly dispensable, theintrons must still be removed precisely because an error of one or two nucleotides wouldshift the reading frame of the resulting mRNA molecule and change the protein it encodes.
Which of the following statements about the proteasome is false? Ubiquitin is a small protein that is covalently attached to proteins to mark them for delivery to the proteasome. Proteases reside in the central cylinder of a proteasome. Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold. The protein stoppers that surround the central cylinder of the proteasome use the energy from ATP hydrolysis to move proteins into the proteasome inner chamber.
Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold.
Which part of a protein is synthesized by a ribosome first? The C-terminus The N-terminus It depends on the protein. It depends on where the ribosome binds to the mRNA. It depends on whether the cell is eukaryotic or prokaryotic.
N-termius
Which of the following methods is not used by cells to regulate the amount of a protein in the cell? Genes can be transcribed into mRNA with different efficiencies. Many ribosomes can bind to a single mRNA molecule. Proteins can be tagged with ubiquitin, marking them for degradation. Nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus into the cytoplasm.
Nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus into the cytoplasm.
A bacterium is suddenly expelled from a warm human intestineinto the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity? (a) Produce lipids with hydrocarbon tails that are longer and have fewer double bonds. (b) Produce lipids with hydrocarbon tails that are shorter and have more double bonds. (c) Decrease the amount of cholesterol in the membrane. (d) Decrease the amount of glycolipids in the membrane.
Produce lipids with hydrocarbon tails that are shorter and have more double bonds.
Unlike DNA, which typically forms a helical structure, different molecules of RNA can fold into a variety of three-dimensional shapes. This is largely because ___________________.
RNA is single-stranded.
Which of the following statements about prokaryotic mRNA molecules is false? A single prokaryotic mRNA molecule can be translated into several proteins. Ribosomes must bind to the 5′ cap before initiating translation. mRNAs are not polyadenylated. Ribosomes can start translating an mRNA molecule before transcription is complete.
Ribosomes must bind to the 5′ cap before initiating translation. Choice (a) would prevent all peptide bond formation. Choice (c) would have no effect on translation until the stop codon was reached. Choice (d) would be likely to result in a mixture of polypeptides of various lengths; a poison mimicking a release factor could conceivably cause only Met-Lys to be made, but this dipeptide would not remain bound to the ribosome.
On a DNA strand that is being synthesized, which end is growing—the 3′ end, the 5′ end, or both ends? Explain your answer.
The 3′ end. DNA polymerase can add nucleotides only to the 3′-OH end of a nucleic acid chain.
Which of the following statements about mRNA lifetime is true? a. The lifetimes of mRNAs produced from different genes will not vary. b. The lifetime of most prokaryotic cell mRNAs is >24 years. c. The long lifetime of most eukaryotic mRNAs makes them an excellent alternative to carbon-14 for dating unicorn and dragon fossils. d. The 5′ and 3′ untranslated regions of an mRNA often contain specific sequences that determine the lifetime of the mRNA molecule.
The 5′ and 3′ untranslated regions of an mRNA often contain specific sequences that determine the lifetime of the mRNA molecule.
You have a bacterial strain with a mutation that removes the transcription termination signal from the Abd operon. Which of the following statements describes the most likely effect of this mutation on Abd transcription?
The Abd RNA from the mutant strain will be longer than normal.
Explain how "light" DNA was separated from "heavy" DNA in the Meselson and Stahl experiments.
The DNA samples collected were placed into centrifuge tubes containing cesium chloride. After high-speed centrifugation for 2 days, the heavy and light DNA products were separated by density.
Since introns do not contain protein-coding information, they do not have to be removed precisely from the pre-mRNA transcript during RNA splicing. For example, it would be fine if one or two of the intron's nucleotides were not removed and remained in the final mature mRNA.
False
Which of the following does not occur before a eukaryotic mRNA is exported from the nucleus?
(a) The ribosome binds to the mRNA.
Indicate whether the following statements are true or false. If a statement is false, explain why it is false. (see next slide) a. When DNA is being replicated inside a cell, local heating occurs, allowing the two strands to separate. b. DNA replication origins are typically rich in G-C base pairs. c. Meselson and Stahl ruled out the dispersive model for DNA replication. d. DNA replication is a bidirectional process that is initiated at multiple locations along chromosomes in eukaryotic cells.
A. False. The two strands do need to separate for replication to occur, but this is accomplished by the binding of initiator proteins at the origin of replication. B. False. DNA replication origins are typically rich in A-T base pairs, which are held together by only two hydrogen bonds (instead of three for C-G base pairs), making it easier to separate the strands at these sites. C. True. D. True.
What is DNA ligase's role?
After Okazaki fragments are synthesized, they must be ligated (covalently connected) to each other so that they finally form one continuous strand. At the nonpermissive temperature this does not happen, and although there may be a range of fragments, the notable band at 200 base pairs is the typical size of an individual Okazaki fragment.
List three ways in which the process of eukaryotic transcription differs from the process of bacterial transcription.
Any three of the following are acceptable. 1. Bacterial cells contain a single RNA polymerase, whereas eukaryotic cells have three. 2. Bacterial RNA polymerase can initiate transcription without the help of additional proteins, whereas eukaryotic RNA polymerases need general transcription factors. 3. In eukaryotic cells, transcription regulators can influence transcriptional initiation thousands of nucleotides away from the promoter, whereas bacterial regulatory sequences are very close to the promoter. 4. Eukaryotic transcription is affected by chromatin structure and nucleosomes, whereas bacteria lack nucleosomes.
Although 3′-to-5′ synthesis of DNA is chemically possible, it does not occur in living systems. Why not?
DNA synthesis from 3′ to 5′ does not allow proofreading. If the last nucleotide added is mispaired and is removed, the last nucleotide on the growing strand is a nucleoside monophosphate and the nucleotide coming in only has a hydroxyl group on the 3′ end. Thus, there is no favorable hydrolysis reaction to drive the addition of new nucleotides.
If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of the fruit fly Drosophila be replicated in only 3 minutes?
Drosophila DNA contains more origins of replication than E. coli DNA.
During the process of translation: incoming tRNAs bind to the A-site. initiation begins with the binding of the ribosomal small subunit to the poly-A tail of the mRNA. the mRNA is translated by one ribosome at a time. the peptide is 'passed' from the tRNA in the P-site to the tRNA in the A-site. Two of the above are correct.
E. 2 correct
Below is the sequence from the 3′ end of an mRNA. 5′-CCGUUACCAGGCCUCAUUCAGUGAUGGCGGAAAAAAAAAAAAAA-3′ If you were told that this sequence contains the stop codon for the protein encoded by this mRNA, what is the anticodon on the tRNA in the P site of the ribosome when release factor binds to the A site? 5'-CCA-3' 5′-UCT-3′ 5′-TCU-3′ 5′-GUC-3′ 5′-CUG-3′
E. CUG
The repair polymerase is the enzyme that proofreads the newly synthesized strands to ensure the accuracy of DNA replication. There is a single enzyme that degrades the RNA primers and lays down the corresponding DNA sequence behind it. DNA ligase is required to seal the sugar-phosphate backbone between all the DNA fragments on the lagging strand. D. The repair polymerase does not require the aid of the sliding clamp, because it is only synthesizing DNA over very short stretches.
False. The repair polymerase is used to fill in the spaces left vacant after the RNA primers are degraded. False. This is a two-step process that requires two different enzymes. First, a nuclease removes the RNA primers. Then, the repair polymerase fills in the complementary DNA sequence. True. True.
For a cell's genetic material to be used, the information is first copied from the DNA into the nucleotide sequence of RNA in a process called __________________. Various kinds of RNA are produced, each with different functions. __________________ molecules code for proteins, __________________ molecules act as adaptors for protein synthesis, __________________ molecules are integral components of the ribosome, and __________________ molecules are important in the splicing of RNA transcripts.
For a cell's genetic material to be used, the information is first copied from the DNA into the nucleotide sequence of RNA in a process called transcription. Various kinds of RNA are produced, each with different functions. mRNA molecules code for proteins, tRNA molecules act as adaptors for protein synthesis, rRNA molecules are integral components of the ribosome, and snRNA molecules are important in the splicing of RNA transcripts.
The piece of RNA below includes the region that codes for the binding site for the initiator tRNA needed in translation. 5′-GUAUCCCCAAGGUAUACAUCCGUCAUGCCGGGGGC-3′ Which amino acid will be on the tRNA that is the second to bind to the A site of the ribosome? arginine (Arg) glycine (Gly) methionine (Met) proline (Pro)
Glycine
Genes in eukaryotic cells often have intronic sequences coded forwithin the DNA. These sequences are ultimately not translated intoproteins. Why? (a) Intronic sequences are removed from RNA molecules by thespliceosome, which works in the nucleus.( b) Introns are not transcribed by RNA polymerase. (c) Introns are removed by catalytic RNAs in the cytoplasm. (d) The ribosome will skip over intron sequences when translating RNAinto protein.
Intronic sequences are removed from RNA molecules by thespliceosome, which works in the nucleus.
Which of the following statements about the newly synthesized strand of a human chromosome is true?
It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis.
You have discovered an "Exo-" mutant form of DNA polymerase in which the 3′-to-5′ exonuclease function has been destroyed but the ability to join nucleotides together is unchanged. Which of the following properties do you expect the mutant polymerase to have?
It will be more likely to generate mismatched base pairs.
Which of the following statements correctly explains what it means for DNA replication to be bidirectional?
The replication forks formed at the origin move in opposite directions.
Which of the following statements about sequence proofreading during DNA replication is false?
The exonuclease activity cleaves DNA in the 5′-to-3′ direction.
The length of a particular gene in human DNA, measured from thestart site for transcription to the end of the protein-coding region, is10,000 nucleotides, whereas the length of the mRNA produced from thisgene is 4000 nucleotides. What is the most likely reason for thisdifference?
The gene contains one or more introns.
Why do phospholipids form bilayers in water? The hydrophobic tail is attracted to water while the hydrophilic head shuns water. The hydrophobic head is attracted to water while the hydrophilic tail shuns water. The hydrophobic tail shuns water while the hydrophilic head is attracted to water. The hydrophobic head shuns water while the hydrophilic tail attracts water.
The hydrophobic tail shuns water while the hydrophilic head is attracted to water.
Which of the following statements is true with respect to this in vitro replication system?
The leading and lagging strands compose one half of each newly synthesized DNA strand.
Telomeres serve as caps at the ends of linear chromosomes. Which of the following is not true regarding the replication of telomeric sequences?
The leading strand doubles back on itself to form a primer for the lagging strand.
The specialized functions of different membranes are largely determined by the__________________ they contain. Membrane lipids are __________________ molecules,composed of a hydrophilic portion and a hydrophobic portion. All cell membranes have the same __________________ structure, with the __________________ of the phospholipids facing into the interior of the membrane and the __________________ on the outside.The most common lipids in most cell membranes are the __________________. The head group of a glycolipid is composed of __________________.
The specialized functions of different membranes are largely determined by the proteins theycontain. Membrane lipids are amphipathic molecules, composed of a hydrophilic portion and ahydrophobic portion. All cell membranes have the same lipid bilayer structure, with the fatty acid tails of the phospholipids facing into the interior of the membrane and the hydrophilic head groups on the outside. The most common lipids in most cell membranes are the phospholipids. The head group of a glycolipid is composed of sugars
Describe the three existing models for DNA replication when these studies were begun, and explain how one of them was ruled out definitively by the experiment you described for part A.
The three models were conservative, semiconservative, and dispersive. The conservative model suggested a mechanism by which the original parental strands stayed together after replication and the daughter duplex was made entirely of newly synthesized DNA. The semiconservative model proposed that the two DNA duplexes produced during replication were hybrid molecules, each having one of the parental strands and one of the newly synthesized strands. The dispersive model predicted that the new DNA duplexes each contained segments of parental and daughter strands all along the molecule. The conservative model was ruled out by the density-gradient experiments.
Which one of the following is the main reason that a typical eukaryotic gene is able to respond to a far greater variety of regulatory signals than a typical prokaryotic gene or operon?
The transcription of a eukaryotic gene is more likely to be influenced by proteins that bind far from the promoter.
Use your knowledge of how a new strand of DNA is synthesized to explain why DNA replication must occur in the 5′-to-3′ direction. In other words, what would be the consequences of 3′-to-5′ strand elongation?
There would be several detrimental consequences to 3′-to-5′ strand elongation. One of those most directly linked to the processes of DNA replication involves synthesis of the lagging strand. After the RNA primers are degraded, the DNA segments remaining will have 5′ ends with a single phosphate group. The incoming nucleotide will have a 3′-OH group. Without the energy provided by the release of PPi from the 5′ end, the process of elongation would no longer be energetically favorable.
Which amino acid would you expect a tRNA with the anticodon 5′-GAC-3′ to carry? aspartic acid (Asp) valine (Val) leucine (Leu) glutamine (Gln)
Valine
In addition to the extracts and the plasmid DNA, are there any additional materials you should add to this in vitro replication system? Explain your answer.
You will probably add exogenous nucleoside triphosphates to serve as the building blocks needed to make new strands of DNA. Although these monomers will be present in the extracts, they will be present at lower concentrations than are normally found inside the cell. They may also be subject to hydrolysis, and the nucleoside diphosphates that are the products of this hydrolysis are not usable substrates for DNA replication. For both of these reasons, it is important to add excess nucleotides to the reaction mixture for efficient DNA replication to occur.
Which of the following might decrease the transcription of only one specific gene in a bacterial cell?
a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site
Amino acids are attached to their tRNA molecules by: aminoacyl-tRNA hydroxylases. peptide bonds. aminoacyl-tRNA synthetases. aminoacyl-tRNA ligases.
aminoacyl-tRNA synthetases.
snRNAs ___________________. a. are important for producing mature mRNA transcripts in bacteria. are translated into snRNPs. b. can bind to specific sequences at intron-exon boundaries through complementary base-pairing. c. are removed by the spliceosome during RNA splicing.
can bind to specific sequences at intron-exon boundaries through complementary base-pairing.
Which of the following membrane lipids does notcontain a fatty acid tail?( a) phosphatidylcholine (b) a glycolipid (c) phosphatidylserine (d) cholesterol
cholesterol
DNA replication is considered semiconservative because ____________________________.
each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand.
Where does most new membrane synthesis take place in a eukaryotic cell? (a) in the Golgi apparatus (b) in the endoplasmic reticulum (c) in the plasma membrane (d) in the mitochondria (e) on ribosomes
in the endoplasmic reticulum
What part of the DNA replication process would be most directly affected if a strain of bacteria lacking primase were used to make the cell extracts?
initiation of DNA synthesis