advance molecular biology

Which of the following statements about the proteasome is false? Select one: a. Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold. b. 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. c. Ubiquitin is a small protein that is covalently attached to proteins to mark them for delivery to the proteasome. d. Proteases reside in the central cylinder of a proteasome.

(a) Once proteins are sent to the proteasome, proteases degrade them. Chaperone proteins provide a place for misfolded proteins to attempt to refold.

Which of the following does not occur before a eukaryotic mRNA is exported from thenucleus? Select one: a. The ribosome binds to the mRNA. b. The mRNA is polyadenylated at its 3′end c. 7-methyl guanosine is added in a 5′-to-5′ linkage to the mRNA. d. RNA polymerase dissociates.

(a) Ribosomes are in the cytosol and will bind to the mRNA once it has been exported from the nucleus.

Which of the following statements about prokaryotic mRNA molecules is false? Select one: a. A single prokaryotic mRNA molecule can be translated into several proteins. b. mRNAs are not polyadenylated. c. Ribosomes can start translating an mRNA molecule before transcription is complete. d. Ribosomes must bind to the 5′cap before initiating translation.

(b) Bacterial mRNAs do not have 5′caps. Instead, ribosome-binding sites upstream of the start codon tell the ribosome where to begin searching for the start of translation.

There are several reasons why the primase used to make the RNA primer for DNA replication is not suitable for gene transcription. Which of the statements below is not one of those reasons? a. Primase initiates RNA synthesis on a single-stranded DNA template. b. Primase can initiate RNA synthesis without the need for a base-paired primer. c. Primase synthesizes only RNAs of about 5-20 nucleotides in length. d. The RNA synthesized by primase remains base-paired to the DNA template.

Choice (b) is true for both primase and RNA polymerase, so it does not describe why primase cannot be used for gene transcription.

Which of the following pairs of codons might you expect to be read by the same tRNA as a result of wobble? Select one: a. AAU and AGU b. CAC and CAU c. CUU and UUU d. GAU and GAA

Choice (c) is the correct answer. These two codons differ only in the third position and also encode the same amino acid, which is the definition of wobble. Although the codons GAU and GAA [choice (b)] also differ only in the third position, they are unlikely in normal circumstances to be read by the same tRNA, because they encode different amino acids.

Which of the following molecules is thought to have arisen first during evolution?

RNA Because RNA is known to catalyze reactions within the cell, because the components of RNA are thought to be more readily formed in the conditions on primitive Earth, and because RNA can contain genetic information, it is the most likely of the three molecules to have arisen first in evolution

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

Transcription in bacteria differs from transcription in a eukaryotic cell because __________________________.

RNA polymerase (along with its sigma subunit) can initiate transcription on its own

In eukaryotic cells, general transcription factors are required for the activity of all promoters transcribed by RNA polymerase II. The assembly of the general transcription factors begins with the binding of the factor _________________ to DNA, causing a marked local distortion in the DNA. This factor binds at the DNA sequence called the _______________ box, which is typically located 25 nucleotides upstream from the transcription start site. Once RNA polymerase II has been brought to the promoter DNA, it must be released to begin making transcripts. This release process is facilitated by the addition of phosphate groups to the tail of RNA polymerase by the factor _______________. It must be remembered that the general transcription factors and RNA polymerase are not sufficient to initiate transcription in the cell and are affected by proteins bound thousands of nucleotides away from the promoter. Proteins that link

TFIID TATA TFIIH mediator deactylase

Which of the following statements is true? Select one: a. A ribosome binds one tRNA at a time. b. rRNA contains the catalytic activity that joins amino acids together. c. Ribosomes are large RNA structures composed solely of rRNA. d. Ribosomes are synthesized entirely in the cytoplasm.

b

You have a piece of DNA that includes the following sequence: 5′-ATAGGCATTCGATCCGGATAGCAT-3′ 3′-TATCCGTAAGCTAGGCCTATCGTA-5′ Which of the following RNA molecules could be transcribed from this piece of DNA? Select one: a. 5′-UAUCCGUAAGCUAGGCCUAUGCUA-3′ b. 5′-AUAGGCAUUCGAUCCGGAUAGCAU-3′ c. 5′-UACGAUAGGCCUAGCUUACGGAUA-3′ d. none of the above

b

The ribosome is important for catalyzing the formation of peptide bonds. Which of the following statements is true? Select one: a. The number of rRNA molecules that make up a ribosome greatly exceeds the number of protein molecules found in the ribosome. b. The large subunit of the ribosome is important for binding to the mRNA. c. The catalytic site for peptide bond formation is formed primarily from an rRNA. d. Once the large and small subunits of the ribosome assemble, they will not separate from each other until degraded by the proteasome

c

Which of the following statements about RNA splicing is false? Select one: a. Conventional introns are not found in bacterial genes. b. Splicing occurs after the 5′ cap has been added to the end of the primary transcript. c. For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene. d. Small RNA molecules in the nucleus perform the splicing reactions necessary for the removal of introns.

c. The primary transcript of a gene can sometimes be spliced differently so that different exons can be stitched together to produce distinct proteins in a process called alternative splicing.

Which of the following methods is not used by cells to regulate the amount of a protein in the cell? Select one: a. Genes can be transcribed into mRNA with different efficiencies. b. Many ribosomes can bind to a single mRNA molecule. c. Proteins can be tagged with ubiquitin, marking them for degradation d. Nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus into the cytoplasm.

d. Proteins are synthesized in the cytoplasm and therefore newly synthesized proteins would not be exported from the nucleus into the cytoplasm.

Where does most new membrane synthesis take place in a eukaryotic cell?

in the endoplasmic reticulum

Genes in eukaryotic cells often have intronic sequences coded for within the DNA. These sequences are ultimately not translated into proteins. Why?

intronic sequences are removed from RNA molecules by the spliceosome, which works in the nucleus

A poison added to an in vitro translation mixture containing mRNA molecules with the sequence 5′-AUGAAAAAAAAAAAAUAA-3′ has the following effect: the only product made is a Met-Lys dipeptide that remains attached to the ribosome. What is the most likely way in which the poison acts to inhibit protein synthesis?

it inhibits the movement of the small subunit relative to the large subunit

RNA in cells differs from DNA in that ___________________.

it is single- structured and can fold up into a variety of structures

Which amino acid would you expect a tRNA with the anticodon 5′-CUU-3′ to carry?

lysine

Total nucleic acids are extracted from a culture of yeast cells and are then mixed with resin beads to which the polynucleotide 5′-TTTTTTTTTTTTTTTTTTTTTTTTT-3′ has been covalently attached. 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 because this is the only type of RNA that is polyadenylated, and its poly-A tail would be able to base-pair with the strands of poly T on the beads and thus stick to them. DNA would not be found in the sample, because the poly-A tail is not encoded in the DNA adn long runs of T are rare in DNA

Which of the following statements is true? Select one: a. Membrane lipids diffuse within the plane of the membrane. b. Phospholipids will spontaneously form liposomes in nonpolar solvents c. Membrane lipids frequently flip- flop between one monolayer and the other. d. In eukaryotes, all membrane-enclosed organelles are surrounded by one lipid bilayer

membrane lipids diffuse within the plane of the membrane

Cholesterol serves several essential functions in mammalian cells. Which of the following is not influenced by cholesterol?

membrane thickness

What do you predict would happen if you created a tRNA with an anticodon of 5′-CAA-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?

methionine would be incorporated into proteins at some positions where leucine should be The 5'-CAA-3' anticodon binds to the 5'-UUG-3' codon, which normally codes for leucine

According to current thinking, the minimum requirement for life to have originated on Earth was the formation of a _______________.

molecule that could catalyze its own replication

Transcription is similar to DNA replication in that ___________________.

nucleotide polymerization occurs only in the 5'-to-3' direction

The plasma membrane serves many functions, many of which 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?

selective permeability

Membranes only allow certain molecules or ions to pass through. This is called______.

selectively permeable

Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes?

switching between lipid bilayer

Which of the following statements is false? Select one: a. If two genes are to be expressed in a cell, these two genes can be transcribed with different efficiencies. b. RNA polymerase is responsible for both unwinding the DNA helix and catalyzing the formation of the phosphodiester bonds between nucleotides. c. A new RNA molecule can begin to be synthesized from a gene before the previous RNA molecule's synthesis is completed. d. Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.

unlike DNA, RNA uses a uracil base and a deoxyribose sugar false because RNA nucleotides contain the sugar ribose

The concentration of a particular protein,X,in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolateda line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X mRNA in the mutant cells are normal. Which of the following mutations in the gene for X could explain these results? Select one: a. a change of the first ATG codon to CCA b. the deletion of a sequence that encodes sites at which ubiquitin can be attached to the protein c. a change at a splice site that prevents splicing of the RNA d. the introduction of a s

(b) The decrease in the level of protein X in the normal cell is most probably due to protein degradation, because levels of mRNA remain constant. The inability of the mutant cell to divide could be due to a mutation that inhibits protein degradation. This would be achieved by the removal of sites for attachment of ubiquitin, which targets proteins for destruction.

Which of the following statements about prokaryotic mRNA molecules is false? Select one: a. A single prokaryotic mRNA molecule can be translated into several proteins. b. mRNAs are not polyadenylated. c. Ribosomes can start translating an mRNA molecule before transcription is complete. d. Ribosomes must bind to the 5′cap before initiating translation.

(d) Bacterial mRNAs do not have 5′caps. Instead, ribosome-binding sites upstream of the start codon tell the ribosome where to begin searching for the start of translation.

1. Although cholesterol is a hydrophobic molecule, it has a hydrophilic head group like all other membrane lipids ________. 2. Phosphatidylserine is the most abundant type of phospholipid found in cell membranes _________. 3. Glycolipids lack the glycerol component found in phospholipids _________. 4. The highly ordered structure of the lipid bilayer makes its generation and maintenance energetically unfavorable _________.

1. true 2.False: Phosphatidylcholine is the most abundant phospholipid found in cell membranes. 3.true 4.false

There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)

15 carbons and 2 double bonds

The instructions specified by the DNA will ultimately specify the sequence of proteins. This process involves DNA, made up of ___________ different nucleotides, which gets_________________ into RNA, which is then _______________ into proteins, made up of ____ different amino acids. In eukaryotic cells, DNA gets made into RNA in the________________, while proteins are produced from RNA in the_______________. The segment of DNA called a _______________ is the portion that is copied into RNA; this process is catalyzed by RNA _______________.

4 transcribed translated 20 nucleus cytoplasm gene polymerase

Below is the sequence from the 3′end of an mRNA. 5′-CCGUUACCAGGCCUCAUUAUUGGUAACGGAAAAAAAAAAAAAA-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′ Correct (a) The stop codon (UAA) is underlined in the mRNA sequence below; this is the only stop codon on this piece of mRNA. The codon (UGG) preceding the stop codon will be binding to a tRNA in the P site of the ribosome when release factor binds to the A site. The anticodon of the tRNA will bind to the codon UGG and will be CCA. 5′-CCGUUACCAGGCCUCAUUAUUGGUAACGGAAAAAAAAAAAAAA-3'

In eukaryotes, but not in prokaryotes, ribosomes find the start site of translation by ____________________________.

scanning along the mRNA from the 5' end

You are studying a disease that is caused by a virus, but when you purify the virus particles and analyze them you find they contain no trace of DNA. Which molecules are likely to contain the genetic information of the virus?

RNA

A mutation in the tRNA for the amino acid lysine results in the anticodon sequence 5′-UAU-3′ (instead of 5′-UUU-3′). Which of the following aberrations in protein synthesis might this tRNA cause? a. substitution of lysine for isoleucine b. substitution of lysine for phenylalanine c. substitution of lysine for tyrosine d. read-through of stop codons

The mutant tRNA Lys will be able to pair with the codon 5′-AUA-3′, which codes for isoleucine.

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? Select one: a. 5′-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3′ b. 5′-UGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUG-3′ c. 5′-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-3′ d. 5′-GGAAAAGGAGAUGGGCAAGGGGAAAAGGAGAUGGGCAAGG-3′

a.

Which of the following might decrease the transcription of only one specific gene in a bacterial cell? Select one: a. a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site b. a decrease in the amount of RNA polymerase c. a decrease in the amount of sigma factor d. a mutation that introduced a stop codon into the DNA that precedes the gene's coding sequence

a. Such changes would probably destroy the function of the promoter, making RNA polymerase unable to bind to it.

Diversity among the oligosaccharide chains found in the carbohydrate coating of the cell surface can be achieved in which of the following ways? Select one: a. varying the types of sugar monomers used b. varying the types of linkages between sugars c. varying the number of branches in the chain d. all of the above

all of the above

Membrane proteins, like membrane lipids, can move laterally by exchanging positions with other membrane components. Which type of membrane proteins is expected to be the least mobile, based on their function?

anchors

Which of the following statements about the genetic code is correct? Select one: 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

snRNAs _____________

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

Which of the following membrane lipids does not contain a fatty acid tail?

chlosterol

New membrane phospholipids are synthesized by enzymes bound to the _____________ side of the _________________ membrane.

cytosolic, endoplasmic reticulum

You have a segment of DNA that contains the following sequence: 5′-GGACTAGACAATAGGGACCTAGAGATTCCGAAA-3′ 3′-CCTGATCTGTTATCCCTGGATCTCTAAGGCTTT-5′ You know that the RNA transcribed from this segment contains the following sequence: 5′-GGACUAGACAAUAGGGACCUAGAGAUUCCGAAA-3′ Which of the followingchoices best describes how transcription occurs? Select one: a. the top strand is the template strand; RNA polymerase moves along this strand from 5′to 3′ b. the top strand is the template strand; RNA polymerase moves along this strand from 3′ to 5′ c. the bottom strand is the template strand; RNA polymerase moves along this strand from 5′ to 3′ d. the bottom strand is the template strand; RNA polymerase moves along this strand from 3′ to 5′

d. The bottom strand can hybridize with the RNA molecule and thus is the template strand. The polymerase moves along the DNA in a 3′-to-5′ direction, because the RNA nucleotides are joined in a 5′- to-3′ polarity.

Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both of these tasks?

flippases

Consider two genes that are next to each other on a chromo some, as arranged in Figure Q7-3. Which of the following statements is true? Select one: a. The two genes must be transcribed into RNA using the same strand of DNA. b. If gene A is transcribed in a cell, gene B cannot be transcribed. c. Gene A and gene B can be transcribed at different rates, producing different amounts of RNA within the same cell.

gene A and gene B can be transcribed at different rates, producing different amounts of RNA within the same cell

The endothelial cells found closest to the site of an infection express proteins called lectins. Each lectin binds to a particular ____________ that is presented on the surface of a target cell Select one: a. oligosaccharide b. aminophospholipid c. polysaccharide d. sphingolipid

oligosaccharide

Which type of lipids are the most abundant in the plasma membrane?

phospholipids

Which three amphipathic lipids are present in the cell membrane?

phospholipids, glycolipids, sterols

A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity?

produce lipids with hydrocarbon tails that are shorter and have more double bonds

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 __________________.

proteins amphipathic lipid bilayer fatty acid tails hydrophilic head groups phospholipids sugars

The sigma subunit of bacterial RNA polymerase ___________________.

recognizes promoter sites in the DNA

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 trancription of a eukaryotic gene can be influence by proteins that bind far from the promoter

Porin proteins form large, barrel-like channels in the membrane. Which of the following is not true about these channels?

they are made primarily of α helices

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.

transcription mRNA tRNA rRNA snRNA