Cell & Molecular Biology ch 1-5 44 muliple choice

What is not true of all cells?

a) They have membrane transport proteins

b) they synthesize proteins on the ribosome

c) they replicate their genome by DNA polymerization 

d) they transcribe their genome by DNA polymerization

e) they use RNA as a template for genomic DNA polymerization 

e) they use RNA as a template for genomic DNA polymerization 

Imagine a segment of DNA (within a gene) encoding a certain amount of info in its nucleotide sequence. when this segment is fully transcribed into mRNA and then translated into protein, in general, what happens?

a) the protein sequence would carry more info compared to the DNA and mRNA sequences, bc its alphabet has 20 letters

b) the protein sequence would carry less info compared to the DNA and mRNA sequences, bc several codons can correspond to one amino acid

c) the amount of info in the mRNA sequence is lower, bc the mRNA has been transcribed using only one of the DNA strands as the template 

d)The amount of information in the mRNA sequence is higher, because several mRNA

molecules can be transcribed from one DNA molecule.

b) the protein sequence would carry less info compared to the DNA and mRNA sequences, bc several codons can correspond to one amino acid

What is NOT true of the plasma membrane?

a)It is totally impermeable.

b) It contains proteins that move materials across the plasma membrane.

c) It contains enzymes that catalyze reactions within the cell.

d) It is made of molecules that are both hydrophilic and hydrophobic.

e) It allows waste materials to be removed from the cell.

a) It is totally impermeable 

What is NOT true regarding the tree of life?

A. Most bacteria and archaea have 1000 to 6000 genes in their genomes.

b. Eukaryotes are more similar to archaea than to bacteria with respect to the proteins

that act on their DNA

C. Most bacteria and archaea have genome sizes between 1 and 10 million nucleotide

pairs, whereas eukaryotic genomes can be millions of times larger.

D. Archaeal species were thought to belong to the eukaryotic world before sequence

analysis placed them in a separate domain of life.

E. Photosynthetic bacteria are thought to be the ancestors of the eukaryotic chloroplasts.

d) Archaeal species were thought to belong to the eukaryotic world before sequence analysis placed them in a separate domain of life. 

What does NOT typically involve horizontal gene transfer?

A. Sexual reproduction in humans

B. Bacteriophage infection of bacteria

C. The evolutionary history of the eukaryotic cell

D. The accidental duplication of a small region of a bacterial chromosome followed by cell

division

E. Introduction of plasmids into bacteria in a laboratory

d) the accidental duplication of a small region of a bacterial chromosome followed by cell division

Mitochondria and chloroplasts are thought to have evolved from free-living aerobic bacteria

that were engulfed by an ancestral anaerobic cell and established a mutually beneficial

(symbiotic) relationship with it. Which statement about these organelles is NOT true?

a) They are similar in size to small bacteria.

b) They have their own circular genomic DNA.

c) They have their own ribosomes.

d) They have their own transfer RNAs.

e) They are found in all eukaryotes.

e) they are found in all eukaryotes

What trait is typical for a hydrophobic molecule?

a) it is able to form hydrogen bonds with itself but not with water

b) it is able to form hydrogen bonds with water 

c) it is charged

d) it is hard to discolve in a solvent 

e) it is incapable of interacting favorably with water 

e) it is incapable of interacting favorably with water 

Weak noncovalent attractions in the cell can be very strong in a nonaqueous environment.

Some of these attractions are as strong as covalent interactions in a vacuum (their bond

energy is approximately 340 kJ/mole), but become more than 25 times weaker (their bond

energy becomes approximately 13 kJ/mole) in water. What type of attraction shows this

phenomenon?

A. Electrostatic attractions

B. Hydrogen bonds

C. van der Waals attractions

D. Hydrophobic force

a) electrostatic attractions

The concentrations of H3O+ and OH− are kept relatively equal inside of the cell due to

what?

A. The presence of buffers

B. Enzymes that destroy excess H3O+ and OH−

C. Diffusion of H3O+ and OH− through the cell membrane

D. Digestion of H3O+ and OH− by lysosomes

E. Utilization of H3O+ and OH− in cellular respiration

a) the presence of buffers 

Two different proteins transiently associate with one another in the cell. Which of the

following would NOT be a means by which these two proteins come together?

A. Electrostatic interactions

B. Hydrogen bonds

C. Van der Waals interactions

D. Covalent bonds

E. Hydrophobic force

D. Covalent bonds

Enzymes are the cell’s catalyst crew. They make the life of the cell possible by carrying out various reactions with astounding performance. Which of the following is NOT true

Regarding cellular enzymes?

a) Enzymes lower the activation energy of the reactions that they catalyze.

b)Enzymes can specifically drive substrate along certain reaction pathways.

c) Enzymes can push energetically unfavorable reactions forward by coupling them to

energetically favorable reactions..

d) Enzymes are proteins, but RNA catalysts, called ribozymes, also exist.

e) Enzymes can change the equilibrium point for reactions that they catalyze.

e) Enzymes can change the equilibrium point for reactions that they catalyze.

A reaction can proceed spontaneously if what occurs?

It increases the disorder in the universe.

It forms a chemical bond.

It results in the loss of an H2O molecule.

It requires an input of energy.

It does useful work for the cell.

It increases the disorder in the universe.

Imagine the reaction A → B with a negative ΔG value under experimental conditions. Which

statement is true about this reaction?

a) The reaction is energetically unfavorable.

b) The reaction proceeds spontaneously and rapidly under these conditions.

c) Increasing the concentration of B molecules would increase the ΔG value (toward more

positive values).

d) The reaction would result in a net decrease in the entropy (disorder) of the universe.

e) The reaction cannot proceed unless it is coupled to another reaction with a positive

value of ΔG.

c) Increasing the concentration of B molecules would increase the ΔG value (toward more

positive values).

ATP is the main energy currency in cells, and it can especially be used to drive condensation

reactions that produce macromolecular polymers. How does ATP normally catalyze the

condensation reaction, which by itself is energetically unfavorable?

a) It transfers its terminal phosphate to an enzyme and is released as ADP.

b) It transfers its two terminal phosphates to an enzyme and is released as AMP.

c) It covalently attaches to both of the substrates.

d) It transfers either one or two terminal phosphate(s) to one of the substrates and is

released as either ADP or AMP.

e) It covalently attaches to the enzyme, forming an enzyme–AMP adduct.

d) It transfers either one or two terminal phosphate(s) to one of the substrates and is

released as either ADP or AMP.

Despite their overall similarity, NADH and NADPH are not used indiscriminately by the cell.

What are the distinctive features of these two carrier molecules?

A. NADPH has an extra phosphate near its nicotinamide ring, giving it distinct electron-

transfer properties.

B. In the cell, NADH is usually in excess over NAD+, but NADP+ is usually in excess over

NADPH.

C. NADH is normally involved in anabolic reactions, whereas NADPH is normally involved in

catabolism.

D. Both NADPH and NADH are recognized by the same enzymes with similar affinities,

since the extra phosphate group in NADPH is not involved in such recognition.

E. In the cell, NADH is found mostly in the form that acts as an oxidizing agent, whereas

NADPH is found mostly in the form that acts as a reducing agent.

E. In the cell, NADH is found mostly in the form that acts as an oxidizing agent, whereas

NADPH is found mostly in the form that acts as a reducing agent.

Which description matches glycolysis rather than the Krebs cycle?

A. It oxidizes acetyl-CoA to CO2.

B. In eukaryotic cells, it is carried out in the cytosol.

C. It produces FADH2.

D. α-Ketoglutarate, one of its intermediates, is used to synthesize the amino acid glutamic

acid.

B. In eukaryotic cells, it is carried out in the cytosol.

Which of the following stretches of amino acid residues would you expect to find in the

interior of protein molecules?

A. Ala-Asp-Asp-Tyr-Arg

B. Gly-Lys-Ser-Pro-Thr

C. Phe-Glu-Gln-Glu-Asn

D. Ala-Val-Leu-Ile-Trp

E. Gly-Tyr-His-Arg-His

D. Ala-Val-Leu-Ile-Trp

Which of the following is NOT the role of molecular chaperones in the folding of cellular

proteins?

A. They assist proteins in folding into their correct conformations.

B. They help prevent formation of protein aggregates.

C. They specify the final three-dimensional shape of proteins.

D. They catalyze the folding of proteins in the crowded environment of the cell.

E. They make the protein-folding process in the cell more reliable.

C. They specify the final three-dimensional shape of proteins.

The observation that proteins often renature into their original conformations after they

have been unfolded by denaturing solvents implies what?

The information needed to specify the three-dimensional shape of a protein is encoded

in its amino acid sequence.

The cell does not need molecular chaperones for survival.

The final folded structure of a protein is usually NOT the one with the lowest free

energy.

Each protein folds into several different conformations inside the cell.

The information needed to specify the three-dimensional shape of a protein is encoded

in its amino acid sequence.

Which statement regarding the marking of a protein by polyubiquitylation to signify

degradation is true?

It requires the hydrolysis of one ATP molecule to ADP per polyubiquitin chain.

It involves covalent attachment of the target protein to the E1 enzyme.

It is carried out by the proteasome complex.

It is typically done on an arginine residue in the target protein.

It involves the recognition of the target protein by an E2–E3 ligase.

It involves the recognition of the target protein by an E2–E3 ligase.

20. What does phosphorylation of a protein by a protein kinase do?

A. It adds two positive charges to the protein.

B. It activates the protein.

C. It deactivates the protein.

D. It can create a binding site for other proteins.

E. It requires the hydrolysis of two molecules of ATP per phosphorylated residue.

D. It can create a binding site for other proteins.

What is the purpose of biomolecular condensates?

a)To streamline cell signaling pathways

b)To disassemble the DNA in the nucleus for mitosis

c)To digest pathogens

d)To compartmentalize a subset of the cell’s macromolecules

c)To form water pockets in the midst of the cytosol

d)To compartmentalize a subset of the cell’s macromolecules

What is true of phase separation, or demixing?

a) It is associated with a favorable change in free energy.

b) It has a larger entropic cost for large polymers than for small molecules.

c) It involves an unfavorable free-energy change due to the entropic cost of gathering

molecules together.

d)It involves no change in free energy.

e)It involves a change in temperature.

c) It involves an unfavorable free-energy change due to the entropic cost of gathering

molecules together.

In the secondary structure of a DNA double helix, a purine (A or G) always base pairs with a

pyrimidine (T or C). Why is this base-pair alignment critical to the structure of DNA?

A. Pairing a purine with a pyrimidine ensures that the proper number of hydrogen bonds is

generated.

B. Pairing a purine with a pyrimidine ensures that the distance between the backbone

strands is constant.

C. Pairing a purine with a pyrimidine ensures that the proper complementary base is

utilized during replication.

D. Biochemically, it is impossible to generate a base pair between two purines or two

pyrimidines.

E. The only way to generate complementary strands is if a purine is paired with a

pyrimidine.

B. Pairing a purine with a pyrimidine ensures that the distance between the backbone

strands is constant.

The chromatin remodeling complexes play an important role in chromatin regulation in the

nucleus. The ability of these complexes to remodel the chromatin structure is dependent on

which enzymatic function?

A. They can slide nucleosomes on DNA.

B. They have ATPase activity.

C. They can interact with histone chaperones.

D. They can remove core histone subunits.

E. They can substitute core histone subunits.

B. They have ATPase activity.

What is a characteristic of a chromatin “reader complex?”

a)It is always coupled to a “writer complex” and spreads specific chromatin modifications.

b)It can recognize any histone code.

c)It binds tightly to the chromatin only when a specific set of histone marks is present.

d)It can only bind to a single specific histone mark.

e)It has at least five protein subunits.

c)It binds tightly to the chromatin only when a specific set of histone marks is present.

Variations in the structure of DNA, such as loops, or the chromatin organization such as

euchromatin or heterochromatin, can influence gene expression and can be inherited by

subsequent generations even though these changes do not result in alterations to the

sequence of nucleotides. What is this type of inheritance called?

A. Epigenetic inheritance

B. Transmorphic inheritance

C. Mendelian inheritance

D. Formative inheritance

A. Epigenetic inheritance

The genetic information carried by a cell is passed on, generation after generation, with

astonishing fidelity. However, genomes are still altered over evolutionary time scales, and

even their overall size can change significantly. Which genome-altering event has increased

the size of the mammalian genome the most?

A. Transposition

B. Point mutation

C. Chromosomal deletion

D. Chromosomal inversion

E. Chromosomal translocation

A. Transposition

Which feature of DNA underlies its simple replication procedure?

a)The fact that it is composed of only four different types of bases

b)The antiparallel arrangement of the double helix

c)The complementary relationship in the double helix

d)The fact that there is a major groove and a minor groove in the double helix

c)The complementary relationship in the double helix

The eukaryotic chromosomes are organized inside the nucleus with a huge compaction ratio

of several thousand-fold and is further accentuated during the mitotic cycle. What

interaction is responsible for such a tight packaging?

A. The various histone proteins that wrap and fold the DNA

B. The nuclear envelope which encapsulates the chromosomes

C. The nuclear matrix that provides a firm scaffold

D. The nucleosome that is the core chromatin structure

A. The various histone proteins that wrap and fold the DNA

Conservation of genomic sequences between humans and chickens is mainly due to a

specific type of selection, whereas the conservation observed between humans and

chimpanzees is mostly due to the short time available for mutations to accumulate. What

type of selection is responsible and what position on the DNA sequences of synonymous

codons are nearly identical between humans and chimpanzees?

A. Purifying; third

B. Homologous; third

C. Pacifying; first

D. Purifying; first

E. Directional; third

A. Purifying; third

Which statement regarding heterochromatin in a typical mammalian cell is true?

a) About 1% of the nuclear genome is packaged in heterochromatin.

b) The DNA in heterochromatin contains all of the inactive genes in a cell.

c)Genes that are packaged in heterochromatin are permanently turned off.

d)The different types of heterochromatin share an especially high degree of compaction.

e)Heterochromatin is highly concentrated in the centromeres but not the telomeres.

d)The different types of heterochromatin share an especially high degree of compaction.

Which statement regarding the mutation rate of genomic DNA in different organisms is

true?

a)Human cells have a much higher mutation rate compared to bacteria when the rate is

normalized to a single round of replication over the same length of DNA.

b)Mutation rates limit the number of essential genes in an organism’s genome.

c)Mutations in the somatic cells cannot be lethal.

d)Even if the mutation rate was 10 times higher than its current value, germ-cell stability

in humans would not have been affected.

b)Mutation rates limit the number of essential genes in an organism’s genome.

A replication fork is shown schematically below. The strand labeled A is called the

strand.

A. Template

B. Primer

C. Leading

D. Lagging

d) lagging 

During DNA replication, what is the role of the single-strand DNA-binding (SSB) proteins?

A. They are generally found more on the leading strand than the lagging strand where they

can impede synthesis.

B. They bind cooperatively to single-stranded DNA and cover the bases to prevent base-

pairing.

C. They prevent the folding of the single-stranded DNA.

d) They bind cooperatively to short hairpin helices that readily form in the single-stranded

DNA.

C. They prevent the folding of the single-stranded DNA.

Which statement regarding eukaryotic replication origins is true?

A.  They are composed of specific, short DNA sequences, wrapped by histones.

b)Firing of a single origin or replication is mediated by dephosphorylation of components

bound to it.

C. Helicases are loaded onto the origin facing toward each other on opposite strands and

pass each other as they begin to move away from the origin.

D.They simultaneously fire once and only once during the cell cycle.

e)They contain a stretch of DNA that is rich in Gs and Cs.

C. Helicases are loaded onto the origin facing toward each other on opposite strands and

pass each other as they begin to move away from the origin.

What do the enzymes topoisomerase I and topoisomerase II have in common?

a)They both have nuclease activity.

b)They both create double-strand DNA breaks.

c)They both require ATP hydrolysis for their function.

d)They both can create winding (tension) in an initially relaxed DNA molecule.

a)They both have nuclease activity.

DNA glycosylases constitute an enzyme family found in all three domains of life. What is a

function of this battery of enzymes?

a)Add sugar moieties to DNA

b)Remove sugar moieties from DNA

c)Add a purine or pyrimidine base to DNA

d)Remove a purine or pyrimidine base from DNA

e)Remove a nucleotide from DNA

d)Remove a purine or pyrimidine base from DNA

Which repair pathway can accurately repair a double-strand break?

A. Base excision repair

B. Nucleotide excision repair

C. Direct chemical reversal

D. Homologous recombination

E. Nonhomologous end joining

D. Homologous recombination

In meiosis, a crossover in one position is thought to inhibit crossing over in the neighboring

regions. This regulatory mechanism does what?

a)Results in a very uneven distribution of crossover points along each chromosome

b)Ensures that even small chromosomes undergo at least one crossover

c)Controls how the Holliday junctions are resolved

d)Behaves randomly, resulting in 50% of double-strand breaks produced during meiosis

being resolved as crossovers

b)Ensures that even small chromosomes undergo at least one crossover

What enzyme is depicted in the following schematic drawing?

A. DNA polymerase

B. RNA polymerase

C. Ribosome

D. Reverse transcriptase

E. Topoisomerase

B. RNA polymerase

Which genes are transcribed in the nucleoli within the eukaryotic nucleus?

A. tRNA

B. rRNA

C. mRNA

D. snRNA

E. telomerase RNA

B. rRNA

How does a eukaryotic cell deal with the superhelical tension in its genomic DNA resulting

from the activity of RNA polymerases?

A.DNA gyrase introduces negative supercoils, keeping the DNA under constant tension.

b)The RNA polymerases are allowed to rotate freely around their templates during

transcription, leading to the relaxation of the tension.

c)DNA topoisomerases rapidly remove the superhelical tension caused by transcription.

d)The nucleosomes adjust the tension by binding to positively supercoiled regions behind

a moving RNA polymerase.

c)DNA topoisomerases rapidly remove the superhelical tension caused by transcription.

The modified nucleotide shown below is NEVER found in mature what?

A. tRNAs

B. Ribosomes

C. Spliceosomes

D. snoRNAs

E. DNA

E. DNA