Cell Bio

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a

hormone.

In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins?

in the cytosol

What type of macromolecule helps package DNA in eukaryotic chromosomes?

proteins

Which RNA is involved in chemical modifications of RNA?

snoRNA

An exported mRNA containing 300 nucleotides can initially be translated into a protein that is approximately how many amino acid residues in length?

100 amino acids

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?

5′-AUAGGCAUUCGAUCCGGAUAGCAU-3′

Which of the following statements is TRUE?

Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.

Which of the following is NOT part of the process known as "oxidative phosphorylation"?

ATP molecules are produced in the cytosol as glucose is converted into pyruvate.

Binding of adrenaline to a GPCR stimulates cAMP synthesis, which can ultimately activate glycogen phosphorylase to break down glycogen to glucose. Which of the following proteins can diminish signal transduction of this pathway?

Activated cyclic AMP phosphodiesterase.

Which of the following statements about the unfolded protein response (UPR) is FALSE?

Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins.

Which of the following conditions is likely to decrease the likelihood of skeletal muscle contraction?

Addition of a drug that blocks Ca2+ binding to troponin.

Which of the following is true about operons?

All genes in the operon are transcribed into one mRNA molecule.

Which of the following would not occur following the unfolded protein response (UPR).

Cell division

In eukaryotes, which of the below underlined codons will be selected as the translation initiator codon (codon number shown in parentheses)? 5'...AUAUGCGCACAUG(1)GCGCGCAAUG(2)AGGGCAGCCGCCAUG(3)GACGCCGCCACCAUG(4)GAGGCGGCAAC...3'

Codon 4

Methotrexate, a chemotherapy drug, is structurally similar to folate. Folate binds and activates the enzyme dihydrofolate reducatase. When methotrexate is bound to dihydrofolate reducatase, it is unable to bind folate and the enzyme is inactive. This is an example of what type of regulation?

Competitive inhibition

In prokaryotes, which of the below underlined codons will be selected as the translation initiator codon (codon number shown in parentheses)? 5'...GAGGAGCGCACAUG(1)CGAGGAGGUAUCCAUG(2)GCUAAGCCGUCCCAUG(3)GACGCCCAUG(4)GAGGGCGGCA...3'

Codon 2

Which of the following statements about the cytoskeleton is FALSE?

Covalent bonds between protein monomers hold together cytoskeletal filaments.

Which RNA is involved in RNA editing?

gRNA

Which of the following is not a method of epigenetic inheritance?

DNA recombination

Which of the following statements is TRUE?

Disulfide bonds stabilize but do not change a protein's final conformation.

Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels?

ER → Golgi → plasma membrane

Certain cells that line the stomach synthesize a digestive enzyme and secrete it into the stomach. Which of the following processes could be responsible for its secretion?

Exocytosis

Which of the following statements about RNA splicing is FALSE?

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.

Consider two genes that are next to each other on a chromosome, as arranged below. Gene A Gene B Which of the following statements is TRUE?

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

Most eukaryotic cells only express 20-30% of the genes they possess. The formation of heterochromatin maintains the other genes in a transcriptionally silent (unexpressed) state. Which histone modification is associated with the formation of the most common type of heterochromatin?

H3 lysine 9 methylation

Which of the following choices best describes GAP (GTPase activating protein) regulation of GTP-binding proteins?

Hydrolyzes GTP to GDP to deactivate the protein.

Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2, as diagrammed below. Which of the following statements is FALSE?

In the absence of a survival signal, Bad is phosphorylated.

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.

What is the role of the nuclear localization sequence in a nuclear protein?

It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore.

How does S-Cdk help guarantee that replication occurs only once during each cell cycle?

It phosphorylates the Cdc6 protein, marking it for destruction.

In the final stage of the oxidation of food molecules, a gradient of protons is formed across the inner mitochondrial membrane, which is normally impermeable to protons. If cells were exposed to an agent that causes the membrane to become freely permeable to protons, which of the following effects would you expect to observe?

Less ATP would be made.

During which stage of mitosis do the chromosomes line up at the cell equator?

Metaphase

Which of the following statements about chromatin is TRUE?

chromatin remodeling affects transcription by altering chromatin structure to allow accessibility to the DNA

Which of the following statements about the function of the centrosome is FALSE?

Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant outside a typical mammalian cell?

Na+

Which of the following statements is TRUE?

Nonpolar amino acids tend to be found in the interior of proteins.

Which of the following methods is NOT used by cells to regulate the amount of a protein in the cell?

Nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus into the cytoplasm.

Peptide bonds are formed between two amino acids through a _______ reaction.

Peptide bonds are formed between two amino acids through a _______ reaction.

During which stage of mitosis does mitotic spindle begin to form?

Prophase

Which of the following statements is TRUE?

Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation.

Which of the following is NOT a eukaryotic transcription factor binding motif?

RING finger

Which of the following statements is FALSE?

RNA polymerase adds bases in a 3′-to-5′ direction; DNA polymerase adds bases in a 5′-to-3′ direction.

Which of the following statements about RNAi is true?

RNAi is induced when double-stranded RNA is present in the cell.

Which of the following descriptions is consistent with the behavior of a cell infected with a virus that inhibits checkpoint mechanisms that normally operates during G2?

The cell would enter M phase under conditions when normal cells would not.

Which family of GTPases control the organization of the actin cytoskeleton?

Rho

Which of the following statements about prokaryotic mRNA molecules is FALSE?

Ribosomes must bind to the 5′ cap before initiating translation.

When does DNA replication occur?

S phase

In the laboratory, you observe cells undergoing mitosis under the microscope. The sister chromatids line up at the cell equator, but they do not not separate. All of the following are possible explanations EXCEPT.

Securin has a mutation which prevents it from binding to separase.

Which of the following statements about the genetic code is CORRECT?

Some amino acids are specified by more than one codon.

Membrane lipids are capable of many different types of movement. Which of these rarely occurs spontaneously in biological membranes? Rotation

Switching or flip-flopping between lipid layers

During translation elongation, a charged tRNA enters the ribosome at which site?

The A site

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.

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 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 statements about skeletal muscle contraction is FALSE?

The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction.

Which of the following statements about the genetic code is CORRECT?

The genetic code is redundant.

Which of the following statements about transport into mitochondria is FALSE?

The protein moves completely through the protein translocator in the outer membrane, then the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane.

Which of the following does NOT occur before a eukaryotic mRNA is exported from the nucleus?

The ribosome binds to the mRNA.

Which of the following does not occur before a eukaryotic mRNA is exported from the nucleus?

The ribosome binds to the mRNA.

The following happens when a G-protein-coupled receptor activates a G protein.

The α subunit exchanges its bound GDP for GTP.

Which of the following is FALSE about molecular chaperones?

They can interact with unfolded polypeptides in a way that changes the final fold of the protein.

Molecular chaperones can work by creating an "isolation chamber." What is the purpose of this chamber?

This chamber serves to protect unfolded proteins from interacting with other proteins in the cytosol, until protein folding is completed.

Endosomes mature into lysosomes, which contain hydrolytic enzymes that are only active in acidic conditions.

True

In transmembrane proteins, both start-transfer sequences and stop-transfer sequences are hydrophobic.

True

Microtubules are important for transporting cargo in nerve cell axons. Notice that the two types of cargo are traveling in opposite directions. The gray cargo is attached to dynein.

True

Steroid hormones can pass through the plasma membrane to interact with intracellular receptors.

True

Which of the following statements is FALSE?

Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.

Which of the following protein families are NOT involved in directing transport vesicles to the target membrane?

adaptins

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

Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called________.

active transport.

Molecules to be packaged into vesicles for transport are selected by ______.

adaptins

The figure below shows how normal signaling works with a Ras protein acting downstream of an RTK. You examine a cell line with a constitutively active (always ON) Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line?

addition of a drug that blocks protein Y from interacting with its target

The poison strychnine binds to the glycine receptor on neurons decreasing its affinity for the neurotransmitter glycine. This is an example of what type of regulation?

allosteric inhibition

The hydrolysis of GTP to GDP carried out by tubulin molecules _____.

allows the behavior of microtubules called dynamic instability.

Complete the sentence with the best option provided below. The primary structure of a protein is the

amino acid sequence

Which of the following channels would not be expected to generate a change in voltage by movement of its substrate across the membrane where it is found?

an aquaporin

Which of the following descriptions best matches the function of a kinase?

an enzyme that catalyzes the addition of phosphate groups to other molecules

Select the best option to fill in the blanks of the following statement: Fermentation is a/an __________ process that converts __________into carbon dioxide and __________.

anaerobic, pyruvate, ethanol

Apoptosis differs from necrosis in that necrosis _____.

causes cells to swell and burst, whereas apoptotic cells shrink and condense.

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in __________ signaling.

contact-dependent

If lactose is absent and glucose is present, transcription of the lactose operon _____.

does not occur because the promoter is blocked by the repressor.

Your friend has just joined a lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles. He wants to start designing some experiments but was not listening carefully when he was told about the molecular defect of this cell line. He is too embarrassed to ask and comes to you for help. He does recall that this cell line forms coated pits but vesicle budding and the removal of coat proteins don't happen. Which of the following proteins might be lacking in this cell line?

dynamin

Your friend has just joined a lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles. He wants to start designing some experiments but was not listening carefully when he was told about the molecular defect of this cell line. He is too embarrassed to ask and comes to you for help. He does recall that this cell line forms coated vesicles but cannot dock with the target membrane. Which of the following proteins might be lacking in this cell line?

dynamin

Signal sequences that direct proteins to the correct compartment are

encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination.

Signal sequences that direct proteins to the correct compartment are ______.

encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination.

The advantage to the cell of the gradual oxidation of glucose during cellular respiration compared with its combustion to CO2 and H2O in a single step is that

energy can be extracted in usable amounts.

Cell membranes maintain asymmetry by __________, which catalyzes transfer of specific phospholipids, such as phosphatidylserine and phosphatidylethanolamine, back to the cytosolic side of the membrane.

flippase

Cells are coated with polysaccharide __________, which can improve cell motility.

glycocalyx

Which of the following processes do NOT take place in the mitochondria?

glycogen breakdown

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is _____.

hormonal

Proteins bind selectively to small-molecule targets called ligands. The selection of one ligand out of a mixture of possible ligands depends on the number of weak, noncovalent interactions in the protein's ligand-binding site. Where is the binding site typically located in the protein structure?

inside a cavity on the protein surface

During RNA splicing _____ are excised and _____ are ligated. exons; intron

introns; exons

Combinatorial control of gene expression _________.

involves groups of transcription regulators working together to determine the expression of a gene.

A protein kinase can act as an integrating device in signaling if it

is activated by two or more proteins in different signaling pathways.

RNA in cells differs from DNA in that

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

In the laboratory, you mutate a gene in neurons and discover that the resulting cells are unable to transport vesicles and organelles to the axon terminal, but they can still transport vesicles and organelles from the axon terminal to the cell body. The gene you mutated is most likely a _________.

kinesin motor protein.

Using genetic engineering techniques, you remove the sequences that code for the ribosome-binding sequences of the bacterial LacZ gene. The removal of these sequences will lead to _______.

no translation of the LacZ mRNA.

Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP?

oxidative phosphorylation

Irradiated mammalian cells usually stop dividing and arrest at a G1 DNA damage checkpoint. Which of the following would occur first?

p53 is phosphorylated.

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

phospholipids

The sigma subunit of bacterial RNA polymerase

recognizes promoter sites in the DNA.

Which of the following structures shorten during muscle contraction?

sarcomere

Which of the following structures shorten during muscle contraction?

sarcomeres

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

scanning along the mRNA from the 5′ end.

Which RNA is involved in RNA silencing?

siRNA

The microtubules in a cell form a structural framework that can have all the following functions except which one?

strengthening the plasma membrane

Which of the following is NOT a chemical group commonly found on core histone N-terminal tails for chromatin regulation?

sulfhydryl

Involved in translation termination, eRF-1 has a structure similar to which of the following choices?

tRNA

Which RNA functions as a carrier of amino acids?

tRNA

In a DNA double helix,

the two DNA strands run antiparallel.

Which of the following is NOT a process that delivers material to the lysosome?

transcytosis

Proteins that are fully translated in the cytosol do not end up in

transport vesicles

Proteins that are fully translated in the cytosol do not end up in ______.

transport vesicles.

Posttranslational modification with ________ marks proteins to be located to the proteasome.

ubiquitin

An action potential is triggered by depolarization of the plasma membrane. This causes ___________ to flicker open, rapidly furthering depolarization of the membrane.

voltage gated Na+ channels