PCB 4023 Practice Exam 1

Despite the diversity, cells resemble each other to an astonishing degree in their chemistry. For example, only four ____ are used to make DNA.

dNTP

The ____ ____ is made up of two concentric membranes and is continuous with the membrane of the endoplasmic reticulum.

nuclear envelope

Ionic bonds form a ____.

Salt

The side chain of the amino acid R under pH 7 is ____.

positively charged

Which of the following amino acid side chains can be phosphorylated by a protein kinase?

Y

Hydrogen bonds are essential to form a(n) ____.

alpha-helix

Which of the following proteins is necessary to stop a mitogenic signaling by disassociating a SH2 domain containing protein (Grb2) from phosphorylated Growth factor receptor?

a Protein Phosphatase

Which of the following is mainly mediated by an ionic bond?

Phospho-tyrosine and SH2 Domain Association

Protein A binds to protein B to form a complex, AB. At equilibrium in a cell, A, B, and AB concentrations are all at 10 nM. Calculate the equilibrium constant for the reaction.

10^8 liters/mole

Choose an example of a motor protein.

Myosin II

Choose an example of a protein of which is a signaling receptor.

Insulin

Choose an example of a protein of which is a signaling receptor.

EGFR

Which of the following is NOT a feature commonly observed in alpha-helices?

Left-handedness

Which of the following is NOT a feature observed in beta-sheets?

Coiled-coil patterns

The alpha-helices and beta-sheets are examples of protein ____.

Secondary structure

A protein ____ is the modular unit from which many larger single-chain proteins are constructed.

Domain

Which of the following molecules shows a significant conformational change in response to binding to ATP?

Myosin II

Which of the following proteins will form a globular protein molecule?

Actin

In a DNA double helix, ____.

the two DNA strands run antiparallel

The N-terminal tail of histone H3 can be extensively modified, and depending on the number, location, and combination of these modifications, these changes may promote the formation of heterochromatin. What is the result of heterochromatin formation?

Gene silencing

Methylation and acetylation are common changes made to histone H3, and the specific combination of these changes is sometimes referred to as “histone code.” Which of the following patterns will probably lead to gene silencing?

Lysine 9 trimethylation

Which of the following best describes the mechanism by which chromatin-remodeling complexes “loosen” the DNA wrapped around the core histones?

They use energy derived from ATP hydrolysis to change the relative position of the DNA and core histone octamer.

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 trimethylation

RNA in cells differ from DNA in that ____.

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

Transcription is similar to DNA replication in that ____.

nucleotide polymerization occurs only in the 5’-to-3’ direction.

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

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

Which of the following statements is false? a) RNA polymerase can start making a new RNA molecule without a primer, and DNA polymerase cannot; b) RNA polymerase does not proofread its work; DNA polymerase does; c) RNA polymerase catalyzes the linkages of the ribonucleotides while DNA polymerase catalyzes the linkage of deoxyribonucleotides; or d) RNA polymerase adds bases in a 3’-to-5’ direction, and DNA polymerase adds bases in a 5’-to-3’ direction?

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

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 prokaryotic gene or operon?

The transcription of a eukaryotic gene can be influenced by proteins that bind far from the promoter.

Which of the following does NOT occur before a eukaryotic mRNA is exported from the nucleus? a) The ribosome binds to the mRNA, b) The mRNA is polyadenylated at its 3’ end, c) A guanine nucleotide methyl group is added to the 5’ end of the mRNA, or d) RNA polymerase disassociates?

The ribosome binds to the mRNA.

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

Most of the genetic code is redundant.

A neuron and a white blood cell have very different functions, For example, a neuron can receive and respond to electrical signals, while a white blood cell defends the body against infection. This is because ____.

the neuron expresses some mRNAs that the white blood cell does not

The distinct characteristics of different cell types in a multicellular organism result mainly from the differential regulation of the ____.

transcription of genes transcribed by RNA polymerase II

The human genome encodes about 21,000 protein-coding genes. Approximately how many such genes does the typical differentiated human cell express at any time?

between 5,000 and 15,000

Which of the following statements about differentiated cells is true?

Some of the proteins found in differentiated cells are found in all cells of a multicellular organism.

Which of the following statements about transcriptional regulators is false? a) transcription regulators interact only with sugar-phosphate backbones on the outside of the double helix to determine where to bind on the DNA helix; b) Transcription regulators will form hydrogen bonds, ionic bonds, and hydrophobic interactions with DNA; c) The DNA-binding motifs of transcription regulators usually bind in the major groove of the DNA helix, or d) The binding of transcription regulators generally does not disrupt the hydrogen bonds that hold the double helix together?

Transcription regulators interact only with the sugar-phosphate backbone on the outside of the double helix to determine where to bind on the DNA helix.

Which of the following is NOT involved in post-transcriptional control: a) the spliceosome, b) Dicer, c) Mediator, or RISC?

Mediator

miRNAs, tRNAs, and rRNAs all ____.

do not code for proteins

MicroRNAs ____. a) are produced from a precursor miRNA transcript, b) are found only in humans, c) control gene expression by base-pairing with DNA sequences, and d) can degrade RNAs by using their intrinsic catalytic activity?

are produced from a precursor miRNA transcript

Which of the following statements about miRNAs is false? a) do not code for proteins, b) act in the nucleus, c) are packaged with other proteins to form RISC, or d) form base pairs with mRNA molecules?

miRNAs are produced from rRNAs.

Which of the following statements about RNAi is true?

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

Which one of the following proteins contains a single Transmembrane (TM) region?

Growth factor receptor (Receptor Tyrosine Kinase)

Which of the following events is necessary for establishing lipid anchor of a membrane protein on the EXTRACELLULAR side? a) Myristoylation, b) Prenylation, c) Glycosylphosphatidylinositol (GPI) anchor, or d) Ubiquitylation?

Glycosylphosphatidylinositol (GPI) anchor

Some proteins are almost as mobile as lipids, whereas others are virtually immobile. Which of the following proteins would be the fastest moving membrane protein?

Bacterial rhodopsin a 7-TM protein

Which of the following statements on SRP (Signal Recognition Particle) is NOT true? a) An ER sequence and an SRP direct a ribosome to the SRP Receptor on the ER membrane, b) SRP binding to the ER sequence on a ribosome pauses translation, c) SRP receptor localizes on the ER membrane, or d) SRP binding to the start transfer sequence will inhibit the ribosome binding to the ER?

SRP binding to the start transfer sequence will inhibit the ribosome binding to the ER.

Which of the following is one of the features of RPTK: a) an intracellular ligand binding domain, b) seven transmembrane domain, c) kinase domain, or GEF activity?

kinase domain

Which one of the following types of molecules associate with activated RPTK: a) MAPK, b) an SH2 domain containing adaptor proteins, c) Ras, or d) heterotrimeric G proteins?

an SH2 domain containing adaptor proteins

MAP Kinase stands for which of the following: a) Microtubule Associated Protein Kinase, b) Mitogen Activated Protein Kinase, c) Microglia Activation Protein Kinase, or d) Mitochondrial Associating Protein Kinase?

Mitogen Activated Protein Kinase

In response to mitogenic signal, cells induce immediate early response genes. Which of the following is one of them: a) RPTK, b) GPCR, c) MAPK, or d) c-Myc?

c-Myc

Under certain situations, cells interpret the same molecular ligands to a RPTK differently through selective downstream signal transduction. For example, RPTK can activate PI3K, Ras, or PLC pathways. Which of the following pathways is most critical for RPTK to suppress programmed cell death?

PI3K/PK(Akt)

There are eight members of phosphatidylinositol. Which of the following is the target (or substrate) for PLC?

PI(4,5)P2

There are eight members of phosphatidylinositol. Which of the following is the target (or substrate) for PI3K?

PI(4,5)P2

In response to a survival signal, the activated PKB(Akt) phosphorylates BAD protein. Does bad protein suppress or promote apoptosis?

promotes

In response to a survival signal, the activated PKB(Akt) phosphorylates BAD protein. Upon phosphorylation, BAD protein does one of the following: a) directly promote apoptosis, b) disassociating from Bcl-2, or c) inactivating Bcl-2?

disassociating from Bcl-2

Which of the following statements is true?

Bcl2 inhibits apoptosis

Which of the following is NOT regulated by the PI3K/PKB/mTOR signaling?

Inhibition of Rb

____ signal transduction pathway inhibits cell cycle progression.

TGF-beta

p53 can induce cell cycle arrest. What is the mediated cell cycle arrest? a) activating ERK2, b) degrading E2F, c) stabilizing Rb, or d) generating CDK inhibitors, such as p21

generating CDK inhibitors, such as p21

Which of the following processes occur only in S phase of the cell cycle? a) Organelle replication, b) Cell growth, c) Chromosome segregation, or d) DNA replication

DNA replication

The period between one M phase and the subsequent M phase is called: a) S phase, b) anaphase, c) interphase, or d) G2 phase?

interphase

Is it true or false that if the Rb protein binds to transcription regulators, the cell will move from G1 phase to S phase?

false

Which of the following inhibits Rb: a) Ras, b) CyclinD/Cdk, c) Myc, or d) Cdc6?

CyclinD/Cdk

Transcription factor E2F is inhibited by ____? a) Rb, b) Myc, c) Ras, or d) Cdc6?

Rb

Is it true or false that p53 can induce the cell to kill itself if damage to its DNA is very severe?

True

The signal to commence DNA replication comes from: a) S-Cdk, b) ORC, c) the destruction of Cdc25, or d) the destruction of M-Cdk?

S-Cdk

RPTK can activate multiple downstream signaling pathways, such as PI3K, Ras, or PLC. Which of the following pathways is usually activated for RPTK to induce cells to proliferate?

Ras/MAPK/Myc

Which of the following statements about the newly synthesized strands of a human chromosome is TRUE? a) It was synthesized from a single origin solely by continuous DNA synthesis, b) It was synthesized from a single origin by a mixture of continuous and discontinuous DNA synthesis, c) It was synthesized from multiple origins solely by discontinuous DNA synthesis or d) It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis?

It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis.

A telomerase is best described as: a) RNA polymerase, b) ligase, c) topoisomerase,d0 DNA polymerase with its bound RNA template, or e) exonuclease?

DNA polymerase with its bound RNA template

Where does the initiator protein bind DNA at the start of replication? a) at a replication fork, b) at an origin of replication, c) at any AT-rich region, d) at a promotor region, or e) at a start codon?

at an origin of replication

Helicase induces DNA supercoiling as the replication fork migrates during replication. Which of the following enzymes reduces Helicase-induced supercoiling as the replication fork migrates during replication: a) Telomerase, b) Ligase, c) DNA polymerase, d) DNA polymerase III, or e) Topoisomerase?

Topoisomerase

Homologous recombination (HR) is an important mechanism in which organisms use a “backup” copy of the DNA as a template to fix double strand breaks without the loss of genetic information. Which of the following is NOT necessary for HR to occur: a) The cell should be at the G2 phase, 2) The cell should be at the G1 phase, c) 3’ DNA strand overhang, or d) a long stretch of sequence similarity?

The cell should be at the G1 phase.

Sometimes replication errors escape proofreading of DNA polymerase and generate a DNA mismatch. Which of the following mechanisms will fix this kind of error?

Mismatch Repair (MMR)

Which of the following would promote cancer development: a) upregulating telomerase, b) by activating DNA repair system, c) by activating TGF-beta signaling, d) by activating p53?

upregulating telomerase

The properties of a lipid bilayer are determined by the structures of its lipid molecules. Predict the properties of the lipid bilayers that would result if the following was the case: phospholipids had only one hydrocarbon chain instead of two. a) still form bilayers or b) form micelles rather than bilayers

form micelles rather than bilayers

The properties of a lipid bilayer are determined by the structures of its lipid molecules. Predict the properties of the lipid bilayers that would result if all of the hydrocarbon chains were saturated: a) Bilayers formed by lipids with saturated hydrocarbon tails would be much less fluidic or b) Their fatty acid tails are trans-conformational.

Bilayers formed by lipids with saturated hydrocarbon tails would be much less fluidic.

A biological membrane can be solubilized with a mild detergent, such as Triton X-100. The shape of the phospholipids in the mixed micelle is which of the following: a) a cone, b) a cylinder, c) a cube, or d) an icosahedron?

a cylinder

Endoplasmic reticulum (ER) is the place where membrane proteins are synthesized. In which of the following does the most new membrane synthesis take place in a eukaryotic cell: a) ER, b) nucleus, c) plasma membrane, or d) mitochondria?

ER

You generated a light-activatable chloride channel and successfully expressed it in a mouse neuron of which function is not known. During the period of the channel activation, the mouse failed to make any memory. What can you say from the experiment?

The targeted neuron is positively involved in memory formation.

Which of the following has the highest cytosolic concentration: a) Na⁺, b) K⁺. C) Mg²⁺, or d) Ca²⁺?

K⁺

Which of the following ions has the lowest cytosolic concentration: a) H⁺, b) K⁺, c) Mg²⁺, or d) Ca²⁺?

H⁺

Is it true or false that cells with aquaporin channels in the plasma membrane can NOT maintain an electrochemical gradient?

False

If all the sodium glucose symporters and the glucose uniporters localize to the basal membrane of the intestinal, epithelial cells (facing the connective tissue), what would be the consequence? a) Glucose molecules would flow from the epithelial cells to the connective tissue, b) Glucose molecules would shuttle between the connective tissue and epithelial cells, c) Glucose molecules would be depleted from the epithelial cells, or d) Glucose molecules cannot be transported to the connective tissue from the epithelial cells?

Glucose molecules would shuttle between the connective tissue and the epithelial cells.

Macrophages remove dead cells by recognizing a signal on their targets: apoptosed cells populate phosphatidylserine on their outer leaflet but not the healthy ones. If you have a mutant cell that is efficiently phagocytosed by macrophages, what would be the problem of the mutant cell?

The mutant cells failed to keep the Phosphatidylserine in the inner leaflet of their plasma membrane.

The resting membrane potential of an animal cell ____, is which of the following: a) has a negative value that can be changed into a positive value, b) is generated by the Calcium ATPase that pumps out positively charged Calcium ions from the cell, c) is generated by the Sodium/Potassium ATPase that pumps out positively charged ions from the cell, or d) is generated by the sodium leak channel?

has a negative value that can be changed into a positive value.

Which of the following statements is true: a) During the action potential propagation, the unidirectional propagation of the action potential is mediated by the sodium potassium mump, b) During the action potential propagation, the three distinct forms/conformations of the voltage sensitive potassium channel spatially localize around the region of action potential, c) During the action potential propagation, the three distinct forms/conformations of the voltage sensitive calcium channel spatially localize around the region of action potential, or d) the sodium ions entering the axon through the voltage sensitive sodium channels diffuse randomly?

The sodium ions entering the axon through the voltage sensitive sodium channel diffuse randomly.

Both excitatory and inhibitory neurons form junctions with muscles. By which of the following mechanisms do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential: a) by closing Na⁺ channels, b) by preventing the secretion of excitatory neurotransmitters, c) by opening K⁺ channels, or d) by opening Cl^- channels?

by opening Cl^- channels