cell bio test 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

the nuclear envelope is made up of ___?

two concentric membranes and is continuous with the membrane of the

endoplasmic reticulum

Ionic bonds form a ____.

Salt

what forms a salt ?

ionic bonds

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

Positively charged

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

Y

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

alpha-helix

what does a protein phosphatase do ?

stops a mitogenic signaling by dissociating an SH2 domain containing protein (Grb2) from phosphorylated Growth factor receptor

Which of the following protein is necessary to stop a mitogenic signaling by dissociating an 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 A + B  AB.

10^8 liters/mole

[10x10-9 ]

____________

[10x10-9 ]. [10x10-9 ]

1___________

[10x10-9 ]

1__________

[10-8 ]

Choose an example of a motor protein.

Myosin II

Myosin 2 is a ___?

motor protein

Choose an example of a protein that is a signaling molecule (ligand).

Insulin

insulin is a ___?

protein that is a signaling molecule (ligand)

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

EGFR

EGFR is a _____?

protein which is a signaling receptor

Which of the following is not a feature commonly observed in α helices?

left-handedness

what are the features of an a helix ?

- one helical turn every 3.6 amino acids

- cylindrical shape

- amino acid side chains that point outward

what are the features of a β sheet ?

- antiparallel regions

- extended polypeptide backbone

- parallel regions

Which of the following is not a feature commonly observed in β sheets?

coiled-coil patterns

The α helices and β sheets are examples of protein _____.

Secondary structure

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

Domain

what is a protein domain ?

the modular unit from which many larger single-chain proteins are constructed

Which of the following molecule 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

what does actin form ?

a globular protein molecule

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 the “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 the 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 differs 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.

(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; DNA polymerase cannot.

(b) RNA polymerase does not proofread its work; DNA polymerase does.

(c) RNA polymerase catalyzes the linkage of ribonucleotides while DNA polymerase catalyzes the linkage of deoxyribonucleotides.

(d) RNA polymerase adds bases in a 3’-to-5’ direction; 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 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.

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

(d) 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; DNA polymerase cannot.

(b) RNA polymerase does not proofread its work; DNA polymerase does.

(c) RNA polymerase catalyzes the linkage of ribonucleotides while DNA polymerase catalyzes the linkage of deoxyribonucleotides.

(d) RNA polymerase adds bases in a 3’-to-5’ direction; 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 typical 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 with a methyl group is added to the 5’ end of the mRNA.

(d) RNA polymerase dissociates.

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

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

(a) All codons specify more than one amino acid.

(b) Most of the genetic code is redundant.

(c) All amino acids are specified by more than one codon.

(d) All codons specify an amino acid.

Most of the genetic code is redundant

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 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 one time?

between 5000 and 15,000

Which of the following statements about differentiated cells is TRUE?

(a) Cells of distinct types express nonoverlapping sets of transcription regulators.

(b) Once a cell has differentiated, it can no longer change its gene expression.

(c) Once a cell has differentiated, it will no longer need to transcribe RNA.

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

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 the sugar– phosphate backbone 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.

(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?

Mediator

Which of the following is involved in post-transcriptional control?

Spliceosome

Dicer

RISC

miRNAs, tRNAs, and rRNAs all ____.

do not code for proteins

Which of the following statements about miRNAs is FALSE?

(a) One miRNA can regulate the expression of many genes.

(b) miRNAs are transcribed in the nucleus from genomic DNA.

(c) miRNAs are produced from rRNAs.

(d) miRNAs are made by RNA polymerase.

miRNAs are produced from rRNAs

Which of the following statements about RNAi is TRUE?

(a) The RNAi mechanism is found only in plants and animals.

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

(c) RISC uses the siRNA duplex to locate complementary foreign RNA molecules.

(d) siRNAs bind to miRNAs to induce RNAi.

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

MicroRNAs ____.

are produced from a precursor miRNA transcript

When is RNAi induced ?

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

Which of the following statement on SRP (Signal Recognition Particle) is NOT true?

1. An ER signal sequence and an SRP direct a ribosome to the SRP Receptor on the ER membrane

2. SRP binding to the ER signal sequence on a Ribosome pauses translation

3. SRP receptor localizes on the ER membrane

4. 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 events is necessary for establishing lipid anchor of a membrane protein on the extracellular side?

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

Growth factor receptor (Receptor Tyrosine Kinase)

Which of the following is one of the features of RPTK?

kinase domain

Which of the following type of molecules associate with activated RPTK?

an SH2 domain containing adaptor protein

MAP Kinase stands for ____.

Mitogen Activated Protein Kinase

In response to mitogenic signal, cells induce immediate early response genes. Which of the following is one of them?

c-Myc

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

PI3K/PKB(Akt)

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:

dissociating from Bcl-2

Which of the following statements is true?

(a). Bcl2 inhibits apoptosis.

(b). Akt kinase inhibits Bcl2.

(c). Akt kinase activates BAD protein.

Bcl2 inhibits apoptosis

_______ signal transduction pathway inhibits cell cycle progression.

TGF-beta

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

Inhibition of Rb

p53 can induce cell cycle arrest. What is the p53 mediated cell cycle arrest?

generating CDK inhibitors such as p21

Which of the following processes occur only in S phase of the cell cycle?

DNA replication

The period between one M phase and the subsequent M phase is called:

interphase

T/F: If the Rb protein binds to transcription regulators, the cell will move from G1 phase to S phase.

F

What inhibits Rb?

CyclinD/Cdk

Transcription factor E2F is inhibited by ____.

Rb

T/F: p53 can induce the cell to kill itself if damage to its DNA is very severe.

T

The signal to commence DNA replication comes from:

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 strand 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.

(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 ______.

DNA polymerase with its bound RNA template

Where does the initiator protein bind DNA at the start of replication?

At an origin of replication

Helicase induces DNA supercoiling as the replication fork migrates during replication. Which kind of enzyme reduces Helicase-induced supercoiling as the replication fork migrates during replication?

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 loss of genetic information. Which of the following is NOT necessary for homologous recombination to occur?

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?

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.

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 the following was the case: if all of the hydrocarbon chains were saturated, _____.

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 _____.

a cylinder

Endoplasmic reticulum (ER) is the place where membrane proteins are synthesized. Where does most new membrane synthesis take place in a eukaryotic cell?

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 ions has the highest cytosolic concentration?

K+

Which of the following ions has the lowest cytosolic concentration?

H+

Cells with aquaporin channels in the plasma membrane can NOT maintain electrochemical gradient. Is this statement true or false?

false

If all the sodium glucose symporter and the glucose uniporter localize to the basal membrane of the intestinal epithelial cells (facing the connective tissue), what would be the happening?

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 _____.

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 sodium potassium pump.

(b) During the action potential propagation, the three distinct

forms (conformations) of the voltage sensitive potassium channel spatially localize around region of the action potential.

(c)During the action potential propagation, the three distinct forms (conformations) of the voltage sensitive calcium channel.

spatially localize around region of the action potential.

(d) The sodium ions entering the axon through the voltage

sensitive sodium channel 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 what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential?

by opening Cl− channels