MCB Exam 2

The following four events occur during cell locomotion: Place them in the correct order.

1) A part of the cell surface protrudes in the direction of cell movement. 2) Lower surface of cell protrusion attaches to substratum, forming temporary anchorage sites. 3) The bulk of the cell is pulled forward over adhesive contacts 4) The cell breaks its rear contacts with the substratum, retracting its trailing edge.

Which of the following types of proteins is NOT made by ribosomes in the cytoplasm?

1) Integral Membrane Proteins 2) Secreted Proteins

Mitosis __________.

1) serves as the basis for producing new cells 2) leads to production of cells that are genetically identical to their parent

Based on this model for cellular migration, what best explains the protein localization in this migrating cell? (the arrow shows the way it is moving)

1)Actin is involved in creating lamelipodia and is a scaffold for contraction of the cell body, so it is throughout the cell. 2) Myosin is only involved in contraction not protrusion, so it is only in the "later" half of the moving cell.

___1______ is an example of a protein that aids in the selective packaging of certain molecules into vesicles. ___2______ is an example of a protein that aids vesicles in recognizing (or selectively interacting with) a target compartment.

1=AP2 2=Rab

Mice are treated with a high dose of Prozac, which blocks reuptake of serotonin from the synaptic cleft, or with a control solution. Sections of brain from both set of animals are prepared and immuno-gold electron microscopy is performed using an antibody against serotonin (a neurotransmitter). Use the following model to answer the following question. What would you predict to see in your experimental results?

A greater number of uncoated vesicles filled with serotonin in the control-treated compared to the Prozac treated

Which of the following proteins would NOT be synthesized at the surface of the ER?

A transcription factor

Based on this model, what do you predict would happen if the Receptor was mutated so that it no longer could bind the blue Protein? Assume both proteins start in Compartment A.

A)All the white and blue proteins would be in compartment A

Which of the following nonmuscle cell activities involves actin filaments often working in concert with myosin motors?

A)cytoplasmic streaming B)phagocytosis C)cell-substratum interactions D)cell locomotion

When the rate of loss of actin subunits from the pointed end of an actin filament is balanced by the rate of their addition to the barbed end

A)the filaments are said to be in steady state B)the length of the filaments remains the same C)treadmilling occurs

When DNA is damaged by ionizing radiation...

ATM detects the damage, p53 is stabilized and phosphorylated, the cell cycle is arrested

Where would you find the normal CFTR channel?

At the plasma membrane

Given this model for regulation of the cell cycle, what protein is most likely mutated in the temp-sensitive mutant in panel B (which grows much longer than wild-type without dividing)?

B, if we could not remove the inhibitory then the cdc2 would not be able to do its job; it would keep growing and be super long

Which coated vesicles move materials in a retrograde direction from the ERGIC and Golgi stack backwards toward the ER?

COPI-coated vesicles

Why can mutations in both copies of p53 lead to cancer?

Cells do not stall in the cell cycle when there is DNA damage

Which of the following basic functions of the cytoskeleton is NOT being performed by microtubles in this image?

Contractility and Motility

Which of the following statements about cyclin is FALSE?

Cyclin degradation is necessary to trigger the transition from G2 to mitosis

Based on this model for the function of pRb, what do you predict would happen in a cell where both copies of the Rb gene were mutated and the Rb protein was non-functional?

E2F would promote gene activation which would promote the G1-S transition and cellular proliferation

The KDEL receptor is responsible for recognizing an ER retention signal on ER proteins. Which of the following would be most likely if yeast cells contained a mutation that made the KDEL receptor non-functional?

ER enzymes would be secreted from the cell rather than stored in the ER.

Where would you find fibronectin?

Extracellular space

Your lab has identified two genes (X and Y) that are associated with cancer. You conduct two sets of experiments. First you take tissue culture cells and knock out Gene X or Gene Y completely. You inject these cells, or the original culture cells, into the leg of a mouse and find that those lacking Gene X induce growth of large tumors, but untreated cells or those lacking Gene Y have little effect. Next, you collect skin cells from a normal mouse and transfect them with the mutated forms of Gene X or Gene Y that are associated with cancer. The cells transfected with Gene Y continue to divide in culture without the need for growth factors, but those transfected with Gene X or untransfected cells die unless growth factors are in the media. What can you conclude?

Gene Y is likely an oncogene and Gene X is likely a tumor suppressor

The primary phenotype of the patient named J D was that:

His cells were able to bind but not internalize LDL.

Why is retinoblastoma more common in individuals who have inherited the RB deletion and have the genetic predisposition for retinoblastoma?

If the RB gene is already mutated or deleted on one of the homologous chromosomes, only one hit rather than two is needed to cause development of retinoblastoma; thus the probability is higher.

Which of the following would be the best way to experimentally determine if a vesicle in an electron micrograph was budding from the ER or fusing with the Golgi?

Immuno-gold labeling for COP II components

Where would you find MEK?

In the cytoplasm

Which of the following experimental results directly linked cyclins to entry of cells into M phase?

Injection of synthetic cyclin mRNA into frog oocytes led to mitosis on a time scale similar to progesterone treatment

An integral membrane protein "X" is synthesized at the surface of the rough ER. While at the ER, the (ultimately) extracellular portion of the protein will be:

Inside the ER

What are microsomes?

Large vesicle-like pieces of ER

NCD is added to the coverslip. It promotes movement of the sperm as shown. Which of the following is true in this experiment.

NCD must move along the microtubules towards the minus end, causing the sperm to move backwards

In experiments by Brown and Goldstein, what was a key difference between normal cultured cells and those from individuals with familial hypercholesterolemia? (in textbook, not same as JD in article)

Only the normal cells could bind significant LDL.

Which of the following occurs when DNA damage is detected?

Phosphorylation of p53.

What effect does the binding of the SRP to the growing polypeptide chain and the ribosome have on protein synthesis?

Protein synthesis ceases temporarily.

Which of the following types of proteins is NOT made by ribosomes on the surface of the Endoplasmic Reticulum ?

Proteins that make up the cytoskeleton

Which of the following BEST describes the role of COP proteins in the endomembrane system?

Serve as coat proteins helping to promote vesicle formation

Which of the following did the researchers NOT know before the start of their study in the research article?

The LDL receptor tail interacts directly with coated-pit components

How are integral membrane proteins thought to enter the lipid bilayer?

The aqueous translocon channel seems to have a gate that continuously opens and closes, giving each nascent polypeptide segment a chance to partition itself into the lipid bilayer's hydrophobic core.

Based on the video of kinesin (and what we have covered about non-hydrolysable analogs), what would you predict would happen if axonal transport was conducted in the presence of non-hydrolysable ATP?

The cargo would stop moving along the microtubules.

Cancer is a genetic disease in that it can be traced to alterations within specific genes, but, in most cases, it is not an inherited disease. Why is that the case?

The genetic alterations in most cancers arise mostly in the DNA of somatic cells during the lifetime of the affected individual.

What kind(s) of modifications are made in proteins as they move through the Golgi complex?

The protein's carbohydrates are modified by a series of stepwise enzymatic reactions.

Which of the following steps in the synthesis of a secreted protein would happen FIRST?

The ribosome binds the mRNA.

Prozac is a drug that selectively inhibits the membrane transporter responsible for reuptake of the neurotransmitter serotonin. What would you predict will happen when a patient takes Prozac.

There is more serotonin signaling than normal

What happened to COPI-coated vesicles within the cell when the cell was treated with GTP analogues that could not be hydrolyzed?

They accumulated in the cytoplasm.

When a microtubule is growing, the plus end is present as an open sheet to which GTP-dimers are added. A cap of GTP-dimers can often form on the growing microtubules during rapid growth periods. How does this cap form?

Tubulin dimers are added to the microtubule faster than the GTP is hydrolyzed

Imagine you are Randy Sheckman and you are trying to provide additional evidence for your model of how vesicles move from the ER to Golgi (shown below). A graduate student in your lab has created a yeast strain that has a mutant form of Sar1p. She purified this mutant protein and showed that it could bind GTP, but could not hydrolyze it. You suggest that she compare the protein from her mutant to the protein from wild-type cells in a vesicle budding and fusion experiment (like the one we examined in class).

Vesicle budding and fusion will occur with the wild-type protein, but only budding will occur at a significant level with the mutant protein.

A "catastrophy" happens:

When tubulin throughout an entire microtubule is bound to GDP, instead of GTP

Based on this model, which of the following do you predict would happen if microtubules were formed in vitro in the presence of GTP or GMPCPP (slowly hydrolysable analog)?

With GMPCPP, microtubules will grow at the same rate, but will have fewer "catastrophes".

Use the image shown to help you answer the following question. Imagine you can inject non-hydrolysable ATP or regular ATP into the neuron pictured. At the time of the injection, the Cargo is somewhere in the middle of the axon. What might you predict will happen?

With regular ATP, Cargo 1 will go to the axon terminal; with non-hydrolysable ATP, Cargo 1 will remain in the middle of the axon.

What causes the rapid drop in Cdk activity that leads to the exit from mitosis and the entry into G1 typically exhibited by cells as they finish division?

a plunge in mitotic cyclin concentration

Vesicles that move through the Golgi complex from the cis-cisternae to the trans-cisternae are said to move in a(n) __________ direction.

anterograde

Which of the following activities in higher vertebrates does not involve cell locomotion?

cleavage in the early embryo

What are the two sites within a cell at which protein synthesis is generally thought to occur?

cytosolic surface of RER and free ribosomes

LDL receptors are found mostly on the outer surface of cells even in the absence of ligand. Where specifically on the cell surface are they found?

in the coated pits

The regulatory subunit of maturation-promoting factor ________.

is called cyclin because its concentration rises and falls predictably as the cell cycle progresses

The endomembrane system when homogenized is broken up into vesicles, which are heterogeneous but similar in size. These vesicles can be purified and, after purification, often retain their biological activity. They are collectively referred to as _________.

microsomes

Profilin is a protein that binds to actin-ATP monomers. It was once thought to be a _______ protein, but new evidence suggests that it probably ________ actin filament growth by catalyzing the dissociation of its bound ____.

monomer-sequestering, promotes, ADP

Blöbel, Sabatini and Dobberstein proposed that the site of protein synthesis is determined by information contained in the N-terminal portion of the protein, the first part to emerge from the ribosome. What did they call their proposal?

the Signal Hypothesis

Which of the models below suggests that the Golgi cisternae are transient structures that form at the cis face of the stack by fusion of membranous carriers from the ER and ERGIC and that each cisterna travels through the Golgi complex from the cis to the trans end of the stack, changing in composition as it progresses?

the cisternal maturation model

What molecules do the AP2 adaptors of the clathrin coat connect?

the cytoplasmic tails of specific membrane receptors and clathrin molecules

Based on this model, predict what might happen if researchers made a fusion protein exchanging the normal cytoplasmic part of the LDL receptor for the cytoplasmic part of the KDEL receptor?

the fusion protein would be retrieved from the Golgi to the ER

To which end of microtubules are tubulin subunits primarily added in vitro?

the plus end

What allows smooth and rough vesicles (microsomes) to be readily separated by density gradient centrifugation?

their differences in density

In order to study the origin of the J D phenotype, the authors of the Davis et. al. paper:

transfected cultured cells with normal LDL receptor or an LDL receptor with a point mutation.