bio exam 3

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For the lactose operon, lactose is a(n):

inducer

The lacZ and lacY genes are transcribed when:

lactose is present and glucose levels are low.

Which type of receptor is involved in rapid responses of muscle cells and neurons?

ligand-gated ion channel

Transcription in prokaryotes is rapidly turned on or off in response to environmental changes and involves both positive and negative regulators. (T/F)

true

Transcriptional regulation in eukaryotic cells requires the coordinated action of many proteins that interact with one another and with DNA sequences near the gene. (T/F)

true

A skin cell in G2 of interphase has _____ as much DNA as it had in G1.

twice S phase, where DNA synthesis occurs, and the chromosomes are all replicated, is in between G1and G2phases of the cell cycle.

At the start of mitosis, how many sister chromatids are present in a human cell?

Use the terms listed to fill in the blanks of each statement that follows. A. signaling cell B. ligand C. receptor D. responding cell In communication between cells, the _____ produces the signaling molecule, also known as the _____; the _____ produces the _____, to which the signaling molecule binds.

A, B, D, C

The CRP-cAMP complex binds the lactose operon when:

glucose levels are low and cAMP levels are high

The extent and duration of a cellular response to a signal depend on the: level of expression of the genes encoding the proteins that terminate the response. level of expression of the genes encoding the signal transduction proteins. concentration of the signaling molecule in the vicinity of the receptor. All of these choices are correct. To terminate a signal, the receptor must no longer bind the ligand, G proteins must hydrolyze GTP to GDP, phosphatases must remove phosphate groups added by kinases, and second messengers must be destroyed or sequestered. binding affinity of the receptor to the signaling molecule.

All of these choices are correct.

What does a ligand-gated channel do? It can be closed and restrict ion flow when signal molecules are absent. It allows ions to move across the plasma membrane. All of these choices are correct. Ligand-gated channels open to allow ions to pass through the membrane when they bind to their signaling molecule. It opens a channel through the plasma membrane when signal molecules bind.

All of these choices are correct.

What is a growth factor? a soluble molecule that can alter gene expression in a cell a small protein that influences cell growth and division a signaling molecule involved in paracrine signaling All of these choices are correct.

All of these choices are correct.

A human cell with a total of 23 chromosomes is:

haploid.

Gene regulation in multicellular organisms leads to differential gene expression and specialized cell functions. (T/F)

true

How are steroid hormone receptors and cell-surface receptors similar?

Both types undergo a conformational change when they bind to their ligand.

Gene regulation is influenced by both genetic and environmental factors. (T/F)

true

Nicotine from cigarette smoke acts as a ligand and associates with the acetylcholine receptor on specific cells in the nervous system. Nicotine eventually produces feelings of pleasure and well-being. The listed statements are descriptions of the events that happen in the cellular response to nicotine. Place the events in the correct order to describe the steps in the signaling pathway. A) The acetylcholine receptor is an ion channel, and when a ligand binds, the ion channel opens . B) An influx of ions carries the signal to the reward areas of the brain. C) Nicotine binds to the transmembrane protein that normally binds the neurotransmitter acetylcholine. D) The signal causes release of dopamine in the brain, which causes good feelings. E) Nicotine is quickly eliminated from the body (causing cravings for more cigarettes to produce good feelings)

C, A, B, D, E

The human body contains approximately 200 major cell types. They look and function differently from one another because each:

expresses a different set of genes

Most ligands form covalent bonds with their associated receptors; these complexes are more or less permanent and can only be broken through the hydrolysis of ATP. (T/F)

False

A cell that is not actively dividing is in what phase of the cell cycle?

Which major checkpoint delays the cell cycle when DNA replication is incomplete?

G2 checkpoint

The figure shows how normal signaling works with a Ras protein acting downstream of a receptor kinase. You examine a cell line in which Ras is always activated even in the absence of a signaling molecule. This causes constant activation of the kinases in the MAP kinase pathway. Which condition would be most likely to turn off this abnormally active signaling pathway?

The addition of a drug that prevents the final kinase from interacting with its target protein in the nucleus.

Gene regulation can occur only during transcription and translation. (T/F)

false

In cell communication, which one of the answer choices is a requirement of the responding cell?

It must express receptor proteins.

Many mutations in receptor kinases that lead to cancer allow the receptor to dimerize and become activated, even in the absence of signaling molecules. An example is a mutant form of the EGF receptor kinase called Her2/neu. An antibody that prevents dimerization of Her2/neu receptor kinases is being tested for its effectiveness in preventing cancer. At which stage does this drug work?

It prevents the receptor from becoming activated.

Which of the statements is true regarding CDKs?

The activity of CDKs change with the cell cycle.

The binding of cAMP-CRP to DNA affects the binding of a repressor. (T/F)

false

Which one of the statements most accurately describes DNA methylation? Methyl groups are most often added to guanines adjacent to cytosines bases in or near the promoter sequence, increasing the probability of gene expression. Methyl groups are most often added to cytosines adjacent to guanine bases in or near the promoter sequence, increasing the probability of gene expression. Methyl groups are most often added to cytosines adjacent to guanine bases in or near the promoter sequence, decreasing the probability of gene expression. Methyl groups are most often added to adenine-thymine base pairs, and this increases the probability of gene expression. Methyl groups are added to most bases in the promoter region of a specific gene so that RNA polymerase and its associated proteins will bind more efficiently.

Methyl groups are most often added to cytosines adjacent to guanine bases in or near the promoter sequence, decreasing the probability of gene expression.

A number of mutations have been described in G proteins that have profound effects on their activity. For example, some mutations greatly increase the affinity of the G protein for GDP, making it very difficult for GDP to be exchanged for GTP. Other mutations prevent the hydrolysis of GTP to GDP. For each of the statements that describe a malfunction in cellular response, indicate the type of mutation that is responsible. A receptor that is continuously activated in the absence of ligand. Which type of mutation is responsible for this malfunction in cellular response? a Ras mutant that cannot hydrolyze GTP to GDP a Ras mutant with high GDP affinity Neither of the other answer options is correct. If the receptor itself is continuously active, it doesn't matter what Ras does. The malfunction must be due to a defect in the receptor.

Neither of the other answer options is correct.

A researcher is evaluating the role of a growth factor during embryonic development. She notices that this factor functions in both neural development and limb development. How is that possible?

Receptors for the growth factor must be present in both neurons and cells in the developing limb.

Replication of DNA in a eukaryote occurs during which phase of the cell cycle?

S phase

Why don't steroid hormones bind to transmembrane cell-surface receptors?

Steroid hormones are nonpolar and therefore are able to cross the cell's plasma membrane, binding to receptors inside the cell

Why don't steroid hormones bind to transmembrane cell-surface receptors?

Steroid hormones are nonpolar and therefore are able to cross the cell's plasma membrane, binding to receptors inside the cell.

During the signal transduction process, the signal often triggers a signal transduction cascade. For example, a single activated receptor can activate hundreds of protein A molecules. Each activated protein A molecule activates hundreds of protein B molecules, and so on, until a cellular response occurs. What purpose does this cascade serve?

The cascade serves to amplify the signal so one activated receptor can have a significant response. The activation of a small number of receptors can activate enzymes or second messengers that activate many signal transduction molecules, greatly amplifying the signal to allow a large cellular response to a small amount of signal.

Which events would happen to a cell if cyclin levels were always high in the cell? Select all that apply. The cell cycle would not stop at checkpoints. The cell would divide rapidly. Protein substrates of CDKs would be constantly phosphorylated. Cyclin-dependent kinases would not be activated.

The cell cycle would not stop at checkpoints. The cell would divide rapidly. Protein substrates of CDKs would be constantly phosphorylated.

You are a medical student working in a cancer research laboratory. Your boss has given you samples of cancer cells and blood from a patient. She has told you that the cells have no mutations in any of their signaling molecule proteins (that is, all the proteins are normal), but that the cells' signaling transduction properties are hyperactive, causing them to divide too rapidly. Which answer choices could account for the increased cell proliferation in the patient? Select all that apply. None of the other answer options are correct. The concentration of a signaling molecule in the patient is higher than usual. The cells taken from the patient have more growth factor receptors than normal. The cells taken from the patient exhibit a reduced level of signal amplification.

The concentration of a signaling molecule in the patient is higher than usual. The cells taken from the patient have more growth factor receptors than normal.

Phosphatases are a family of enzymes that remove phosphate groups from specific proteins; these phosphate groups had been added to the proteins by protein kinases. Vanadate is an inhibitor of phosphatases in eukaryotic cells. What effect would vanadate have on the response of cells to signals received by receptor kinases?

The response of the cell would last longer than it normally would.

What would happen to a signaling pathway if phosphatases had reduced levels of function?

The response to the signal would persist longer after activation.

The cellular processes that control the rate and manner of gene expression are called:

gene regulation

Recall from the text in the example of cell communication in Streptococcus pneumoniae that the rate of DNA uptake by pneumococcal cells increases sharply when they are at high density, due to changes in gene expression brought about by signaling between cells. If the pneumococcal cells did not express receptor protein, how would the rate of DNA uptake be affected when the cells reach high density?

There would be no increase in the rate of DNA uptake

Many scientists use chemical inhibitors to interfere with normal signaling pathways within eukaryotic cells. If such inhibitors are large, nonpolar molecules, what is the likely method of action of these chemical inhibitors?

These chemical inhibitors likely bind to receptors on the cell surface and interfere with receptor activation or signal-receptor binding.

Imagine that a researcher is studying the embryonic development of mice that do not express the signal molecule Delta. What will likely be true of these mice?

These mice will have fewer glial cells compared to their normal counterparts.

How do new cyclin proteins appear in the cytoplasm?

They are made through protein synthesis.

How do CDKs promote cell division?

They phosphorylate proteins that allow passage through cell cycle checkpoints.

Gene regulation in multicellular organisms leads to differential gene expression and specialized cell functions. (T/F)

True

Epigenetic mechanisms can include: Select all that apply. mutations. X-inactivation .histone modification. cytosine methylation. chromatin remodeling.

X-inactivation .histone modification. cytosine methylation. chromatin remodeling.

What is the very first effect of ligand binding to a G protein-coupled receptor?

a conformational change in the cytoplasmic domain of the receptor

You are studying a newly discovered growth factor. You find that this growth factor stimulates the proliferation of cells grown in the laboratory. You have also found that the receptor that binds the growth factor is a receptor kinase that activates Ras, which activates the MAP kinase pathway. Which mutations affecting this growth factor pathway would you expect to promote uncontrolled cell proliferation? Select all that apply. a mutation that prevents entry into the nucleus of the last kinase in the MAP kinase pathway a mutation that prevents the GTPase activity of Ras a mutation that inactivates the phosphatase that dephosphorylates the activated receptor a mutation that prevents dimerization of the receptora mutation that blocks the kinase activity of the receptor

a mutation that prevents the GTPase activity of Ras a mutation that inactivates the phosphatase that dephosphorylates the activated receptor

Which of the answer choices would be considered a cell-surface receptor? a protein that acts as an enzyme that attaches phosphate groups to substrates a protein that causes GDP to be exchanged for GTP in a G protein a protein that binds a nonpolar steroid hormone and activates transcription a protein that forms a channel that allows ions to enter the cell when a ligand binds Ligand-gated ion channels are a type of cell surface receptor. They are transmembrane proteins that are normally closed until the signal binds, which causes the channel to change conformation and allow ions to pass through the membrane.

a protein that forms a channel that allows ions to enter the cell when a ligand binds

A researcher is using a small molecule inhibitor that prevents phosphorylation as a tool to manipulate a signaling pathway. What is the most likely target of this small molecule inhibitor?

a receptor Kinase

A researcher is using a small molecule inhibitor that prevents phosphorylation as a tool to manipulate a signaling pathway. What is the most likely target of this small molecule inhibitor?

a receptor kinase

Which type of cell-surface receptor undergoes changes in phosphorylation in response to binding of its ligand?

a receptor kinase

A protein on a cell surface that binds to a signaling molecule is an example of which element of cellular communication?

a receptor protein

Signal amplification relies on:

a sequential increase in the different components, wherein a single, activated component can activate many copies of the next component in the pathway.

A cell that responds to an environmental condition by the release of a chemical is an example of which element of cellular communication?

a signaling cell

In the context of cell signaling, to what does the term ligand refer

a signaling molecule that binds to the receptor

For the lactose operon, the CRP-cAMP is a(n):

activator

Cell division is regulated by: signals that indicate that the cell has reached a sufficient size. growth factor signals. signals about the nutritional status of the cell. All of these choices are correct. signals that indicate that DNA has been replicated.