GCD ch 20 q bank

What type of junctions can be used to bend epithelial sheets into tubes?

adherens

Which type of junction involves a connection to the actin cytoskeleton?

adherens junctions

________________ involve cadherin connections between neighboring cells and are anchorage sites for actin filaments.

adherens junctions

induced pluripotent stem cells are created by the expression of a set of key genes in cells derived from...

adult tissues so that these cells can differentiate into a variety of cell types

Proteoglycans in the extracellular matrix of animal tissues...

allow cartilage to resist compression

Are collagen found in animals, plants, or both?

animals

Are intermediate filaments found in animals, plants, or both?

animals

Hemidesmosomes are important for

attaching epithelial cells to the extracellular matrix

When a cell senses DNA damage, the cell cycle is inhibited until the damage is fixed. Given the importance of DNA repair mechanisms, how can their failure can lead to the production of cancer cells with a competitive advantage over normal cells?

A cell with a defect in its DNA repair mechanisms will have an increased mutation rate, thus increasing its chances to acquire further mutations that give it (and its progeny) a competitive growth advantage.

What is an example of a genetic change that cannot convert a proto-oncogene into an oncogene?

A mutation that introduces a stop codon immediately after the codon for the initiator methionine.

Ras is a GTP-binding protein that is often defective in cancer cells. A signal from a growth factor through a receptor tyrosine kinase often stimulates normal cells to divide. When the receptor tyrosine kinase binds the growth factor, Ras is stimulated to bind GTP. Ras in turn activates proteins that promote cell proliferation. A common mutation in cancerous cells causes Ras to behave as though it were bound to GTP all the time. A. Why is this mutation advantageous to cancerous cells? B. Your friend decides that the signaling pathway involving the Ras protein is a good target for drug design, because the Ras protein is often defective in cancer cells. Your friend designs a drug that will turn off the receptor tyrosine kinase by preventing it from dimerizing. Do you think that this drug will affect cells that have a defective Ras protein that acts as if it were always bound to GTP? Why or why not?

A. A Ras mutation that causes Ras to behave as though it were bound to GTP all the time is advantageous to cancer cells because Ras is then activated and turns on the activities of proteins required for cell proliferation. If the cell proliferation proteins are always turned on, the cancer cell will be able to proliferate at an unregulated rate, outgrowing its normal neighbors. The ability to proliferate in a signal-independent fashion is one of the hallmarks of a cancer cell. B. Unfortunately, a drug that blocks activation of the receptor that activates Ras will be unlikely to have a useful effect on a cell containing mutant Ras protein that behaves as though it were constantly activated. Because Ras acts downstream of the receptor, the activating mutation makes its effect felt, regardless of the state of the receptor on which Ras activation would normally depend: mutant Ras that is always active is no longer dependent on the receptor for activation. Therefore, blocking the ability of the receptor to dimerize and activate Ras will probably not affect the cells containing the mutant Ras protein.

What cell structure is involved with collagen?

basal lamina

Are microtubules found in animals, plants, or both?

both

What is the function of blood vessels?

bring oxygen and remove waste

A basal lamina is...

a thin layer of extracellular matrix underlying an epithelium

Cells that are terminally differentiated...

can no longer undergo cell division

An adult hemopoietic stem cell found in the bone marrow...

can undergo self-renewing divisions for the lifetime of a healthy animal

Name the three key mechanisms important for maintaining the organization of cells into tissues

cell communication, selective cell-cell adhesion, cell memory

Place the following in order of their replacement times, from shortest to longest. epidermal cell nerve cell bone matrix red blood cell cell lining the gut

cell lining the gut, epidermal cell, RBC, bone matrix, nerve cell

What cell structure is involved with cellulose?

cell wall

Fibers made from __________________ (the most abundant organic macromolecule on Earth) are found in plant cell walls, and provide tensile strength.

cellulose

What are the main structures providing tensile strength in plant cell walls?

cellulose fibers

tight junctions are formed from...

claudins and occludins

What molecule is not found in plants?

collagen

What are the main structures providing tensile strength in animal connective tissue?

collagen fibers

What is the function of lymphocytes?

combat infection

What cell structure is involved with cadherin?

desmosomes

What cell structure is involved with keratins?

desmosomes

__________________ join the intermediate filaments in one cell to those in the neighboring cell.

desmosomes

What is the function of macrophages?

dispose of dying cells

true or false A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell.

false

true or false Because gap junctions do not allow ions to pass through, they are not used for electrically coupling cells.

false

true or false Cells can attach to a collagen matrix by using fibronectin, an integral membrane protein.

false

true or false Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells.

false

true or false Enzymes embedded in the plasma membrane synthesize the collagen in the extracellular matrix extracellularly.

false

true or false Integrins use adaptor proteins to interact with the microtubule cytoskeleton.

false

true or false Proteoglycans are a major component of compact connective tissues but are relatively unimportant in watery tissues such as the jellylike substance in the interior of the eye.

false

true or false in connective tissue, the intermediate filaments within the cells are important for carrying the mechanical load.

false

What cell structure is involved with connexons?

gap junction

____________ permit the passage of small molecules from one cell to its adjacent cell.

gap junctions

__________________ anchor intermediate filaments in a cell to the extracellular matrix.

hemidesmosomes

Mouse embryonic stem (ES) cells come from the...

inner cell mass of early embryos

At desmosomes, cadherin molecules are connected to

intermediate filaments

What are the main structures providing tensile strength in animal epidermis?

intermediate filaments

A malignant tumor is more dangerous than a benign tumor because...

its cells invade other tissues

In woody tissues, the __________________ in the cell walls makes the tissue more rigid and waterproof.

lignin

The deposition of the cell wall is directed by the __________________ cytoskeleton.

microtubule

What is the function of fibroblasts?

organize connective tissues

In plant cells, __________________ generates the turgor pressure that drives cell growth.

osmosis

Are cell walls found in animals, plants, or both?

plants

Are cellulose found in animals, plants, or both?

plants

____ are found only in animal cells

plasmodesmata

Plants have cell walls, but cell growth is possible in the developing tissue because the __________________ cell walls are expandable.

primary

What is the function of Schwann cells?

provide electrical insulation for axons

Fibroblasts organize the collagen of the extracellular matrix by..

pulling the collagen into sheets or cables after it has been secreted

The __________________ cell walls are deposited once growth has stopped, and can be specially adapted to their function.

secondary

A major distinction between the connective tissues in an animal and other main tissue types such as epithelium, nervous tissue, or muscle is...

the amount of extracellular matrix in connective tissues

A stem cell divides into two daughter cells. One of the daughter cells goes on to be come a terminally differentiated cell. What is the typical fate of the other daughter cell?

the other daughter cell typically remains a stem cell.

What cell structure is involved with claudins?

tight junctions

What cell structure is involved with occludins?

tight junctions

Which type of junction contributes the most to the polarization of epithelial cells?

tight junctions

___________ prevent the leakage of molecules between adjacent cells

tight junctions

Both multicellular plants and animals have

tissues composed of multiple different cell types

True or false Integrins can switch to an activated state by binding to an extracellularmatrix molecule.

true

true or false An activated integrin molecule takes on an extended conformation.

true

true or false Chemical carcinogens cause cancer by changing the nucleotide sequence of DNA.

true

true or false Gap junctions can close in response to extracellular signals.

true

true or false Gene amplification of a tumor suppressor gene is less dangerous than gene amplification of a proto-oncogene.

true

true or false Glycosaminoglycans are components of proteoglycan.

true

true or false Inactivation of tumor suppressor genes leads to enhanced cell survival and proliferation.

true

true or false Individuals with only one functional copy of a tumor suppressor gene are more prone to cancer than individuals with two functional copies of a tumor suppressor gene.

true

true or false Integrins can switch to an activated state by binding to an intracellularprotein.

true

true or false Molecules up to 1000 daltons in molecular weight can move across gap junctions.

true

true or false Proteoglycans can act as filters to regulate which molecules pass through the extracellular medium.

true

true or false Proteoglycans can resist compression in the extracellular matrix.

true

true or false The microtubule cytoskeleton directs the orientation in which cellulose is deposited in the cell wall.

true

true or false The negative charge associated with proteoglycans attracts cations, which cause water to be sucked into the extracellular matrix.

true

true or false Tobacco use is responsible for more than 20% of all cancer deaths.

true

true or false Viruses cause some cancers.

true

true or false gap junctions are made of connexons.

true

Rb is a tumor suppressor gene; its normal function is to help restrain cell division. Loss of both copies of Rb is a causative factor in some kinds of cancer. You propose to treat these cancers by injecting the patients with a viral vector that carries a copy of the Rb gene and has the ability to infect all the cells of the body, thereby artificially driving expression of Rb in all the cells, including the cancer cells. Your colleague says "No!—You'll simply kill the patient, because you will halt cell division throughout the body." A. Why would halting cell division throughout the body kill a full-grownadult person? B. Is your colleague right in thinking that forced expression of Rb in everycell will halt all cell division?

A. Many vital tissues in the adult body, including the lining of the gut, the epidermis, and the system of blood cells, require continual renewal, which is dependent on stem cells and cell division. Cessation of cell division will lead to a disappearance of these tissues, with fatal consequences. B. No, your colleague is not right to assume this. Cells that express the Rb gene can proliferate: whether or not they do so depends on whether the Rb protein is phosphorylated (allowing cell division) or unphosphorylated (blocking cell division).

How do reproductive cloning and therapeutic cloning differ?

Embryos are placed into foster mothers during reproductive cloning but not during therapeutic cloning.

Squeaky has developed liver disease and will not live much longer without a liver transplant. After you see your friend on TV talking about her new method for growing mouse livers, you immediately grab your cell phone to ask her whether Squeaky could have one of the newly grown livers. Just as you are about to dial your friend, you remember something you learned in cell biology and realize that instead, you should ask your friend about possibly using therapeutic cloning for Squeaky's benefit. Why do you think that one of the newly grown livers may not work in Squeaky? Why would therapeutic cloning solve this problem?

For organ transplantation to be successful, the donor and the recipient should be as close a genetic match as possible to minimize the risk of immunological rejection. Because you found Squeaky in the fields of New Hampshire, Squeaky is likely to have genetic differences from the FG426 inbred laboratory mice. Therapeutic cloning may help save Squeaky because it is a method for generating ES cells from Squeaky himself—cells that will be genetically identical to Squeaky. You hope that your friend will be successful when applying her methods to the ES cell line derived from Squeaky and can grow a functional liver for him.

Drugs that block the function of oncogenic proteins hold great promise in the fight against cancer. Should cancer researchers also be attempting to design drugs that will interfere with the products of tumor suppressor genes? Explain.

Oncogenic proteins lead toward cancer, because they have excessive or unregulated activity in comparison with the corresponding normal proteins. Blocking this activity with a drug molecule that simply clogs the active site of the oncogenic protein removes the danger. For a tumor suppressor gene, the danger lies in a loss of function, and there is generally no simple way for a drug molecule to restore a protein function that has been lost. It is therefore hard to see how we could achieve any useful effect on cancer by means of drugs that interfere with tumor suppressor gene products. A drug that simply inhibited their function would be expected to promote, not cure, cancer.

A certain mutation in the receptor for epidermal growth factor (EGF) causes the mutated receptor protein to send a positive signal along the associated intracellular signaling pathway even when the EGF ligand is not bound to it. This signal leads to abnormal cell proliferation in the absence of growth factor. On the basis of this information, would you class the gene for the EGF receptor as a tumor suppressor gene or a potential oncogene? Explain your answer.

The mutation described leads toward cancerous cell behavior (excessive proliferation) by making the gene product hyperactive.The mutant gene is therefore, by definition, an oncogene.This effect is seen even if only one copy of the gene is affected; in other words, the mutation is dominant, as is typical for an oncogene. Mutations that delete an EGF receptor gene would be expected to have either no effect or an inhibiting effect on cell division. Thus, the normal EGF receptor is classed as a potential oncogene (a proto-oncogene).