chapter 20

Give three examples of epithelial sheets found in the human body.

-bladder -intestinal tract -heart -skin

refer to question 20-4. Why do you suppose these two different cell types attach differently to the extracellular matrix?

Epithelial cells need stability and fibroblast need movement. forces for pulling on the matrix or for driving crawling movement are generated by the actin cytoskeleton. In mature epithelium, focal contact sites are presumably less prominent because the cells are largely fixed in place and have no need to crawl over the basal lamina or actively pull on it.

some have speculated that Abraham Lincoln had Marfan Syndrome. What protein is mutated? What about President Lincoln may have caused these speculations?

The fibrillin-1 protein on chromosome 15. President Lincoln was speculated to have this syndrome because he was so tall.

cells in the stem of a seedling that is grown in the dark orient their microtubules horizontally. How would you expect this to affect the growth of the plant?

The turgor pressure allows the growth through the surface. The horizontal orientation of the microtubules will be associated with horizontal orientation of cellulose microfibils deposited in the cell walls. the growth of the cell wall will be in a vertical direction, expanding the distance between cellulose microfibrils without stretching them.

proteaoglycans are characterized by the abundance of negative charges on their sugar chains. How would the properties of these molecules differ if the negative charges were not as abundant?

Water wouldn't absorb and it would be more compressible

Which of the following substances would you expect to spread from one cell to the next through (a) gap junctions and (b) plasmodesmata: glutamic acid, mRNA, cyclic AMP, Ca 2+, G proteins, and plasma membrane phospholipids?

a. glutamic acid, cyclic AMP, Ca2+ b. glutamic acid, cyclic AMP, Ca2+, plasma membrane phospholipids

anchoring junction that connects actin filaments in one cell to those in the next cell

adherens junction

the exposed free surface of an epithelial cell

apical surface

a thin mat of extracellular matrix that separates epithelial sheets, and many other types of cells such as muscle or fat cells, from the connective tissue.

basal lamina

a member of a family of proteins that mediate Ca 2+ dependent cell-cell adhesion in animal tissues.

cadherin family of proteins

fibrous protein that, in its many forms, is a major component of the extracellular matrix and connective tissue

collagen

type of anchoring, usually formed between two epithelial cells, characterized by dense plaques or protein into which intermediate filaments in the two adjoining cells insert.

desmosomes

complex network of polysaccharides (such as GAGs or cellulose) and proteins (such as collagen) secreted by cells that serves as a structural element in tissues and also influences tissue development and physiology.

extracellular matrix

gap junctions connect the cytoskeleton of one cell to that of a neighboring cell or to the extracellular matrix

false, adherens junctions

Cellulose is synthesized inside the cell then exported by exocytosis

false, cellulose is assembled outside the cell

the extracellular matrix is a relatively inert scaffolding that stabilizes the structure of tissues.

false, the extracellular matrix is dynamic

because of their rigid structure, proteoglycans can withstand a large amount of compressive force

false, they are negatively charged and absorb a lot of water

Like the extracellular matrix of animal cells, plant cell walls are composed almost entirely of protein

false, unlike the extracellular matrix of animal cells, plant cell walls are composed almost entirely of cellulose

common cell type in connective tissue that secretes an extracellular matrix rich in collagen and other EM molecules

fibroblast

extracellular matrix protein that binds to integrins to promote adhesion of cells to the matrix and to provide guidance to migrating cells during embryogenesis

fibronectin

water-filled pore in the plasma membrane of animal cells formed by a ring of 6 protein subunits, which link to an identical assembly in an adjoining cell to form a continuous channel between the two cells

gap junction

like-like protein interactions in which a molecule on one cell binds to an identical, or closely related, molecule on an adjacent cell.

hemophilic binding

principal receptor on animal cells for binding most extracellular matrix proteins, including collagens, fibronectin, and laminins.

integrins

Gap junctions are dynamic structures that, like conventional ion channels, are gated: they can close by a reversible conformational change in response to changes in the cell. The permeability of gap junctions decreases within seconds, for example, when the intracellular Ca2+ concentration is raised. Speculate why this form of regulation might be important for the health of a tissue.

ions present in high concentration rush into the cell and metabolites leak out. influx Ca2+ into a sick cell causes its gap junctions to dose immediately effectively isolating the cell and preventing damage from spreading in this way.

stem cells which are more limited in the types of cells that can develop from them (most adult stem cells)

multipotent stem cells

communicating cell to cell junction in plants in which a channel of cytoplasm lined by plasma membrane connect tow adjacent cells through a small pore in their cell walls.

plasmodesmata

stem cells that can become a significant variety of different cell types but are no longer totipotent (generally only embryonic stem cells)

pluripotent stem cells

describes a structural property of epithelial sheets, and their individual cells, which have one surface attached to the basal lamina below and the opposite surface exposed to the medium above.

polarized

Thin and extensible cell covering on new plant cells that can accommodate their growth

primary cell walls

rigid cell covering laid down in layers inside the initial covering once the cell growth has stopped.

secondary cell wall

Your mom is coming to dinner. All you have for a salad is wilted lettuce. You use your knowledge from cell biology to fix the problem. what do you do?

soak the lettuce in tap water because the lettuce will reabsorb water by osmosis.

Gelatin is primarily composed of collagen, which is responsible for the remarkable tensile strength of connective tissue. It is the basic ingredient of jello; yet, as you probably experienced many times yourself while consuming the strawberry-flavored variety, jello has virtually no tensile strength. Why?

the collagen is denatured when boiled. When cooling, disordered fibers form a tangled mess that turn into gel.

Why do you suppose epithelial cells lining the gut are renewed frequently, whereas most neurons last for the lifetime of the organism?

the gut is exposed to acid and rapid turnover protects the organism from harmful consequences, as wounded and sick cells are discarded. neurons live in protected environments and it depends on complex system of connections with other neurons.

Discuss the following statement: "if plant cells contained intermediate filaments to provide the cells with tensile strength, their cell walls would be dispensable."

the plant would have a problem with osmotic pressure because there is no cell wall for turgor pressure. Cell wall is their major defense against pathogens. Intermediate filament network can't provide osmotic pressure for cells

a puzzling observation is that the change of a glycine residue into another amino acid is most detrimental if it occurs toward the amino terminus of the rod-forming domain. Suggest an explanation.

this statement is true because the mutation is at the beginning of chain where it begins to fold.

an occluding junction which seals adjacent epithelial cells together, preventing the passage of most dissolved molecule from one side of the epithelial sheet to the other.

tight junction

stem cells that can become any cell in the body (general only very early embryonic stem cells)

totipotent stem cells

a wilted plant leaf can be likened to a deflated bicycle tire.

true

skin cells are continually shed and are renewed every few weeks; for a permanent tattoo, it is therefore necessary to deposit pigment below the epidermis

true

the basal lamina is specialized layer of extracellular matrix to which sheets of epithelial cells are attached.

true

the cells in a plant can be viewed as forming a syncytium, in which many cell nuclei share a common cytoplasm.

true

tight junction perform two distinct functions: they seal the space between cells to restrict paracellular flow and they fence off membrane domains to prevent the mixing of apical and basolateral proteins

true

virtually all epithelia are anchored to other tissues on their basal side and free of such attachment on the apical side

true

although stem cells are not differentiated, they are specialized and therefore give rise only to specific cell types

true, embryonic cells can give rise.

the large internal hydrostatic pressure that develops in plants cells due to the osmotic imbalance between the cell interior and the fluid in the plant cell wall.

turgor pressure

through the exchange of small metabolites and ions, gap junctions provide metabolic and electrical coupling between cells. why, then, do you suppose the neurons communicate primarily through synapses rather than through gap junctions?

with synapses there is more room for regulation and integration. they also allow signals to be modulated and to be integrated with other signals received by the cell. Gap junctions are like simple joints between electrical components and synapses are like complex relay devices.

Would you expect collagen mutations to be detrimental if only one of the two copies of a collagen gene is defective?

yes, because 50% of the proton is defected.