Cell Communities: Tissues, Stem Cells, And Cancer Pt. 1

Front 1

What is the extracellular matrix?

Back 1

A complex network of polysaccharides and proteins secreted by cells. A structural component of tissues that also influences their development and physiology.

Front 2

Describe the structure of the urine-collecting ducts if a human kidney.

Back 2

Each is made of closely packed "principal" cells. These form epithelial tubes. The ducts are embedded in an extracellular matrix populated by other cell types.

Front 3

What is an epithelial tissue?

Back 3

It forms the covering of all body surfaces, lines body cavities and hollow organs, and is the major tissue in glands. Basically, it does for multicellular organisms what the plasma membrane does for a single cell.

Front 4

Into what do cells organize?

Back 4

Tissues, which often assemble into organs.

Front 5

Describe the tissue layers in the lumen of a mammal gut.

Back 5

1. Epithelium made of epithelial cells

2. Connective tissue

3. Smooth muscle cells (circular fibers, then longitudinal fibers)

4. More connective tissue

5. More epithelium

Front 6

True or false: each tissue is an organized assembly of cells, held together either by cell-cell adhesions or extracellular matrix, but never both.

Back 6

False. It can be either/or as well as both.

Front 7

What are plant tissues strengthened by?

Back 7

Cell walls.

Front 8

What are two different cell wall polysaccharides?

Back 8

Cellulose and pectin.

Front 9

Where is pectin more often seen? What about cellulose?

Back 9

1. Dominates outer layer of cells, which only have primary cell walls (deposited while cell is still growing).

2. Seen in inner layers, which have thicker, more rigid secondary cell walls (deposited after cell growth has ceased).

Front 10

What gives plant cell walls their tensile strength?

Back 10

Cellulose microfibrils

Front 11

What is a cellulose microfibril made from? What kind of bond links the subunits?

Back 11

A bundle of cellulose molecules. These molecules are long, unbranded chains of glucose. Each subunit is inverted with respect to its neighbors and joined to them via a beta 1,4-linkage.

Front 12

Roughly how many cellulose molecules are held together via hydrogen bonds in a single cellulose microfibril?

Back 12

About 16

Front 13

Describe the structure of a portion of the primary plant cell wall.

Back 13

It is between the middle lamina and plasma membrane. Microfibrils provide tensile strength. Other polysaccharides crosslink the microfibrils. Pectin then fills the spaces between microfibrils, providing resistance to compression.

Front 14

What is the middle lamina? What is it rich in?

Back 14

A layer rich in pectin that cements one cell wall to another.

Front 15

What governs the direction in which the growing cell enlarges?

Back 15

Plants cells grow and change shape, but cellulose microfibrils resist stretching. So, the orientation of the cellulose microfibrils within the cell wall influences the direction. Each cell tends to elongate in a direction perpendicular to the orientation of the microfibrils.

Front 16

What determines the final shape of a plant organ?

Back 16

The direction in which its cells expand.

Front 17

What is turgor pressure?

Back 17

The force within the cell that pushes the plasma membrane against the cell wall.

Front 18

True or false: microtubules direct the deposition of cellulose in the plant cell wall.

Back 18

True

Front 19

What determines the orientation of newly deposited extracellular cellulose microfibrils?

Back 19

The orientation of the underlying intracellular microtubules.

Front 20

What is the purpose of cellulose synthase?

Back 20

It is a large, integral membrane enzyme complex that continuously synthesizes cellulose microfibrils on the outer surface of the plasma membrane. These enzymes move in the membrane, spinning out new polymers and laying down a trail of oriented cellulose microfibrils behind them.

Front 21

What dictates the orientation in which microfibrils are laid down?

Back 21

The path followed by cellulose synthase, but also microtubules just under the plasma membrane, which are aligned exactly with the cellulose microfibrils outside the cell. The microtubules essentially serve as tracks.

Front 22

What do animal tissues consist largely of?

Back 22

Extracellular matrix.

Front 23

What are the four major types of animal tissues? Which one has the basic architectural distinction?

Back 23

1. Connective (this one has the distinction)

2. Epithelial

3. Nervous

4. Muscular

Front 24

What is different about connective tissue compared to the other three?

Back 24

Extracellular matrix is plentiful and carries the mechanical load. In the other tissue types, extracellular matrix is scanty and cells are directly joined to one another and carry the mechanical load themselves.

Front 25

In connective tissues, where are the cells that produce extracellular matrix?

Back 25

Scattered throughout the tissue.

Front 26

What provides the tensile strength for connective tissues? (Examples: tendons, skin dermis, bones cartilage).

Back 26

A fibrous protein called collagen. It is a protein found in all animals. Mammals have about 20 different collagen genes.

Front 27

Describe the structure of collagen.

Back 27

It is long, stiff, and each molecule has a triple-stranded helical structure. These are then organized into collagen fibrils which are bundled together into collagen fibers.

Front 28

What creates collagen? Describe the process by which collagen fibrils are created.

Back 28

Connective tissue cells that inhabit the extracellular matrix, called Fibroblasts in many connective tissues.

1. Collagen is synthesized as a procollagen molecule with unstructured peptides at either end.

2. These peptides prevent collagen from assembling in the fibroblasts

3. Extracellular procollagen proteinases remove the terminal peptides as collagen is secreted, producing mature collagen.

4. From here, the molecules can self-assemble into ordered collagen fibrils.

Front 29

What can cause abnormally stretchy skin?

Back 29

A genetic syndrome that results in a defect of collagen assembly. Arises from the lack of the enzyme that converts procollagen into collagen or a defect in procollagen itself.

Front 30

How are collagen fibrils arranged in the skin of some animals (not including mammals)?

Back 30

In a plywood like pattern. Successive layers of fibrils are laid down nearly at right angles to each other.

Front 31

What influences the alignment of collagen fibers?

Back 31

Fibroblasts.

Front 32

What is fibronectin?

Back 32

An extracellular matrix protein that provides a link between other extracellular matrix proteins (such as collagen) and the extracellular matrix.

Front 33

What is transmembrane integrin?

Back 33

They are receptor protein dimers located in the plasma membrane that bind to fibronectin to tether it and whatever it's holding to the actin cytoskeleton inside the cell.

Front 34

What causes integrin to switch to an active conformation?

Back 34

Binding to molecules on either side of the plasma membrane (like fibronectin and actin adaptor proteins). Integrin consists of an alpha and a beta subunit, which can both switch between a folded, inactive form and an extended, active form.

Front 35

What makes the integrin mechanical linkage across the cell membrane reversible?

Back 35

The conformational change caused by binding on one side alters it so the opposite end rapidly forms a counterbalancing attachment to the appropriate structure.

Front 36

How do cells resist compression? (Collagen provides tensile strength, so quit answering that)

Back 36

Glycosaminoglycans (GAGs). They are negatively charged polysaccharide chains usually covalently linked to core proteins to form proteoglycans. Essentially, they are space-fillers in the extracellular matrix of connective tissues.

Front 37

What is hyaluronan?

Back 37

A simple GAG made up of a single long chain of up to 25,000 repeated disaccharide units, each carrying a negative charge.

Front 38

What is a stratified epithelium? A simple epithelium?

Back 38

1. A multicellular sheet that is many cells thick. (Ex: epidermis)

2. A multicellular sheet that is only one cell thick (Ex: lining of the gut).

Front 39

What are the four basic types of epithelia? What do they rest on?

Back 39

1. Columnar (lines most organs of digestive tract)

2. Squamous (Flat. Found in capillaries and tissues where rapid diffusion is required)

3. Cuboidal (Lines kidney tubules, walls of respiratory system, etc)

4. Stratified (Depends on what kind of stratified)

They rest on a thin extracellular matrix called the basal lamina.

Front 40

What are the two surfaces a polarized sheet of epithelial cells has?

Back 40

Basal and apical. The basal surface sits on the basil lamina. The apical surface is free.

Front 41

True or false: the polarity of epithelial sheets is crucial for function. Give an example.

Back 41

True. Example is the simple columnar epithelium that lines the small intestine of an animal. Consists of two cell types, absorptive (brush border) and goblet. The former takes up nutrients, and the latter secretes mucus. If they were oriented the wrong way, they wouldn't be able to do their jobs.

Front 42

What are tight junctions?

Back 42

They make an epithelium leakproof and separate its apical and basolateral surfaces. Areas where the membranes of two adjacent cells join together to form a barrier. They bind cells together, prevent solute diffusion between the cells, and also help to maintain the polarity of cells.

Front 43

What seals the adjacent cells together in tight junctions?

Back 43

Branching strands of transmembrane proteins called claudins and occludins.

Front 44

What binds epithelial cells to one another and to basal lamina?

Back 44

Cytoskeleton-linked junctions.

1. Transmembrane Cadherin molecules in the plasma membranes of adjacent cells bind to each other extracellularly.

2. Cadherins are attached inside the cell via linker proteins to cytoskeletal filaments (actin filaments or keratin intermediate filaments)

3. When cadherins become concentrated at a point if attachment, they create an adherens junction.

Front 45

How do epithelial sheets form epithelial tubes and vesicles?

Back 45

1. Contraction of apical bundles of actin filaments linked from cell to cell via adherens junctions causes the epithelial cells to narrow at their apex.

2. When contraction is oriented along one axis, you get a tube.

3. When contraction is equal in all directions, you get a vesicle.

Front 46

What links the keratin intermediate filaments of one epithelial cell to those of another?

Back 46

Desmosomes.

On the cytoplasmic surface of the interacting plasma membranes is a dense plaque composed of a mixture of intracellular linker proteins. A bundle of keratin filaments is attached to the surface of each plaque. The cytoplasmic tails of cadherin proteins bind to the outer face of each plaque. Cadherin extracellular domains interact to hold cells together.

Front 47

What are hemidesmosomes?

Back 47

They anchor keratin filaments in an epithelial cell to the basal lamina. The linkage is mediated by transmembrane attachment complex containing integrins rather than cadherins.

Front 48

What do gap junctions allow?

Back 48

Cytosolic inorganic ions and small molecules to pass from cell to cell. This allows neighboring cells to have a direct channel of intercytosolic communication.

Front 49

Describe how gap junctions are formed.

Back 49

1. The neighboring membranes are penetrated by protein complexes called connexons. Which are formed by 6 identical protein subunits.

2. Two connexons join across the intercellular gap to form an aqueous channel connecting the cytosols of the two cells

Front 50

True or false: extracellular signals cannot regulate the permeability of gap junctions.

Back 50

False. They can. For example, treatment of the retina with the neurotransmitter dopamine reduces the permeability of gap junctions and hampers the spread of injected dyes (used to label the neurons in this experiment).

Front 51

Review the types of cell junctions found in epithelia in animal cells.

Back 51

1. Tight junctions

2. Adherens junctions

3. Desmosomes

4. Gap junctions

5. Hemidesmosomes

Tight junctions are peculiar to epithelia. The others also occur in modified forms in various nonepithelial tissues.

Front 52

What connects the cytoplasms of adjacent plant cells?

Back 52

Plasmodesma. Each is lined with a plasma membrane common to the two connected cells. Also usually contains a fine tubular structure (desmotubule) derived from smooth Endoplasmic Reticulum.