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Histology II > Cell Structure 3 > Flashcards

Cell Structure 3 Flashcards

0
Q

What are the three main components of the cytoskeleton and what are their respective sizes?

A
  1. Actin (7.5 nm smallest)
  2. Intermediate filaments (8-12 nm)
  3. Microtubules (25 nm largest)
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1
Q

What is the function of the cytoskeleton?

A
  1. Mechanical support and tensile strength: prevents cell from being squashed
  2. Motility: movement of organelles, ability of cells to migrate (neutrophil chasing bacteria), contraction
  3. Regulation: signaling regulated through cytoskeleton
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2
Q

Where are Actin microfilaments generally found?

A

Forming a supporting layer underneath plasma membrane called “actin cortex.” Provides a point where integral membranes get anchored. Can also be found in bundles in microvilli.

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3
Q

Where are intermediate filaments generally located?

A

Enwrap or enclose the nucleus. Provide enormous tensile strength. Anchored to desmosomes. Distribute stress forces.

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4
Q

Where are microtubules generally found?

A

Originate from the centrosome (microtubule organizing center, MTOC). Radiate out into interior. Provide highway for movement of materials within cell. For example, vesicular movement from one golgi part to the next or secretory vesicles.

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5
Q

What are microfilaments composed of?

A

Monomers of actin.

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6
Q

At what end are actin monomers added?

A

The plus end. Also known as the growing end.

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7
Q

What is the process known as treadmilling?

A

New actin monomers are added to the plus end, old ones are being relieved at the minus end. Can be used as a source of energy for the cell.

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8
Q

What are the main functions of actin?

A
  1. maintain cell shape (tension-bearing elements)
  2. cytoplasmic streaming
  3. cell motility
  4. muscle contraction (associate with myosin)
  5. cell division (cleavage ring forms, responsible for division of one cell into two cells; completion of mitosis)
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9
Q

What do actin-binding proteins do?

A

Bundling, cross-linking (actin cortex), filament-severing (cut actin filaments down, reorganize), capping, motor (drag other organelles along actin filaments).

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10
Q

What are the main functions of intermediate filaments?

A

Hold things. Wrap around nucleus. Maintain relationships between organelles. Spacial orientation is important function. Tension bearing (distribute stress within cell). Support nuclear envelope and form points of attachment for heterochromatin.

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11
Q

What are intermediate filaments made up of?

A

Fibrous sub-units. They are structurally homologous but biochemically distinct. Fiber subunits bundle together. Share common body plan but made up of different proteins in each fiber.

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12
Q

Intermediate filaments are important in providing mechanical strength. They allow epidermal cells in skin to resist stress. Stress can be distributed across large sheet of cells. What happens when there is failure of intermediate filaments. Either by exceeding max stress or deficiency?

A

Failure due to excess stress causes blisters. Cell sheers apart and fluid filled blister forms.

Gene mutation: Epidermolysis bullosa simplex
lightest touch causes blisters to form. Horrific blisters due to fact skin is very fragile, due to the fact that IF is either missing or disrupted.

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13
Q

What mutation causes epidermolysis bullosa simplex? (blistering of skin)

A

Mutations in cytokeratins. This results in fragile skin and spontaneous blistering from lack of functioning intermediate filaments.

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14
Q

Where are Class I intermediate filaments found?

A

They are composed of acidic and basic cytokeratins and found in epithelia cells.

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15
Q

Where are Class IV intermediate filaments found?

A

These are nuclear lamins A, B, C. Line the nuclear envelope.

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16
Q

Where are Class III intermediate filaments found?

A

These are neurofilament proteins and are found in neurons.

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17
Q

Where are class II intermediate filaments found?

A
  1. Vimentin polypeptides, found in cells of mesenchymal origin (endothelial cells, smooth muscle)
  2. Desmin polypeptides, found in muscle cells.
  3. Glial fibrillary acidic protein found in Glial cells.
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18
Q

Why are classes of intermediate filaments important? What makes them clinically relevant?

A

Intermediate filaments can be used to identify cellular origins. Antibodies have been developed against all types of classes. Staining with an antibody can identify what type of cell you are looking at. Can use this technique to figure out where tumor has originated from. Is it metastatic or in situ?

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19
Q

What are the characteristics of microtubules?

A

Long, straight, rigid cylinders formed by polymerization of alpha and beta tubulin dimers (9+2 in cilia).
Polarized, have a plus end and a minus end.

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20
Q

At what end does polymerization of microtubules occur?

A

Microtubules both grow and depolymerize at the PLUS end.

21
Q

When GTP levels are high what happens to microtubules?

A

Rapid elongation. When GTP levels are low dissociate quickly. This is known as “dynamic instability”. Depending on what is going on inside the cell will affect the growth or shortening of microtubules.

22
Q

Where is the minus end of microtubules embedded?

A

In the microtubule organizing center (MTOC). All emanate from MTOC.

23
Q

What are kinesin and dynein involved with? What cytoskeleton component are they associated with?

A

Microtubules are a substrate for two molecular motors-kinesin and dynein. These are both ATPases involved in transport of membrane bound organelles (secretory vesicles, mitochondria). Molecules have two arms, body with a leash that binds to vesicle, in presence of atp, conformational changes cause the structure to move along the length of the microtubule.

24
Q

What does it mean that kinesin is an anterograde motor?

A

Moves from the minus (-) end towards plus (+) end.

25
Q

What does it mean that dynein is a retrograde motor?

A

It moves from the plus end toward the minus end.

26
Q

Where does the apical surface face?

A

The lumen.

27
Q

What are the three types of surface specializations?

A
  1. Apical specializations (villi or cila)
  2. Lateral wall specializations (associated with adhesive and communicative contacts)
  3. Basal wall specializations (adhesive contact between basal membrane and cell membrane that sits on top of it )
28
Q

What is the structure of a microvilli?

A

1-2 microns long, 80 nm in diameter
Core has a bundle of actin filaments, that project down and interact with web of actin below-“actin cortex”
Non-motile

29
Q

What is the purpose of microvilli?

A

To increase the surface area for absorption.

30
Q

What symptoms would be associated with a patient with Microvillus Inclusion Disease (MID).

A

Microvilli are present as cellular inclusions instead of being generated on surface of cell. Generally found in infants who have uncontrollable diarrhea. Unable to absorb nutrients in the gut, water follows nutrients so unable to absorb water. Goes right through them. Lack microvilli that increase surface area.

31
Q

What is the function of cilia?

A

To move fluid over the surface of epithelium.

32
Q

What are cilia made of?

A

Microtubules, which interact (anchor) with basal bodies.

33
Q

What does the formation of microtubules look like in cilia?

A

Axoneme: longitudinal microtubules are arranged in 9+2 organization.
9 Doublets around perimeter, pair of singlets in center. Anchored to basal body.
Dynein motor: anchored to one of the doublets, and middle set of microtubules.
Responsible for whip like movement. Also found in flagella- same 9+2 arrangement.

34
Q

What symptoms would a patient with Kartegener’s Syndrome present with?

A

Respiratory problems because constant movement of mucus is not possible. Mucus pulls in bottom of lungs, soup for bacteria! Infertility, sperm can’t swim. Heart on wrong side. Organs tend to be reversed.Dynein arms are missing in cilia.

35
Q

Describe Stereocilia. Where are they found?

A

Found in epididymal cells in testes. Thought to be cilia but are NOT. Actually have actin filaments at their core. Long microvilli.

36
Q

Describe Kinocilia. Where are they found?

A

Cilia- have axoneme. Lacks central microtubule (9+0 axoneme)- non-motile. Involved in signal transduction. Present on hair cells in inner ear.

37
Q

What is the terminal bar (junctional complex) made up of?

A

Related to cell adhesion. Zonula occludens, zonula adherens, macula adherens (desmosomes).

38
Q

What is the important function of tight junctions (zonula occludens)?

A

Provides a barrier to the movement of both water, and solute molecules between the cells. Every cell has this barrier that separates this extracellular compartment, from the next one. Prevents movement of solute particles through region between two sets of cells. Consists of complex of proteins occludin and claudin.

Second function: Acts as barrier to diffusion of proteins within cell membrane. Prevents movement of integral proteins.

39
Q

What is one way that bacteria cause diarrhea?

A

Bacteria break down tight junctions (zonula occludens). “Leaky gut” syndrome. No barrier, water falls back down it’s concentration gradient into gut. Typical with irritable bowel syndrome.

40
Q

What do adherence junctions depend on for adhesive interactions?

A

Ca 2+ dependent adhesive interactions, mediated by cadherin proteins. Adherens display homophilic adhesive interactions. Cadherin proteins bind to other cadherin proteins on adjacent cell membrane, mediate adhesive interactions. Inside cell have linking proteins, that ultimately connect this cell with actin filaments.

41
Q

What do desmosomes do?

A

Demosomes are points of adhesion. Spot wells between cells. Points at which intermediate filaments are anchored. Intermediate filaments are anchored to desmoplakin/pakoglobin attachment plaque.

42
Q

What is the main purpose of gap junctions?

A

Mediate communication between cells. Each cell membrane has a structure called connexons, proteins arranged around a central aqueous pore. When connexons align between two adjacent cells, get free flow of ions and small particles between adjacent cells. Cyclic amp can flow through. Coordinate activity (electrical, metabolic, etc.) in whole group of cells.

43
Q

What is the function of the basement membrane?

A

Cell adhesion. Cell membrane sits on top of basement membrane (extracellular matrix) provides a site of cell adhesion.Provides a point where intermediate filaments are anchored to cell and cell itself is anchored to basement membrane.

44
Q

What is the basement membrane made up of?

A

Glycoproteins, collagen, fibernectins, laminin. Composed of basal lamina, reticular fibers (collagen) and anchoring plaques. Basically a supporting material for cell to sit on and adhere to.

45
Q

What are the main components and functions of the basement membrane?

A
  1. laminin
  2. type IV collagen
  3. enactin
  4. perlecan

Functions: support, substrate for adhesion, in kidneys also plays a role in filtration of urine

46
Q

What autoimmune disorder is characterized by antibodies against desmosomes and hemidesmosomes?

A

Pemphigus: antibodies against adhesive contacts results in epidermal blistering and loss of extracellular fluid

also affects epithelial lining in gut, mouth, skin, etc.
Now immune suppressant drugs can help, used to be 90% fatal.

47
Q

What are the main symptoms of Alport’s Syndrome?

A

Inherited a defect in structure of type IV collagen which is important in the kidneys and filtration structure. Causes blood in the urine. Permeability of basement membrane changes, allows blood to escape into urine.

48
Q

How is cell adhesion related to cancer?

A

Mutation and altered expression of various cell adhesion genes can cause inability to regulate metastasis.

49
Q

What is the role of integrins?

A

Integrins are transmembrane proteins composed of alpha and beta heterodimer (two sub-units). Important in signal transduction via coupling to second messenger system. Signaling structures can cause changes in actin cytoskeleton.

Histology II (4 decks)

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