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28 Flashcards

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Biology 101 flashcards
1
Q

describe the structure of a hemidesmosome

A

specialized structure composed of a dense plaque of PRO (often plectin), keratin fibers are embedded in the fiber

Keratin is linked to the outside of the cell by integrin 

Integrin binds ECM PROs
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2
Q

what results in tighter attachments to the ECM than focal adhesions?

A

hemidesmosomes

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3
Q

what occurs when hemidesmosomes aren’t functioning properly?

A

Defect in integrin results in epidermolysis bullosa where there’s a loss of hemidesmosomes, the lower layer of the epidermis fails to attach to the basal lamina & chronic blistering is seen

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4
Q

how many cells is a human comprised of?

A

20-40 trillion

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5
Q

how do cells recognize each other?

A

cell adhesion molecules (CAMs)

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6
Q

how are CAMs grouped?

A

2 categories depending on how they pair with each other:

Homophilic or heterophilic

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7
Q

homophilic

A

CAMs binds to each other

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8
Q

heterophilic

A

bind to diff kinds of PROs

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9
Q

where are selectins most commonly found?

A

epithelial cells

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10
Q

structure of selectins

A

integral PRO with extracellular domains that bind particular carbs on other cells

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11
Q

role of selectins

A

mediate interactions with leukocytes

lymphocytes roll along endothelial cells within capillaries

selectins are involved in one of the first adhesions, then integrins assist in the leukocyte’s entry through the epithelium

adhesion causes intracellular signaling (to indicate to the cell to change shape to allow entry)

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12
Q

how do selectins bind to white blood cells?

A

look for the sugar grps

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13
Q

immunoglobulin

A

antibodies, immune sys PROs that recognize foreign molecules

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14
Q

immunoglobulin cell adhesion molecules (ig-CAM)

A

cell bound integral immunoglobulin PROs

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15
Q

are Ig-CAMs hetero or homo?

A

homo & hetero

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16
Q

when are Ig-CAMs heterophilic?

A

in immunity-related cells & activities

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17
Q

Ig-CAM location

A

lymphocytes, vascular & neural cells

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18
Q

how does the Rhinovirus use ICAMs? & how is this treated?

A

it attaches to the cell by binding to Ig-CAMs & then delivers its RNA

ICAM fragments are provided to inhibit the surface & prevent the virus from attaching

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19
Q

Ig cell adhesion PRO L1 role

A

assists in growth of nerve cells, mutants have severe neural probs: mental retardation & hydrocephaly (fluid accumulation in ventricles of brain)

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20
Q

describe the structure of cadherin

A

integral glycoPRO

have 5 tandem domains

anchored to the actin network with adaptor PROs (such as catenin)

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21
Q

what is the role of calcium in cadherins?

A

calcium ions separate the 5 domains

provide subunit stability & ensure they’re in the proper orientation

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22
Q

are cadherins homophilic or heterophilic?

A

homophilic

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23
Q

what determines the strength of a cadherin interaction?

A

number of cadherins

greater number of cadherins = greater strength of adhesion

24
Q

what occurs to cadherins during embryogenesis?

A

when cells need to migrate to growing tissue, they need to separate from each other. Therefore, the cadherins are endocytosed & lose their adhesive properties

as new cell contact develops new cadherins are produced to attach again to form tissues - promotes cells of similar types ot adhere

25
Q

adherens junctions

A

junction b/w cells using cadherin molecules

attach to the actin network through catenin adaptor PRO

connect the actin network to the periphery of the cell

26
Q

what do adherens junctions look like in epithelial cells?

A

form a belt around the apical ends of cells - maintains tissue integrity

27
Q

whre are adherens junctions most commonly found?

A

epithelial cells

28
Q

what occurs when there is a loss of function of adherens junctions?

A

metastasis in cancer cells

cancer cells migrate to a diff part of the body

29
Q

desmosome structure

A

disc-shaped

2 special types of cadherins:
extracellular
Intracellular - anchored to plaque PROs, plaque PROs are anchored to IFs (keratin)

create point contacts, not a belt

30
Q

where are desmosomes present?

A

cells subjected to mechanical stresses (ex: muscles, epithelia etc.)

31
Q

pemphigus vulgaris

A

autoimmune disorder

attacks cadherin PROs in desmosomes resulting separation of the epithelial cells that form the connective tissue & blistering occurs

32
Q

where are tight junctions located?

A

apical ends of epithelia cells

33
Q

tight junction structure

A

found at the apical ends

CAMs: occludins & claudins

form a line of spot welds on both PMs

34
Q

what is the permeability of claudins?

A

can be permeable to certain ions allowing for controlled leakage

35
Q

loss of function of tight junctions

A

mutation in claudins

tissue failure

mutation in claudin-1 means the skin epidermis leaks water & animals will die of dehydration (mice)

cannot prevent water loss

36
Q

what is the role of tight junctions in the lungs? & how does this go wrong?

A

heregulin is a growth factor attached to the apical surface of PMs
the heregulin receptors are on the basolateral surface

when the sheet of cells are broken, heregulin can reach its receptors & trigger autocrine stimulation of mitosis to heal the wound

chronic bronchitis of smokers, asthma & cystic fibrosis increase the permeability of the airway epithelium. This results in an increase of autocrine stimulation & accounts for proliferation. Too much proliferation can result in cancer

37
Q

describe the structure of gap junctions

A

integral PRO connexin

ring of 6 connexins form a connexon

2 connexons (1 from each cell) bind to form a channel (homophilic)

38
Q

how many diff connexin PROs are there?

A

20

39
Q

what is the function of gap junctions?

A

permits flow of small molecules (gated channel, passive flow)

enables coordination of cells (rapid signaling for cells to act in synchrony)

sweep particulates out of the lungs

cAMP & IP3 are delivered to adjacent cells when hormones trigger a single cell (movement of cilia, peristalsis of gut)

40
Q

describe the movement through gap junction channels?

A

permits flow of small molecules

gate channel

passive flow

regulated by the number of connexons –> increase the number of connexons = increase the flow

41
Q

tight junctions

A

seals gap b/w epithelial cells

42
Q

adherens junctions

A

connects actin filament bundle b/w cells

43
Q

desmosomes

A

connects IFs b/w cells

44
Q

gap junctions

A

allows the passage of small water-soluble molecules from cell to cell

45
Q

CAMs of tight junctions

A

occludins & claudins

46
Q

CAMs of adherens junctions

A

cadherin

47
Q

CAMs of desmosomes

A

2 types of cadherin (intracellular & extracellular)

48
Q

CAMs of gap junctions

A

connexin

49
Q

function of tight junctions

A

brings PMs to almost the point of fusion, prevent easy flow of liquid & solutes & responsible for integrity

50
Q

adherens junctions

A

connects actin filament bundle b/w cells

51
Q

function of desmosomes

A

hold cells together that endure mechanical stresses

52
Q

what are the diffs b/w hemidesmosomes & desmosomes?

A

hemi –> integral, integrins

desmosomes –> not integral, cadherins

53
Q

plasmodesmata

A

channels that connect plant cells

54
Q

how many plasmodesmata does a plant cell have?

A

b/w 10^3 & 10^5

55
Q

describe the plasmodesmata structure

A

Channel is lined with PM & usually contains a desmotubule which is derived from the SER

56
Q

how is the flow of molecules regulated in plasmodesmata?

A

Flow is regulated by the desmotubule diameter

actin & myosin wrap around the desmotubule & close off the gap

57
Q

how do viruses use plasmodesmata?

A

modify plasmodesmata PROs to cause it to open wider to allow the passage of the virus from one cell to the other

C Bio (30 decks)

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