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biomed 2 > Cell Bio - Cell adhesion and signalling > Flashcards

Cell Bio - Cell adhesion and signalling Flashcards

1
Q

difference between planktonic and sessile bacteria

A

planktonic - freely existing in bulk solution
sessile - attached to a surface or within a biofilm

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2
Q

what does the extracellular matrix (ECM) consist of

A

network of proteins and polysaccharide chains that are manufactured by cells, secreted and modified outside the cell by several different enzymes.

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3
Q

what are the functions of the ECM

A

mechanical - tensile and compressive strength and elasticity
protection - buffering against extracellular changes and water retention
organisation - control of cell behaviour by binding of growth factors and interactions with cell surfaces

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4
Q

what secretes the matrix macromolecules

A

fibroblasts

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5
Q

what forms bones and cartilage

A

bones - osteoblasts
cartilage - chondroblasts

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6
Q

what are the main macromolecular components of the ECM

A

glycosaminoglycans
fibrous protein
non-collagen glycoprotein

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7
Q

structure of glycosaminoglycans (GAG)

A

GAGs are unbranched polymers of repeated disaccharide derivatives, including amino sugars, sulfated acetylamino sugars and uronic acids

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8
Q

what are the properties of GAG’s

A

Acidic and negatively charged
Attract positive ions (eg Na+) which attracts water causing gel formation
Comprise 10% of ECM mass but 90% of volume
GAGs (especially hyaluronan) provide compressive strength
Metabolically cheap bulking agent

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9
Q

what is hyaluronan

A

GAG
107kDa
spun out of the cell membrane

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10
Q

function of hyaluronan

A

used to hold together open spaces in the ECM that would otherwise be filled up with cells

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11
Q

structure of a proteoglycan

A

serine-rich protein decorated with hundreds of O-linked acidic or sulfated GAG’s

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12
Q

what is aggrecan

A

common proteoglycan in the ECM
Its core protein is decorated with around 100 chondroitin and 30 keratan chains.

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13
Q

what does aggrecan bind to

A

hyaluronan via adaptor proteins

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14
Q

what is the function of the primary cell wall in plants

A

flexibility allowing expansion and remodelling

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15
Q

composition of the primary cell wall

A

cellulose
hemicellulose
pectin

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16
Q

function of the secondary cell wall

A

rigid providing strength

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17
Q

composition of secondary cell wall

A

cellulose
hemicellulose
lignin

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18
Q

what accounts for 20% of primary cell wall dry weight

A

xyloglucan

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19
Q

what is the backbone of xyloglucan composed of

A

1,4-linked β-D-Glcp residues

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20
Q

what occurs to 1,4-linked β-D-Glcp residues

A

are substituted at O6 with mono-, di-, or triglycosyl side chains.

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21
Q

where does galacturonic acid occur (Gala)

A

homogalacturonan (HG)
rhamnogalacturonan (RG)

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22
Q

function of pectin demethylase

A

demethylates pectin
makes it available for crosslinking via Ca2+ bridges

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23
Q

what is an occluding junction

A

seals cells together forming an impermeable barrier

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24
Q

anchoring junctions

A

attaches cells to other cells or the ECM

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25
Q

communicating junctions

A

allows exchange of chemical/electrical information between cells

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26
Q

function of adheren junctions

A

important role in determining shape of multicellular structures
forms an indirect link between actin cytoskeletons

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27
Q

what do adhesion belts allow

A

reshaping of epithelial cells
form vesicles

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28
Q

function of desmosome junctions

A

indirectly link intermediate cytoskeletons
provides mechanical strength

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29
Q

what are channel-forming junctions

A

creates a link between the cytoplasm of two cells

30
Q

what are plasmadesmata

A

plant equivalent to gap-junctions

31
Q

structure of gap junctions

A

each channel is comprised of individual connexin subunits
can be homomeric or heteromeric
assemble into homotypic or heterotypic channels

32
Q

where are new connexons added

A

periphery via exocytosis

33
Q

what does a mutation in connexin 26 lead to

A

– mutation leads to death of cells in the organ of Corti (electrically active sensory epithelium) Congential deafness

34
Q

what can mutations in connexins lead to

A

cateracts and demyelinating disease in peripheral nerves

35
Q

what is a signal-relaying junction

A

basically a synapse

36
Q

difference between cadherins and integrins

A

cadherins - mediate cell-cell attachment
integrins - mediate cell-matrix attachments

37
Q

what proteins constitute tight junctions (TJ)

A

claudin
junctional adhesion molecules (JAM’s)
occludin
ZO

38
Q

what is claudin

A

a four-pass transmembrane protein that constitutes TJ strands

39
Q

what are junctional adhesion molecules (JAM’s)

A

class of cell–cell adhesion molecules with two Ig repeats that localize to TJs.

40
Q

what are occludins

A

four-pass transmembrane protein localized at TJs.

41
Q

what are ZO proteins

A

(zonula-occluding) family proteins: TJ- undercoating scaffolding proteins

42
Q

where are cadherins found and not found

A

in all animals and choanoflagellates
not present in plants, fungi, archaea or bacteria

43
Q

name a non-classical cadherin and its function

A

desmocollin
forms desmosome structures

44
Q

why is Ca2+ important for cadherin function

A

binds to the hinge regions of cadherin, prevents flexing
removal of Ca2+ reduces binding affinity at N-terminal
destabilisation leads to proteolytic degradation

45
Q

function of catenins

A

form a link between the intracellular cadherin domain and the actin filament

46
Q

what is the dual role of β-catenin

A

Intracellular anchor protein at adherens junctions
Transcriptional regulator in Wnt signalling

47
Q

function of vascular endothelial cadherin (VEC)

A

required for endothelial survival
required for response to vascular endothelial growth factor (VEGF)
VEGF binds to a receptor tyrosine kinase that requires VE cadherin as a cofactor

48
Q

structure of integrins

A

Comprised of 2 non-covalently associated glycoprotein subunits
Short intracellular C-terminal
- Large extracellular N-terminal domain

49
Q

difference in roles of the extracellular domain and the intracellular domain of integrin

A

extracellular - binds extracellular matrix proteins or cell
surface ligands of other cells
intracellular - links (usually via Talin) to the actin cytoskeleton

50
Q

what does allosteric regulation allow for

A

switching between active and inactive state

51
Q

describe outside-in activation of integrins

A

Binding of an extracellular ligand to an integrin results in binding to the cytoskeleton
Transmission of a force via the cytoskeleton

52
Q

describe inside-out activation of integrins

A

Intracellular regulatory molecules such as phosphoinositide (PIP2) activate Talin

Causes strong binding of Talin to β integrin chain

In turn this activates the extracellular domain of integrin to bind extracellular ligands

PIP2 can be produced in response to extracellular signals.

Complex crosstalk between different signalling processes

53
Q

what is heterophilic binding

A

binding to a different type of molecule

54
Q

what is a lectin and their function and an example

A

cell surface carbohydrate binding protein
Mediate transient cell-cell adhesion in the bloodstream
Control binding of white blood cells to the endothelial cells lining the blood vessels

55
Q

what are the 3 different types of selectins and where are they present

A

L-selectin - on white blood cells
P-selectin - on platelets and endothelial cells activated by an inflammatory response
E-selectin - on activated endothelial cells

56
Q

what causes lymphocytes to bind and become trapped

A

In lymph organs endothelial cells express oligosaccharides recognised by L-selectin on lymphocytes

57
Q

structure of intracellular adhesion molecules (ICAM)

A

ICAMs have an extracellular domain characteristic of antibodies

58
Q

difference between ICAM/VCAM and NCAM in terms of binding

A

ICAM/VCAM - heterophilic binding to integrins
NCAM - homophilic binding

59
Q

what charge do neural cell adhesion molecules (NCAM) have and why

A

negative
high concentration of sialic acid chains

60
Q

what are the difference between cadherin and NCAM mutations

A

cadherins - lethal
NCAM - more subtle effects

61
Q

how does fascicilin3 function

A

functions in recognition of the tissue by neuronal growth cones

62
Q

what does fascicilin3 form

A

homophilic adhesions

63
Q

what holds the pre/post-synaptic membranes together

A

cadherins
Ig superfamily
neuroligins
neurexins

64
Q

where does plant cell adhesion occur

A

middle lamella - pectin rich domain

65
Q

what are the different domains of pectin

A

HGA - homogalacturonan
RGII - rhamnogalacturonan I
RGI - rhamnogalacturonan I
XGA - xylogalacturonan

66
Q

what can cause loss of plant cell adhesion

A

Defects in synthesis of plant cell wall polysaccharides

67
Q

what are the advantages of single cell organisms for models

A

Fastgrowth in chemically defined media
Relatively cheap culture media
Several molecular tools for manipulation
Extensive knowledge of its genetics and genomics
Extensive knowledge on its transcriptome, proteome, and metabolome
Several strains are considered biosafety level 1 (K12)

68
Q

what are the disadvantages of using single celled organisms for models

A

doesn’t have a nucleus/chromatin, not all protein modification mechanisms e.g. glycosylation

69
Q

features of yeast as model organisms

A

Rapid growth (1.5 or 2.5 hours)
Non-pathogenic
Efficient transformation by exogenous DNA
Efficient homologous recombination
Simple genetic screens

70
Q

what are the advantages of organoids over 2D cultures

A

more physiologically relevant than monolayer culture models.
far more amenable to manipulation of niche components, signalling pathways and genome editing compared to in vivo models.

biomed 2 (18 decks)

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