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cell structure and cell interactions Flashcards

1
Q

what is a cytoskeleton

A

system of filaments

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2
Q

what does the cytoskeleton allow

A

changes in shape to grow, divide, adapt to changing environments & move

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3
Q

three main types of cytoskeleton

A
  1. actin filaments (also called microfilaments)
  2. microtubules
  3. intermediate filaments
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4
Q

role of actin filaments & where does energy come from

A

determine the shape of the cell’s surface & are necessary for locomotion

ATP

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5
Q

role of microtubules

A

determine the positions of membrane-enclosed organelles & direct intracellular transport

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6
Q

role of intermediate filaments

A

provide mechanical strength e.g., nuclear envelope

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7
Q

role of accessory proteins

A

help with assembly of cytoskeleton

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8
Q

what is the cytoskeleton made of

A

large number of small subunits

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9
Q

can the subunits of a cytoskeleton diffuse in the cytosol & if so what does this allow

A

small subunits can diffuse rapidly in the cytosol & this allows for rapid reorganisation with subunits quickly disassembling & reassembling elsewhere

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10
Q

what does the cytoskeleton determine

A

polarity by their configuration

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11
Q

two types of cytoskeleton

A

dynamic or stable

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12
Q

4 different roles of actin protein

A
  • gives structure to cell body
  • form projections called microvilli
  • form long directional fibers = stress fibers
  • essential component for striated muscle
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13
Q

shape of actin protein monomer

A

globular monomer with cleft in the middle where ATP is found

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14
Q

what do the actin monomers form

A

form filaments (2 protofiliments form a double helix) with a pos and neg end

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15
Q

define nuceleation

A

the growth of filaments = monomers added to end of trimer

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16
Q

what is a trimer of an actin

A

they are made up of 3 monomers which act as stable nucleus

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17
Q

what alters the dynamics of actin

A

actin-binding proteins

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18
Q

structure of microtubules

A

globular monomer, 2 forms = alpha or beta tublin with a binding pocket for GTP

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19
Q

what protein is in microtubules

A

tubulin

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20
Q

two types of tubulin and what is the difference

A

GTP bound = ‘T form’ = plus end and monomers are added to this end
GDP bound = ‘D form’ = minus end and monomers dissociate from this end

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21
Q

what is a centrosome and where is it located

A

= a microtubule organising centre (MTOC)

& located near the nucleus where the minus end is attached/orientated towards the MTOC to form a sphere like with the plus ends sticking out

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22
Q

why are microtubules dynamically unstable

A

they rapidly change between growing and shrinking state

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23
Q

what are intermediate filaments made out of

A

variety of proteins that form a strong rope fibers e.g., nuclear lamina

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24
Q

types of intermediate filaments

A
  1. nuclear = nul
  2. vimentin-like
  3. epithelial
  4. axonal
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25
Q

structure of intermediate filaments

A

2 dimers interact, forming a staggered tetra and associate in groups of 8 forming long filaments

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26
Q

role of regulatory accessory proteins

A

to regulate the attachement of cytoskeleton filaments to one another and other cell components which allows the regulation of the number, geometry, length and stability of the filaments

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27
Q

role of motor proteins x2

A
  1. bind to polarised cytoskeleton filaments and move along them e.g., carry membrane-enclosed organelles to their appropriate locations in the cell
  2. cause cytoskeleton filaments to exert tension or slide against each other, generating force e.g., muscle contraction, cell division
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28
Q

example of a motor protein for actin filaments

A

myosin

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29
Q

how does myosin work

A

interacts with actin to produce contractile forces e.g., in muscle

  • each myosin head binds and hydrolyses ATP to “walk” along an actin filament towards the plus end from minus end
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30
Q

what are the three classes of myosin & difference

A 
class I = associates directly with membranes = assist in endocytosis 
class II = involved in muscle contraction = form bundles that interact with the filaments = facilitate muscle movement 
class III = interact with organelle receptors = transporting organelles along actin filaments
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31
Q

example of motor proteins for microtubules

A

kinesins & dyneins

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32
Q

role of kinesins & dyneins

A

transport cargo along microtubules

= both use conversion of ATP to ADP for energy

kinesins = anterograde transport - goes outside cell

dyneins = retrograde transport - goes inside cell

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33
Q

steps: cytoskeleton role in cell division

A
  1. a fibroblast in a dish has a spread out actin structure, with microtubules emanating from a microtubule “organising centre” o
  2. the actin filaments disassemble so that the cell stops moving and becomes round, while at the same time the microtubules reconfigure into the mitotic spindle
  3. actin filaments form a contractile ring around the centre to pinch the cell into 2
  4. when cell division is complete, the actin & microtubule structures reconfigure into their interphase structures, forming 2 flattened, smaller daughter cells
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34
Q

when do cells migrate

A

during normal development, wound healing, immune function, and cancer cell metastasis

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35
Q

cytoskeleton role in cell migration steps:

A
  1. EXTENSION extends lamellipodia at the cell leading edge
  2. ADHESION lamellipodia adhere to the substratum by formation of focal adhesions. mediates a connection between the actin cytoskeleton and extracellular matrix proteins
  3. TRANSLOCATION actin-myosin II-dependent contraction (stress fibers) at the rear of the cell propels the bulk of the cytoplasm forward
  4. DE-ADHESION & ENDOCYTIC CYCLING at the back of the cell. the trailing edge of the cell remains attached to the substratum until the tail eventually detaches and contractile force retracts into the cell body
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36
Q

what are cilia and flagella built from

A

microtubules and dynein

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37
Q

define flagella

A

= allow sperm & many protozoa to swim through liquid

stable structure formed by cytoskeleton

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38
Q

define cilia

A

beat with a whip-like motion to either propel cells or move liquid over the surface of cells e.g. in respiraotry tract they sweep layers of mucus, trapped particles or dirt and bacteria up to the mouth to be eliminated

stable structure formed by cytoskeleton

39
Q

how is movement produced in cilia and flagella

A

by the bending of it’s core called the anexome

40
Q

role of cytoskeleton

A
  1. protects contents of cells by providing mechanical strength, determines the cell’s shape and polarity
  2. adds in internal organisation by acting as pathways for transport of cargo by motor proteins
  3. allows for whole-cell locomotion
  4. allow the cell to re-organise & split during cell division
41
Q

example of accessory proteins

A

motor proteins

42
Q

what is the extracellular matrix

A

the matrix in which cells live

43
Q

example of tissue with lots of ECM and few cells

A

cartilage

44
Q

example of tissue with little ECM and lots of cells

A

brain

45
Q

what are the two main classes of macromolecules in ECM

A
  1. glycosaminoglycan

2. fibrous proteins such as collagen

46
Q

what is glycosaminoglycan

A

gel-like substance

47
Q

structure of glycosaminoglycan

A

unbranched polysaccharide chains composed of repeating disaccharide units

48
Q

charge of glycosaminoglycan

A

highly neg charge

49
Q

are glycosaminoglycan hydrophilic or hydrophobic and what effect does this have on structure

A

tend to form highly extended conformations that occupy a large volume for their mass, forming gels

50
Q

effect of the negative charge on glycosaminoglycan

A

high density negative charge attracts cations (especially especially Na+) causing large amounts of water to be sucked in = ability to withstand compressive forces e.g., cartilage in the knee

51
Q

four main groups of glycosaminoglycan (GAGs)

A
  1. Hyaluronan
  2. chondroitin sulfate
  3. heparin sulfate
  4. keratan sulfate
52
Q

what forms proteoglycans

A

All GAGs except hyaluronan covalently attached to a protein core

53
Q

can proteoglycans be large

A

yes can be huge for example, aggrecan (major component of cartilage) which has more than 100 GAG chains

54
Q

can proteoglycans form larger complexes with other proteoglycans

A

yes

55
Q

functions of proteoglycans

A
  • serve as a selective sieve
  • chemicals signalling
  • regulate proteolytic enzymes and inhibitors
  • act as cell surface co-receptors
56
Q

role of collagens

A

give structure to ECM,

57
Q

do intermediate filaments associate with motor proteins

A

no

58
Q

what energy is used by microtubules

A

GDP

59
Q

define lamellipodia

A

flattened extension of a cell, the front end

60
Q

define substratum

A

surface in which the cell attaches to

61
Q

what proteins are in collagen

A

fibrous proteins that give tensile strength to tissues

62
Q

structure collagen

A

Primary feature is its long, stiff, triple
-stranded
helical structure

63
Q

collagen fibrils

A

collagen fibers that assembly into higher order polymers called collagen fibrils

64
Q

how does collagen resist tensile force

A

fibres organised in different ways

65
Q

role of elastin

A

gives stretch to tissues

66
Q

what is the main component of elastic fibres

A

elastin

67
Q

what is elastin sometimes interwoven with to reduce stretchiness

A

stiff, inelastic collagen

68
Q

role of glycoproteins

A

the glue of the ECM

- have specific binding sites for other matrix molecules & cell surface receptors

69
Q

example of glycoprotein

A

fibronectin = allows ECM to attach to cells

70
Q

two forms of fibronectin

A
  1. soluble form (circulating in blood)
  2. insoluble form as fibronectin fibrils on the surface of cells that have fibronectin-binding proteins such as integrins
71
Q

what do integrins link & what does this produce

A

fibronectin to the actin cytoskeleton inside the cell, producing tensile force which
stretches them and allows them to bind to other fibronectin molecules to form fibrils

72
Q

reasons cells in the ECM need to be synthesised & degraded x3

A
  • Remodelling of tissues to adapt to stress e.g. bone
    ― To enable cell division while embedded in matrix
    ― To enable cells to travel through the matrix e.g. white blood cells in response to infection or injury
73
Q

what degrades matrix components

A

extracellular proteolytic enzymes called proteases such

as matrix metalloproteases

74
Q

structure of basal lamina (base membrane)

A

Thin (40-120nm), tough, flexible sheet of matrix molecules

75
Q

role & location of basal lamina

A
  1. underlying all epithelia and surrounding individual muscle, fat and Schwann cells
  2. acting as a selective filter (e.g. kidney glomerus)
  3. selective barrier, e.g. allowing in immune cells while keeping out fibroblasts from
    connective tissue
  4. determine cell polarity
  5. organise proteins in adjacent plasma membranes
  6. promote cell survival, proliferation or differentiation
  7. serve as highways for cell migration
76
Q

what are the components in basal lamina

A

lamini
epithelial cells
collagen type IV
glycoprotein nidogen, fibronectin, perlecan

77
Q

role of laminin

A

primary organiser of the sheet structure

78
Q

collagen type IV structure

A

triple-helical rope-like
fibrils that form a flexible, felt-like network
giving basal lamina its tensile strength

79
Q

what is the extracellular matrix made of

A
  1. glycosaminoglycan poly-saccharide chains

2. fibrous proteins (collagen, elastin, fibronectin)

80
Q

summmary

  • role of the three fibrous proteins
  • role of glycosamioglycan
A

elastin - provides elasticity and strength

collagen - provides tensile strength

fibronectin - glues everything together by acting as a binding protein

  • glyco = gel-like substance able to withstand compressive force
81
Q

how is ECM secreted and degraded

A

by cells within it

82
Q

what do cell-matrix junctions link

A
  1. link the cytoskeleton of the cell to the ECM = allows cells to move through ECM & monitor changes in mechanical properties
  2. cytoskeletal filaments link to basal lamina
83
Q

what do cell to cell junctions link

A

cells linked to cells made from cytoskeletal filaments = transmit stress

84
Q

what are the four main anchoring junction types

A
  1. tight junction
  2. cell-cell anchoring junctions
  3. channel-forming junction
  4. cell-matrix anchoring junctions
85
Q

tight-junctions

A

seals gaps between epithelial cells

86
Q

adherens junctions (cell to cell)

A

connects actin filament bundle in one cell with that in the next cell

87
Q

desmosome (cell to cell)

A

connects intermediate filaments in one cell to those in the next cell

88
Q

gap junction (channel-forming)

A

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

89
Q

hemidesmosome (cell-matrix)

A

anchors intermediate filaments to cell to extracellular matrix

90
Q

actin-linked cell-matrix junction (cell-matrix)

A

anchors actin filaments in cell to ECM

91
Q

cadherins main role

A

cell to cell attachement = resist external forces that pull cells apart e.g., cells of skin stay together when stretched, pinched or poked

92
Q

integrin main role

A

cell to matrix attachment

93
Q

characteristics of cadherins

A

dynamic and adaptable = altered or rearranged or affected by forces

hc (11 decks)

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