cell structure and cell interactions Flashcards
1
Q
what is a cytoskeleton
A
system of filaments
2
Q
what does the cytoskeleton allow
A
changes in shape to grow, divide, adapt to changing environments & move
3
Q
three main types of cytoskeleton
A
- actin filaments (also called microfilaments)
- microtubules
- intermediate filaments
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
5
Q
role of microtubules
A
determine the positions of membrane-enclosed organelles & direct intracellular transport
6
Q
role of intermediate filaments
A
provide mechanical strength e.g., nuclear envelope
7
Q
role of accessory proteins
A
help with assembly of cytoskeleton
8
Q
what is the cytoskeleton made of
A
large number of small subunits
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
10
Q
what does the cytoskeleton determine
A
polarity by their configuration
11
Q
two types of cytoskeleton
A
dynamic or stable
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
13
Q
shape of actin protein monomer
A
globular monomer with cleft in the middle where ATP is found
14
Q
what do the actin monomers form
A
form filaments (2 protofiliments form a double helix) with a pos and neg end
15
Q
define nuceleation
A
the growth of filaments = monomers added to end of trimer
16
Q
what is a trimer of an actin
A
they are made up of 3 monomers which act as stable nucleus
17
Q
what alters the dynamics of actin
A
actin-binding proteins
18
Q
structure of microtubules
A
globular monomer, 2 forms = alpha or beta tublin with a binding pocket for GTP
19
Q
what protein is in microtubules
A
tubulin
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
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
22
Q
why are microtubules dynamically unstable
A
they rapidly change between growing and shrinking state
23
Q
what are intermediate filaments made out of
A
variety of proteins that form a strong rope fibers e.g., nuclear lamina
24
Q
types of intermediate filaments
A
- nuclear = nul
- vimentin-like
- epithelial
- axonal
25
structure of intermediate filaments
2 dimers interact, forming a staggered tetra and associate in groups of 8 forming long filaments
26
role of regulatory accessory proteins
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
27
role of motor proteins x2
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
28
example of a motor protein for actin filaments
myosin
29
how does myosin work
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
30
what are the three classes of myosin & difference
```
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
```
31
example of motor proteins for microtubules
kinesins & dyneins
32
role of kinesins & dyneins
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
33
steps: cytoskeleton role in cell division
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
34
when do cells migrate
during normal development, wound healing, immune function, and cancer cell metastasis
35
cytoskeleton role in cell migration steps:
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
36
what are cilia and flagella built from
microtubules and dynein
37
define flagella
= allow sperm & many protozoa to swim through liquid
stable structure formed by cytoskeleton
38
define cilia
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
how is movement produced in cilia and flagella
by the bending of it's core called the anexome
40
role of cytoskeleton
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
example of accessory proteins
motor proteins
42
what is the extracellular matrix
the matrix in which cells live
43
example of tissue with lots of ECM and few cells
cartilage
44
example of tissue with little ECM and lots of cells
brain
45
what are the two main classes of macromolecules in ECM
1. glycosaminoglycan
| 2. fibrous proteins such as collagen
46
what is glycosaminoglycan
gel-like substance
47
structure of glycosaminoglycan
unbranched polysaccharide chains composed of repeating disaccharide units
48
charge of glycosaminoglycan
highly neg charge
49
are glycosaminoglycan hydrophilic or hydrophobic and what effect does this have on structure
tend to form highly extended conformations that occupy a large volume for their mass, forming gels
50
effect of the negative charge on glycosaminoglycan
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
four main groups of glycosaminoglycan (GAGs)
1. Hyaluronan
2. chondroitin sulfate
3. heparin sulfate
4. keratan sulfate
52
what forms proteoglycans
All GAGs except hyaluronan covalently attached to a protein core
53
can proteoglycans be large
yes can be huge for example, aggrecan (major component of cartilage) which has more than 100 GAG chains
54
can proteoglycans form larger complexes with other proteoglycans
yes
55
functions of proteoglycans
- serve as a selective sieve
- chemicals signalling
- regulate proteolytic enzymes and inhibitors
- act as cell surface co-receptors
56
role of collagens
give structure to ECM,
57
do intermediate filaments associate with motor proteins
no
58
what energy is used by microtubules
GDP
59
define lamellipodia
flattened extension of a cell, the front end
60
define substratum
surface in which the cell attaches to
61
what proteins are in collagen
fibrous proteins that give tensile strength to tissues
62
structure collagen
Primary feature is its long, stiff, triple
-stranded
helical structure
63
collagen fibrils
collagen fibers that assembly into higher order polymers called collagen fibrils
64
how does collagen resist tensile force
fibres organised in different ways
65
role of elastin
gives stretch to tissues
66
what is the main component of elastic fibres
elastin
67
what is elastin sometimes interwoven with to reduce stretchiness
stiff, inelastic collagen
68
role of glycoproteins
the glue of the ECM
| - have specific binding sites for other matrix molecules & cell surface receptors
69
example of glycoprotein
fibronectin = allows ECM to attach to cells
70
two forms of fibronectin
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
what do integrins link & what does this produce
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
reasons cells in the ECM need to be synthesised & degraded x3
- 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
what degrades matrix components
extracellular proteolytic enzymes called proteases such
| as matrix metalloproteases
74
structure of basal lamina (base membrane)
Thin (40-120nm), tough, flexible sheet of matrix molecules
75
role & location of basal lamina
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
what are the components in basal lamina
lamini
epithelial cells
collagen type IV
glycoprotein nidogen, fibronectin, perlecan
77
role of laminin
primary organiser of the sheet structure
78
collagen type IV structure
triple-helical rope-like
fibrils that form a flexible, felt-like network
giving basal lamina its tensile strength
79
what is the extracellular matrix made of
1. glycosaminoglycan poly-saccharide chains
| 2. fibrous proteins (collagen, elastin, fibronectin)
80
summmary
- role of the three fibrous proteins
- role of glycosamioglycan
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
how is ECM secreted and degraded
by cells within it
82
what do cell-matrix junctions link
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
what do cell to cell junctions link
cells linked to cells made from cytoskeletal filaments = transmit stress
84
what are the four main anchoring junction types
1. tight junction
2. cell-cell anchoring junctions
3. channel-forming junction
4. cell-matrix anchoring junctions
85
tight-junctions
seals gaps between epithelial cells
86
adherens junctions (cell to cell)
connects actin filament bundle in one cell with that in the next cell
87
desmosome (cell to cell)
connects intermediate filaments in one cell to those in the next cell
88
gap junction (channel-forming)
allows the passage of small water-soluble molecules from cell to cell
89
hemidesmosome (cell-matrix)
anchors intermediate filaments to cell to extracellular matrix
90
actin-linked cell-matrix junction (cell-matrix)
anchors actin filaments in cell to ECM
91
cadherins main role
cell to cell attachement = resist external forces that pull cells apart e.g., cells of skin stay together when stretched, pinched or poked
92
integrin main role
cell to matrix attachment
93
characteristics of cadherins
dynamic and adaptable = altered or rearranged or affected by forces
