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MCB > MCB9 - Cell Shape, Behaviour and Adhesion > Flashcards

MCB9 - Cell Shape, Behaviour and Adhesion Flashcards

1
Q

What processes is a cells cytoskeleton involved with

A 
Contraction
Motility
Shape
Vesicular transport
Adhesion
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2
Q

Define polymerisation

A

Linking of individual monomer subunits to form an elongated multi-molecular chain or filament

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3
Q

What are the two types of adhesions found in cells.

A

Cell-cell adhesions and cell-extracellular matrix adhesions.

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4
Q

What causes filaments of the cytoskeleton to assemble and disassemble

A

External and internal stimuli

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5
Q

Why is the cytoskeleton described as dynamic

A

Protein polymers are constantly assembled and dissembled in accordance to varying stimuli

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6
Q

What are the three components of the cytoskeleton

A

Intermediate filaments
Microtubules
Microfilaments

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7
Q

Give example of stimulus that has an effect on cytoskeletal structure

A

E.g cell division stimulus has effect on microtubules

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8
Q

Describe mechanical strength of microtubules

A

Readily bend but break under minimal force

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9
Q

Describe mechanical strength of microfilaments

A

Cannot be deformed and break only with moderate strength

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10
Q

Describe mechanical strength of intermediate filaments

A

Can be readily deformed and resist great forces.

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11
Q

Define tensile strength

A

Amount of force required to break something upon stretching

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12
Q

What is a protofilament

A

Linear string of protein subunits bonded together

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13
Q

Why are multiple protofilaments stronger than a single protofilament

A

Single protofilament requires only one bond to be broken whereas multiple protofilaments require multiple bonds to be broken

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14
Q

What physical property do lateral bonds provide in cytoskeletal elements

A

Lateral bonds provide rope like properties ensuring that the protofilament is strong and resistant to tensile strength

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15
Q

How can the mechanical strength of the three cytoskeletal elements be determined.

A

Mechanical deformation of the cytoskeletal elements with the physical properties observed.

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16
Q

Discuss polarity in cytoskeletal filaments.

A

Results in + and - end of the cytoskeletal filaments. Due to the differences in amino acids that constitute the protein make up.

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17
Q

Discuss shape of monosubunit in comparison to same subunit in polymer.

A

Shape becomes slightly altered to aid conformation of the polymer.

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18
Q

Discuss rate of subunit addition at the + and - end.

A

Minus end has slow rate of subunit addition.

Positive end has fast rate of subunit addition.

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19
Q

Which nucleotide binding is most stable.

A

Triphosphate filament subunit binding is more stable than diphosphate filament subunit binding.

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20
Q

Which nucleotide subunit binds to microtubules

A

GTP

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21
Q

Which nucleotide subunit binds to microfilaments

A

ATP

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22
Q

Which nucleotide subunit binds to intermediate filaments

A

None

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23
Q

How do diphosphate nucleotide subunits form triphosphate nucleotide subunits on binding to cytoskeletal elements

A

Diphosphate is exchanged for triphosphate. It is not phosphorylated.

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24
Q

Which cytoskeletal filaments have polarity

A

Microtubules and microfilaments ONLY

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25
Q

What monomer makes up microtubules

A

Heterodimers of alpha and beta tubulin

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26
Q

What monomer makes up microfilaments

A

Globular actin

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27
Q

What monomer makes up intermediate filaments

A

Varies with type of intermediate filaments (based on location and function)

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28
Q

What are the three movement types of cytoskeleton filaments

A

Shrinking
Elongating
Treadmills got

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29
Q

Discuss shrinking in context of dynamics of cytoskeleton.

A

Rate of loss of subunits is greater at one end than it is at other end so overall loss of subunit leading to shrinking effect.

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30
Q

Discuss elongation in context of cytoskeleton dynamics.

A

Rate of addition of subunits is greater at one end meaning overall effect is addition of subunits resulting in elongation.

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31
Q

Discuss treadmilling in context of cytoskeletal dynamics

A

Rate of addition at one end is equal to rate of loss at other end resulting in treadmilling effect.

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32
Q

When does polymerisation remain at a steady rate in cytoskeletal elements

A

When addition of subunit s is equal to subtraction of subunits

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33
Q

Define critical concentration for cytoskeletal polymerisation

A

Local concentration of subunits which maintains the length of the polymer. Can be different for + and - end

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34
Q

How can the speed of polymerisation be enhanced.

A

When seed is present giving the polymerisation a starting point. No lag phase is observed.

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35
Q

Discuss rate of cytoskeletal polymerisation when no seeds are present.

A

Lag phase observed until small oligomers can be produced by subunits.
Oligomers then act as seeds resulting in exponential growth of cytoskeletal polymerisation rate.
When addition and loss of subunits equal out, an equilibrium is reached.

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36
Q

Give one function of microtubules

A

To act as tracks for molecular motor proteins e.g. dynein , to carry cargo such as transport vesicles around the cell.

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37
Q

How many protofilaments are present in the cross section of a microtubules

A

13

38
Q

Which subunit of microtubules is associated with its respective nucleotide.

A

Both alpha and beta monomers of tubulin bind to GTP however only beta GTP is hydrolysed to GDP

39
Q

What cap is present on microtubules

A

GTP or GDP cap where GTP is more stable than GDP

40
Q

What factors affect stability of microtubules

A

Microtubule binding proteins, signalling events, local environment influences

41
Q

Where do microtubules originate from and describe its structure.

A

Originate at centrosomes made from 2 centrioles. Centrioles are cylindrical structure made from microtubules triplets.

42
Q

Describe the centrosome matrix and its relation to microtubules

A

Centrosome matrix surrounds microtubules and it contains lambda tubulin complexes which have the ability to behave as seed sites

43
Q

Define and discuss MTOC

A

Microtubules organising centre e.g. the centrosome, which allows microtubules to radiate out from

44
Q

Define dynein and its role.

A

Molecular motor protein aiding connection between microtubules and dynastic complex for vesicular transport

45
Q

What are the two microtubules motor proteins and their differences

A

Dynein - moves cargo from + to - I.e. from periphery to centre
Kinesins - moves cargo from - to + I.e. from centre to periphery

46
Q

Discuss structure of cilia and flagella

A

Microtubule core with 9+2 arrangement (axenome)

47
Q

Differences between cilia and flagella

A

Cilia - numerous in number and on cell surface.

Flagella - fewer but have longer protrusions on cell surface

48
Q

Discuss the role of linking proteins associated with microtubules

A

Linking proteins bind two microtubules together which aid Bending and prevent sliding

49
Q

Link between cell division and microtubules

A

Microtubules form mitotic spindle which originate from centrosomes. This is vital for chromosome separation

50
Q

What are the three types of microtubules that exist during cell division

A

Astral microtubules. Kinetochore microbuulues. Inter polar microtubules

51
Q

What are astral microtubules and describe their structure

A

Microtubules that radiate from centrosome to cell periphery

52
Q

What are kinetochore microtubules and discuss their structure

A

Microtubules that span from the centrosome to the sister chromatids in the middle, connected at the kinetochore.

53
Q

What are interpolar microtubules and discuss their structure

A

Microtubules that span from one centrosome to the other, without passing the sister chromatids.

54
Q

Describe structure of intermediate filaments

A

Two linear proteins twist around each other forming a twisted dimer. Two dimers lie laterally with both ends the same (-NH2) sticking out, forming a staggered tetramer. The tetramer associated laterally to form strands. 8 strands join together to form intermediate filament strand.

55
Q

What is a desmosome and it’s purpose

A

Junction at cell periphery which connect intermediate filaments between adjacent cells.

56
Q

What are Hemidesmosomes and how are they different to desmosomes.

A

Hemidesmosomes are junctions between cell base and extracellular matrix.

57
Q

Give example of defective intermediate filament and what disease it causes.

A

Defective cytokeratins leads to fragility in the epidermis and can cause severe blisters - epidermolysis bullish simplex.

Defective desmin (muscle intermediate filament) Leads to muscle fibre loss and progressive muscle weakening

58
Q

What is the link between intermediate filaments and cancer.

A

Cancer cells retain characteristics of cells from which they develop. If type of intermediate filament can be identified, type of cancer can be identified and so potential treatments

59
Q

Where in the cell, do cytokeratins terminate

A

Desmosomes - cell cell junctions

60
Q

What is the nuclear lamina

A

Mesh work of lamin intermediate filaments on the internal surface of the inner nuclear membrane of the nuclear envelope

61
Q

Discuss the role nuclear lamina play in mitosis

A

To aid mitosis, enzymes phosphorylated nuclear lamins resulting in the breakdown of the nuclear envelope. This is after the chromosomes have formed (DNA replication) so the nuclear envelope faragments and the chromosome remain free in the cytoplasm. Nuclei of two daughter cells form and nuclear lamina become dephosphorylated when results in the fragments being bound together to reform the nuclear lamina.

62
Q

How many isoforms of actin exist

A

6 isoforms

63
Q

Discuss the role of Arp2/3 in actin polymerisation.

A

Activating factor activates Arp2/3 complex. This acts as a seed to allow the build up of actin polymers.growth occurs at a 70 degree angle to the mother filament. The Arp2/3 complex acts as the minus end

64
Q

What is the role of formin in actin polymerisation.

A

Formin causes branches of actin polymers to grow linearly to the mother filament. FH2 domain stabilises newly formed actin dimer allowing it to behave as a seeding site. FH1 domain of formin and profilin work together to build actin polymer linearly

65
Q

Give types of actin binding proteins in actin polymerisation

A 
Capping protein
Severing protein 
Bundling protein 
Branching protein 
Cross linking protein
Contraction producing protein 
Stabilising protein
66
Q

What is the role of capping proteins in polymerisation

A

Add a cap to the end of actin polymers preventing addition or removal of subunits at either end

67
Q

How do severing proteins work in actin polymerisation

A

Bind to middle of actin filaments causing them to break

68
Q

What is the role of branching proteins in actin polymerisation

A

Allows actinpolymers to grow as branches off of an existing actin polymer

69
Q

What occurs if cells lack filamins

A

Formation of balloon like membrane features known as blebs

70
Q

What occurs when cells express filamins

A

Formation of lamellipods which aid cell motility

71
Q

What is the role of filamins

A

Cross linking of actin filament to form an actin mesh

72
Q

What are myosin

A

Family of motor proteins that work with actin microfilaments to aid cell crawling or contraction

73
Q

Why are skeletal muscle fibres multinucleate

A

As they contain more than one nucleus

74
Q

Discuss actin myosin movements in muscle contraction.

A

Myosin head binds, pulls and releases actin filaments in continuous cycle which results in muscle contraction.

75
Q

When does cell adhesion become switched on

A

Early in embryonic development - 16 cell stage

76
Q

Define tissues.

A

Groups of cells whose type, organisation and architecture are integral to function. Continues the cells, EXM and tissu fluid

77
Q

Define ECM and what it consists of

A

Material deposited by cells forming the extracellular insoluble region. Consist of fibrillation proteins (collagens and elastics) and hydrated gel e.g. proteoglycans

78
Q

What are the differences between cells and connective tissue in their adhesions

A

Cells have cell-cell adhesions and cell-matrix adhesions.

Connective tissue have only cell-matrix adhesions

79
Q

What are the three principles of cell adhesion

A

Different requirements for adhesion.
Adjustment occurs by cells.
Signalling in cells can be triggered.

80
Q

Give example of when cells adjust their adhesions and explain why is it necessary.

A

E.g. if epithelium becomes damaged, cells surrounding the damage loosen their cell-cell adhesions allowing cells to migrate and proliferate to fill up the damaged area.

81
Q

What are the two types of cell cell adhesions and describe what they are

A

Homophobic - cell adhesion molecules (CAMs) bind specifically to same type of CAM on other cell.
Heterophilic - CAMs bind to other types of CAMs on other cells

82
Q

Are cell-matrix adhesions homophobic or heterophilic

A

Heterophilic

83
Q

Discuss differences between diffuse and clustered cell adhesions

A

Diffuse - transient adhesions are less stable but allow movement.
Clustered - high density resulting in strong attachments

84
Q

Discuss structure of CAMs and how their link to internal cytoskeletal filaments

A

CAMs are transmembrane Proteins. Link to internal cytoskeleton filaments via linker proteins or intracellular adaptor proteins. Mechanical continuity is present.

85
Q

What are the four types of junctions for cell adhesions and their main functions

A

Anchoring - adhesion/mechanical integrity of tissue
Occluding - seals spaces between cells and segregates regions of plasma membrane
Channel forming - two way communication between adjacent cells allowing small molecules to pass
Signal relaying - one way communication e.g. synapses

86
Q

Link between tissue formation and CAMs

A

Cells with differing expressions of the same CAM will separate forming tissue with high expression in middle and low expression of outside, or reverse.
Cells with different CAMs will separate forming different tissues.

87
Q

Which cytoskeleton element do desmosomes and adherents junctions link to.

A

Desmosomes - intermediate filaments

Adherents junctions - actin filaments

88
Q

Discuss process of cell crawling

A

Actin polymerisation at cell front forms cell protrusions called lamellipods. Lamellipods adhere to substratum moving cell forward. Actin-myosin contractions retract the cell at the rear. Cycles of protrusions and retractions result in cell crawling.

89
Q

How are lamellipods continuously reformed with discussion of actin polymerisation.

A

Actin monomers readily available at rear of front of cell. Actin polymerisation proteins e.g. Arp2/3 proteins

90
Q

Give examples of key signalling protein in actin organisation and what they do

A

Rho - stimulates bundling of F actin to form stress fibres
Rac - lamellipod formation
Cdc42 - formation of narrow F actin forming filopodia

MCB (13 decks)

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