MCB9 - Cell Shape, Behaviour and Adhesion Flashcards
What processes is a cells cytoskeleton involved with
Contraction Motility Shape Vesicular transport Adhesion
Define polymerisation
Linking of individual monomer subunits to form an elongated multi-molecular chain or filament
What are the two types of adhesions found in cells.
Cell-cell adhesions and cell-extracellular matrix adhesions.
What causes filaments of the cytoskeleton to assemble and disassemble
External and internal stimuli
Why is the cytoskeleton described as dynamic
Protein polymers are constantly assembled and dissembled in accordance to varying stimuli
What are the three components of the cytoskeleton
Intermediate filaments
Microtubules
Microfilaments
Give example of stimulus that has an effect on cytoskeletal structure
E.g cell division stimulus has effect on microtubules
Describe mechanical strength of microtubules
Readily bend but break under minimal force
Describe mechanical strength of microfilaments
Cannot be deformed and break only with moderate strength
Describe mechanical strength of intermediate filaments
Can be readily deformed and resist great forces.
Define tensile strength
Amount of force required to break something upon stretching
What is a protofilament
Linear string of protein subunits bonded together
Why are multiple protofilaments stronger than a single protofilament
Single protofilament requires only one bond to be broken whereas multiple protofilaments require multiple bonds to be broken
What physical property do lateral bonds provide in cytoskeletal elements
Lateral bonds provide rope like properties ensuring that the protofilament is strong and resistant to tensile strength
How can the mechanical strength of the three cytoskeletal elements be determined.
Mechanical deformation of the cytoskeletal elements with the physical properties observed.
Discuss polarity in cytoskeletal filaments.
Results in + and - end of the cytoskeletal filaments. Due to the differences in amino acids that constitute the protein make up.
Discuss shape of monosubunit in comparison to same subunit in polymer.
Shape becomes slightly altered to aid conformation of the polymer.
Discuss rate of subunit addition at the + and - end.
Minus end has slow rate of subunit addition.
Positive end has fast rate of subunit addition.
Which nucleotide binding is most stable.
Triphosphate filament subunit binding is more stable than diphosphate filament subunit binding.
Which nucleotide subunit binds to microtubules
GTP
Which nucleotide subunit binds to microfilaments
ATP
Which nucleotide subunit binds to intermediate filaments
None
How do diphosphate nucleotide subunits form triphosphate nucleotide subunits on binding to cytoskeletal elements
Diphosphate is exchanged for triphosphate. It is not phosphorylated.
Which cytoskeletal filaments have polarity
Microtubules and microfilaments ONLY
What monomer makes up microtubules
Heterodimers of alpha and beta tubulin
What monomer makes up microfilaments
Globular actin
What monomer makes up intermediate filaments
Varies with type of intermediate filaments (based on location and function)
What are the three movement types of cytoskeleton filaments
Shrinking
Elongating
Treadmills got
Discuss shrinking in context of dynamics of cytoskeleton.
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.
Discuss elongation in context of cytoskeleton dynamics.
Rate of addition of subunits is greater at one end meaning overall effect is addition of subunits resulting in elongation.
Discuss treadmilling in context of cytoskeletal dynamics
Rate of addition at one end is equal to rate of loss at other end resulting in treadmilling effect.
When does polymerisation remain at a steady rate in cytoskeletal elements
When addition of subunit s is equal to subtraction of subunits
Define critical concentration for cytoskeletal polymerisation
Local concentration of subunits which maintains the length of the polymer. Can be different for + and - end
How can the speed of polymerisation be enhanced.
When seed is present giving the polymerisation a starting point. No lag phase is observed.
Discuss rate of cytoskeletal polymerisation when no seeds are present.
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.
Give one function of microtubules
To act as tracks for molecular motor proteins e.g. dynein , to carry cargo such as transport vesicles around the cell.
How many protofilaments are present in the cross section of a microtubules
13
Which subunit of microtubules is associated with its respective nucleotide.
Both alpha and beta monomers of tubulin bind to GTP however only beta GTP is hydrolysed to GDP
What cap is present on microtubules
GTP or GDP cap where GTP is more stable than GDP
What factors affect stability of microtubules
Microtubule binding proteins, signalling events, local environment influences
Where do microtubules originate from and describe its structure.
Originate at centrosomes made from 2 centrioles. Centrioles are cylindrical structure made from microtubules triplets.
Describe the centrosome matrix and its relation to microtubules
Centrosome matrix surrounds microtubules and it contains lambda tubulin complexes which have the ability to behave as seed sites
Define and discuss MTOC
Microtubules organising centre e.g. the centrosome, which allows microtubules to radiate out from
Define dynein and its role.
Molecular motor protein aiding connection between microtubules and dynastic complex for vesicular transport
What are the two microtubules motor proteins and their differences
Dynein - moves cargo from + to - I.e. from periphery to centre
Kinesins - moves cargo from - to + I.e. from centre to periphery
Discuss structure of cilia and flagella
Microtubule core with 9+2 arrangement (axenome)
Differences between cilia and flagella
Cilia - numerous in number and on cell surface.
Flagella - fewer but have longer protrusions on cell surface
Discuss the role of linking proteins associated with microtubules
Linking proteins bind two microtubules together which aid Bending and prevent sliding
Link between cell division and microtubules
Microtubules form mitotic spindle which originate from centrosomes. This is vital for chromosome separation
What are the three types of microtubules that exist during cell division
Astral microtubules. Kinetochore microbuulues. Inter polar microtubules
What are astral microtubules and describe their structure
Microtubules that radiate from centrosome to cell periphery
What are kinetochore microtubules and discuss their structure
Microtubules that span from the centrosome to the sister chromatids in the middle, connected at the kinetochore.
What are interpolar microtubules and discuss their structure
Microtubules that span from one centrosome to the other, without passing the sister chromatids.
Describe structure of intermediate filaments
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.
What is a desmosome and it’s purpose
Junction at cell periphery which connect intermediate filaments between adjacent cells.
What are Hemidesmosomes and how are they different to desmosomes.
Hemidesmosomes are junctions between cell base and extracellular matrix.
Give example of defective intermediate filament and what disease it causes.
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
What is the link between intermediate filaments and cancer.
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
Where in the cell, do cytokeratins terminate
Desmosomes - cell cell junctions
What is the nuclear lamina
Mesh work of lamin intermediate filaments on the internal surface of the inner nuclear membrane of the nuclear envelope
Discuss the role nuclear lamina play in mitosis
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.
How many isoforms of actin exist
6 isoforms
Discuss the role of Arp2/3 in actin polymerisation.
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
What is the role of formin in actin polymerisation.
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
Give types of actin binding proteins in actin polymerisation
Capping protein Severing protein Bundling protein Branching protein Cross linking protein Contraction producing protein Stabilising protein
What is the role of capping proteins in polymerisation
Add a cap to the end of actin polymers preventing addition or removal of subunits at either end
How do severing proteins work in actin polymerisation
Bind to middle of actin filaments causing them to break
What is the role of branching proteins in actin polymerisation
Allows actinpolymers to grow as branches off of an existing actin polymer
What occurs if cells lack filamins
Formation of balloon like membrane features known as blebs
What occurs when cells express filamins
Formation of lamellipods which aid cell motility
What is the role of filamins
Cross linking of actin filament to form an actin mesh
What are myosin
Family of motor proteins that work with actin microfilaments to aid cell crawling or contraction
Why are skeletal muscle fibres multinucleate
As they contain more than one nucleus
Discuss actin myosin movements in muscle contraction.
Myosin head binds, pulls and releases actin filaments in continuous cycle which results in muscle contraction.
When does cell adhesion become switched on
Early in embryonic development - 16 cell stage
Define tissues.
Groups of cells whose type, organisation and architecture are integral to function. Continues the cells, EXM and tissu fluid
Define ECM and what it consists of
Material deposited by cells forming the extracellular insoluble region. Consist of fibrillation proteins (collagens and elastics) and hydrated gel e.g. proteoglycans
What are the differences between cells and connective tissue in their adhesions
Cells have cell-cell adhesions and cell-matrix adhesions.
Connective tissue have only cell-matrix adhesions
What are the three principles of cell adhesion
Different requirements for adhesion.
Adjustment occurs by cells.
Signalling in cells can be triggered.
Give example of when cells adjust their adhesions and explain why is it necessary.
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.
What are the two types of cell cell adhesions and describe what they are
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
Are cell-matrix adhesions homophobic or heterophilic
Heterophilic
Discuss differences between diffuse and clustered cell adhesions
Diffuse - transient adhesions are less stable but allow movement.
Clustered - high density resulting in strong attachments
Discuss structure of CAMs and how their link to internal cytoskeletal filaments
CAMs are transmembrane Proteins. Link to internal cytoskeleton filaments via linker proteins or intracellular adaptor proteins. Mechanical continuity is present.
What are the four types of junctions for cell adhesions and their main functions
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
Link between tissue formation and CAMs
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.
Which cytoskeleton element do desmosomes and adherents junctions link to.
Desmosomes - intermediate filaments
Adherents junctions - actin filaments
Discuss process of cell crawling
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.
How are lamellipods continuously reformed with discussion of actin polymerisation.
Actin monomers readily available at rear of front of cell. Actin polymerisation proteins e.g. Arp2/3 proteins
Give examples of key signalling protein in actin organisation and what they do
Rho - stimulates bundling of F actin to form stress fibres
Rac - lamellipod formation
Cdc42 - formation of narrow F actin forming filopodia
