Week 8 - Cytoskeleton Flashcards
What are the three roles of a cytoskeleton
Cell shape
Cell strength
Movement
What are the three types of cytoskeleton filament
Actin filaments
Microtubules
Intermediate filaments
What is the role of actin
Cell surface shape, whole cell locomotion and pinching one cell into two
What is the role of microtubules
Position of organelles, intracellular transport and motitic spindle
What is the role of intermediate filaments
Mechanical strength
How does each filament get utilised in the small intestine
Actin - enables microvilli formation and connects to cell junctions
Intermediate - anchors across cell to provide structure and strength via desmosomes
Microtubules - run from basal to apical surfaces providing transport network
What are filaments held together by and why are they strong
Non covalent interactions which when multiple filaments join together are very strong collectively
Describe how actin forms
G actin monomers polymerise to form 2 protofilaments which twist to form F actin which is in a helix shape
Describe F actin structure
Large clefts which bind to ATP and all G actin faces same way to make it polar
Describe nucleation
The first step in formation of a new structure via self assembly
What is the critical condition of actin determined by
Rate of addition of G actin (K on) and rate of dissociation of G actin (K off)
Describe how G actin associates and dissociates
If [G actin]> critical condition then G actin added
If [G actin]< critical condition then G actin dissociated
Define treadmilling
Where subunits are added at + end and removed from - end yet the length remains constant
Explain how Microtubules are formed
Polymerisation of tubulin heterodimers to form subunits which form protofilaments. 13 protofilaments form a hollow cylinder with a central lumen
Explain how Microtubules are polar
Alpha tubulin at the - end and beta tubulin at the + end creates polarity
Why are Microtubules unstable
Dissociation of tubulin GDP is favourable at the plus end, so it tends to grow a cap and shrink.
Minus end is stable at the MTOC
What is the MTOC
The centrosome
What are two distinct features of centrosomes
A pair of centrioles and pericentriolar material (protein matrix)
What is the site of nucleation for Microtubules
Gamma tubulin ring complex found on the pericentriolar material
What are the two associated motor proteins for microtubules
Kinesin and dynein
What does kinesin do
Moves towards the + end of the Microtubules (anterograde = away from centre)
What does dynein do
Move towards the - end of the Microtubule (retrograde = towards centre)
Describe intermediate filaments
Great tensile strength, non polar and no associated motors
Give an example of intermediate filaments in a cell
Nuclear laminar
Name the 4 types of tissue
Epithelial
Muscle
Nervous
Connective
What are the three types of cell junction
Anchoring junction
Occluding junction
Communicating junction
Describe anchoring junctions
Anchor cytoskeleton between cells or between cells and Extracellular matrix
Describe occluding junctions
Prevents passage of ions and small molecules between cells
Describe communicating junctions
Direct connections between cytoplasm of two cells
Anchoring junctions: what do adherens junctions do
Connects actin filament of one cell with actin filament of another cell
Anchoring junctions: What do desmosomes do
Connects intermediate filaments from one cell to intermediate filaments of another cell
Anchoring junctions: What do Actin linked cell matrix (FA) junctions do
Anchors actin filaments in cell to extracellular matrix
Anchoring junctions: what do hemidesmosome do
Anchors intermediate filaments in a cell to the extracellular matrix
What do gap junctions do
Allow passage of small water soluble molecules between cells
What is the name for the transmembrane protein responsible for cell cell attachment in anchoring junctions
Cadherins
What is the name for the transmembrane protein responsible for cell matrix attachment
Integrins
What is the term for when Cadherins bind to the same type of cadherin
Homophilic adhesion (different type is heterophilic adhesion)
What is cadherin binding dependant on
Extracellular Ca2+
What is the extracellular matrix
Network of proteins carbohydrates and water which provide support for cells and tissues and secreted by fibroblasts
Hat are the three types of macromolecule in the ECM
Glycosaminoglycans
Fibrous proteins
Glycoproteins
