cytoskeleton, centrioles and cell junctions Flashcards
1
Q
which cells have a well developed cytoskeleton
A
- polarised cells
- mechanically challenged cells: adhesion
- mobile cells
2
Q
functions of the cytoskeleton
A
- to spatially organise the intracellular components
- determine cell shape
- maintain molecular architecture
- provide mechanical strength and resistance
- generate cell movement
- structural/mechanical, architectural, transport
3
Q
where is the cytoskeleton
A
extends from the cell nucleus to cell membrane (or vice versa)
4
Q
elements of cytoskeleton
A
- 3 types of filaments
- derived from assembly of different classes of proteins
- 2.5 nm: microtubules
- 10nm: intermediate filaments
- 6nm: actin filaments
5
Q
microtubules
A
- hollow cylinders
- tubulin dimers polymerise to form filament, 19 filaments form a tube (alpha and beta)
- polarised
- dynamic
- minus end: alpha-tubulin dimer: toward nucleation site
- plus end: growing end to which GTP-bound dimers are incorporates
6
Q
MTOC
A
- microtubule-organising center
- centriole/centrosome
- structure from which microtubules emerge
- 2 nine sets of microtubule triplets arranged in cylinders perpendicular to each other
- microtubule nucleation is unfavorable in normal conditions
- y-tubulin ring complex provides stable binding sites for tubulin dimers
7
Q
three microtubule localisations in the cell
A
- cell in interphase: spread out from a peri-nuclear position and connected to organelles
- in cell division: in spindle-like transient structures
- ciliated cell: in bundles as permanent structures
8
Q
microtubule functions
A
- intracellular vesicular transport: guide for movements of molecular motors:
- kinesins move toward plus end from cell centre to periphery
- dyneins move toward minus end to MTOC
- maintenance of cell shape and polarity
-selective stabilisation of microtubules determines cell polarity - allocation and movement of intracellular organelles
- organelles tend to be aligned along microtubules
- e.g. mitochondria maintained during muscle contraction - attachment of chromosomes to the mitotic spindle and their movement during division
- movement of cilia and flagella
- 9 couples to 2 by linkers
- axonemal dyneins: binding proteins: drive the sliding of one microtubule against another and the bending of the flagella
- flagella: connection proteins
9
Q
intermediate filaments
A
- non-polarised,no energy is required for assembly
- heterogenous: based on different protein isoforms varying in tissues: diff can be in same cell: essential proteins: pathology: mutations lead to disease
- formation: central rod shaped helix domains with highly variable globular domains at ends- head: N terminal, tail: C-terminal- 2 attach and coil then interact with other coils: coiled coil dimers - different filaments interact
10
Q
desmin
A
- muscle-specific protein and a key subunit of the intermediate filament in cardiac, skeletal and smooth muscles
- dystrophy: coils aggregate instead of forming filaments due to mutation from alanine to proline
11
Q
lamins
A
- intermediate filaments also present in nuclear envelope
- lamins form a meshwork: nuclear lamina beneath inner face of envelope
- expressed in all cells
12
Q
intermediate filament functions(2)
A
- holding and supporting organelles at intracellular level
- cell attachment and support at tissue level
13
Q
six classes of tissue-specific intermediate filaments
A
- based on protein sequence: based on structural similarities
1-2.: acidic and basic keratins
3. protein: vimentin,desmin (glial fibrillary acid,peripherin)
4. neurofilaments
5. lamins
6. beaded filaments (phankinin and filensin) - protein specific to some tissues: tumour recognition
13
Q
microfilaments
A
- actin filaments expressed by every cell
- polymerisation of globular actin molecules (G-actin) to form filamentous actin (F-actin)
- depends on G-actin concentration and actin-binding proteins
- requires K+, Mg2+ and ATP
- two F actins form a filament
- growing end: plus end: actin bound to ATP
- minus end: actin bound to ADP
14
Q
actin filament organisation
A
- depends on interacting proteins
- bundling proteins: create actin filament bundles
- filament-severing proteins: cut long filament in short filament
- capping proteins: block further addition of G-actin
- corss-linking proteins: cross-link actin filament to each other
- motor proteins: move along actin filament
