cell movement Flashcards
what is cell motility
the ability of a cell to move
it can either be swimming (free moving through something) or crawling (bound to something and moving across it)
what are the 3 things needed for cell motility
an energy source
guidance
mechanical interaction with things outside the cell
what is the structure of microtubules
hollow tubes made up of alpha and beta tubulin protein subunits
they are made up of 13 protofilaments consisting of alternating tubulin dimers
the contain cilia to move cargo
what is the structure of an axoneme
has a 9+2 microtubule assembly (9 outer doublets or pairs and 2 inner singular microtubules)
radical spokes connect the inner pair and 9 outer doublets
dynein arms are used for movement
why is the axoneme polar
on one side of the molecule dynein arms join adjacent microtubules and on the other side they don’t
this allows only one side to change shape
how do dynein arms create movement in the axoneme
dynein allows the joined microtubules to slide past each other which causes the axoneme to bend
microtubules are anchored to the axoneme by cross-links so it will move like a wave
how do nexin crosslinkers prevent movement in the axoneme
forms cross-links between microtubules to prevent them sliding past each other
how does dynein affect the movement of cilia and flagella
if the inner arm is involved it will create a wave-like movement
if the outer arm is involved it will create a power-stroke movement
what are basal bodies and how are they structured
the point where the axoneme reaches the cell, they work with the centromere to control cell movement
they have a 9x3 microtubule arrangement (9 sets of 3 joined microtubules)
what is the extracellular matrix (ECM)
a meshwork of proteins and hydrated macromolecules
it is made up of collagen and elastic fibres for strength and structure, adhesion proteins such as laminin and sugars
what is the role of the ECM
it regulates migration, tissue integrity and cell shape, proliferation and differentiation
there are different types of specialised ECM such as hair, skin and bones
what is the structure and function of collagen in the ECM
provides a framework for cells
has a repetitive structure of 3 amino acids that forms long chains
3 long chains come together to form a triple helix
how is collagen synthesised
- the peptide chains are hydroxylated using ascorbic acid allowing cross-links to form between them
- collagen cables self-associate and are secreted by fibroblasts and epithelial cells to form a fibril
- the fibrils are bundled together to form collagen fibres
what is the structure and function of elastin in the ECM
made up of tropoelastin subunits that are cross-linked using lysyl oxidase to form elastin
the more they stretch they gain structure to provide uniform elasticity
what are glycoaminoglycans (GAG’s) in the ECM
disaccharide chains that are highly charged allowing them to hold water and interact with signalling molecules
what is the structure and function of laminin
a mat of ECM that makes up the edge of the skin
it will self-assemble and has binding sites for other ECM proteins
at the ends of laminin molecules there are integrin binding sites which allows cells to adhere to the ECM
what is the structure and function of fibronectin
a series of globular domains with a negatively charged loop where integrins can bind
it will self-assemble and has binding sites for other ECM proteins
it forms disulfide bonds to crosslink with itself
what are integrins in the ECM
they will bind to the ECM through divalent cations and form dimeric proteins with alpha and beta subunits
they have transmembrane protein domains to transmit signals across the cell membrane
what are focal adhesions in the ECM
protein complexes that form links between integrins and the actin cytoskeleton
what happens if integrins and focal adhesions have defects
integrin defects: cause problems with platelet adhesion in blood clotting and leukocyte adhesion in immune responses
focal adhesion defects: causes embryos to die
what are hyaluronan complexes in the ECM
they hold water in the body
consist of hyalauronic acid linked to proteoglycans and link proteins
what are adherens junctions
form a belt around cells to keep them anchored to the cytoskeleton
they are made up of epithelial cadherins which is linked to the actin cytoskeleton and link cells together
what are desmosomes and what do they do
adhering proteins that form cell-cell junctions by interacting with cadherins
they are very strong and can withstand high mechanical stress
what are hemidesmosomes
half desmosomes that attach cells to the basal lamina
they use integrins to link them to the ECM
what is the basal lamina
a thin layer of ECM that separates cells from connective tissue
it maintains tissue structure and repair
what is pemphigus disease
an immune disease that causes the skin’s integrity to degrade
the body attacks a cadherin called desmoglein that holds together keratinocytes in the skin
what are tight junctions
join cells together and prevent movement of water and ions
made up of claudin and occludin proteins
they are used for trans and paracellular transport
they can be fully or semi permeable
what is the structure of tight junctions
made up of lots of layers in case one layer is damaged
strands of occludin and claudin proteins form ridges in the membrane
there are different types of claudins which give different properties
what are gap junctions
cluster together between cells to form small passages between cell membranes for communication
they allow movement of small molecules such as water, sugars, ions, ATP and amino acids
what is the structure of gap junctions
connexin proteins form channels in gap junctions
they can be arranged as homomeric (same types) or heteromeric (different types to create different channels)
what are selectins
adhesion proteins that are expressed when blood vessels are damaged
they bind to sugars on the surface of white blood cells and cause them to form cell-cell junctions to repair the damage
what are the 4 components of actin
filopodium, lamellipodium, stress fibres and cortical actin
what is the process of actin-based motility
- cytokine provides direction for actin movement, it stimulates formation of the filopodium for movement
- lamellipodium allows the cell to move forwards
- adhesion allows the cell to grab onto something
- stress fibres pull the cell body towards it
what is actin turnover
ability to polymerise on one end and repolymerise on the other end
what are the differences and similarities between microtubules and actin fibres
both are polarised and have a plus and minus end
both are fast-growing at the plus end which makes it more stable
actin has ATP and microtubules have GTP
actin is solid and microtubules are hollow
microtubules are longer than actin
