Cell structure and tissues Flashcards
What are the interactions between cells in multicellular organisms?
• Cell adhesion molecules
• tight junctions
• desmosomes
• gap junctions
What are the interactions between cells and their surroundings in multicellular organisms?
• the basal lamina
• the extracellular matrix
What are the requirements in multicellular organisms for cells?
• to stick together and to the basal lamina or extracellular matrix
• to communicate with each other
• to co ordinate their activities
• to interact with other cell types
What are the requirements in multicellular organisms for epithelia and the typical junctions between epithelial cells?
• epithelia need to form impermeable barriers between body cavities eg gut lining, blood vessels
Junctions
- tight junctions
- gap junctions
- desmosomes
- adherens junctions
What is the function of Tight junctions?
seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them
What is the function of adherens junction
joins an actin bundle in one cell to a similar bundle in a neighbouring cell
What is the function of desmosome
joins the intermediate filaments in one cell to those in a neighbour
What is the function of gap junctions
forms channels that allow small water soluble molecules (including ions) to pass from cell to cell)
What is the function of emidesmosome
anchors intermediate filaments in a cell to the basal lamina
what are the properties of cell adhesion molecules?
• mosaics of multiple distinct domains
• clustered: cell junctions
• adhesions: strong and long lasting
• also present in immune system
How are integrins activated?
by binding to a molecule on either side of the membrane
What are the properties of tight junctions?
• intercellular adhesion complexes
- semipermeable
- size and charge selective
• control paracellular diffusion of ions and solutes
• border between the apical and basolateral domains of the plasma membrane
- establish and maintain compartments with different fluid compositions
What do adherens junctions do?
• connect bundles of actin and myosin filaments running parallel to plasma membrane
• allows contraction of epithelial layers
• play a role in formation of epithelial tubes
what type of junctions do cadherins and integrins contain?
• Cadherin: contains junctions connent cells to one another
• Integrins: contains junctions connect cells to the substratum
What do desmosomes do?
• join cells together
• connect the intermediate filaments running parallel networks of adjacent cells
• anchor cytoskeleton to plasma membrane
• connect cytoskeleton of surrounding cells giving strength
What do gap junctions do?
• pores connect adjoining cells to:
- allow ion movement between cells, chemical and electrical coupling between adjacent cqkles
- important for intercellular signalling
• allows co ordination of activities in a sheet of cells eg muscle contraction
• rapid transmission of nerve impulses bc it can pass directly through cells eg muscle
What is the basement membrane and what does it do? (basal lamina)
• thin dense layer of ECM
• forms supporting structure and scaffolding for epithelial tissue (composition varies)
• separates organs and tissues, maintains tissue structure and function
• functions
- structural support
- prevention if tumor invasion
- regulation of cell behaviour
The extracellular matrix is a fibrous network of proteins and polysaccharides that fills spaces between cells. what are these
• Glycosaminoglycans: form a hydrated gel like substance into which fibres are embedded
• when linked to proteins are then called proteoglycans
• fibrous proteins eg collagen for structural and fibronectin for adhesiveness
• Fibroblasts
- produces the components of ECM
- secreted into surrounding environment to assemble into final structure
• pre collagen
- does nor assemble, needs to be processed in the extra cellular space
What is the extracellular matrix (ECM)
• helps hold cells and tissues together
• plays active role in embryogenesis, wound healing and cell migration
How does collagen form a triple helix
• collagen fibrils form by lateral interactions of triple helices
• bundles of collagen fibrils run perpendicular to each other
• collagen orientation varies between the different tissues
How is the ECM extracellular matrix used in health and diseases?
• ECM interacts with cells to regulate gene expression
- impacts on drug metabolism resistance
- understanding such interactions can hep develop personalised med
• changes to ECM components associated with disease
• implication in tumour development- therapeutic target?
