MCB 9: Cell shape, Behaviour and Adhesion (Part II) Flashcards
When does cell adhesion get switched on during embryonic development?
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What is a tissue?
- a tissue is a group or groups of cells whose type, organisation and architecture are integral to their function
- tissues are made up of cells, extracellular matrix and fluid
What is the extracellular matrix?
What are cell adhesion molecules (CAMs)?
- molecules that bind to other cells, or the extracellular matrix (ECM) to allow for the cells in a multicellular organism to interact with each other
Describe the types of cell adhesion and how this helps differentiate between epithelial cells and connective tissue cells
Epithelial cells:
- two types of adhesion:
- cell-cell adhesion
- cell-matrix adhesion: adhesion to the basal lamina
Connective tissue cells:
- cells are surrounded by matrix and not touching each other
- they will have adhesions with the matrix but don’t have any cell-cell adhesions
What are the three general principles of cell adhesion?
1. Cells have different adhesion requirements
- some cells form extensive adhesions with other cells to form coherent layers that act as barriers separating tissue compartments
- however, some connective tissue cells avoid contact with other cells and are fully surrounded by the matrix to which they adhere
2. Adhesion can be adjusted by the cell
- cell adhesion molecules can be activated/deactivated adn cells can change the amount and type of cell adhesion molecules at their cell surface
- this allows them to adapt to different situations
e. g. when an epithelium is damaged, the cells surrounding the area of damage loosen the cell-cell adhesions and begin to migrate and proliferate to fill the damaged area
3. Cell adhesion can trigger signalling in cells
- when cells adhere to each other, or to the extracellular matrix, biochemical signals can be initiated in the cell
- cells use this type of mechanism to adapt to their environment, and even direct their growth and differentiation
What are the two major classes of cell-cell adhesion?
- homophilic binding
- heterophilic binding
What is homophilic binding?
- homophilic adhesion is when adhesion molecules on one cell specifically bind to the same class of molecule on another cell
What is heterophilic binding?
- a specific interaction of different types of molecules on other cells
When would cell adhesion be transient and when would it be more organised and stable?
- sometimes adhesion needs to be short-lived
- e.g. when immune cells are migrating during inflammation or when cells are migrating to heal wounds
- the CAMs involved in transient cell-cell or cell-matrix adhesion may be diffuse on the cell surface or temporarily clustered
- when cells are part of a stable tissue structure, adhesion molecules can be clustered into organised adhesive junctions
What is the strength of individual cell adhesion molecule interactions?
What if they are clustered?
- individual cell adhesion molecule interactions are very weak
- but when clustered at high density, they add up to a strong attachment
- like velcro
Describe the general molecular behaviour of adhesion molecules with the help of the diagram
- most CAMs are transmembrane molecules so they have an extracellular part, transmembrane region and an intracellular part
- the diagram shows both cell-cell adhesions and cell-matrix adhesions which are both connected to the internal cytoskeleton
- molecules have linker proteins that attach them to different components of a cell cytoskeleton
- this allows mechanical continuity between extracellular adhesion and the interior of the cell
- mechanical continuity is a key to a number of processes
What are the four main types of junction and what are their main functions?
Anchoring Junctions:
- adhesion and mechanical integrity of tissues
Occluding Junctions:
- sealing the spaces between cells and segregating regions of the plasma membrane
Channel-forming junctions:
- allowing two-way communication between adjacent cells by allowing ions and small molecules to pass between cells
Signal-relaying junctions:
- one-way communication between neurones and their targets, the chemical synapse
Summarise the molecular composition of anchoring cell junctions
What does this diagram show?
What do these diagrams show?
Describe how cell adhesion molecules play a role in neural tube formation
Cell adhesion molecules span the plasma membrane and link directly to the cytoskeleton. True or false?
- False
- as adhesion molecules associate to the cytoskeleton via linker proteins
