Signalling - gap junctions & autocrine Flashcards
How does direct cell signalling work?
Cells must be in direct contact. Surface proteins interact, allowing one-way or bidirectional signalling if both cells undergo changes.
What are gap junctions?
Protein channels that connect adjacent cells, allowing small molecules like ions, amino acids, and peptides to pass bidirectionally.
Why do epithelial cells have continuous direct signalling?
Because they are tightly packed and maintain constant contact.
How can researchers study gap junctions?
Using small fluorescent dyes like Lucifer Yellow, which can pass through and be observed.
What factors regulate gap junctions opening or closing?
Calcium (Ca²⁺) levels and pH influence the gating of gap junctions.
What is autocrine signalling?
A cell produces and responds to its own signalling molecules.
What determines whether molecules can pass through gap junctions?
Size and charge selectivity. For example, Lucifer Yellow (negative charge) can pass, while Ethidium Bromide (positive charge) has limited passage.
How do different connexins affect gap junction function?
There are 21 connexin genes, and different combinations influence selectivity for charge and molecule passage.
What proteins form gap junctions?
Connexins—each has four transmembrane domains and forms connexons, which align to create gap junctions.
What diseases are associated with gap junction loss?
Heart failure, cancer, neurological disorders, and skin conditions.
How are gap junctions regulated?
Through translation, post-translational modification, assembly, and internalization for degradation or recycling.
How can gap junctions impact cancer progression?
They may either promote tumour spread or suppress growth by facilitating apoptosis or immune evasion.
How does the loss of gap junctions cause congenital cataracts?
Mutations in connexin 46 and 50 impair nutrient transport in the lens, leading to clouding and vision loss.
How does autocrine signalling differ from paracrine signalling?
Paracrine signalling affects nearby cells, while autocrine signalling acts on the same cell that secretes the ligand.
What are the two feedback mechanisms in autocrine signalling?
Negative feedback: Ligand binding stops further ligand production.
Positive feedback: Ligand binding enhances more ligand production.
How does autocrine signalling contribute to immune responses?
Activated T cells release IL-2, which binds to their own receptors, driving further proliferation.
Give an example of physiological autocrine signalling.
Platelet-activating factors stimulate cell proliferation in an exponential manner.
How does pathological autocrine signalling promote cancer?
Cancer cells produce their own growth signals, bypassing normal regulatory controls and accelerating proliferation.
