BIO - Cell Communication

1. coordinate activities

2. respond to environmental signals

3. maintain homeostatis

Cell communication allows cells to c_______ a_______, r_______ t_ e_______ s______, and m_______ h________

intracellular signaling

cell communication that occurs within the cell

Phosphorylation

most common chemical modification that takes place during intracellular signaling

intercellular signalling

communication that exists between cells

ligands

Cell releases signaling molecules called ______ into the extracellular matrix, carry the message and diffuse in the extracellular matrix towards the target cell

1. gap junctions or neurotransmitters

2. paracrine

3. autocrine

4. endocrine

communication in intracellular signalling via g__ j_____ or n_____________, p________, a________, e______

1. localized

2. local or systemic

Range of Effect
1. Intracellular Signalling
2. Intercellular Signalling

1. second mesengers, kinases, phosphatases

2. hormones, cytokines, neutotransmitters, direct cell contact

Signal Molecules
1. Intracellular Signalling (sm,k,p)
2. Intercellular Signalling (h,c,n,dcc)

Intracellular Signalling

Signal that affects processes like gene expression and metabolism and involves signal transduction pathways inside the cell

Intercellular signalling

coordinates cell function across tissues or organ and involves chemical or physical signals between vells

Autocrine

• cell releases signaling molecules that act back on the same cell

• Often involves growth factors, cytokines, and hormones

Juxtacrine

cells exchange signals through direct physical contact, without the need for the release of signaling molecules into the extracellular space

Tight junctions

• Specialized connections between two adjacent cells that form a seal at the cell membrane, preventing substances from leaking between the cells

• claudins, Occludins, Junctional Adhesion Molecules

Adherent junction

• cell–cell adhesion structures that connect one cell to another through cadherin proteins linked to actin filaments of the cytoskeleton.

• Cadherins (calcium-dependent adhesion molecules) and linked to actin filaments via catenins.

Desmosomes

• spot welds

• hold adjacent cells tightly together, especially in tissues that experience mechanical stress

• • Desmogleins and Desmocollins, plakoglobin, and desmoplakin and intermediate filaments (keratin)

Hemidesmosome

• cell-to-extracellular matrix junctions that anchor epithelial cells to the basement membrane

• Found at the basal surface of epithelial cells

• anchors or nails that fasten a carpet

• integrins (α6β4)

• Collagen XVII (BP180)

• Plectin & BP230

Gap junctions

acts as a communicating channel that lets ions and small molecules pass directly between the cytoplasm of neighboring cells.

Paracrine

cell communication where signals act on nearby cells (short distance, local effect).

endocrine

• form of long-distance cell communication where specialized cells release signaling molecules (hormones) into the bloodstream

1. signal reception

2. signal transduction

3. cellular response

4. Termination

3 stages of Cell Signaling

Signal Reception

a signal (often in the form of a molecule, like a hormone or neurotransmitter) binds to a specific receptor on the surface of the target cell or inside the cell.

Signal Transduction

The signal converted, into a form that can bring about a specific cellular response.

Cellular response

• refers to the final action a cell takes after receiving and processing a signal

Termination

It ensures that the signaling pathway is properly regulated and does not lead to prolonged or inappropriate cellular responses

Signaling molecule

• hormone, neurotransmitter, growth factor

• can be hydrophobic or hydrophilic which may bind to surface or intracellular receptors

Membrane-bound receptors

found on the cell surface and are necessary for ligands that cannot cross the cell membrane

Intracellular receptors

found in the cytoplasm or nucleus and typically bind to small, hydrophobic ligands

Cell-surface receptors

￭ G-protein-coupled receptors: interact with G-proteins inside the cell.

￭ Tyrosine kinase receptors-important roles in regulating cell growth and differentiation.

￭ Ion channel receptors: crucial in nerve impulse transmission and muscle contraction.

G-protein-coupled receptors

interact with G-proteins inside the cell

Tyrosine kinase receptors

important roles in regulating cell growth and differentiation.

Ion channel receptors

crucial in nerve impulse transmission and muscle contraction

Intracellular receptors

moves into the nucleus and directlyinfluencesgeneexpression

Protein phosphorylation and dephosphorylation

process of adding or removing a phosphate group (usually from ATP) to a protein, typically at serine, threonine, or tyrosine residues.

Secondary messengers

small, non-protein molecules or ions that relay signals received by receptors to target molecules

Cyclic AMP

Generated from ATP by the enzyme adenylyl cyclase which activates protein kinase A (PKA)

Calcium ions

Released in response to signals like hormones or neurotransmitters

1. Inositol trisphosphate

2. diacylglycerol

1. helps release calcium from internal stores, while

2. activates protein kinase C (PKC), which phosphorylates other proteins.

Protein-protein interactions

involve two or more proteins binding together to transmit a signal, assemble complexes, or perform functions cooperatively within the cell.

Receptor-Ligand Interactions

Receptors on the cell membrane bind to specific ligands activating intracellular proteins through interaction

Scaffold Proteins

bind several other proteins to organize signaling complexes, enhancing signal specificity and efficiency

Adaptor Proteins

do not have enzymatic activity but facilitate the interaction between signaling proteins, like Grb2 in the Ras-MAPK pathway.