Signal Transduction Ch. 11 videos 1&2

Cell signaling (multicellular)

• Cells require constant signaling from their environment, other cells, and their own interior

The diagram shows different examples of cells getting various combinations of signals, which enable them to perform specific functions.

1. Cell 1 is getting signals from signals A,B,C to tell it to survive

2. Cell 2 is getting signals from A, B, C AND D, E, which tells it to divide

3. Cell 3 is getting signals from A, B, C AND F, G telling it to mature

4. Cell 4 has no signals which means it should undergo apoptosis

unicellular cell communication

Single-celled organisms can communicate with each other

yeast cell communication

• They communicate by secreting soluble factors on each other. also known as mating factors

• The Saccharomyces cerevisiae yeast has two different factor types, the “a” type and the “α” type

• The “a” type and “α” type yeast can only mate with each other, so they send each other the mating factors, and can only bind to each other’s receptors 

Quorum sensing

• Prokaryotes, single-celled organisms, can use this to cell signal

• a form of bacterial communication where cells release signal molecules to sense their population density 

local signaling

whens cells communicate with nearby cells, or with cells in direct contact with them.

Direct contact local signaling

Gap junctions in animal cells, plasmodesmata in plant cells, and Transmembrane proteins for cell-to-cell recognition all allow for direct local signaling

Plasmodesmata

channels in land plant and algal cell walls that connect the cytoplasm of neighboring cells, allowing for direct transport and communication of molecules like sugars, ions, proteins, and RNA

gap junctions

Protein channels in animal cells that connect the cytoplasm of adjacent cells, allowing direct passage of ions, small metabolites, and signaling molecules without entering the extracellular space

cell-to-cell interactions: Transmembrane proteins

Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane

Non direct contact local signaling

paracrine signaling and Autocrine signaling

paracrine signaling

• Animal cells may use secreted messenger molecules (molecules travel short distances) to communicate with the target cell

• The target cell must have a specific receptor for that messenger molecule 

synaptic signaling

a specific type of paracrine signaling. An axon will extend to target cell, and release neurotransmitters.

Autocrine signaling

the secreting cell will send a signal, and it binds back on itself on its own receptor

long distance signaling

endocrine signaling

endocrine signaling

the secreting cell will send signals into the blood stream and travel down the blood vessel to the target cell

signaling molecules

can be either polar or nonpolar. 

• Nonpolar molecules easily travel through the plasma membrane. The signal molecule will enter the target cell and bind to a receptor inside the target cell. when the receptor binds to the signal, the receptor will go through a. conformational change (steroids are generally non-polar, e.g., cortisol)

• polar signal molecules will find their receptor embedded in the plasma membrane (polypeptides and amino acids generally polar, e.g., secretin and epinephrine, respectively)

ligand

signal molecule

4 main types of receptors

1. Intracellular receptors

2. ion channel receptors

3. G-protein-linked receptor

4. Protein kinase (enzyme-linked) receptors

Intracellular receptors

• located in the cytoplasm and nucleus

• binds to nonpolar signal molecules

• is often a transcription factor (After the ligand binds to the receptor, the receptor will go through a conformational change, which allows the ligand+receptor unit to change location, into the nucleus to aid in transcription)

Ion channel receptors

• transmembrane receptor

• When a ligand binds to the receptor, a conformational change causes the channel's "gate" to open, allowing specific ions (like Na⁺, K⁺, Ca²⁺, or Cl⁻) to flow across the cell membrane

• “ligand-gated ion channel” (the presence of a ligand determines if the channel is open or closed)

Neuron signaling is an example 

G- protein linked receptor

a receptor bound to a G protein

Protein kinase receptors

• kinase is an an enzyme that puts a phosphate group on something

• Upon binding to a ligand, the kinase receptor will transport phosphate groups to proteins

signal transduction pathway 

an external signal, such as a hormone or neurotransmitter, triggering a series of molecular events, that forms the cells response to the signal.

basically a ligand binds to surface receptor→intracellular events occurs→these events trigger the the cellular response