bio ch 9

autocrine signaling

a cell signal released from the cell binds to the same cell/targets itself

signaling across gap junctions

signaling molecules released by the cell affect target cells that are connected by gap junctions

- found in animal cells and in plasmodesmata in plant cells

paracrine signaling

signaling molecules released by the cell only affect target cells that are nearby

endocrine signaling

cell signals are hormones (must travel in the blood stream) that are released into the blood stream and act on targeted cells that are distant/close to the cell

receptors

protein molecules in the target cell or on its surface that bind ligand/signal

• two types: internal receptors and cell-surface receptors

internal receptors

located inside the cytoplasm of the cell and respond to signals that can pass through the cell membrane, like LIPID hormones

• directly affect/act on gene expression without having to pass the signal on to other receptors or messengers, altering protein synthesis

cell surface receptors

located on the cell membrane; respond to PROTEIN signals/ligands that cannot pass through the membrane, such as neurotransmitters or growth factors.

• initiate signal transduction pathways, leading to cellular responses

types:

• ion channel, G protein, enzyme linked

ion channel receptor

protein ligand binds to channel and opens it to let in a specific ion

g-protein receptor

protein ligand binds to receptor causes GTP to displace GDP or GMP

enzyme-linked receptor

protein ligand binding to receptor contains amino acids like TYR adding Phosphates which triggers response inside

hydrophobic signal

its receptors would be found inside the cell

• example of them would be steroids or lipid based

hydrophilic signal

receptors are found outside of the cell membrane

• example of them are peptides or proteins

signal transduction

getting message from outside to inside

when a signal/ligand binds to a receptor and the signal is transmitted through the cell membrane and into the cytoplasm continuing the signal

(when extracellular messengers bind to the cell surface receptors)

• The physical or chemical signal is then transmitted through the rest of the cell as a series of molecular events

phosphorylation

attaching Phosphates to molecules

• is added to nucleotides like GMP

• are added to residues of amino acids like serine, threonine, and tyrosine

second messenger

when an activated membrane receptor removes 2 phosphate groups from ATP into cAMP “cyclic AMP” inside the cell, which activates proteins within the cell.

• are critical since the 1st messenger (a protein or peptide) can’t get through the membrane.

• cAMp, DAG, & IP3

signal pathways

everything that happens on the inside after transduction

chain of events including second messengers, enzymes, and activated proteins that follow signal binding to a receptor

• then produces a signal to cause a response in the cell

gene expression

activating a particular gene in the DNA of the nucleus to create a response (turning on a gene)

cellular metabolism

after a receptor is activated a second messenger is activated (cAMP, DAG, or IP3) which can cause an increase of metabolism in a cell

• leads to a ready supply of glucose

cell growth

growth factors bind to tyrosine kinases and initiate a pathway

• tyrosine kinase is also involved in cell growth, wound healing, and tissue repair

apoptosis

initiated (programmed) cell death (a good thing!)

• assists in development and the maintenance of a healthy organism by regulating cell numbers, sculpting areas of tissue, deleting structures, and getting rid of cells that are too damaged to be repaired

• process occurs when the cell signals are terminated by degrading ligands and or other types of signals

• Without this, poorly mutated cells would cause the organism to not be the best fit for the environment and the species

signal termination

mark the end of a gene transcript and determine which DNA sequences are expressed in the cell

• signals the end of a transcription or translation

• Important so the signal pathway does not continue longer than needed

signal initiation

helps coordinate functions and interactions involving receptors that bridge the cellular membrane

signal integration

activation of 2 different cell surface receptors that work together/merge to activate/enhance the same output response

yeast signaling

• these cells communicate by releasing a signaling molecule called mating factor.

• The mating factor binds cell-surface receptors in nearby yeast cells.

• They stop their normal growth cycles and initiates cell signaling that includes protein kinases and GTP-binding

Bacteria signaling

• uses molecules called autoinducers for signaling in signal cell organisms.

• Population is often the key factor for signaling

  • When cell density is low, autoinducers diffuse away from the cell

  • when density is high, more autoinducers are present