Cell Communication

juxtacrine

direct contact

phagocytes

engulf foreign substances

cytotoxic T cels

bind to and lyse infected cells

B cells

produce specific antibodies to bind to antigens, marking pathogens for inactivation or destruction

Memory B cells

remember pathogens and secrete antibodies that bind to foreign antigen and disable it

paracrine

signaling molecules travel a short distance

growth factors

stimulate nearby cells to grow and divide

endocrine

long distance/hormonal signaling

animal endocrine signaling

Endocrine glands release hormones, which travel via circulatory system to target cells, which recognize and respond to hormones

plant endocrine signaling

Hormones travel vascular tissue (xylem & phloem) or through air as a gas (ethylene gas) 

intracellular receptors

found in cytoplasm or nucleus and for hydrophobic hormones or small gases. hormone binds to receptor, activating it and the hormone and receptor enter nucleus and act as a transcription factor by turning on specific genes

ligand-gated ion channels

Ligand binds to specific reception site on channel protein to open/close gate to allow/block diffusion of specific ions 

reception

1. Ligand binds to receptor at cell surface

2. Receptor changes shape

3. Receptor becomes activated and can now react with other molecules  

ligand

signaling molecules, such as a hormone

transduction

• Pathway of steps that converts a signal to a form that can bring about a response 

• Uses relay molecules (usually proteins) to transmit and amplify signal 

• second messages - cAMP and Ca2+

kinase

(phosphorylation) transfer P-groups from ATP to a protein

phosphatase

(dephosphorylation) remove P-groups from proteins

second messages

a step in transduction - cAMP and Ca2+

• Small nonprotein molecules or ions that broadcast signal into cytoplasm

• Amplification possible from step to step (i.e. many cAMPs formed at once)

• Relay molecules act to signal next molecule, until cell elicits response

response

• Turns genes on/off - transcription factors (proteins that may attach to a gene and prevent OR turn on transcription)

• Regulate activity of a protein: working faster or slower, open ion channel, change in cell metabolism, enzyme activation, rearrangement of cytoskeleton

negative feedback

if a system is perturbed, this feedback mechanism return system to target set point

positive feedback

mechanisms amplify responses/processes