3.1

cells utilize 3 basic methods of communication

1. contact dependent

2. local chemicals (paracrine)

3. long distance signaling

gap junctions

• protein channels that connect adjacent cells

• small molecules can pass directly from cell to cell

• good for fast, unregulated communication

receptor

protein that recognizes a specific signaling molecule and sends some signal within cell to change behavior

local communication involved the

diffusion of chemical signals

the endocrine and nervous system carry out

long distance communication

endocrine

chemical

• hormones travel through blood

nervous

electrical + chemical

• action potentials (electrical nerve impulses) and neurotransmitters (signaling molecules)

signaling involved

generation, reception, transduction, and response

signaling generation

another cell, self, environmental stimulation

signal reception

cytoplasmic or membrane receptor

changes in cell signaling component

direct effect or signal transduction

response

changes to protein activity and/or abundance

hydrophobic signals through membrane

• membrane permeable (direct diffusion)

• cytoplasmic or nuclear receptors often directly regulate DNA

• ex: steroids like testosterone and estrogen

hydrophillic signals through membrane

• membrane impermeable (can’t directly cross membrane)

• membrane receptors

• signal ‘transduced’ into cell

• ex: proteins

agonist

mimics signaling molecule

• activates receptor/pathway

antagonist

blocks receptor

• inhibits receptor/pathway

signaling transduction

internal amplification

• enzyme mediated

  • phosphorylation cascade, one enzyme activates the next

• small molecule-mediated

  • second messenger- signaling molecule that is created and has effects inside of cell

first messenger

extracellular signal molecule

second messengers

• activated intracellular molecules

• ions (Ca2+), nucleotides (cAMP), lipid-derived (IP3), gases (NO)

• often produced by enzymes activated by receptor

Response depends on

signals, receptors, response molecules

response alters protein

abundance (nuclear) and activity (cytoplasmic)

mechanisms of signal termination

1. destroy signal

2. remove signal

3. remove receptor

destroy signal

enzymes break down signal

remove signal

re-uptake transporters bring signals back inside cells

remove receptor

endocytosis of receptor prevents cell from responding to further signals

the action potential

the electrical signal that is sent along a neurons axon. it can also be called a nerve impulse or the neuron “firing”

wire

charged particles move along a wire over time

axon

charged particles enter and leave axon and that event (action potential) moves along the axon over time

neuron at rest (not signaling)

• inside of cell is negatively charged

• resting charge and concentration gradients maintained by sodium - potassium pump

voltage gated sodium channels: self perpetuating wave generators

• negative charge inside cells keep channel closed

• positive charge inside cells makes channel open

  • opening one channel activates its neighbors

sequential activation of sodium channels moves

action potential down axon

slow opening voltage gated potassium channels make inside

negative again, preparing for next action potential

the axon hillock

where action potentials starts, where the axon attached to the cell body

• the first area that contains voltage gated channels

• if the cell receives enough excitatory signals through its dendrites, it will activate the channels and fire an action potential

information is usually encoded in the

frequency of action potentials and the number of neurons activated

pathogens are

agents that cause disease

• viruses, bacterial pathogens, eukaryotic pathogens

antigens

the adaptive immune system recognizes specific pathogens by recognizing organic molecules specific to that pathogen (usually proteins or sugars)

antibodies

proteins produced by B cells which recognize antigens

antibodies either

1. surround pathogens, making it difficult for them to attach to surface or invade cells

2. antibodies also help endocytic cells recognize and consume pathogens

B cells emerge from

bone marrow with different and random antibodies that recognize different potential antigens

signaling with T helper cells allows for immune response

• contact dependent antigen presentation activates T helper cells

• T helper cells release signaling molecules that further activate B cells

• these signaling molecules are responsible for symptoms of inflammation, including fever and fatigue