Module 5: Cell Communication

why do cells communicate

there are a lot of them and they all need to communicate to stay health with eachother and their environment. Both single and multicellular organisms need to do this

how concentration of cells in bacteria affect chemical signals

the more cells the stronger the chemical signal

quorum sensing

chemical signal conccentrations allow bacteria to monitor local cell density

what happens when threshold(max) levels of signaling are reached

the bacteria responds by:

• the formation of fruiting bodies/spores (thick walls that allow bacteria to survive low nutrient conditions)

• formation of biofilms (large sheets of films of bacteria, form when there are a lot of nutrients)

• secretion of toxins (some signals are a danger sign, so toxins form to protect themselves)

direct cell comunication

• junctions

• cell-to-cell connections

indirect cell communication

the cell sending the signal will create a signaling molecule and that then travels to the target or recieving cell

paracrine signaling

local (target/signaling cell are close together)

synaptic signaling

local (specific to neurons, when the signaling molecules reaches the end a neuro transmitter is released)

endocrine signaling

long distance (hormones travel through bloodstream to get to target)

step 1 cell signaling

Reception: target cell detects/recieves signal

step 2 cell signaling

transduction: message is relayed into the cell. The connection between the signal/response. often a series of steps

step 3 cell signaling

response: target cell changes behavior based on signal

where r signal receptors found

• in the cytoplasm/nucleus (few)

• In the membrane (most)

ligand

a molecule that binds to another molecule. Receptors bind to this

where r intracellular receptors located

cytoplasm/nucleus of target cell

characteristics of ligand binding to intracellular receptor

the ligand has to be able to pass through the membrane to reach the receptor so they have to be:

• hydrophobic

• steroid hormones

• thyroid hormones

• small (nitric oxide)

Intracellular Aldosterone Signaling

1) Aldosterone secreted by adrenal glands on kidneys

2) circulates / enters cells throughout body using endocrine signaling

3) aldosterone binds to receptors in the cytoplasm of the kidney

4) Complex travels into the nucleus

5) Causes cell to make a protein it wasn’t before leading to

• change in water/Na+ balance in Kidneys

• blood volume change

cell surface receptors

1) ion channel receptors

2) g protein coupled receptors

3) receptor tyrosine kinases

ligand gated ion channells

span the entire membrane from top to bottom

• Ligand binds and channel opens

• ions will pass through down the concentration gradient triggering a cell response

GTP

when a protein is attached to this it acts as an on switch

GDP

when a protein is attached to this it acts as an off switch

G protein coupled receptors (on/off switch)

most proteins are off and turn on for a signal, when there is a signal the GDP get taken off and the cell brings in a molecule of GTP turning the protein on, triggering a response. When the signal ends GTP converts to GDP, by 1 phosphate being removed

steps of g protein coupled receptor

1) ligand bings to GPCR and activates it

2) G protein is activated and is able to touch the GPCR, which makes the change from GDP to GTP

3) The g protein will then detach from the GPCR and attach to an enzyme

4) The g protein is then inactivated (looses P)

phosphorylation

adds phosphates to molecules

dephosphorylation

removes a phosphate to form a protein

protein kinases

add phosphates to molecules

protein phosphotases

removes a phosphate to turn off a protein

Receptor tyrosine kinases

1) ligand binds to two RTK subunits in the membrane (when they are seperate = inactive)

2) RTK subunits dimerize and become active

3) RTK phosphyroylates itself on tyrosine

4) Since RTK are kkinases they can attach proteins, so when they become active they start phsophorylating themselves, they add the phosphate groups on the amino acid tyrosine (using 6 ATP)

5) other signaling proteins bind to the phosphorylated RTK leading to cell responses

signal transduction

1) the signal is transmitted across the membrane

2) the first protein activates the second protein in the strucutre, the second protein activates the 3rd protein

3) this continues until the cell activates the protein that will screate a cellular response which is why this is often referred to as a reaction cascade

second messsenger

how information is transmitted within the cell, either produced or released from storage with the presence of the first messenger

first messenger

extracellular signal

examples of 2nd messenger

cAMP, IP3, calcium ions

signal amplification

taking a weak signal and increasing the strength of the cellular response

pathway branches

2 different responses

cross talk

occurs between 2 pathways

saturation

how many of the receptors are bound to ligand

specificity

receptors and ligands mush have matching shapes in order to bind to eachother

competition

similarly shaped molecules can compete for binding to the same receptor

primary ligand

leads to a base level of signaling

agonist

leads to increased level of signaling (epinephrine)

antagonist

blocks signaling (antihistamines)

scaffolding proteins

can serve as anchoring points for enzymes involved in successive steps in a chemical reaction (a signaling complex). this can assist with rapid signal transduction

apoptosis

programmed cell death and is controlled by mutliple signaling pathways, they shrink, condense and then collapse, the plasma membrane blebs, and remnants are eliminated through phagocytosis, it is important in development

ced-4 and ced-3

pro apotosis proteins

what inhibits ced 4 activity

ced-9

biological process behind apoptosis

ced-4 and ced-3 are pro apotosis proteins, when they are activated they activate other proteases and nucleases which kill DNA/RNA which lead to apoptosis, Ced-9 inhibits Ced-4 activity, the signaling molecule deactivated ced-9 so ced-4 can work