Biology, Ch 11

cell to cell communication is essential for

multicellular and unicellular organisms

fight or flight response is triggered by

epinephrine

the concentration of signaling molecules allowed bacteria to sense

local population density

cells in multicellular organisms communicate by

chemical messengers

animal and plant cells have cell junctions that directly connect the

cytoplasm of adjacent cells

in local signaling, animal cells may communicate by

direct contact, or cell to cell recognition

in long distance signaling, plants and animals use chemicals called

hormones

ability of a cell to respond to a signal depends on whether or not it has a

receptor for that signal

a cell secretes a molecule that binds back onto its own receptor

autocrine

local mediators

paracrine

nerve cell signal transmission (neurotransmitters released into synaptic cleft)

synaptic

long acting, wide spread (hormones secreted into the bloodstream)

endocrine

this person discovered how the hormone epinephrine acts on cells

earl w. sutherland

a signaling molecule binds to a receptor protein causing it to change shape

reception

the binding between a signal molecule, the ligand and

receptor is highly specific

a shape change in a receptor is often the

initial transduction of signal

most receptors are

plasma membrane proteins

cascades of molecular interactions relay signals from receptors to target molecules in the cell

transduction

signal transduction

involves multiple steps

multistep pathways can

amplify a signal

multistep pathways provide more opportunities for

coordination and regulation of response

transfer phosphates from ATP to protein

protein kinases

protein kinases transfer phosphates from ATP to protein, a process called phosphorylation

protein kinases

removes phosphates from proteins

protein phosphatases

protein phosphatases remove the phosphates from proteins

dephosphorylation

these systems acts a molecular off and on switches

phosphorylation, dephosphorylation

which enzyme activates proteins by adding a phosphate

kinase

which enzyme deactivates proteins by removing a phosphate

phosphatase

what molecules can freely pass through the membrane

hydrophobic

which type of ligand would bind to a receptor in inside the cell

lipid soluble

which type of ligand would bind to a receptor in the plasma membrane

water soluble

what kind of molecule is a steroid?

lipid

steroid hormones would bind to

intracellular receptors

trimeric GTP binding protein

G proteins

g proteins are either in the

active or inactive state

active state has GTP

bound

when the ligand binds the G-protein coupled receptor, this causes a change in shape that

activates the G protein

activating the g protein starts a chain of events that involve intracellular mediators

secondary messengers

water soluble signal molecules that span the plasma membrane and bind to specific sites

cell surface receptors

3 main types of membrane bound receptors

G protein coupled receptors

receptor tyrosine kinases

ion channel receptors

alpha helixes make up this level of protein structure

2

the largest family of cell surface receptors

g protein coupled receptors

a GPCR is a plasma membrane receptor that works with the help of a

peripheral G protein

A or B

B

G proteins are composed of three proteins

a, b and y subunits

the a subunit goes one way and the b and y go together another way

when the G protein is activated

b and y are active when they are not

attached to the a subunit

the a subunit has

GTPase activity

the G proteins is active when it has

GTP bounded

will automatically hydrolize a phosphate and have GDP bound

GTPase activity

GTPase activity is enhanced by

GTPase activating proteins

when the G protein binds to the GPCR, the alpha subunit ejects

GDP and accepts GTP

alpha detaches from beta/gamma subunits

they are now active

the G protein self hydrolyses a

phosphate, forming GDP

alpha will reform with beta/gamma subunits

they are inactive

the extracellular ligand that binds to the receptor is a pathways

first messenger

small, nonprotein, water soluble molecules or ions that spread throughout the cell by diffusion

second messengers

second messengers participate in pathways initiated by

GPCRs and RTKs

common second messengers

cyclic AMP, calcium ions

one of the most widely used second messengers

cyclic AMP

an enzyme in the plasma membrane, converts ATP to cAMP in response to an extracellular signal

adenylyl cyclase

a ligand binds to the G-protein Coupled Receptor (GPCR)

cAMP pathway 1

the binding of the ligand (hormone) activates the GPCR

cAMP pathway 2

the active GPCR is able to bind to the G-protein

cAMP pathway 3

the G-protein enects a GDP and accepts a GTP molecule. the G-protein is now active

cAMP pathway 4

the a subunit of the G-protein with the GTP disassociates from the B and Y subunits

cAMP pathway 5

the a subunit of the G-protein with the GTP goes to the adenylyl cyclase and activates it

cAMP pathway 6

the active adenylyl cyclase transforms ATP into cAMP

cAMP pathway 7

cAMP activates a protein kinase A (PKA)

cAMP pathway 8

cAMP is inactivates by phosphodiesterases

cAMP pathway 9

the PKA phosphorylates proteins

cAMP pathway 10

the phosphorylated proteins are now active and can change the cell activity

cAMP pathway 11

the G-protein eith GTP bound will hydrolyse the phosphate from GTP. how has GDP bound and is inactive. it will reform with the B and Y subunits and this inactivates them

cAMP pathway 12

which enzyme activates proteins by adding a phosphate

kinase

which enzyme deactivates proteins by removing a phosphate

phosphatase

which enzyme produces cAMP

adenylyl cyclase

what does the alpha subunit of the g protein activate

adenylyl cyclase

which enzyme deactivates cAMP

phosphodiesterase

the cAMP pathway can also activate the

transcription of specific genes

the PKA activated by cAMP can turn on transcription of DNA using a

CRE binding protein

calcium ions act as a

second messenger

calcium is an important second messenger because cells can regulate

its concentration

how are G proteins activated

eject GDP accept GTP

how are the alpha subunits of the G proteins deactivated

dephosphorylate GTP

how are G proteins coupled receptors activated

ligand binds to G protein coupled receptor

phosphorylates tyrosine amino acids on signaling proteins

receptors tyrosine kinases

membrane receptors that attach phosphates to tyrosines

receptor tyrosine kinases

a receptor tyrosine kinase can trigger

multiple signal transduction pathways

abnormal functioning of these are associated with many types of cancers

RTKs

these receptors cross the plasma membrane once - single transmembrane proteins

RTKs

RTKs are… it takes two RTKs to function

dimers

binding of the ligand causes two RTKs to come together and link to form a dimer

dimerize

when two RTKs link together, they phosphorylate tyrosine residues on each other

autophosphorylation, requires ATP

two ligands binds to two RTKS

RTK/RAS/MAP pathway 1

the two RTK dimerize and phosphorylate each other, activating each other

RTK/RAS/MAP pathway 2

the active RTKs activate proteins by phosphorylating them, leading to cellular activity

RTK/RAS/MAP pathway 3

acts as a gate when the receptor changes shape

ligand gated ion channel

pecific ionswhen a signal molecule binds as a ligand to the receptor, the gate allows

through a channel

important in neuron signal transmission

ligand gated ion channel

lipid soluble and small signaling molecules bind to

receptors inside the cell