Chapter 9: Cell Communication Flashcards
cells detect and respond to signals in the
extracellular environment
signals coordinate activities in a
multicellular organisms
when a signal binds to a receptor:
the conformation
leads to
the conformation of the receptor changes
this leads to a response inside the cell
apoptosis
(programmed cell death)
signals can even intentionally cause a cell to die
cells respond to a changing environment so when glucose is present yeast cells make
more glucose transporters to bring glucose into cell
cells communicate with
each other and the environment
phototropism in plants
environmental signal:
auxin
response
blue light
auxin (hormone, cellular signal) moves to shaded part of plant stem and causes cells in shaded side of stem to elongate
stem bends towards light
hi amounts of auxin on
shaded part
types of cell signaling are
direct intracellular
contact direct signaling
endocrine
paracrine
autocrine
the type of cell signaling is determined by
whether contact between cells occurs and if the signal molecule is a short or long distance signal
direct intracellular signaling
cell junctions allow signaling molecules to pass from one cell to another through gap junctions
example: Electrical signaling in cardiac muscle
contact dependent signaling
molecules bound to the surface of cells serve as signals to cells coming in contact with them
example: neutron growth in the brain and in the immune system, natural killer cells can distinguish between healthy self cells and foreign cells (pathogen) based on antigens on the cell surface
autocrine signaling
cells secrete signaling molecules that bind to their own cell surface and nearby cells (self)
regulates their own growth and also growth of neighboring cells
example: cell density limits cell growth (contact inhibition)- normal cells stop growing when they contact each other and form one orderly layer of cells but cancer cells don’t stop growing in contact and make unorganized clumps of cells, tumors
short distance signals
paracrine signaling
signal does not affect cell that produces it, but only affects neighboring cells
example: nuerotransmitter, signal from nerve cells and local mediators, growth factors
short distance signals
endocrine signaling
signals call hormones travel long distances and are usually longer lasting in effect
hormone travels through blood
long distance
only cells that have ___ can respond to the signal
correct receptor
target cells
cells that have a receptor for a signal/ hormone
the signal / hormone and its receptor have
complementary shapes (lock and key)
types of signal molecules
hormones: endocrine signal
local mediators: autocrine and paracrine
neurotransmitter: paracrine
hormones are secreted by
produced in
signal
endocrine cells into blood
one tissue, act in a different tissue
long distance
local mediators are secreted into
act on
signal
extracellular fluid
neighboring cells
short distance
neurotransmitters are released from
communication between
signal
nerve cells at synapse
nerve to nerve cell or nerve to muscle cell
short distance
when a signal molecule binds to its receptors it causes
different signal molecules have
signal binds to receptor->
a response in the target cell
different types of receptors
response
hydrophilic signal molecules are __ receptors
description
cell surface
can’t pass through pm
signal binding domain on exterior pm
most protein hormones (insulin)
neurotransmitters
local mediators
hydrophobic signal molecules are __ receptors
description
intracellular
passes through pm
enters the cell and binds to the receptor in cytoplasm / nucleus
most steroid hormones (estrogen, cortisol)
hydrophobic protein hormones
signal receptor complex moves into the nucleus where it acts as a transcription factor to turn genes on and off
types of receptors
found
catalytic receptors (receptor + enzyme)
ion channel receptors (receptor + ion channel)
G protein linked (3 part system)
found on the cell surface -> signal binds on external side of plasma membrane
catalytic receptors
function
receptors
enzyme
dual function
signal binding domain in external side pm
catalytic domain (tyrosine kinase activity) on cytoplasmic side of pm
catalytic receptor: EGF receptor
signal
activated receptor -> _=
EGF - epidermal growth factor
signal binding activates enzyme portion of receptor
activated receptor -> response=cell division
growth factors control
the cell cycle and cell division
ion channel linked receptors have ___ function and they are
dual
1) receptor: signal binding domain on external side of pm
2) ion channel: binding of signal controls opening of channel (ligand-gated ion channel)
when the signal binds to the receptor the ion channel __ and the __ __ the cell
opens
ions enter
Ion channel linked receptor: muscle contraction process
1) nerve cell releases neurotransmitters
2) acetylcholine (neurotransmitter) binds to its receptor on pm of muscle cell
3) acetylcholine receptor is a ligand gated ion channel. Binding of acetylcholine to receptor opens the ion channel
4) Na+ enters the muscle cell through the acetylcholine receptor
5) increase in Ana+ -» muscle contraction
Ion channel linked receptor: muscle contraction
Nerve cell releases __ and then they bind to its ___ and __ Na+ channel. __ enters the muscle cell -»> ___
neurotransmitters (acetylcholine)
receptor in muscle cell
opens
Na+
muscle contracts
G-protein linked receptors is a __ system and they are
3
1) receptor in pm (inactive-> active)
2) G protein in pm (inactive-> active)
3) target enzyme in pm (usually inactive-> active)
signal transduction pathway
signal
activates receptor
activates G protein
activates target enzyme (pm)
produce second messenger
target proteins (cytoplasm/nucleus)
response
Three stages of cell signaling are
receptor activation
signal transduction
cellular response
Receptor activation
signals
respond
signaling molecule binds to receptor
signal=1* messenger=ligand
cell can respond to signal only if it has a receptor
cell signaling pathway
signal-> receptor-> 2nd messenger-> response-> enzyme activation, changes in gene expression
signal transduction
activated receptor stimulates a sequence of changes- a signal transduction pathway
signal binds to receptor usually on external side of pm
signal transmitted from pm to interior of cell (activate/inactive cytoplasmic enzymes, may involve a phosphorylation cascade, turn on/off genes
involves second messengers and they turn on and off key enzymes: cAMP, Ca++, calmodulin, IP3, DAG
result is cellular response to a signal
fast cell signaling
slow
activation or inactivation of existing enzymes
synthesis of new enzymes
enzymes are regulated by
phosphorylation and dephoshorylation
kinase: adds a phosphate to a protein
phosphatase: removes a phosphate from a protein
cycles of +P/-P regulates enzyme activity
phosphorylation
changes the shape of an enzyme
some enzymes are activated and others are inactivated when phosphorylated
amplification of the signals
1 hormone activates 1 receptor
1 receptor activates many G proteins
1 G protein activates 1 target enzyme
1 target enzyme produces 1000s cAMP
1 cAMP activates 1 protein kinase A
1 protein kinase A activated 1000 enzymes
result -l1 hormone molecules produces very large response in cell
a signal may produce…
why?
different responses in different cell types
signal binds to receptor and the receptor activation will have different effects depending on which target enzymes are expressed in a cell type
signal producing different responses example of epinephrine
glycogen breakdown in muscle, liver
Fatty acid production in adipose
increased heart rate, blood pressure in cardiovascular system
increase breathing rate
fight or flight response
when an animal is in dance what happens
make as much atp as possible (use stored energy for muscle contraction
increase blood flow to heat and muscles, increase circulation to extremities, widen air ways, increase breathing rate
Reduce blood flow to skin, kidneys and digestive system to allow most of blood to crucial organs
apoptosis
controlled cell death
kill old damaged or disease cells
remove webbing between toes and fingers
prune neurons as infant brain matures
if cells that should die by apoptosis live too long->
cancer
types of cell death
necrosis- occurs after sever tissue injury (swelling and rupture of cells)
apoptosis- controlled cell death (series of events that leads to dismantling of cell contents. Must kill cell but need to prevent the release of digestive enzymes that would damage adjacent cells)
why would you use apoptosis?
To kill a specific cell that may have damaged dna for example
Steps in apoptosis
1) chromosomes condense and accumulate near edge of nucleus
2) volume of cytoplasm decreases
3) cell produces blobs
4) nucleus and organelles fragment
5) DNA cut into small pieces by apoptosis specific DNAase
6) accumulation of certain lipids in outer leaflet of pm= eat me signal or phagocytic cells
7) cell fragments into apoptotic bodies
final stage of apoptosis
cell fragments are destroyed by a phagocytic white blood cell
Triggers of apoptosis
Cell death signals (cascade 3= executioner caspace, triggers apoptosis)
withdrawal of survival factors (mitochondria) (survival factor= anti apoptosic proteins)
release of cytochrome c from mitochondria
extensive dna damage
Cancer normal growth
balance between cell division and apoptosis (death of damaged cells)
Cancer
Uncontrolled cell growth
increase cell division (presence of oncogene)
prevent apoptosis (absence of a tumor suppressor gene)
Causes of cancer
cells with damaged /mutated dna keep dividing
- under express genes for apoptosis / prevent cell division
- over express genes that trigger cell division
- under express genes for dna repair
different cancers have different
chromosomal abnormalities
Prostate cancer cells
Many tetraploid chromosomes
chromosome 8
chromosome 2: TRPM8
HeLa cell karyotype
from cervical cancer
usually 82 chromosomes
