cell communication- AP bio

cell communication is

crucial in reproduction

the yeast identifies its mates by

chemical signaling; two sexes: a and alpha (each type secretes a specific signaling molecule, a factor and alpha factor)

singnal transduction pathways

process by which a signal on a cell’s surface is converted into a specific cellular response in a series of steps

signaling molecules evolved first in

ancient prokaryotes and were then adopted for new uses by single celled eukaryotes and multicellular descendants

communication takes two

ligand and receptor

ligand

signaling molecule

ligand ex.

proteins, individual amino acids, steroids, ions

receptor

protein that detects specific ligands, lock and key type fit

the type of signaling a cell uses is

based on the distance between the cell it is trying to signal

4 main types of cell signaling

direct communication, paracrine signaling, endocrine signaling, synaptic signaling

autocrine signaling is another important signaling event

occurs when a cell signals itself, important in the immune system

direct contact

cells are touching, one cell can recognize the molecules on the adjacent cell; orchestrates early embryo development

ex of direct contact

plant cells: plasmodesmata; animal cells: gap junctions

paracrine signaling

ligands produced by cells can travel through extracellular fluid and be ready by other local cells; short lived molecules; short lived molecules

paracrine signaling two outcomes

read by another cell; degraded by enzymes

endocrine signaling

ligand released by a cell and makes its way to the circulatory system; can spread to the entire body; long lived molecules known as horomones; used extensively in plant and animals

synaptic signaling

rapid communication with distant cells using nerve cells long fiber like extensions; used by the nervous system

in synaptic signaling: ligands are called

neurotransmitters

chemical synpase

association of the neuron and its target cell

process of cell communication

1. ligand receptor binding

2. transduction: receptor sends signal throughout the cell

3. cell responds to the signal

stage 1 of cell communication: reception

a chemical signal binds to a cellular protein, typically at the cell’s surface

stage 2 of cell communication: transduction

binding leads to a charge in the receptor that triggers a series of changes along a single transduction pathway

stage 3 of cell communication: response

the transduced signal triggers a specific cellular activity

reception

occurs when a signal molecule (ligand) binds to a receptor protein

types of receptor proteins

plasma membrane receptor proteins, intracellular receptors proteins

binding of a signaling molecule (ligand) to its

specific receptor induces a conformational change

most ligands are

water soluble and large

by binding to receptor proteins on the plasma membrane

it influences cell activities

three major types of receptors

G-protein linked receptors, tyrosine kinase receptors, ion channel receptors

G protein linked receptor consists of

a receptor protein associated with a G protein on the cytoplasmic side; include: year mating factors, epinephrine, hormones, nuerotransmitters

G protein linked receptor has

seven alpha helices spanning the membrane

The G protein acts as an

on and off switch

if GDP is bound

the G protein is inactive

if GTP is bound

the G protein is active

The G protein can also act as a

GTpase enzyme and hydrolyzes the GTP which activated it to GDP; this change turns the G protein off; the whole system can shut down quickly when the extracellular signal molecule is no longer present

an individual tyrosine kinase receptor consists of several parts

an extracellular signal binding site, a single alphas helix spanning the membrane, and intracellular tail with several tyrosines

when ligands bind to

two receptor polypeptides a dimer is formed

the dimer add phosphates to the

tyrosine tails of the other polypetide, this activates a variety of relay proteins

more than one transduction pathway

can be triggered at once

ion channels (ligands gated ion channel)

protein pores that open or close in response to a chemical signal

ion channels allow or blocks

ion flow

binding by a ligand changes the

protein’s shape and opens the channel

ion flow changes the

concentration inside the cell

the ion channel closes

when the ligand dissociates

ligand gated ion channels are

very important in the nervous system

intracellular receptors bind

hydrophobic ligands

hydrophobic ligands can

easily cross the plasma membrane

main class of intracellular receptors are

nuclear receptors

testosterone like other hormones travels

through the blood and enters cells throughout the body

in the cytosol, hormones bind and

activate receptor proteins

the activated proteins by the hormones enter the

nucleus and turn on genes that control male characteristics

step 2: transduction

signal initiated by conformational change of receptor protein

when receptors are membrane proteins

the transduction stage is usually a multi step pathway

multistep pathways can

amplify a signal

at each step in transduction, the signal

is transduced into a different form; commonly a shape change in a protein

in transduction, change in shape of protein is brought by

phosphorylation

phosphorylation occurs

when a phosphate group is added

dephosphorylation occurs

when a phosphate group is removed

phophorlyation occurs when a

phosphate group is added

kinase proteins

enzyme that adds a phosphate to an amino acid

dephosphorylation occurs when a

phosphate group is removed

phophstases

enzyme that removes a phosphate group

in transduction, there are many signal pathways including

phosphorylation cascades

phosphorylation cascades

a process in which a series of protien kinases add a phosphate to the next one in line, activating it; phosphatase enzymes then remove the phosphates

in transduction, there are secondary messengers

small, nonprotein, water soluble molecules or ions that act as secondary messengers to carry the signal to the target (ex. cyclic AMP)

ligand would be the

primary messengers since they get the signal first

cyclic AMP is made from

ATP

a common secondary messenger is

cAMP

binding of the receptor activates a

G protein that activates adenyly cyclase in the plasma membrane

after the activation of adneylyl cyclase, the cAMP diffuses and

activates a theronine kinase, which phosphorylates other proteins

Ca ions can serve as

a messenger because the protein pumps usually keep it at lower concentrations in the cytosol than outside the cell

IP₃ is the ligands for a

gated calcium channel in the membrane of the ER (which stores Ca ions at high concentrations)

when IP3 binds to ER, Ca ions flows into the cytosol,

where it activates proteins of many signaling pathways

increasing cytosolic concentrations of Ca ions cause many responses in animal cells,

including muscle contraction, secretion of certain substances, and cell division

increasing cytosolic concentrations of Ca ion in plant cells,

it is involved in adaptive responses to environmental stresses, such as drought or cold

step 3: response

in response to a signal, a cell may regulate activities in the cytoplasm or transcription in the nucleus

ex of response

signaling pathways regulate enzyme activity and cytoskeleton rearrangement in the cytoplasm

in response, other pathways regulate genes

they do this by activating transcription factors, proteins that turn specific genes on or off

specificity of the signal

the same signal molecule can trigger different responses; many responses can come from one signal