bio unit 4

Cell communication

the process by which cells send and receive signals

Direct contact signaling

communication through physical cell-to-cell contact

Gap junctions

direct cytoplasmic connections between animal cells

Plasmodesmata

direct cytoplasmic connections between plant cells

Chemical signaling

communication using secreted molecules

Paracrine signaling

short-distance local signaling

Synaptic signaling

neurotransmitters crossing a synapse (short distance)

Endocrine signaling

long-distance signaling using hormones in bloodstream

Hormones

long-distance chemical messengers

Exocytosis

process that releases chemical signals from a cell

Signal synthesis

occurs in the ER or cytoplasm

Signal processing

occurs in the Golgi apparatus

Reception

ligand binds to receptor

Steroid hormone receptor location

inside the cell

Protein hormone receptor location

on the cell membrane

Receptor location difference

steroids can cross membranes; proteins cannot

Cell specificity

only cells with the correct receptor respond to a signal

Signal transduction pathway

the process of converting a signal into a response

Reception (definition)

ligand binds to receptor protein

Transduction

converting the signal to a cascade inside the cell

Response

the final cellular action produced

Phosphorylation cascade

chain of kinases activating each other

Kinase

enzyme that adds phosphate groups

Phosphatase

enzyme that removes phosphate groups

Protein modification

phosphorylation or conformational shape changes

Cellular response example 1

enzyme activation

Cellular response example 2

gene expression change

Cellular response example 3

secretion of a molecule

Why different cells respond differently

different receptors or proteins inside

Ligand

signaling molecule that binds a receptor

Receptor

protein that detects the ligand

Ligand-binding domain

part of receptor where ligand attaches

GPCR

receptor that activates a G-protein when ligand binds

GPCR after binding

G-protein swaps GDP for GTP and activates another enzyme

Tyrosine kinase receptor

forms a dimer and autophosphorylates

Ion channel receptor

opens channel for ions when ligand binds

Signal amplification

one ligand produces many activated molecules

Transduction initiation

receptor changes shape after ligand binds

Second messenger

small molecule that amplifies the signal

cAMP

common second messenger

Calcium ions (Ca²⁺)

second messenger used in muscle and nerve signaling

Second messenger function

relays and amplifies signals inside the cell

Ligand-gated ion channel response

ions flow in and change cell activity

Environmental stimulus

external factor that triggers a response

Environmental response example 1

bacteria moving toward nutrients

Environmental response example 2

plants bending toward light

Apoptosis

programmed cell death

Reason for apoptosis

removes damaged or unnecessary cells

Transcription factor

protein that turns genes on or off

How TF changes gene expression

binds DNA and alters transcription

Signal changes phenotype

by altering gene expression

Mutation in receptor

ligand cannot bind → no response

Effect of receptor mutation

signal pathway does not activate

Mutation in transduction protein

signal cannot be passed along

Effect of transduction mutation

reduced or no cellular response

Chemical pathway interference

may activate or block signaling

Chemical activator example

caffeine increases cAMP

Chemical inhibitor example

antihistamines block histamine receptors