Foundations of Biology Chapter 9

Cell communication

The process through which cells can detect, interpret, and respond to signals in their environment

Signal

An agent that can influence the activities of a cell

Receptor

Cellular protein that can recognize a signaling molecule

Direct intracellular communication

Passage of signals between adjacent cells through gap junctions; involves diffusion

Contact dependent signaling

Membrane bound signals in one cell bind to membrane bound receptors on another cell's surface

EX) Notch signal pathway, quorum sensing

Autocrine signaling

Cell secretes signaling molecules that bind to receptors on its own surface and the surface of neighboring cells of the same type; density dependent

Paracrine signaling

Cell secretes signaling molecules that do not affect itself but influences the behavior of nearby target cells; short and localized signal

EX) Neurotransmitters

Endocrine signaling

Long distance signaling between cells via hormones which are long lasting

1. Receptor Activation

2. Signal Transduction

3. Cellular Response

Three stages of cell signalling (general)

Alter metabolism/cell function

Enzymes can elicit this cellular response

Alter cell shape/movement

Structural proteins can elicit this cellular response

Alters gene expression

Transcription factors can elicit this cellular response

Ligand

Signaling molecule which is specific to a receptor

Ligand receptor complex

Structure formed when the ligand and the receptor collide in the correct orientation and with enough energy

Dissociation constant (Kd)

The equilibrium constant between the ligand and the protein

High

Low Kd indicates a (high/low) affinity of a ligand for a receptor

Cell surface receptor

Receptor found in plasma membranes which enables a cell to respond to different kinds of signaling molecules

Enzyme linked receptor

Receptor found in all living species which has an extracellular domain to bind signaling molecules and an intracellular domain for catalytic function

EX) Protein kinases

G protein coupled receptor (GPCR)

Receptor found in eukaryotic cells that interact with G proteins

G protein

Intracellular protein that binds GTP and GDP to activate signalling pathways (lipid anchored protein)

Ligand gated ion channel

Cell receptor that binds ligands and functions as an ion channel; bind of the ligand opens or closes the channel

Receptor tyrosine kinases (RTKs)

Enzyme linked receptor found in all animals that attaches phosphate groups onto Tyr groups in receptor or other cellular proteins

Growth factor

A protein that stimulates cells to grow and divide

First messenger

Extracellular signaling molecule that binds to cell surface receptors

Second messenger

Small ion/molecule that relay signals inside the cell

cAMP

Small effector molecule that acts as a second messenger; generated from ATP

1. Amplification (many cAMP activated from one signal leads to phosphorylation of more target proteins)

2. Speed (second messengers diffuse rapidly through cytosol)

Two advantages to using second messengers in cell signaling

Differential gene regulation

Expression of genes differs under various environmental conditions and in specialized cell types

Apoptosis

Programmed cell death

1. Cell shrinks, nucleus condenses

2. Plasma membrane forms extensions (blebs)

3. Blebs break away and cell destroys self

Apoptosis steps (3)

Embryonic development, maintain proper cell #s, eliminates infected/tired cells

Roles of apoptosis (3)

Death receptor

Receptor in plasma membrane of eukaryotic cells that promotes apoptosis upon activation

Capase

Enzyme activated during apoptosis which digests proteins

Mitochondrial pathway

DNA damage causes mitochondria to release cytochrome C into cytosol which complexes with apoptosomes that activate capases to digest cell