Chapter 11.1 Cell Communication

Cellular InternetCell to cell communication is essential in

order for organisms to coordinate activities that develop, survive and reproduce

Cell communication between cells is also important and more complicated in unicellular organisms

Biologists have discovered some universal mechanisms of cell regulation and these same small set of cell signals appear repeatedly

- evidence of evolutionary relatedness of all life

Signal ConversionWhat kind of cell conversation do you think would

be most prevalent?Sex – is the answer – reproduction- Chemical signaling of yeast in the attraction

of a cells and alpha cellsSignal transduction pathway – process of

converting a signal on a cell’s surface into a specific response in a series of steps

-striking similarities between way yeast cells and animal cells communicate- suggests same signals used today evolved before multi-cellular organisms existed

Yeast Cell Communication

Local SignalingCell have different ways of communicating

messagesa. Direct contact – cell junctions connect cytoplasms of adjacent cells-signaling substances dissolved in the cytosol pass freely in adjacent cells-possible in plant and animal cellsb. Cell-Cell recognition – communication between membrane bound surface molecules(remember glycoproteins & glycolipids)-important for embryonic development & immune response

Local and Long DistanceLocal regulators – influence cells

by secreting messenger molecules to target cells

- known as Paracrine signaling- Ex: growth factors targeting numerous cells to grow and multiply- Synaptic signaling – electrical signal between nerve cells is converted to chemical signal

or neurotransmitter, that travels across the synapse to next nerve cell or target nerve cell pathway

Long Distance SignalingHormones – chemical messengers that are

released by specialized cells into vessels or glands to target cells in other parts of the body.

- vary in size and typeEx: ethylene in plants causes

ripening – only 6 atoms (C2H4)Insulin – regulates sugar levels in

blood- protein of thousands of atoms

Stages of Cell Signaling1. Reception – target cell’s detection of a signal molecule

from outside the cell- usually involves binding of a receptor protein on the surface or within cell

2. Transduction – signal molecule changes receptor protein to initiate phase.

-converts signal to form that will evoke a cellular response- may occur as a single step, but most often is a

series of relay molecules3. Response – signal triggers a cellular response

Chapter 11.2 ReceptionMost signal receptors are plasma membrane

proteinsReceptor proteins in or on the target cell all

it to hear the signal and respond to itLigand – refers to a molecule specifically

binding to another molecule-ligand binding usually causes a receptor

protein to change in shape -signal molecule fits like a key in a lock

and allows activation and interaction with other molecules leading to signal transduction

Membrane ReceptorsG protein linked receptors – extremely widespread

and diverse in function such as embryonic development and sensory reception

Examples are yeast mating factors, neurotransmitters, hormones, and epinephrine

Diseases such as cholera, pertussis, and botulism make victims sick by producing toxins that block G protein function

- G protein acts as a molecular switch on or off to trigger certain cellular responses

- Enzyme attachment to G protein is temporary allowing rapid shutdown to pathway

G Protein Receptor

Membrane ReceptorsReceptor tyrosine kinases – help cell regulate and

coordinate many aspects of cell growth & reproductionCan trigger more than one signal transduction pathway

( up to 10) from single ligand eventKinase is an enzyme that catalyzes the transfer of

phosphate groups (ATP to tyrosine)- two receptor tyrosine kinases exist close to one

another- signal molecule binding cause association of

receptors (forming a dimer)- each tyrosine kinase adds a phosphate from ATP to

activate receptor protein- activated proteins attract relay proteins that trigger

transduction pathways that lead to cellular response

Tyrosine Kinase

Membrane ReceptorsIon channel receptors – signal

molecule (ligand) has specific shape that allows binding with receptor channel

-binding on extracellular side allows the opening of the channel to certain ions

- ions flow in or out cause rapid change in concentration to exert cellular response

- ligand dissociates from receptor cause gate or channel to close

*Ex: neurotransmitter signals between neurons

Intracellular ReceptorsTypically found in the cytoplasm or the

nucleus of a cellHydrophobic nature or small size allows the

movement of these receptors into the cellEx: steroids – travel through the blood

entering cells all over the body. - target cells only contain receptor

molecule for that steroid in the cytoplasm, - binding occurs, then activation, in which receptor molecule enters nucleus to turn

on specific genes (transcription factors)

Intercellular receptors