Modification of Cell Surface/ Cell Communication

Mader 5.4

Learning Objectives:

Learning Objectives:LO 3.34 The student is able to construct explanations of cellcommunication through cell-to-cell direct contact or throughchemical signaling. [See SP 6.2]LO 3.35 The student is able to create representation(s) that depicthow cell-to-cell communication occurs by direct contact or froma distance through chemical signaling. [See SP 1.1]

Learning Objectives:LO 3.36 The student is able to describe a model that expresses thekey elements of signal transduction pathways by which a signal isconverted to a cellular response. [See SP 1.5]

Essential knowledge 3.D.2: Cells communicate with each other throughdirect contact with other cells or from a distance via chemical signaling.

a. Cells communicate by cell-to-cell contact.• Plasmodesmata between plant cells that allow material to betransported from cell to cell.

b. Cells communicate over short distances by using local regulatorsthat target cells in the vicinity of the emitting cell.• Neurotransmitters• Plant immune response• Quorum sensing in bacteria• Morphogens in embryonic development

c. Signals released by one cell type can travel long distances to targetcells of another cell type.

Essential knowledge 3.D.3: Signal transduction pathways link signalreception with cellular response.a. Signaling begins with the recognition of a chemical messenger, aligand, by a receptor protein.Evidence of student learning is a demonstrated understanding of eachof the following:1. Different receptors recognize different chemical messengers,which can be peptides, small chemicals or proteins, in a specificone-to-one relationship.2. A receptor protein recognizes signal molecules, causing thereceptor protein’s shape to change, which initiates transductionof the signal.To foster student understanding of this concept, instructors canchoose an illustrative example such as:• G-protein linked receptors• Ligand-gated ion channels• Receptor tyrosine kinases

b. Signal transduction is the process by which a signal is converted to acellular response.Evidence of student learning is a demonstrated understanding of eachof the following:1. Signaling cascades relay signals from receptors on cell targets,often amplifying the incoming signals, with the result ofappropriate responses by the cell.2. Second messengers are often essential to the function of thecascade.To foster student understanding of this concept, instructors canchoose an illustrative example such as:• Ligand-gated ion channels• Second messengers, such as cyclic GMP, cyclic AMPcalcium ions (Ca2+), and inositol triphosphate (IP3)3. Many signal transduction pathways include:i. Protein modifications (an illustrative example could be howmethylation changes the signaling process)ii. Phosphorylation cascades in which a series of proteinkinases add a phosphate group to the next protein in thecascade sequence

Cell Surfaces in Plants and Animals

• The extracellular matrix of animal cells are more complex than the cell surfaces of plants or other sessile organisms with cell walls

Fibroblasts creating an extracellular matrix for the purposes of healing a wound

Plant cell separated by a cell wall constructed of cellulose

Extracellular Matrix• The extracellular matrix of various

tissues varies between being quite flexible, as in cartilage, and being rock solid as in bone

Animal Cell Extracellular Matrix

•Created by the cells it surrounds•Made from polysaccharides and structural proteins•Gives tissue strength and elasticity•Polysaccharides and proteoglycans work with the proteins in the cell membrane to allow for rapid diffusion of nutrients and hormones

How do hormones(ligands) act on target cells• Lipid-based hormones– hydrophobic & lipid-soluble• diffuse across cell membrane & enter cells• bind to receptor proteins in cytoplasm & nucleus• bind to DNA as transcription factors

– turn on genes

• Protein-based hormones– hydrophilic & not lipid soluble• can’t diffuse across cell membrane• bind to receptor proteins in cell membrane• trigger secondary messenger pathway• activate internal cellular response

– enzyme action, uptake or secretion of molecules…

nucleus

target cell

DNA mRN

A protein

blood

proteincarrier

S

S

S

S

Action of lipid (steroid) hormones

binds to receptor protein

cytoplasm

becomes transcription factor

ex: secreted protein = growth factor (hair, bone, muscle, gametes)

2

4

6

cross cell membrane

1

steroid hormone

mRNA read by ribosome

5

plasma membrane

protein secreted

7

3

Action of protein hormones

activatesenzyme

activatesenzyme

activates enzyme

ATP

produces an action

P1

2

3

cytoplasm

receptor protein

response

signal

secondarymessengersystem

signal-transduction pathway

acts as 2° messenger

target cell

plasma membrane

binds to receptor protein

proteinhormone

ATPactivatescytoplasmicsignal

cAMP

GTP

activatesG-protein

transduction

adrenal glandEx: Action of epinephrine (adrenaline)

activatesprotein kinase-A

activatesglycogen phosphorylase

activates adenylyl cyclase

epinephrine

liver cell

releasedto blood

1

25

receptorproteinin cell membrane

cytoplasm

6glycogen

activatesphosphorylase kinase

GTP

cAMP4

activatesG protein

ATP

glucose

activates GTP

3

signal

transduction

response7

GDP

Benefits of a 2° messenger system

Amplification!

signal

receptor proteinActivated adenylyl cyclase

amplification

amplification

amplification

amplification

GTP G protein

product

enzyme

protein kinase

cAMP

Not yetactivated

1

2

4

35

6

7

FAST response!

amplification

Cascade multiplier!

Junctions Between Cells• Depending upon the function of tissue, the

cells that make up that tissue will be connected to each other in various manners

JunctionsAnchoring Junctions-Skin, Heart, Stomach, and Bladder where tissue gets stretchedTight Junctions-Intestines, Kidneys, and the blood brain barrierGap Junctions-Smooth muscle where ions need to flow between cells to coordinate activity

Junctions Between Animal Cells

Junctions Between Plant Cells