Cell Communication and Cell Signaling Why is cell signaling - - PowerPoint PPT Presentation

Cell Communication and Cell Signaling

Why is cell signaling important?

Why is cell signaling important?

• Allows cells to communicate and coordinate

functions/activities of the organism

• Usually involves the cell membrane

Cell Communication

• Communication involves transduction of

stimulatory or inhibitory signals from other cells, organisms or the environment

• Correct and appropriate signal transduction

pathways are generally under strong selective pressure

Single-Celled Organisms

• Signal transduction pathways influence how

the cell responds to its environment

• Example: quorum sensing in bacteria

Multicellular Organisms

• Signal transduction pathways coordinate the

activities within individual cells that support the function of the organism as a whole

• Example: Epinephrine stimulation of glycogen

breakdown in mammals

Cell Communication

Local Signaling

Long Distance Signaling

Cell Junctions Cell to Cell Contact Local Regulators

Hormones Neural Circuits

Local Signaling: Cell Junctions

• Plasmodesmata in plant cells and gap

junctions in animals

• Allows signaling molecules to pass readily

between adjacent cells

Local Signaling: Cell-to-Cell Contact

• Communication through direct interaction

between molecules extending from the surface of the cells (glycolipids and glycoproteins)

• Example: tissue development and immune

responses

Local Signaling: Local Regulators

• Local regulators are signaling molecules that
• nly target cells in the vicinity of the emitting

cell

• Examples: paracrine signaling and synaptic

signaling

Evolution: Paracrine Signaling

• Paracrine factors involved in differential development are

similar between different species

• Evidence of common ancestry, highly conserved in animals

from fruit flies to humans Receptor and Pathway Groups:

• Fibroblast Growth Factor Family (blood vessel, wound

healing, limb development, embryonic development)

• Hedgehog Family (embryonic development, bilateralism)
• Wnt Family (bone, heart, muscle, regeneration of tissue)
• TGF – β Family (immunity, cell proliferation)

Long Distance Signaling: Hormones

• Endocrine signals (hormones) produced by

endocrine cells travel long distances through the blood to reach all parts of the body

• Example: Insulin produced in pancreas,

targets liver cells

Plants Have Hormones!

• Ethylene – gaseous hormone that ripens fruit
• Auxin – chemical messenger that influences

fruit development and cell growth

Long Distance Signaling: Neural Circuits

• Neurons may transmit messages (nerve

impulses) over a long distance

Local or Long Distance - Cell Signaling Pathway is Similar Reception Transduction Response

Cell Signaling Pathway

Stage 1: Signal Reception

• Signaling begins with the recognition of a

chemical messenger (ligand) by a receptor protein

• Complementary shapes

Types of Receptor Proteins

• Transmembrane Proteins (within the cell

membrane) – also known as extracellular receptors

• G Protein-Coupled Receptors (GPCRs)
• Ligand-Gated Ion Channels
• Intracellular Receptors (within cytoplasm or

nucleus)

• Targeted by lipid soluble ligands (pass

through the plasma membrane)

Transmembrane Protein Receptors: GPCRs

Transmembrane Protein Receptors: Ligand-Gated Ion Channels

Intracellular Receptors

Receptor Proteins

• Different receptors recognize different

chemical messengers, which can be peptides, small chemicals, or proteins, in a specific one- to-one relationship

• A receptor protein recognizes signal

molecules, causing the receptor protein’s shape to change, which then initiates transduction of the signal

Review of Signal Reception

• What occurs during Stage 1: Signal

Reception?

• What is a ligand?
• What is the difference between

transmembrane protein receptors and intracellular receptors?

Stage 2: Signal Transduction

• Signal transduction is the process by which a

signal is converted to a cellular response

• One step or a series of many steps

Signal Transduction

• Signaling cascades relay signals from

receptors to cell targets, often amplifying the incoming signals

• Second messengers are often essential to the

function of the cascade cyclic AMP (cAMP) or calcium ions (Ca2+)

Signaling Cascade

• Protein kinases – turn “on” or activate

proteins by adding phosphates to the proteins (phosphorylation cascade)

• Protein phosphatases – turn “off” or

deactivate proteins and kinases by removing phosphates from the proteins (dephosphorylation)

Second Messengers

Review of Signal Transduction

• What occurs during Stage 2: Signal

Transduction?

• What is the function of a protein kinase?
• What is the function of a protein phosphatase?
• Identify a second messenger.

Stage 3: Cellular Response

• The signal transduction pathway initiates a

change in cellular activity

• Response occurs in the cytoplasm or nucleus

Response: Regulation of Protein Synthesis

• Most signaling pathways activate transcription

factors

• Transcription factors regulate cellular responses

by:

• Turning a gene “on”

Protein OR

• Turning a gene “off”

No protein OR

• Regulating the activity of a particular protein

Testosterone Cellular response increases gene activity for proteins involved in:

• Muscle mass
• Bone growth
• Body hair
• Reproductive tissue

Blood Glucose Regulation

Cell Signaling Summary