Cell Communication Topics 4.1 through 4.2 Topic 4.1 Cell - - PowerPoint PPT Presentation

Cell Communication

Topics 4.1 through 4.2

Topic 4.1 Cell Communication

Importance of Cell Communication

• Cell signaling allows cells to communicate with
• ne another and coordinate the

functions/activities of the organism

• Communication pathways usually involve the

plasma membrane

Cell Communication

• Cells communicate with one another through

cell-to-cell contact or from a distance via chemical signaling

• Correct and appropriate signal transduction

pathways are generally under strong selective pressure

Single-Celled Organisms

(How Bacteria “Talk”, 18:14)

• In single-celled organisms, cell communication

pathways influence how the cell responds to its environment

• Example: quorum sensing in bacteria

Multicellular Organisms

• In multicellular organisms, cell communication

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

Cell-to-Cell Contact Chemical Signaling

Immune System Cells

Plasmodesmata

Local Regulators Hormones

Examples of Cell-to-Cell Contact

Plasmodesmata

• Microscopic channels which traverse the cell

walls of plant cells and some algal cells, enabling transport and communication between them

• Allow material to be transported from cell to

cell (proteins, ions, etc.)

Immune System Cells

• Some immune cells interact by cell-to-cell

contact

• Examples include antigen-presenting cells

(APCs), helper T-cells, and killer T-cells

What are antigens and antibodies?

• Antigen: any substance that causes the

immune system to produce antibodies (“antibody-generating”)

• Antibodies: Y-shaped proteins that are

produced by B cells, identify and neutralize pathogens (antigens)

How Antibodies Work

Immune Cell: Antigen-Presenting Cell

(Antigen Processing and Presentation Animation 2:30)

• Antigen-presenting cells process and present

antigens for recognition by certain lymphocytes such as T cells

• Examples of antigen-presenting cells include

macrophages, dendritic cells, and B cells

MHC Molecules

Immune Cell: Helper T

• Helper T cells are the most important cells in

adaptive immunity

• Three ways in which helper T cells “help” the

immune response:

– stimulate B cells to produce more antibodies to the specific antigen – activate and increase the number of macrophages – activate cytotoxic (killer) T cells to kill infected cells

Helper T Cells

Immune Cell: Cytotoxic (Killer) T

• Cytotoxic T cells target and destroy cells that

are infected with pathogens

Examples of Chemical Signaling

Local Regulators

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

emitting cell (short distance)

• Examples of local regulators include

neurotransmitters, morphogens, and quorum sensing

Local Regulator: Neurotransmitters

Local Regulator: Morphogens

• Morphogens are a group of chemicals that are

involved in the patterning of cells during embryonic development

Local Regulator: Quorum Sensing

• Bacteria produce and release chemical signal

molecules called autoinducers that increase in concentration as a function of cell density

Hormones

• Hormones produced by endocrine cells travel

long distances, through the blood, to reach their target cells

• Examples of hormones include insulin and

human growth hormone

Insulin Signaling Pathway

(Insulin Signaling Animation 4:42)

• Insulin is produced by the pancreas and

targets cells of the liver, skeletal muscle and fat

Plant Hormones

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

fruit development and cell growth

Topic 4.2 Introduction to Signal Transduction

Signal Transduction Pathway

• The general pathway of signal transduction for

cell-to-cell contact or chemical signaling is the same

Signal Transduction Pathway

Professor Dave Explains Signal Transduction (6:32)

Signal Transduction

• Signal transduction pathways link signal

reception with a cellular response

• Many signal transduction pathways include

protein modification (shape change) and phosphorylation cascades

Stage 1: Signal Reception

• Signaling begins with the recognition of a

chemical messenger – a ligand - by a receptor protein in a target cell

• The ligand has a complementary shape to the

receptor

Ligand Types

• The chemical messengers, or ligands, can be a

peptide, a small chemical, or protein, in a specific one-to-one relationship with the receptor

Types of Receptor Proteins

• Receptor proteins may be embedded within

the plasma membrane or located within the cytoplasm or nucleus

Transmembrane Receptors

• Embedded within the membrane, also known

as extracellular receptors

• Examples include GPCRs and ligand-gated ion

channels

G protein-coupled receptors (GPCRs)

• An example of a receptor protein found in

eukaryotes, thousands of different types

• The epinephrine signaling pathway involves a

GPCR

Epinephrine Signaling Pathway

Epinephrine Signaling Animation 3:10

Ligand-Gated Ion Channels

Intracellular Receptors

• Located within the cytoplasm or nucleus
• Targeted by lipid soluble ligands that are able

to pass through the plasma membrane

Stage 2: Signal Transduction

• Signal transduction is the process by which a

signal is converted to a cellular response

• After the ligand binds, the intracellular

domain of a receptor protein changes shape, initiating transduction of the signal

• Occurs in one step or a series of many steps

Signal Transduction

• Signaling cascades relay signals from

receptors to cell targets, often amplifying the incoming signals

• Some signaling cascades utilize second

messengers (such as cyclic AMP, or cAMP) during the signal transduction pathway to relay and amplify the intracellular signal

Enzymes Involved in Signal Transduction

• 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

Stage 3: Cellular Response

• The signal transduction pathway initiates a

change in cellular activity

• Response occurs in the cytoplasm or nucleus

Cellular Response

• Cellular responses include cell growth,

secretion of molecules, or gene expression, among others

• Most signaling pathways activate

transcription factors that control the cellular response –Examples: Epidermal growth factor and testosterone

Epidermal Growth Factor

• Signaling pathway that promotes cell growth

and division

Testosterone Cellular response increases gene activity for proteins involved in:

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

Transcription Factors

• Transcription factors regulate cellular responses

by:

• Turning “on” genes

Protein OR

• Turning “off” genes

No protein OR

• Regulating the activity of a particular protein

Signal Transduction Review