Topic 1-4 AP Biology: Cell Communication and Signal Transduction

What is cell-to-cell communication responsible for?

The growth and development of multicellular organisms​

Direct Contact

communication through cell junctions​

Example of direct contact in animal cells

gap junctions

Example of direct contact in plant cells

plasmodesmata

What can pass freely between adjacent cells?

Signaling substances and other material dissolved in the cytoplasm

What is an example of direct contact in immune cells?

Antigen presenting cells (APCs) communicating to T cells

Local regulators

a secreting cell will release chemical messages (local regulators/ligands) that travel a short distance through the extracellular fluid​

What do the chemical messages cause in local regulation?

The chemical messages will cause a response in a target cell

Paracrine signaling

secretory cells release local regulators (ie growth factors) via exocytosis to an adjacent cell​

Synaptic signaling

Occurs in animal nervous systems​- Neurons secrete neurotransmitters, diffuse across the synaptic cleft (space between the nerve cell and target cell​)

What do animals and plants use for long distance signaling?

hormones

Long Distance Signaling in Plants

Plants release hormones that travel in the plant vascular tissue (xylem and phloem) or through the air to reach target tissues​

Long Distance Signaling in Animals

Endocrine Signaling- Specialized cells release hormones into the circulatory system where they reach target cells​

Example of Long Distance Signaling

Insulin is released by the pancreas into the bloodstream where it circulates through the body and binds to target cells​

What type of communication involves a cell secreting a substance to an adjacent target cell?

paracrine signaling

Plant cells in direct contact with each other can diffuse substances through these structures to communicate. What are they?

Plasmodesmata

Cell-to-cell message: Reception

Ligand binds to the receptor

Cell-to-cell message: Transduction

Signal is converted

Cell-to-cell message: Response

A cell process is altered

Reception

the detection and receiving of a ligand by a receptor in the target cell

Receptor

macromolecule that binds to a signal molecule (ligand)

What do all receptors have?

All receptors have an area that interacts with the ligand and an area that transmits a signal to another protein​

What happens when the ligand binds to the receptor?

The receptor activates via a conformational change

What does reception allow?

Allows the receptor to interact with other cellular molecules​ and it initiates transduction signal

Where are receptors?

Receptors can be in the plasma membrane or intracellular

What is the most common type of receptor involved in signal pathways?

Plasma Membrane Receptors

What kind of ligands do plasma membrane receptors bind to?

Polar, water-soluble, large

Examples of Plasma Membrane Receptors

G protein coupled receptors (GPCRs) and ligand-gated ion channels

Where are intracellular receptors found?

In the cytoplasm or nucleus of a target cell

What kind of ligands do intracellular receptors bind to?

Ligands that can pass through the plasma membrane

Examples of Intracellular Receptors

Hydrophobic molecules: steroid & thyroid hormones, gases like nitric oxide

Transduction

the conversion of an extracellular signal to an intracellular signal that will bring about a cellular response

What does transduction require?

Requires a sequence of changes in a series of molecules known as a signal transduction pathway

How does the signal transduction pathway regulate protein activity?

• Phosphorylation by the enzyme protein kinase​

• Relays signal inside cell​

• Dephosphorylation by the enzyme protein phosphatase​

• Shuts off pathways​

• A change in shape means a change in function

What happens to the signal during transduction?

The signal is amplified

Second messengers

Second messengers: small, non-protein molecules and ions help relay the message and amplify the response

What is a common second messenger?

Cyclic AMP (cAMP)

Response

the final molecule in the signaling pathway converts the signal to a response that will alter a cellular process

Examples of Response

1. Protein that can alter membrane permeability​

2. Enzyme that will change a metabolic process​

3. Protein that turns genes on or off​

What are the three stages of cell signaling?

Reception, Transduction, Response

What is the actual “signal” being transduced in a signal transduction pathway?

a ligand

How is this “signal” passed from outside to inside the cell?

Through transduction: during transduction the signal is relayed by protein kinases and amplified by second messengers

What can signal transduction pathways influence?

how a cell responds to its environment

What changes can signal transduction pathways result in?

Changes in gene expression and cell function

Examples of Effects of Signal Transduction Pathways

Altered phenotypes or cell death

What will result in a change to the transduction of the signal?

Mutations to receptor proteins or to any component of the signaling pathway

Some diseases, such as cancer and diabetes, are caused by defective protein phosphatases. Explain how such a defective protein would affect a signal transduction pathway.​

Protein phosphatases are responsible for dephosphorylation of molecules. If they are defective, then they will not be able to perform their function, which would result in an alteration to the signaling pathway. They are also partially responsible for stopping signal pathways, if they are defective the signal pathway would continue.