chapter11

What are the three stages of cell signaling?

What are the three stages of cell signaling?

signaling reception, transduction, and response

biofilm

an aggregation of bacterial cells adhered to a surface

quorum sensing

A concentration of signaling molecules allows bacteria to sense local population density

the regulation of gene expression in response to fluctuations in cell-population density

signal transduction pathway

The binding of a mating factor at the cell surface initiates a series of steps

How cells communicate with each other in local signaling?

Animal cells communicate by direct contact

animal and plant cells has cell junctions that connects cytoplasm of adjacent cells

paracrine signaling

animal cells communicate using secreted messenger molecules that travel only short distances

Autocrine signaling

the cell signals itself

Synaptic signaling

occurs in the animal nervous system when a neurotransmitter is released in response to an electric signal

hormones

In long-distance signaling, plants and animals use molecules

hormonal (or endocrine) signaling

in animals specialized cells release hormones, which travel to target cells via the circulatory system

ligand

The binding between a signal molecule (ligand) and receptor is highly specific

Reception

the target cell detects a signaling molecule that binds to a receptor protein on the cell surface

G protein-coupled receptors

are cell-surface transmembrane receptors that work with the help of a G protein extremely widespread and diverse in their functions

G protein

bind the energy-rich G T P and are all very similar in structure

receptor tyrosine kinases

membrane receptors that catalyze the transfer of phosphate groups from A T P to another protein

ligand-gated ion channel

receptor acts as a gate that opens and closes when the receptor changes shape

how the G protein signal transduction pathway works

In signal transduction, first the GPCR gets activated by changing its conformation which resulted from binding of agonist/ligands to the extracellular region of GPCR. This activated GPCR further activate the inactive G protein to active G protein complex by dissociating the Gα from Gβγ.

Intracellular Receptors

found in the cytoplasm or nucleus of target cells

Transduction

Cascades of molecular interactions transmit signals from receptors to relay molecules in the cell

Protein kinases

transfer phosphates from A T P to protein, a process called phosphorylation

phosphorylation cascade

Many relay molecules in signal transduction pathways are protein kinases

chain reaction of enzymes creating thousands of protiens

Protein phosphatases

rapidly remove the phosphates from proteins, a process called dephosphorylation

second messenger

small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion

Cyclic A M P (c A M P)

a small molecule produced from A T P, is one of the most widely used second messengers

inositol triphosphate

Pathways leading to the release of calcium

Adenylyl cyclase

an enzyme in the plasma membrane, converts A T P to c A M P in response to an extracellular signal

diacylglycerol

Pathways leading to the release of calcium as additional second messengers

What is the difference between a nuclear response and a cytoplasmic response?

A nuclear response involves the alteration of gene expression, while a cytoplasmic response involves the activation of an enzyme or the opening of an ion channel.

Scaffolding proteins

large relay proteins to which several other relay proteins are attached

increase the signal transduction efficiency by grouping together different proteins involved in the same pathway

Inactivation

If the concentration of external signaling molecules falls, fewer receptors will be bound

• Unbound receptors revert to an inactive state

Apoptosis

prevents enzymes from leaking out of a dying cell and damaging neighboring cells

can be triggered by signals from outside the cell or inside

may be involved in some diseases (for example, Parkinson’s and Alzheimer’s)

caspases

The main proteases of apoptosis …a family of endoproteases that provide critical links in cell regulatory networks controlling inflammation and cell death.

four aspects of signal regulation:

1. Amplification of the signal (and thus the response)

2. Specificity of the response

3. Overall efficiency of response, enhanced by scaffolding proteins

4. Termination of the signal

Scaffolding proteins

are large relay proteins to \n which several other relay proteins are attached

can increase the signal \n transduction efficiency by grouping together \n different proteins involved in the same pathway

protease

an enzyme which breaks down proteins and peptides.

nuclease

enzymes that degrade nucleic acids, either DNA or RNA. DNases degrade DNA and RNases degrade RNA.