Cell communication - C&M

intercellular

between cells

intracellular

inside cells

signaling cells

these cells release chemical signals called ligands

ligands

these interact with protein receptors in target cells:

• these & receptors SPECIFICALLY bind to each other

• aka signaling molecules

paracrine

move by diffusion through extracellular matrix

• synaptic signals & neurotransmitters

endocrine

signals from distant cells; typically produce a slower response w/ a long-lasting effect

• hormones

autocrine

a cell secretes a signal molecule that binds to receptors on its OWN SURFACE, leading to changes within that same cell

• cancer cells

• cell death signaling

• developing embryonic cells

direct signaling across gap junctions

this involves intracellular mediators that allow small signaling molecules to move b/t cells

• plasmodesmata — entire plant is a signaling network; only small molecules/ions can cross the gap

internal receptors

hydrophobic signaling molecules diffuse across the PM & interact w/ intracellular receptors:

• many are transcription factors that interact w/ DNA in the nucleus (regulate gene expression)

cell-surface receptors

• ion channel-linked

• G-protein-linked

• enzyme-linked

ion channel-linked receptor

gated ion channels form a pore through the PM that opens when the signaling molecules binds

ions flow into/out of cell:

• this flow changes the electrical charge difference across the PM

  • triggers a cellular response

G-protein-linked receptor

a ligand binds & activates G-proteins, causing a signaling cascade

ex. Vibrio cholera

• produces a toxin that modifies these receptors in the intestines

• leads to severe diarrhea, dehydration, & death

enzyme-linked receptors

a ligand binds & causes intracellular signaling cascades through enzymes

ex. growth factors/mutations

• lead to growth abnormalities like dwarfism or cancers

small hydrophobic ligands

• steroid hormones have similar chem. structs. to cholesterol

• can diffuse directly across the PM where they interact w/ internal receptors

water soluble ligands

these typically bind to cell-surface receptors

gas ligands

one example is nitric oxide:

• affected by nitroglycerin (treatment for heart disease) & Viagra

signal transduction

• ligand binds to a receptor

• signal is transmitted through the cell membrane & into the cytoplasm

• continues the signal

dimerization

2 receptors bind to each other to form a stable complex

signaling pathway

chain of events that happens after a ligand binds to a receptor & include:

• 2nd messengers

• enzymes

• activated proteins

signal integration

signals from 2 or more different cell-surface receptors merge to activate the same response in the cell

phosphorylation

method of intracellular signaling:

• phosphate group is added to residues of serine, threonine, & tyrosine (AAs)

  • kinase — enzyme that catalyzes the transfer of a phosphate group

second messengers

small molecules that propagate a signal (after ligand-receptor binding)

• cyclic AMP (cAMP) — activate/inactivate proteins in a cell; is terminated when an enzyme converts it to AMP

responses to the signal

• gene expression

• increase in cellular metabolism

• cell growth

apoptosis

cell death; signals are terminated by degradation of ligands or by other signals

• embryonic development — cells b/t fingers & toes undergo this

yeast

• single-celled

• can communicate by releasing a signaling molecule called a mating factor

• mating factor binds to cell-surface receptors in nearby cells

• stop normal growth cycles & initiate a signaling cascade

quorum sensing

a chemical language that bacteria use to communicate:

• autoinducers are released into the environment

• as the bacterial population grows, autoinducers increase

• at a certain concentration, the bacteria recognize that they’re part of a community & can coordinate their behavior