BIO202 Lecture 10

Internal balance

affected by the external environment through biochemical or chemical signalling

Symbiotic

mutualistic relationship

Hawaiian bobtail squid

bacteria colonize specialized organs, allowing it to blend in with environment and improve camouflage when catching prey

Bacteria in squid

can detect light that is reflecting off ground and reflect it back, lets squid get rid of its shadow

Tadpole

grows, changes shape and grows external and internal organs to become a sexually reproductive adult

External conditions met

tadpole produces hormones via endocrine system that start metamorphosis

Thyroxine

exposure speeds up limb growth and accelerates growth of the pelvic hind limbs in axolotl

Axolotl

healing/regenerative qualities

Intracellular signalling

withing cytoplasm of one cell

Intercellular signalling

between 2 different cells

Chemical signalling

needs a ligand and a receptor

Autocrine signalling

self-target, used by larval cells and cells infected with virus for cell death

Gap junctions

cell targets a cell connected by a gap junction

Paracrine

signal travels to a nearby cell, quick and short message

Endocrine

cell targets distant cell through the bloodstream, slow and long message; general message (not targeted)

Hydrophilic

water loving, exists in water, ECF and cytoplasm, peptide hormones (not lipid soluble)

Hydrophobic

steroid, membrane/lipid soluble

Intracellular receptor

not on membrane, floating in cytoplasm; bind to a receptor in cytoplasm or mitochondria and alter DNA transcription

Hydrophobic chemicals

carried by carrier water-soluble proteins to target cells

Ligand-receptor complex

undergo conformational change, can bind to DNA, facilitates rate of transcription, controls which/how many proteins are formed

Extracellular (membrane bound) receptors

bind to a receptor on the cell surface, changing conformation of the receptor

Ligand binding, hydrophobic, intracellular

Extracellular receptor domains

Hydrophilic chemicals

cannot cross the phospholipid bilayer

Ion channels

allow ions through, inside is hydrophilic and specific

G protein coupled receptor

ligand gated receptor associated with the G protein

Signalling molecule

receptor triggers activation of alpha subunit to exchange GDP for GTP

GTP

has stored potential energy that triggers secondary messenger

Secondary messenger cAMP

amplifies message

Enzyme receptor

tyrosine kinase, bound to membrane with a single alpha helix

Signalling molecules bind

tyrosine residues are phosphorylated

Phosphorylation

triggers cellular response in target cells

Phosphatase enzymes

remove the phosphates when the signal is complete (inactivation)