chemical signalling notes (from sirius revision combined with kognity)

chemical signalling is the process where cells, tissues & organisms communicate with each other through signalling molecules

ligands

the signalling molecules are called ligands

  • so ligands are ions or molecules that bind to a protein receptor

  • include hormones, calcium ions, neurotransmitters

when the ligand binds to its site on the molecule, it can trigger a conformational change in the structure

  • this change to structure can result in a change in gene expression or a change in cellular response

ligands are specific to their receptors (similar to enzymes)

ligand remains unchanged (different from enzymes)

ligand sticks with the receptor for a longer period of time (different from enzymes)

quorum sensing

bacterial cells communicate with each other to coordinate their group behaviour in response to cell density. once population threshold is reached, the bacteria coordinate the expression of different traits

bacteria involved in quorum sensing release autoinducers (small signalling molecules) which diffuse & accumulate in their environment

  • the autoinducers bind to regulators & induce or repress gene expression

signalling chemicals

hormones are involved in longer processes & released by endocrine glands (effect over greater distances)

neurotransmitters are involved in quicker processes & travel through synaptic gap (localized effect)

cytokines are passed between nearby cells

  • can have multiple effects depending on binding site

differences & similarities between neurotransmitters & hormones

they are both:

  • soluble in water

  • are small

  • hv a shape compatible with a receptor

hormones can consist of:

  • steroids

  • amines

  • peptides

neurotransmitters can consist of:

  • amines

  • amino acids

  • gases

  • esters

differences between transmembrane & intracellular receptors

if a signalling molecule can enter the cell

  • receptor protein is located in cell (it’s intracellular)

  • so the receptor is covered in hydrophilic amino acids

if signalling molecule can’t enter the cell

  • then the receptor protein is located on the membrane (is transmembrane protein)

    • this means one section is embedded in the membrane & the other protrudes out of membrane

    • this means the receptor has to have hydrophilic & hydrophobic amino acids

transduction pathways

transduction pathways - series of events that occur after the ligand binds to its receptor

2 types of transduction pathways: intracellular pathway & transmembrane pathway

intracellular pathway - ligand enters cell & binds to receptor. the complex will enter the nucleus where it will regulate gene expression

transmembrane pathway - ligand binds to receptor & receptor changes shape. this produces a secondary messenger molecule which will cause changes in the cell

GPCR (G-protein coupled receptors)

it is a transmembrane protein

GDP (guanosine diphosphate) binds to GPCR & the protein doesn’t do anything

GPCR becomes active only when the ligand (GTP - guanosine triphosphate) binds to it

  • this means that GDP is replaced by GTP

  • this causes the protein complex to disassemble & causes changes within the cell

Epinephrine

is the same? or similar to adrenaline

it cannot enter the cell

so it will bind to GPCR, causing the conversion of ATP into cAMP ( a secondary messenger molecule)

  • this amplifies the message

Kinase

a kinase is an enzyme that phosphorylates molecules by removing a phosphate group from ATP & transferring it to the molecule

tyrosine kinase is an enzyme that transfer the phosphate to tyrosine (an amino acid) in a protein

insulin

remember insulin is important for glucose uptake

it will bind to the receptor

causes tyrosine kinase to transfer phosphate group to proteins

causes conformational change in the glucose channels

this will cause the glucose channels to be embedded in the cell membrane

this allows insulin to enter the cell