C2.1 Chemical signaling

Ligand

small molecule that binds reversibly to a receptor to deliver a signal

Receptor

Protein to which the ligand binds

signal transduction pathway

process of convertion of an electrical signal into a specific response

Quorum sencing in bacteria definition

mechanism by whcih bacteria can alter group bevairou dependiing on the population density

Quorum sencing in bacteria mechanism

1. Bacteria secrete a ligand called autoinducer

2. With increasing numbers of bacteria the autoinducer concnetration also increases

3. When autoinducer concnetration reaches a threshold the gene expression of whole population is changed

Quorum sensing in Vibrio Fisheri bioluminescence

1. Bacteria reproduce

2. Produce autoniducer which exists to the external environment

3. More bacterias reporuce creating more autoniducer

4. When threshold level outisde is reached the autoinducer moves back to bacterial cell to bind to a protein called LuxR

5. LuxR then binds to binding site on DNA called lux box

6. The section of DNA is activated by this lux box and begins the production of luminescent protein called luciferase

Categories of animal siganling chemicals

• hormones

• neurotransimtter

• cytokines - glycoproetin acts as messangers increase cell reporduction

• calcium ions - cell signaling and muscles

Hormones what can they be composed of

• amines and proteins - hydrophilic → can bind on surfaces

• stereoids - hydrophobic → can pass through bilayer

Neurotransimtter what are they composed of

• amines

• amino acids

• nitrous oxides

• peptides

all hydrophilic as they bind to receptors on teh surface of a cell membrane

Hormones fucntion

regulation → homeostatis, developemnet and reproduction

Reasons for chemical diveristy between neurotramitters and hormones

• some create a long lasting effect while some short

• some have to travel longer distances

• they act on diffrent target cells

• diffrent ligans work in diffrent ways

• allows for specific receptors

Where transmembrane receptor

embedded in the cell membrane

Where intracellular receptor

found in the cytoplasm or nucleus

What binds to transmembrane receptor

hydrophilic ligand as it cant pass into the cell

What bind to intracellular recptos

hydrophobic ligand as onyl those can pass though the bilayer

Protein domain

part of polypetide chain that is self stabilising and folds independently

transmemebrane receptors prtoein domains

extracellular domain and cytoplasimc domain allowing for intercations outside and inside teh cell

Transmembrane receptor type

• enzymatic receptor → single pass protein → binds to ligand on extracellular activating enzymes intarcellularly

• chemically agted ion channel → multipass protein with central pore → gates that open and close

• g protein coupled receptor → multipass proetin with intracellualr binding site for G protein → binds with ligand to activate g protein

Acetylcholine

• binds to receptor which is a gated ion channel binding causes influx of positive ions into cell changing the membrane potential

G protein coupled recepor pathway

1. A ligand (epinephrine) binds to the GPCR which is a transmmebrane protein and the ligand binds on extracellular side

2. This changes the shape of teh GPCR

3. This activates G protein leading to loss of GDP and attachemnt of GTP (from alpha subunit of G protein)

4. ACtivated g protein activates an enzyme called adenlyl cyclase activates the conversion of ATP to cAMP (enzyme also actiavted by alpha subunit)

5. cAMP serves as a secondary messanger spreading the signal inside the cell

What is a kinase

enzyme that cataylses removal of a phosphate group from ATP and gives it to another substance

tyrosine kinase activity

1. Insulin binds to the extracellular domain of receptor tyrosine kinase

2. This causes a conformational change and activation of receptor

3. The receptor autophosphorylates on the intracellualr domain

4. This actiavtes a signaling cascade

5. GLUT4 secretory vesicles fuse with the plasma membrane

6. the GLUT4 glucose transporters allow for glucose to enter the cell via facilitated diffusion

Testosterone oestradiol and progestorone as ligands

they are hydrophobic sterioids hence can bind to intracelluar receptors

1. When the ligand binds it craetes a receptor-signal complex

2. The complex moves into the nucleus and binds with DNA affecting trasncirption

Negative feedback: blood glucose levels

1. beta islet cells produce insulin

2. alpha islet cell produce glycogen

Positive feedback: fever

when pathogen enetrs the body temp rises causing a large deviation from normal temp