IB Biology HL C2

Chemical signally

ligand

signalling molecule that binds selectively to a binding site

binding site

site that ligand interacts with that causes a change in the receptor

enzyme vs ligand

both are selective to their sites

ligands remain changed in receptor, whereas substrates change into products

ligands can remain in the receptor for quite some time, where substrates are ejected once they turn into products

quorum sensing

change in behaviour of a colony when its population density reaches a certain threshold

ex. biomutualistic relationship between bobtail squid and vibrio fischeri

bioluminescence by V.fisheri

transmembrane vs intracellular receptors

location of reception, distribution of amino acids, types of chemicals

transmembrane receptors

outside of cell

hydrophobic amino acids and middle is hydrophilic

protein hormones, neurotransmitters, cytokines

insulin receptor

intracellular receptors

inside of cell, cytoplasm or nucleoplasm

exterior is all hydrophilic amino acids

steroid hormones, Ca ions

estrogen receptor

types of ligands

cytokines

hormones

neurotransmitters

Ca ions

hormones

secreted by endocrine glands

travels through blood stream

longterm/slow response

have receptor proteins

neurotransmitters

presynaptic transmission/nervous signalling

rapid/short response

ex. dopamine

cytokines

proteins that send chemical messages to other cells nearby

mostly for gene expression

Ca ions

muscle fibres: binds to receptor on actin, allowing myosin heads to be exposed

neurons: facilitates neurotransmitter transport

transmembrane receptor examples

receptors that activate g proteins, epinephrine receptors

insulin receptors (tyrosine kinase)

neurotransmitter receptors (acetylcholine)

G protein coupled receptors

3 subunits: alpha, beta, gamma

when ligand binds, GPCR shape changes allowing GDP to be replaced by GTP

adrenaline and GPCR

adrenaline activated G protein and adenylyl cyclase enzyme which catalyzes formation of cAMP

rapid cAMP formation amplifies signal of GPCR that trigger fight or flight

kinase

enzyme that transfers phosphorylates from ATP to another molecule

tyrosine kinase

enzymes that phosphorylates with tyrosine kinase

alpha subunits are extracellular

beta subunits are intracellular

insulin and tyrosine kinase

insulin acts as ligand on extracellular side of the insulin receptor

insulin binds, kinase phosphorylates tyrosine dimerize, allowing autophosphorylation

signals GLUT-4 vesicle and glucose into cell

steroid hormones

amphipathic lipid molecules that can pass through cytoplasm

generally related to gene expression

estradial

released in ovary

binds to cells in uterus (proliferation of the endometrium)

binds to cells in hypothalamus (expresses GnRH)

progesterone

released from ovary

binds to cells in uterus (thickens endometrium)

binds to cells in hypothalamus (inhibits GnRH release)

positive feedback loop

change that amplifies its own effect (intensifies initial stimulus)

ex. release of Ca ions

negative feedback loop

self-regulation pathway that reduces initial activity ex. testosterone release in males

increase in GnRH → increase in LH → increase in testosterone → decrease in GnRH

hormones type of molecules

amines (melatonin), steroids, peptides

neurotransmitters type of molecules

gasses, amino acids, amines, esters

resting potential

electrical potential across the plasma membrane of a cell that is not conducting an impulse

-70mV for neuron

how is resting potential created

polarized membrane created

due to imbalance of positive and negative charges across membrane

sodium potassium pump creating resting potential

pumps 3 Na+ out o cell and 2 K+ into cell

exterior of membrane in more positive compared to interior

action potential

depolarization and repolarization of the electrical potential across the plasma membrane of a cell

depolarization

voltage gated Na+ channels open, resulting in influx of Na+

inside of cell becomes positive, outside becomes negative

membrane potential reaches +30mV

repolarization

voltage gated Na+ channels close, voltage gated K+ channels open that diffuse K+ out of cell

restoration of resting potential

sodium potassium pump uses ATP to transport 3Na+ out and 2K+ in, which restores charge/resting potential

refractory period

nerve conducting impulse cannot be activated until resting potential is reached

1-10 ms

hyperpolarization

voltage gated K+ channels are slow to close, which causes short period of undershoot where outside of cell is more positive than resting potential

nerve impulse

action potential starts at axon hillock and propagated along axon to synaptic terminals

propagated by local currents

can only move in one direction

local currents

movement of Na+

reduces concentration gradient in neighbouring polarized part of neuron axon

makes membrane potential rise from -70mV to -50mV

postsynaptic potentials

threshold potential must be reached (at axon hillock) for action potential to continue

requires many synaptic transmissions

if threshold reached, allows neuron to act as decision making aspect of CNS

excitatory postsynaptic potentials

small changes in potential in postsynaptic membranes

causes action

acetylcholine

neurotransmitter used in neuromuscular junctions and CNS, binds to receptors in presynaptic neurons

enzymes break it apart to prevent overstimulation

remade after being reabsorbed from synaptic cleft

inhibitory postsynaptic potentials

causes membrane potential in cell body to become more negative (hyperpolarization)

blocks action

summation

postsynaptic potentials require release of multiple neurotransmitters for action potential

combines effects of excitatory and inhibitory neurotransmitters to determine if threshold is reached

signals from different sources → decision making in CNS

temporal summation

one presynaptic neuron repeatedly causing excitatory postsynaptic potentials

spatial summation

several adjacent presynaptic neurons causing excitatory postsynaptic potentials within a few milliseconds

exogenous chemicals

chemicals that enter the body from an outside source and affect the nervous system

can block or promote synaptic transmission

neonicotinoids

inhibits binding of acetylcholine → blocks nerve impulses for movement

acts as pesticide/insecticide

can’t be broken down by acetylcholinesterase enzymes → paralyzes insect and results in death

cocaine

blocks dopamine reuptake → buildup of dopamine in synaptic gap and overstimulation of postsynaptic cell

addictive because of overwhelming pleasurable feeling

consciousness

state of awareness that involves active and passive thinking

eg. bird flight

systems involved in internal communication

endocrine system

nervous system

neuron structure

dendrites (short branched nerve fibres that receive impulses), cell body, axons (elongated nerve fibres that conduct impulse to other cells)

neuron

send electrical impulses as a temporary and rapid change in voltage

saltatory conduction

nerve impulse jumps from note to node

very rapid transmission (100m/s)

myelinated axon

axon has sheath of myelin (coating of many layers of phospholipid bilayer)

myelin is made up of Schwann cells and nodes of Ranvier

diameter and speed of impulse relationship

nerve fibres with larger diameter transmit impulses faster

less resistance

synapse

fluid filled junction in between two neurons

contains synaptic cleft

allows transmission of nerve signal

pain receptors

nociceptors, generally ends of sensory neurons

send action potential to spinal cord if threshold potential is reached

pain perception

occurs in cerebral cortex as impulses are received from spinal cord

evaluated by prefrontal cortex, where decision making is done