c2.1 chemical signalling Flashcards
ligand
molecule that binds selectively to a specific site on another molecule
how do ligands prevent other substances from binding [2]
shape + chemical properties of the ligand and ligand-binding site has to match
- shape is specific
- chem: postive/negative
what other ways can the receptors make it fit
induce fit so ligand can fit on receptor
- change in shape is only temporary
what does binding of a signalling chemical to a receptor do
sets off a sequence of responses within a cell
2 types of signalling chemicals + why
- can enter the cells
- cant enter the cells
- big + charged (polar)
location of chemicals that dont enter the cell
receptors- plasma membrane of target cell
binding site- facing the exterior
location of receptor protein
extends across the membrane with a region extending into the cytoplasm
what are receptor proteins known as
transmembrane receptors
where would he hydrophilic and hydrophobic amino acids be on the transmembrane receptors
outside- hydrophilic amino acids
inside- hydrophobic amino acids
location of receptor proteins for the chemicals that do go inside
in the cytoplasm/nucleus
what are the receptors responsible for the chemicals that do go inside called
intracellular receptors
intracellular receptors characteristics [2]
- soluble
- hydrophilic amino acids
why do intracellular receptors have hydrophilic amino acids
remain dissolved in the aqueous fluid of the cytoplasm/nucleus
how does the signalling molecule enter the cell
endocytosis
how does quorum sensing in bacteria work
- bacteria release a signalling molecule in a low rate to indicate population in the area
- when there is sufficient binding of signalling molecule to receptors in a cell → gene expression will change
what does it mean when the bacteria have sensed a quorum
a fixed number for an activity to go ahead
quorum sensing in bacteria eg [2]
- bacteria living symbiotically with deep sea animals will switch on bioluminescence and glow when they sense a high bacteria population when living inside sea animals
- bacteria on our teeth forms a biofilm when they have reached a high population
where are hormones secreted form
endocrine glands
where are hormones released into
bloodstream (might not stay in blood)
eg of hormones [2]
- testosterone
- insulin
where are neurotransmitters released from
presynaptic neurone
when are neurotransmitters released
when action potential reaches the end of neuron
eg of neurotransmitters [2]
- acetylcholine
- dopamine
functional categories of signalling chemicals in animals [4]
- hormones
- neurotransmitters
- cytokines
- calcium ions
where are cytokines secreted from + where do they perform their function
almost all cells in the body
acts on the cell that produced them/nearby cells
importances of cytokines [2]
important in the immune system and cell division
cytokines eg
interleukin
what are calcium ions used for [2]
- muscle fibre- sarcoplasmic reticulum use calcium to initiate muscle contraction
- neurones- use calcium to secrete neurotransmitters into the synapse
amines
compounds and functional groups that contain a basic nitrogen with a lone pair
steroid
organic compound with four fused rings arranged in a specific molecular configuration
how far do neurotransmitters have to travel for them to deliver their effect + where do they reach
small distance
reach the postsynaptic neurone
how far do hormones have to travel for them to deliver their effect + how
greater distances
carried in the bloodstream
where will LH from the pituitary gland travel to
testes/ovaries
how do acetylchloline receptors work
- acetylcholine is released
- binds to the acetylcholine receptor (transmembrane receptor) on postsynaptic neurone → changes shape
- opens sodium channel
- positively charged sodium ions diffuses into postsynaptic neurone → changes membrane potential (causes depolarisation)
- new action potential starts
G-protein coupled receptors (GPCRs)
activates a second protein to pass on signals into the cell
what is the G-protein made up of
3 subunits (α, β and γ)
when is the G protein inactive
when GDP is bound to the α submit
what happens when a ligand binds to the receptor [2]
- receptor changes shape
- GDP detaches
how is the G protein activated
GTP bind + activate
what happens when the G protein is activated
changes inside the cell
what happens when the G protein is active
GTP-bound alpha subunit and the beta-gamma dimer will relay messages in
the cell by interacting with other membrane proteins
2 types of activity triggered by G proteins
- stimulation
- inhibition
role of beta-gamma dimer
social messenger
what causes the different activities triggered by the G proteins
the receptor/the G protein
mechanism of adrenaline receptor (a GPCR) [4]
- adrenaline binds to adrenaline receptor → changes its shape + activates a G protein
- G protein activates adenylyl cyclase → breaks ATP in the cytoplasm to cyclic AMP (cAMP)
- cAMP acts as a second messenger → triggers a sequence of responses within the cell to enable fight or flight response
- eventually activates an enzyme (glycogen phosphorylase) to break down glycogen into glucose in liver cells)
why is a second messenger needed
chemical signals cant go into the cell
what does tyrosine kinase do
add phosphate form ATP to the amino acid tyrosine in a protein
transmembrane receptors with tyrosine kinase activity eg
insulin receptor
how insulin receptor works [4]
- insulin binds to receptor on plasma membrane → changes shape of receptor
- 2 tyrosine kinases at the tail forms a dimer → phosphorylates each other
- starts a sequence of events that ends with vesicles containing glucose transporters to move to plasma membrane
- so glucose diffuses into the cell faster
can steroid hormones pass thru (hydrophobic)
yes
what do steroid hormones bind to + what do they form
bind to intracellular receptors in the cytoplasm
forms hormone-receptor complex
mechanism of steroid hormones
- enter the nucleus
- attaches to DNA → promote gene transcription →particular polypeptide is produced
steroid hormones eg [3]
- oestradiol
- progesterone
- testosterone
what happens w oestradiol before and during ovulation + product
binds to a receptor inside the cytoplasm of hypothalamus cell
forms hormone-receptor complex
effect + mechanism of oestradiol to cells in the hypothalamus
mechanism- move to nucleus + act as a transcription factor
effect- enhance the transcription of gonadotropin-releasing hormones in hypothalamus
effect of gonadotropin-releasing hormones
triggers release of LH and FSH from anterior pituitary gland
where is progesterone made
ovary
mechanism of progesterone
- diffuse into cells of endometrium
- bind to intracellular receptors to form hormone-receptor complex
- enter the nucleus
- acts as transcription factor for several genes
importance of insulin-like growth factor binding protein and Indian Hedgehog
important for growth and differentiation in endometrium to promote successful embryo implantation
eg regulation of cell signalling pathways by positive feedback
calcium-induced calcium release
eg regulation of cell signalling pathways by negative feedback [3 steps]
- hypothalamus releases GnRH → stimulates LH release in anterior pituitary gland
- LH stimulates Leydig cells in testes to release testosterone
- increased testosterone level signals hypothalamus to stop releasing GnRH + anterior pituitary gland to stop releasing LH
= end product inhibits its own production
