c2.1 (chemical signalling) Flashcards
what is a ligand? give 4 examples of signaling ligands in animals
a chemical that binds to another specific molecule
horomones, neurotransmitters, cytokines, calcium ions
define specificity (in relation to binding)
the ability of the binding site of a receptor to bind specific ligands
define quorum sensing
is a mechanism which allows bacteria to modulate group behaviour
look at c2.1 slides 8 & 9
-
what are cytokines?
small signaling proteins
calcium ions are used for signaling within ___ and ____. how does each process involve calcium ions?
muscle fibres = upon signal for contraction, calcium ions move out of sarcoplasmic reticulum, attach to proteins of the sarcomere, triggering muscle contraction
neurons = calcium ions trigger secretion of a neurotransmitter into the synaptic gap via exocytosis
amines are small molecules synthesized by modification of amino acids. give 2 examples of amines & what they were synthesized from
melatonin from tryptophan
epinephrine (adreneline) from tyrosine
steroid hormones are ____ derived from _____
lipids, cholesterol
1 example of ligand used in local signaling & 1 example of ligand used in distant signaling
local = neurotransmitters across the synaptic gap
distant = hormones travelling in the bloodstream
receptor proteins can be classified by their location on or in a cell. what are the 2 main types & where are they found?
what signalling molecules typically bind to each one?
cell surface receptors, also known as transmembrane receptors, are integral membrane proteins (peptide horomones & neurotransmitters bind)
intracellular receptors are those found inside the cell (steroids bind)
hydrophilic signaling molecules cannot cross the membrane lipid bilayer. what type of receptors do they bind to?
transmembrane receptors
transmembrane receptor structure x3
an extracellular portion that binds the signalling molecule
a region of hydrophobic amino acids that are able to interact with the hydrophobic tails of the phospholipids in the core of the membrane
an intracellular portion composed of hydrophilic amino acids that are in contact with the aqueous solution of the cytoplasm
types of transmembrane receptors x3
GPCRs (G protein-coupled receptor)
enzymatic receptors
ion channels
why do intracellular receptors have hydrophilic amino acids arranged on their surface?
so they can remain dissolved in the aqueous fluids
define signaling pathway & its 3 main steps
the process in which binding of an extracellular chemical to a receptor is translated into changes in the cell
reception: the process by which a cell detects a signal in the environment
transduction: the process of activating a change within the cell
response: the change that occurs in the cell as a result of the signal
when a signaling molecule binds to its receptor, what happens?
a change in the shape of the receptor
(in relation to transduction) activated receptors act in four general ways: (each with example)
intracellular receptors that directly alter gene transcription (such as the testosterone receptor)
transmembrane receptors that are ligand-gated ion channels and allow specific ions to flow into or out of the cell (such as the nicotinic acetylcholine receptor)
transmembrane receptors that activate GTP binding proteins (G-proteins) inside the cell (such as the epinephrine receptor)
transmembrane receptors with enzymatic activity (such as the insulin receptor)
define signaling cascade
a series of metabolic reactions in which one reaction triggers the next, in a linear fashion
first messengers = ?
second messengers = ?
1st = signaling molecules
2nd = intracellular signaling molecules released by the cell in response to extracellular signaling molecules
what are some common second messengers? x3
cAMP, nitric oxide and Ca2+ ions
signaling cascades are only necessary for what (& why)?
hydrophilic ligands that must bind transmembrane receptors because they cannot cross the plasma membrane
different types of cellular responses to a chemical signal x3
changes in gene expression
changes in cell metabolism
changes in cell shape or movement
two major types of gated channel proteins & how they work
voltage gated: open and close in response to changes in the electrical potential of a cell membrane
ligand gated: open to allow ions to pass through the membrane only when a chemical messenger, or ligand, has also bound to the channel
watch a video on Ach & binding
-
all GPCRs consist of ___ and embedded in a ____
(look at image after)
a single polypeptide that is folded into a globular shape
cell’s plasma membrane
in GPCRs, what is attached/attaches to the extracellular loops?
signalling molecules
in GPCRs, what is attached/attaches to the intracellular loops?
a protein complex called a G-protein composed of 3 subunits (alpha 𝞪, beta 𝛃, and gamma 𝞬)
watch a video or read something on inactive GPCRs
-
GPCR activation occurs when: x5 steps
a ligand binds to the GPCR, causing the receptor to change shape
the shape changes causes GDP to detach from the alpha subunit of the G-protein.
GTP (guanosine triphosphate) binds in its place
binding of GTP causes the G protein subunits to dissociate into two parts: the GTP-bound alpha subunit and a beta-gamma dimer
both parts remain anchored to the plasma membrane, but they are no longer bound to the GPCR, so they can now diffuse to interact with other membrane proteins
humans alone have nearly 1,000 different GPCRs, and each one is highly specific to a particular signaling molecule, including: x4
odor molecules and pheromones
taste molecules
hormones (such as glucagon, epinephrine, GnRH, and oxytocin )
neurotransmitters (such as acetylcholine)
common examples of medicinal drugs which are aimed at GPCRs x3
depression medications, chemotherapy drugs, diabetes medicines
effects which adrenaline has x6
increase in ventilation rate
hydrolysis of glycogen by the liver, releasing glucose into the bloodstream
stimulates skeletal muscle contraction
release of sweat
increase in heart rate
constrict muscles around artery walls to increase blood pressure
epinephrine binds to cells with a transmembrane receptor called the ____
adrenergic receptor (a GPCR)
epinephrine signal transduction begins when the activated alpha subunit of the G-protein activates an enzyme in the cell membrane called ______
adenylate cyclase
The activated adenylate cyclase catalyzes the conversion of ___ in the cytoplasm to ______
ATP, cyclic AMP (cAMP)
what does cyclic AMP (cAMP)’s structure look like?
a single phosphate is attached to two carbons of the ribose sugar linked to adenine
insulin is used to integrate the response of multiple organs in an effort to do what? how is this done?
maintain blood glucose homeostasis
insulin causes cells to uptake glucose from the blood to be used in cellular respiration or converted to glycogen
insulin binds to cells with a type of transmembrane receptor called what?
the intracellular tail of the receptor is a what? what process can it perform?
receptor tyrosine kinase (RTK)
tyrosine kinase enzyme that can transfer a phosphate group from ATP to another molecule (phosphorylation)
insulin receptor activation occurs when: x3 steps
insulin binds to the receptor
the binding of insulin causes structure of receptor to change, making the two tails connect
tyrosine kinase in the tail of the receptor phosphorylates multiple tyrosines on the other tail
one of the results of the insulin signaling cascade is the movement of ____ embedded with _____ proteins to the plasma membrane
when the ____ fuse with the plasma membrane, the protein becomes part of the plasma membrane
vesicles, glucose-transport (GLUT)
vesicles
binding of a steroid hormone to its receptor leads to changes in gene expression. what are the 6 steps to this?
hormone diffuses through the cell membrane
hormone binds to the receptor within the cytoplasm or nucleus, forming a hormone-receptor complex
hormone-receptor complex attaches to the DNA at a specific gene
hormone-receptor complex acts as a transcription factor, turning “on” the transcription of the DNA into mRNA
mRNA is translated into a protein at the ribosome
protein has an effect in the cell
how does binding of testosterone to its receptor leads to muscle growth? x6 steps
testosterone diffuses through the cell membrane of a muscle cell
testosterone binds to its receptor within the cytoplasm, forming a hormone-receptor complex
the hormone-receptor complex moves into the nucleus through a nuclear pore, where it acts as a transcription factor. the hormone-receptor complex attaches to the DNA at the gene that codes for a protein called the serum response factor
binding of the hormone-receptor complex to the DNA activates the transcription of the serum response factor gene into mRNA
mRNA is translated into a serum response factor protein
serum response factor protein causes growth of the muscle cell
binding of oestradiol to its receptors in the hypothalamus can either inhibit or promote release of gonadotropin-releasing hormone (GnRH).
what are the steps for the positive feedback of oestradiol on the hypothalamus that leads to ovulation? x6
oestradiol diffuses through the cell membrane of a hypothalamus cell
oestradiol binds to its receptor within the cytoplasm, forming a hormone-receptor complex
hormone-receptor complex moves into the nucleus through a nuclear pore, where it acts as a transcription factor and attaches to the DNA at the gene that codes for the gonadotropin-releasing hormone (GnRH)
activates the transcription of the GnRH gene into mRNA
the mRNA is translated into a GnRH protein
the GnRH protein causes the pituitary to release a surge of luteinizing hormone (LH), in turn triggering ovulation
binding of progesterone to its receptor in cells of the uterus leads to proliferation of the endometrium during the uterine cycle.
what are the steps for progesterone’s growth of the endometrium during the menstrual cycle and pregnancy? x6 steps
progesterone diffuses through the cell membrane of endometrial cell
progesterone binds to its receptor within the cytoplasm, forming a hormone-receptor complex
hormone-receptor complex moves into the nucleus through a nuclear pore, where it acts as a transcription factor, where the hormone-receptor complex attaches to the DNA at the gene that codes for a protein called the insulin-like growth factor
binding of the hormone-receptor complex to the DNA activates the transcription of the insulin-like growth factor gene into mRNA
mRNA is translated into a insulin-like growth factor protein
insulin-like growth factor protein causes cellular proliferation, which leads to the growth of the endometrium during the menstrual cycle and pregnancy.
in negative feedback, a product of the signal transduction pathway does what?
INHIBITS another component at the start of the pathway, reducing the signal cascade (the end-products inhibits its own production)
testosterone production is regulated by negative feedback. what are the steps to this? x4
testosterone produced in the testes enters the bloodstream and travels to the hypothalamus and pituitary gland
hypothalamus detects the level of testosterone in the blood
if testosterone levels are too high, the hypothalamus sends a signal to the pituitary gland to stop sending signals to the testes
pituitary gland stops sending signals to the testes, which results in a decrease in testosterone production
in positive feedback, a product of the signal transduction pathway does what?
further ACTIVATES another component of the pathway, enhancing the signal cascade
