Chapter 9: Cell Communication Flashcards
intercellular signalling
communication between cells
intracellular signalling
communication within a cell
signalling cell
cell that delivers signals to other cells
ligand
molecule that binds to another specific molecule
receptor
protein that can receive ligands from signalling cells
target cell
cell that has a receptor to receive ligands from signalling cells
What are the four categories of chemical signalling in multicellular organisms?
Paracrine signalling, endocrine signalling, autocrine signalling and direct signalling across gap junctions
paracrine signal
signalling between nearby cells
How do paracrine signals reach the target cell?
They diffuse through the extracellular matrix towards the target cell
What happens to a paracrine signal after it has reached its target cell?
It is degraded by enzymes or removed by neighbouring cells
Why do paracrine signals last a short time?
Removing the paracrine signal quickly reestablishes the concentration gradient so signals can travel freely again
synaptic signal
chemical signal that travels between nerve cells
neurotransmitter
ligand released by nerve cells
chemical synapse
small space between nerve cells
How are signals propagated through nerve cells?
They are propagated by electrical impulses
How are signals transferred from nerve cell to nerve cell?
Neurotransmitters are released from the signalling nerve cell to the target nerve cell
What happens to neurotransmitters after they have been received by the target cell?
They are destroyed by enzymes or are reabsorbed for further use
What type of chemical signalling is synaptic signalling?
Paracrine signalling
endocrine signal
signalling between cells that are very far away
endocrine cell
cells that secrete and send hormones in endocrine signalling
hormone
signalling molecules that are the ligands in endocrine signalling
How do hormones travel from the signalling cell to the target cell?
They travel through the bloodstream
How is endocrine and paracrine signalling different?
- Endocrine signalling is slower and longer lasting
2. Endocrine signalling ligands are found in lower concentrations
autocrine signal
when the signalling cell binds to the ligand that it produces
What cells are affected in autrocrine signalling?
The signalling cell and sometimes the neighbouring cells are affected
When does autocrine signalling usually occur?
During early development of an organism to ensure cells develop correctly
intracellular mediator
small molecule that transfers signals inside a cell
How can intracellular mediators diffuse to other cells?
Through gap junctions and plasmodesmata
internal receptor
receptors that are found in the cytoplasm of a cell
In what process are internal receptors often involved in?
They are used to regulate mRNA synthesis
How do internal receptors control DNA transcription?
When a ligand binds to an internal receptor, a DNA binding site is exposed on the receptor, which binds to DNA in the nucleus to promote transcription
cell-surface receptor
cell surface integral proteins that bind to external ligands
How much of the plasma membrane does a cell-surface receptor span?
They are all transmembrane receptors
What are the three components of a cell-surface receptor?
An extracellular, transmembrane and intracellular domain
What are the three types of cell-surface receptors?
Ion channel-linked receptors, G-protein-linked receptors and enzyme-linked receptors
ion channel-linked receptor
channel proteins that have a binding site for ligands to allow ions through
G-protein-linked receptor
receptor that activates G-proteins to transmit signals to membrane components
How many transmembrane domains does a G-protein-linked receptor have?
Seven
G-protein-coupled receptor
G-protein-linked receptor that has a G-protein bound to it
heterotrimeric G-protein
G-protein made up of an alpha, beta and gamma subunit
How are G-proteins activated?
An inactive G-protein binds to the receptor, and when a signalling molecule binds to the receptor, GDP in the alpha subunit is released and replaced with GTP, then the activated G-protein is split into an alpha and beta-gamma fragment to be used
How does an active G-protein become inactive?
The GTP in the alpha subunit is hydrolysed to GDP, and the alpha and beta-gamma fragments come back together to form an inactive G-protein
What are the main symptoms of cholera?
Dehydration and diarrhoea
What bacterium is responsible for cholera?
Vibrio cholerae
Which part of the body does Vibrio cholerae invade?
The small intestines
How does Vibrio cholerae invade the small intestines?
It produces a toxin called choleragen which modifies a G-protein to be constantly active and leads to water loss from the body
enzyme-linked receptor
receptors that have intracellular domains that interact directly with an enzyme or is an enzyme itself
What is the transmembrane domain of an enzyme-linked receptor like?
It is a single alpha-helical region spanning the membrane
How does an enzyme linked receptor work?
When a ligand binds to the extracellular domain, a signal is transferred through the membrane to activate the enzyme
receptor tyrosine kinase
enzyme-linked receptor that phosphorylates tyrosine residues to transmit a signal
How does a receptor tyrosine kinase work?
Ligands bind to two nearby receptor tyrosine kinases which are dimerised and the tyrosine residues are phosphorylated for a cellular response
What type of molecules are the main small hydrophobic ligands?
Steroid hormones
What is the main female sex hormone?
Estradiol
estrogen
group of steroid hormones in the female body
What is the main male sex hormone?
Testosterone
What is the precursor to all steroid hormones?
Cholesterol
What are the two main types of ligands?
Small hydrophobic ligands and water-soluble ligands
water-soluble ligand
ligand that is polar and cannot enter the cell unaided
nitric oxide
gas that acts as a ligand
Why is nitric oxide a good ligand?
It can diffuse across the plasma membrane
signal transduction
continued propagation of a signal through the cytoplasm
In which type of receptors does signal transduction occur in?
Cell-surface receptors
Why does signal transduction happen in surface-cell receptors but not internal receptors?
Internal receptors can move and interact with the cytoplasm and nucleus, but since surface-cell receptors are integrated with the membrane, they must use signal transductioin
dimerisation
when two molecules bind to each other
signalling pathway
the chain of events that follows after the activation of a receptor’s intracellular domain
downstream event
event that occurs after a certain point
upstream event
event that occurs before a certain point
signal integration
when signals from two or more different receptors merge to trigger the same response
What are the two main methods used in intracellular signalling?
Phosphoryation and using second messengers
amino acid residue
R group of an amino acid
What is usually phosphorylated in intracellular signalling?
Nucleotides or amino acid residues of proteins
Which amino acid residues are usually phosphorylated in intracellular signalling?
Serine, threonine and tyrosine residues
Where does a phosphate group bind to during phosphorylation in intracellular signalling?
It replaces the hydroxyl group of the amino acid
What does the phosphorylation of serine and threonine residues do in intracellular signalling?
It often activates an enzyme
What does the phosphorylation of tyrosine do in intracellular signalling?
It either affects an enzyme or it creates a binding site that interacts with the downstream events of a signalling pathway
second messenger
small molecule that propagates a signal after a ligand has bound to a receptor
Which ion is used as a common second messenger?
Ca2+
Where do calcium ions come from in intracellular communication?
They are stored in cytoplasmic vesicles or are accessed from outside the cell
Why is calcium used as a second messenger?
Membrane pumps constantly remove calcium ions, so the concentration gradient created allows for easy movement of the ions
How are calcium ions used as a second messenger?
Ligand-gated calcium ion channels allow ions outside the cell and inside vesicles to enter the cytoplasm, triggering a cellular response
cyclic AMP
molecule synthesised from ATP and acts as a second messenger
What is the main role of cyclic AMP?
To bind to an enzyme called cAMP-dependent kinase
A-kinase
cAMP-dependent kinase
How is cAMP made from ATP?
Adenylyl cyclase cleaves a pyrophosphate from ATP to create cAMP
pyrophosphate
Two phosphate groups joined together to create P2O7
Which enzyme synthesises cAMP from ATP?
Adenylyl cyclase
What is the main role of A-kinase?
It regulates many metabolic pathways by phosphorylating serine and threonine residues
inositol phospholipid
type of phospholipid that is found in small quantities in the plasma membrane
inositol
carbohydrate that is a glucose isomer
What is the structure of an inositol phospholipid?
It is a phospholipid with a inositol as its phosphate head group
What is the main inositol phospholipid involved in cellular signalling?
Phosphatidylinositol
What is created when PI is phosphorylated?
Either PI-phosphate or PI-bisphosphate
PIP
phosphatidylinositol-phosphate
PIP2
phosphatidylinositol-bisphosphate
Which two second messengers can PIP2 be cleaved into?
Diacylglycerol and inositol triphosphate
Which enzyme cleaves PIP2 into DAG and IP3?
Phospholipase C
DAG
diacylglycerol
IP3
inositol triphosphate
What does DAG do as a second messenger?
DAG stays in the membrane after being cleaved and activates protein kinase C
PKC
protein kinase C
What does IP3 do as a second messenger?
It diffuses into the cell after being cleaved and binds to ligand-gated calcium channels in the ER to release Ca2+
EGF
epidermal growth factor
EGFR
epidermal growth factor receptor
What is the role of EGF?
To regulate protein synthesis
How is EGFR activated?
When EGF binds to EGFR, tyrosine residues are phosphorylated and a signalling pathway is triggered
inhibitor
molecule that binds to a protein to reduce or prevent function
How does PKC activate DNA transcription?
It phosphorylates serine and threonine residues in Iκ-B, which allows NF-κB to initiate RNA transcription
Iκ-B
inhibitor protein that prevents RNA transcription
NF-κB
regulatory protein required in RNA transcription
What is another name for cAMP-dependent kinase?
Protein kinase A
PKA
protein kinase A
What receptor does adrenaline activate?
Beta-adrenergic receptors
What happens when beta-adrenergic receptors are activated?
They release cAMP
What happens when adrenaline increases cAMP levels?
It activates PKA which in turn activates two enzymes?
Which two enzymes does PKA activate during an adrenaline rush?
GPK and GS
GPK
glycogen phosphorylase kinase
GS
glycogen synthase
What happens when GPK is activated?
It activates glycogen phosphorylase
GP
glycogen phosphorylase
What happens when GP is activated?
Glycogen is catabolised into glucose
What happens when GS is activated?
The cell is unable to form glycogen from glucose
growth factor
ligands that promote cell growth
MAPK/ERK pathway
chain of proteins in a cell that communicates a signal from a cell-surface receptor to nuclear DNA
apoptosis
programmed cell death
How can apoptosis be triggered?
When abnormalities are detected in the cell or from external signalling
How is apoptosis necessary for embryonic development of vertebrates?
Web-like tissue between fingers and toes must be eliminated through apoptosis
How is apoptosis necessary in T-cell development?
Immature T-cells that bind to self proteins undergo apoptosis to prevent further harm
T-cell
immune cell that binds to foreign molecules for self destruction
phosphatase
enzymes that remove phosphate groups attached by kinases
phosphodiesterase
enzyme that degrades cAMP into AMP
How is cAMP degraded into AMP?
Phosphodiesterase degrades cAMP into AMP
mating factor
signalling molecule secreted by yeast to indicate that they are ready to mate
How do budding yeast cells mate?
Two haploid yeast cells combine to form a diploid cell and then start to bud offspring
What happens when mating factor binds to a cell-surface receptor in yeast?
Yeast stops its normal growth cycle and a signalling pathway is triggered
Why was yeast mating studied extensively?
Their signalling pathways had protein kinases, GTP-binding proteins and other similarities
quorum sensing
method of cellular communication in bacteria to determine bacteria density
autoinducer
signalling molecule that bacteria secrete to communicate with other bacteria of its kind
What do autoinducers do?
They can turn certain genes on and off
What happens when there is a high concentration of bacteria?
Concentration of autoinducers increases, which triggers many genes, including autoinducers, creating a positive feedback loop
biofilm
large and complex colonies of bacteria
How do biofilms attack a host?
Bacteria in the biofilm exchange signals to coordinate the release of toxins to attack the host
