Chapter 9: Cell Communication Flashcards
1
Q
intercellular signalling
A
communication between cells
2
Q
intracellular signalling
A
communication within a cell
3
Q
signalling cell
A
cell that delivers signals to other cells
4
Q
ligand
A
molecule that binds to another specific molecule
5
Q
receptor
A
protein that can receive ligands from signalling cells
6
Q
target cell
A
cell that has a receptor to receive ligands from signalling cells
7
Q
What are the four categories of chemical signalling in multicellular organisms?
A
Paracrine signalling, endocrine signalling, autocrine signalling and direct signalling across gap junctions
8
Q
paracrine signal
A
signalling between nearby cells
9
Q
How do paracrine signals reach the target cell?
A
They diffuse through the extracellular matrix towards the target cell
10
Q
What happens to a paracrine signal after it has reached its target cell?
A
It is degraded by enzymes or removed by neighbouring cells
11
Q
Why do paracrine signals last a short time?
A
Removing the paracrine signal quickly reestablishes the concentration gradient so signals can travel freely again
12
Q
synaptic signal
A
chemical signal that travels between nerve cells
13
Q
neurotransmitter
A
ligand released by nerve cells
14
Q
chemical synapse
A
small space between nerve cells
15
Q
How are signals propagated through nerve cells?
A
They are propagated by electrical impulses
16
Q
How are signals transferred from nerve cell to nerve cell?
A
Neurotransmitters are released from the signalling nerve cell to the target nerve cell
17
Q
What happens to neurotransmitters after they have been received by the target cell?
A
They are destroyed by enzymes or are reabsorbed for further use
18
Q
What type of chemical signalling is synaptic signalling?
A
Paracrine signalling
19
Q
endocrine signal
A
signalling between cells that are very far away
20
Q
endocrine cell
A
cells that secrete and send hormones in endocrine signalling
21
Q
hormone
A
signalling molecules that are the ligands in endocrine signalling
22
Q
How do hormones travel from the signalling cell to the target cell?
A
They travel through the bloodstream
23
Q
How is endocrine and paracrine signalling different?
A
- Endocrine signalling is slower and longer lasting
2. Endocrine signalling ligands are found in lower concentrations
24
Q
autocrine signal
A
when the signalling cell binds to the ligand that it produces
25
What cells are affected in autrocrine signalling?
The signalling cell and sometimes the neighbouring cells are affected
26
When does autocrine signalling usually occur?
During early development of an organism to ensure cells develop correctly
27
intracellular mediator
small molecule that transfers signals inside a cell
28
How can intracellular mediators diffuse to other cells?
Through gap junctions and plasmodesmata
29
internal receptor
receptors that are found in the cytoplasm of a cell
30
In what process are internal receptors often involved in?
They are used to regulate mRNA synthesis
31
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
32
cell-surface receptor
cell surface integral proteins that bind to external ligands
33
How much of the plasma membrane does a cell-surface receptor span?
They are all transmembrane receptors
34
What are the three components of a cell-surface receptor?
An extracellular, transmembrane and intracellular domain
35
What are the three types of cell-surface receptors?
Ion channel-linked receptors, G-protein-linked receptors and enzyme-linked receptors
36
ion channel-linked receptor
channel proteins that have a binding site for ligands to allow ions through
37
G-protein-linked receptor
receptor that activates G-proteins to transmit signals to membrane components
38
How many transmembrane domains does a G-protein-linked receptor have?
Seven
39
G-protein-coupled receptor
G-protein-linked receptor that has a G-protein bound to it
40
heterotrimeric G-protein
G-protein made up of an alpha, beta and gamma subunit
41
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
42
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
43
What are the main symptoms of cholera?
Dehydration and diarrhoea
44
What bacterium is responsible for cholera?
Vibrio cholerae
45
Which part of the body does Vibrio cholerae invade?
The small intestines
46
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
47
enzyme-linked receptor
receptors that have intracellular domains that interact directly with an enzyme or is an enzyme itself
48
What is the transmembrane domain of an enzyme-linked receptor like?
It is a single alpha-helical region spanning the membrane
49
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
50
receptor tyrosine kinase
enzyme-linked receptor that phosphorylates tyrosine residues to transmit a signal
51
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
52
What type of molecules are the main small hydrophobic ligands?
Steroid hormones
53
What is the main female sex hormone?
Estradiol
54
estrogen
group of steroid hormones in the female body
55
What is the main male sex hormone?
Testosterone
56
What is the precursor to all steroid hormones?
Cholesterol
57
What are the two main types of ligands?
Small hydrophobic ligands and water-soluble ligands
58
water-soluble ligand
ligand that is polar and cannot enter the cell unaided
59
nitric oxide
gas that acts as a ligand
60
Why is nitric oxide a good ligand?
It can diffuse across the plasma membrane
61
signal transduction
continued propagation of a signal through the cytoplasm
62
In which type of receptors does signal transduction occur in?
Cell-surface receptors
63
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
64
dimerisation
when two molecules bind to each other
65
signalling pathway
the chain of events that follows after the activation of a receptor's intracellular domain
66
downstream event
event that occurs after a certain point
67
upstream event
event that occurs before a certain point
68
signal integration
when signals from two or more different receptors merge to trigger the same response
69
What are the two main methods used in intracellular signalling?
Phosphoryation and using second messengers
70
amino acid residue
R group of an amino acid
71
What is usually phosphorylated in intracellular signalling?
Nucleotides or amino acid residues of proteins
72
Which amino acid residues are usually phosphorylated in intracellular signalling?
Serine, threonine and tyrosine residues
73
Where does a phosphate group bind to during phosphorylation in intracellular signalling?
It replaces the hydroxyl group of the amino acid
74
What does the phosphorylation of serine and threonine residues do in intracellular signalling?
It often activates an enzyme
75
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
76
second messenger
small molecule that propagates a signal after a ligand has bound to a receptor
77
Which ion is used as a common second messenger?
Ca2+
78
Where do calcium ions come from in intracellular communication?
They are stored in cytoplasmic vesicles or are accessed from outside the cell
79
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
80
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
81
cyclic AMP
molecule synthesised from ATP and acts as a second messenger
82
What is the main role of cyclic AMP?
To bind to an enzyme called cAMP-dependent kinase
83
A-kinase
cAMP-dependent kinase
84
How is cAMP made from ATP?
Adenylyl cyclase cleaves a pyrophosphate from ATP to create cAMP
85
pyrophosphate
Two phosphate groups joined together to create P2O7
86
Which enzyme synthesises cAMP from ATP?
Adenylyl cyclase
87
What is the main role of A-kinase?
It regulates many metabolic pathways by phosphorylating serine and threonine residues
88
inositol phospholipid
type of phospholipid that is found in small quantities in the plasma membrane
89
inositol
carbohydrate that is a glucose isomer
90
What is the structure of an inositol phospholipid?
It is a phospholipid with a inositol as its phosphate head group
91
What is the main inositol phospholipid involved in cellular signalling?
Phosphatidylinositol
92
What is created when PI is phosphorylated?
Either PI-phosphate or PI-bisphosphate
93
PIP
phosphatidylinositol-phosphate
94
PIP2
phosphatidylinositol-bisphosphate
95
Which two second messengers can PIP2 be cleaved into?
Diacylglycerol and inositol triphosphate
96
Which enzyme cleaves PIP2 into DAG and IP3?
Phospholipase C
97
DAG
diacylglycerol
98
IP3
inositol triphosphate
99
What does DAG do as a second messenger?
DAG stays in the membrane after being cleaved and activates protein kinase C
100
PKC
protein kinase C
101
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+
102
EGF
epidermal growth factor
103
EGFR
epidermal growth factor receptor
104
What is the role of EGF?
To regulate protein synthesis
105
How is EGFR activated?
When EGF binds to EGFR, tyrosine residues are phosphorylated and a signalling pathway is triggered
106
inhibitor
molecule that binds to a protein to reduce or prevent function
107
How does PKC activate DNA transcription?
It phosphorylates serine and threonine residues in Iκ-B, which allows NF-κB to initiate RNA transcription
108
Iκ-B
inhibitor protein that prevents RNA transcription
109
NF-κB
regulatory protein required in RNA transcription
110
What is another name for cAMP-dependent kinase?
Protein kinase A
111
PKA
protein kinase A
112
What receptor does adrenaline activate?
Beta-adrenergic receptors
113
What happens when beta-adrenergic receptors are activated?
They release cAMP
114
What happens when adrenaline increases cAMP levels?
It activates PKA which in turn activates two enzymes?
115
Which two enzymes does PKA activate during an adrenaline rush?
GPK and GS
116
GPK
glycogen phosphorylase kinase
117
GS
glycogen synthase
118
What happens when GPK is activated?
It activates glycogen phosphorylase
119
GP
glycogen phosphorylase
120
What happens when GP is activated?
Glycogen is catabolised into glucose
121
What happens when GS is activated?
The cell is unable to form glycogen from glucose
122
growth factor
ligands that promote cell growth
123
MAPK/ERK pathway
chain of proteins in a cell that communicates a signal from a cell-surface receptor to nuclear DNA
124
apoptosis
programmed cell death
125
How can apoptosis be triggered?
When abnormalities are detected in the cell or from external signalling
126
How is apoptosis necessary for embryonic development of vertebrates?
Web-like tissue between fingers and toes must be eliminated through apoptosis
127
How is apoptosis necessary in T-cell development?
Immature T-cells that bind to self proteins undergo apoptosis to prevent further harm
128
T-cell
immune cell that binds to foreign molecules for self destruction
129
phosphatase
enzymes that remove phosphate groups attached by kinases
130
phosphodiesterase
enzyme that degrades cAMP into AMP
131
How is cAMP degraded into AMP?
Phosphodiesterase degrades cAMP into AMP
132
mating factor
signalling molecule secreted by yeast to indicate that they are ready to mate
133
How do budding yeast cells mate?
Two haploid yeast cells combine to form a diploid cell and then start to bud offspring
134
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
135
Why was yeast mating studied extensively?
Their signalling pathways had protein kinases, GTP-binding proteins and other similarities
136
quorum sensing
method of cellular communication in bacteria to determine bacteria density
137
autoinducer
signalling molecule that bacteria secrete to communicate with other bacteria of its kind
138
What do autoinducers do?
They can turn certain genes on and off
139
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
140
biofilm
large and complex colonies of bacteria
141
How do biofilms attack a host?
Bacteria in the biofilm exchange signals to coordinate the release of toxins to attack the host
