1What is the purpose of cell signalling?
To allow cells to monitor their environment and respond to external stimuli
2How do cells communicate with each other?
Through chemical signalling molecules
3What is a ligand?
A chemical messenger released from a signalling (sender) cell
4What is the first step of cell signalling?
Detection of a stimulus by a target cell receptor
5What happens after ligand detection?
Signal transfer to the cytoplasmic side of the membrane
6What follows signal transfer?
Transmission through a signalling pathway to effector molecules
7What is the final step of cell signalling?
A specific cellular response
8What determines whether a cell responds to a signal?
Whether it has the appropriate receptor
9What happens if a cell lacks a receptor for a ligand?
It ignores the signal
10What are the five major types of cell signalling?
Autocrine, paracrine, endocrine, neural, and direct contact
11What is autocrine signalling?
Cells respond to signalling molecules they produce themselves
12Give examples of autocrine signalling molecules
Growth factors and prostaglandins
13What is paracrine signalling?
Signalling to nearby target cells
14Give examples of paracrine signalling
Inflammatory signalling and regulation of cell differentiation
15What is endocrine signalling?
Hormones released into the bloodstream to act on distant target cells
16Why is endocrine signalling considered the most common type?
Hormones travel through the bloodstream and can act throughout the body
17What are the two main classes of hormones?
Water-soluble and lipid-soluble
18How do water-soluble hormones signal?
By binding to cell-surface receptors
19Give examples of water-soluble hormones
Insulin and adrenaline
20How do lipid-soluble hormones signal?
By diffusing through the membrane to intracellular receptors
21Give examples of lipid-soluble hormones
Sex hormones and thyroid hormones
22What is neural signalling?
Rapid signalling via neurotransmitters released from nerve cells
23Where are neurotransmitter receptors located?
On the target cell membrane
24Give an example of neural signalling
Nerve-to-nerve or nerve-to-muscle transmission
25What is direct contact signalling?
Signalling through physical contact between adjacent cells
26What is an example of direct contact signalling?
Cell differentiation during embryonic development
27Where are intracellular receptors located?
In the cytoplasm or nucleus
28What type of ligands bind to intracellular receptors?
Lipid-soluble or very small signalling molecules
29Give examples of ligands that bind to intracellular receptors
Steroid hormones and nitric oxide (NO)
30How can intracellular receptors act as gene regulators?
They regulate transcription of target genes
31Give examples of gene-regulating intracellular receptor ligands
Cortisol, oestrogens, progesterone, vitamin D, thyroid hormone
32How can intracellular receptors act as enzymes?
They activate enzymatic activity upon ligand binding
33Give an example of enzyme-type intracellular receptor signalling
Nitric oxide activating guanylyl cyclase
34What is the effect of nitric oxide signalling in blood vessels?
Smooth muscle relaxation
35What defines a cell-surface receptor?
A receptor embedded in the plasma membrane
36What are the two key domains of a cell-surface receptor?
Extracellular ligand-binding domain and intracellular cytoplasmic domain
37How many classes of cell-surface receptors are described?
Three
38What are the three classes of cell-surface receptors?
Ligand-gated ion channels, enzyme-coupled receptors, and G protein-coupled receptors (GPCRs)
39What is the function of ligand-gated ion-channel receptors?
Rapid transmission of nervous signals across synapses
40What is an enzyme-coupled receptor?
A receptor with intrinsic or associated enzymatic activity
41Give an example of an enzyme-coupled receptor
Receptor tyrosine kinase (RTK)
42What are GPCRs responsible for?
Sight, taste, smell, and many signalling pathways
43In which organisms are GPCRs found?
Eukaryotes only
44Approximately how many functional GPCRs are encoded in the human genome?
About 800
45What structural feature do GPCRs share?
Seven membrane-spanning alpha helices
46What proteins do GPCRs interact with?
G proteins
47What are the three subunits of a G protein?
Alpha (α), beta (β), and gamma (γ)
48What nucleotide binds inactive G proteins?
GDP
49What nucleotide binds active G proteins?
GTP
50What happens when a ligand binds to a GPCR?
The receptor changes conformation
51How does GPCR activation affect the G protein?
The α subunit exchanges GDP for GTP
52What happens after GTP binding to the α subunit?
α dissociates from the βγ complex
53What does the activated α subunit do?
Interacts with a target membrane protein and initiates downstream signalling
54How is GPCR signalling terminated?
GTP is hydrolysed to GDP by the α subunit
55What happens after GTP hydrolysis?
The G protein returns to its inactive state and subunits reassociate
56What are second messengers?
Intracellular relay molecules that transmit signals from receptors to targets in the cell
57Why are second messengers important?
They amplify the original signal
58Which receptor types commonly use second messengers?
Some enzyme-coupled receptors and most GPCRs
59What are the three major classes of second messengers?
Cyclic nucleotides, IP3/DAG, and calcium ions (Ca²⁺)
60What cyclic nucleotides act as second messengers?
cAMP and cGMP
61What enzyme produces cAMP?
Adenylyl cyclase
62What activates adenylyl cyclase?
An activated G protein
63What is the role of protein kinase A (PKA) in signalling?
Mediates downstream effects of cAMP
64What enzyme is involved in the IP3 and DAG pathway?
Phospholipase C
65What intracellular store releases calcium in this pathway?
The endoplasmic reticulum
66What is signal amplification?
Increase of signal strength within the cell
67Why is signal amplification necessary?
Signalling molecules are often present at low concentrations
68How does amplification occur?
Through cascades of second messengers and protein kinases
69Can the same ligand cause different responses in different cells?
Yes
70What determines different responses to the same ligand?
The receptor type and intracellular signalling pathway
71Give an example of ligand-specific response variation
Acetylcholine affecting heart pacemaker cells
72How does acetylcholine slow heart rate?
βγ subunits open potassium (K⁺) channels, reducing pacemaker activity
73What happens when the G protein is inactivated in this pathway?
Potassium channels close
74How is cell signalling linked to disease?
Disrupted signalling pathways can cause abnormal cell responses
75What disease process is linked to abnormal signalling pathways?
Cancer