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BGM2002 CS > L1 - Introduction to cell signalling > Flashcards

L1 - Introduction to cell signalling Flashcards

1
Q

What is cell signalling?

A

A complex system of communication that governs basic cellular activities & coordinates cell actions

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2
Q

Cell signalling affects a cells ability to…

A

Regulate cellular processes

Respond to its environment

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3
Q

Cell signalling affects…

A
  • Development
  • Tissue repair
  • Immunity
  • Movement
  • Diseases
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4
Q

What does cell survival depend on?

A

Depends on receiving & processing information from the environment

A cell is exposed to 100s of different extracellular signal molecules but must respond selectively to a limited set of signals

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5
Q

Importance of cell signalling in humans

A

During embryological development, cells exchange signals to determine which specialised role each cell will adopt

Specialised cells: must communicate to form a tissue & maintain its function

Different cells (cell types) must produce a coordinated response to support the organism as a whole

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6
Q

What happens when we get defects or dysregulation in signalling pathways?

A

Disease

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7
Q

What are the 5 basic types of cell signalling?

A
  • Gap junctions
  • Autocrine
  • Paracrine
  • Endocrine
  • Synaptic
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8
Q

No distance signalling

A

Gap junctions

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9
Q

Short distance signalling

A

Autocrine

Paracrine

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10
Q

Long distance signalling

A

Endocrine

Synaptic

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11
Q

What are gap junctions?

A

Cytoplasmic channels between adjacent cells: connect cytoplasm to adjacent cells

Maintain homeostasis in connected cells for ion balance

Can allow passage of signal molecules: electrical & metabolic coupling between cells

They provide metabolic cooperation between adjacent cells

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12
Q

Example of direct contact signalling

A

The APC

Antigen display: becomes the message passed from macrophage to T helper cell

APC: APC presents the antigen complexed with MHC II on its surface to be recognised by the helper T cell

Leads to the activation of other immune cells

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13
Q

What is autocrine signalling?

A

Cell signals to itself

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14
Q

Example of autocrine signalling

A

IL-2 secreted by monocytes in response to external stimuli can bind to receptor on secreting monocytes

Secretion of growth/survival factors by tumour cells

Commonly used by immune cells

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15
Q

What is paracrine signalling?

A

Cell signals to neighbouring cells

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16
Q

Examples of paracrine signalling

A

Wnt & Hedgehog signalling pathways

Inflammatory mediators

17
Q

Paracrine signalling

Cancer cell migration control through a paracrine loop

A

Production of epidermal growth factor (EGF) by tumour-associated macrophages (TAM) to increase the invasiveness & migration of neighbouring breast tumour cells that express the EGF receptor (EGFR)

Secretion of colony-stimulating factor 1 (CSF1) by invasive tumour cell recognised by tumour-associated macrophages expressing CSF1R receptors

Results in the migration of cancer cells towards macrophages

Clever way of using the immune system to its advantage

18
Q

Paracrine signalling

Histamine release by mast cells during allergic reaction

A

When exposed to pollen, pollen binds to IgE on the mast cell

This activates the mast cell

Degranulation occurs causing the release of histamine

Histamine works on the local environment to increase vascular permeability causing runny nose & watery eyes

Sneezing as a result of histamine acting on neurones

19
Q

Paracrine signalling

Neuronal signalling

A

Electrical signal (fast communication) along the nerve cells trigger neurotransmitter release

Neurotransmitter is a chemical signal

20
Q

What does a neurotransmitter do?

A

Diffuses across synapse
Binds to receptor on other neurone
Triggers responses in cells or target tissues (neurons, muscles, or glands)
Remains in synapse – broken down after use

Specificity: determined by synaptic contact between secreting neuron & target cell

Can be inhibited to control the amount of signal travels – modulation

21
Q

Endocrine cells

A

Secrete hormones into the blood where hormones travel to specific target cells that recognise them

Specificity: target cells have receptors for binding a specific hormone

22
Q

Synaptic signalling

A

Neurones can have very long axons & target cells far away

Neurones secrete neurotransmitter

Specificity: arises from the synaptic contacts between a nerve cell & the specific target cells

23
Q

Types of signals received by cells

A

Signalling molecules

1 signal can cause a multitude of cell responses in the target cell

Intracellular & extracellular signals

24
Q

What are signalling molecules?

A

Mostly chemical signals

Act either locally, at short range or long distance

Act at very low concentrations (typically ~ 10-8 M) - signal amplification

Recognised with high affinity by specific receptors

25
Q

Intracellular & extracellular signals

A

Water soluble signal molecules bind EC domains of cell-surface receptors (cannot readily cross membrane)
• Eg. peptide hormones, growth factors, hydrophilic neurotransmitters

Small, hydrophobic signal molecules can pass through the plasma membrane & bind to intracellular receptors in the nucleus or cytoplasm
• Eg. steroid hormones & NO

26
Q

How do cells convert an extracellular signal to a cellular response?

A

RECEPTION

TRANSDUCTION

CELL RESPONSE

27
Q

What is reception?

A

The target cell detects a signalling molecule present in the exogenous environment

28
Q

What is transduction?

A

Signal is converted into another signal & relayed by molecules

29
Q

What is cell response?

A

Specific cellular effects produced in response to signalling molecules

30
Q

Challenges associated with cell signalling

A

1 signal can have different effects in distinct cell types

Multicellular organisms are constantly exposed to a variety of extracellular signals

31
Q

Solution to 1 signal having different effects in distinct cell types

A

Different cell types have different receptors for the same signal & induce different signalling cascades
• Muscarinic acetylcholine receptors
• Nicotinic acetylcholine receptors

32
Q

Solution to multicellular organisms constantly being exposed to a variety of extracellular signals

A

Cells have a variety of signalling mechanisms & collections of receptors

Signalling pathways integrate information to provide a coordinated response by sharing molecules between different pathways – organised in protein networks

Feedback mechanisms

33
Q

Characteristics of cell signalling

A

SPECIFICITY

INTEGRATION & COORDINATION

AMPLIFICATION & FEEDBACK

34
Q

Specificity in cell signalling

A

Signal molecules should be specific to only reach target cells
– Receptor specificity for the ligand
– Transmission signal across the plasma membrane
– Specific receptors expressed in distinct cell types

35
Q

Integration & coordination in cell signalling

A

Each cell receives multiple EC signals + many signalling molecules are diffusing about in cells

If 2 or more signals have opposite effects on a metabolic pathway, the outcome result should reflect the integration of these signals to ensure a coordinated response

Signalling may interfere with core physiological processes

The intracellular relay system for the different signals interact (using common relay molecules) so that the presence of 1 signal modifies the responses to another

36
Q

Feedback loops in cell signalling

A

At each step, feedback loops can modify the signal & the output acts back to regulate the process

37
Q

What is deactivation?

A

Degradation / recycling of molecules

38
Q

What is adaptation/desensitisation?

A

Cells can adjust their sensitivity to a signal under prolonged exposure to a stimulus to decrease a cell response to that level of stimulus
– Inactivation of receptor by endocytosis, degradation or phosphorylation

Desensitisation may lead to tolerance & can lead to the loss of medicinal effectiveness of some medicines that are over prescribed

BGM2002 CS (14 decks)

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