1 - Basics of communication Flashcards
Why are signalling systems needed?
- Coordinate the activities of cells/tissues in a multi-cellular organism
- neurotransmission
- homeostasis
Types of signalling between cells
- free diffusion between cells
- via cytoplasmic connections
- direct cell-to-cell contact
signalling by free diffusion
autocrine, paracrine, endocrine
autocrine signaling
signalling and reception by the same cell
- cells secrete chemicals that modify its own behaviour
- associated with growth regulation
paracrine signaling
signalling between nearby cells
- effects are local and short-lived
- coordinates actions of neighbouring cells in embryonic development
endocrine signalling
signalling between distant cells (by hormones)
- endocrine glands secrete hormones into extracellular spaces, which then diffuse into the circulatory system
synaptic signalling
A highly specific and localized type of paracrine signalling between two nerve cells or between a nerve cell and a muscle cell.
signalling via cytoplasmic connections
Transfer of signal from one cell to its neighbour through pores in the membrane
• The fastest mode of cell-cell communication
signalling by cell-to-cell contact
Involves specific interactions between surface molecules on one cell and receptors on another cell
• Responsible for cell-cell recognition in animals
• Important in embryonic development and immune response
types of signalling molecules
local regulators and hormones
what do local regulators do?
act on cells in the vicinity (autocrine + paracrine)
what do hormones do? (signalling)
act at a distance (endocrine)
what types of local regulators are there?
- growth factors
- gases
- prostaglandins
- neurotransmitters
growth factors
Peptides or proteins that stimulate cell proliferation
May have >1 target cells and hence >1 function
gases (nitric oxide)
acts as a paracrine signal molecule - Synthesized from arginine by nitric oxide synthase
-Induces vasodilation in the cardiovascular system
who discovered nitric acid as a signalling molecule?
Furchgott, Ignarro and Murad (1998)
prostaglandins
modified fatty acids
functions include:
- Excitability of the uterine wall during childbirth (induces labour)
- Induction of fever and inflammation in the immune system
Neurotransmitters
- Acetylcholine
- Biogenic amines
- Amino acids
- Neuropeptides
- Some neurotransmitters are inhibitory, some are excitatory, and some can be either
- Some occur in both the central nervous system and the peripheral nervous system
hormones
Secreted by endocrine glands and transported in the bloodstream
• Hormone production controlled by neuroendocrine system (hypothalamus is control centre)
major glands of the endocrine system
- pineal
- hypothalamus
- pituitary
- thyroid
- parathyroid
- thymus
- adrenal
- pancreas
- ovaries
- testes
simple endocrine pathway
endocrine cells respond directly to an internal or environmental stimulus by secreting a particular hormone
negative feedback
A primary mechanism of homeostasis, whereby a change in a physiological variable that is being monitored triggers a response that counteracts the initial fluctuation.
Homeostasis
maintenance of a relatively stable internal environment in the face of stress from the external and internal environments
2 main classes of hormone
- peptides/proteins
2. steroids
peptides/proteins
- Bind to receptors on the cell surface
* Trigger events within cell cytoplasm through second messengers
steroids
- Manufactured from cholesterol
* Can pass across lipid bilayer of plasma membrane and bind to receptors within cell
signal transduction pathway
The conversion of a signal at the cell surface to a specific cellular response
3 main stages of signal transduction
- reception of signal at cell surface
- transduction of the signal
- cellular response -output
Reception of the signal at cell surface
Involves binding of a signal molecule to a specific receptor at the cell surface, changing the conformation of the receptor
transduction of the signal
Converting the signal into a response is usually multiple steps
multistep pathways
- Can amplify a signal: A few molecules can produce a large cellular response
- Provide more opportunities for coordination and regulation
The cellular response - output
- The response may occur in the cytoplasm or may involve action in the nucleus
- Some pathways regulate the activity of enzymes
- Other pathways switch on genes by activating transcription factors
Signal Specificity
Different cells respond to the same signal in different ways because of differences in signal receptor proteins, relay proteins, and proteins needed to carry out the response
• Pathway branching and ‘cross-talk’ further help the cell coordinate incoming signals
