Lecture 8 Flashcards
What is signalling transduction
Process in which binding of an extracellular messenger to the cell surface receptor is translated into changes in biochemistry, cell biology, and gene transcription that make it possible for the cell to respond to the information that was received
What is amplification
An increase in the number of copies of a gene or genome
Does signal transduction use hydrophobic or hydrophilic messangers
Hydrophilic (transported through water) messengers
What can the first messanger of signal transduction be
The first messenger can be hormones, neurotransmitters, ect
What type of proteins are found in receptors of signal transduction? Give an example of one
Several G-Proteins are associated with each receptor
— Ex. guanine nucleotide-binding proteins
What is the second messenger of signal transduction
cAMP (cyclic adenosine monophosphate)
What are the 2 roles of cAMP
1) Ensuring cascade activation of one protein (protein kinase A) activates another
2) In the cytoplasm, a “kinase” phosphorylates a target and usually uses ATP as a phosphate donor
What are the 2 parts of signalling systems
1) Channel-liked receptors (neurotransmitters)
2) Secondary messangers (Ca2+, cGMP)
What are the first 3 steps of hydrophilic messengers
1) One messenger binds to one receptor
2) Several G proteins are activated
3) Each G protein activates an adenylate cyclase
What are the last 3 steps of hydrophilic messengers
4) Each adenylate cyclase generates 100s of cAMP molecules
—– Phosphodiesterase is the degradation of cAMP very rapidly
—– Used when you need to turn a signal OFF
5) Each cAMP activates a protein kinase A
6) Each protein kinase A phosphorylates hundred of proteins
Signal transduction - explain signal cascading during exercise
1) Epinephrine (chemical messenger)
2) Increases cAMP formation
3) Activates Protein kinase A
4) Activates hormone sensitive lipase
5) Activates lipolysis and release of fatty acids to provide fuel during exercise
What are the properties of hydrophilic (or llipophobic) messengers
Chemical class: AAs, amines, peptides
Storage in secretory cell: Secretory vesicles
Mechanism of secretion: Exocytosis
Transportation of blood: Disolved
Location of receptor: plasma membrane
Signal transduction mechanism: Open/close ion channels, activate membrane-bound enzymes, G proteins and second messenger systems
Relative time to onset on response: fast
Relative duration of response: short
Relative half life: short
What are the properties of hydrophobic (or lipiphilic) messengers
Chemical class: Steroids, eicosanoids, thyroid hormones
Storage in secretory cell: None
Mechanism of secretion: Diffusion
Transportation of blood: Bound to carrier protein
Location of receptor: cytosol or nucleus
Signal transduction mechanism: After transcription of mRNA
Relative time to onset on response: Slow
Relative duration of response: Long
Relative half life: Long
What is neurocrine signalling
Chemical signalling facilitated in neurons or nerve cells
Characteristics of neurocrine signalling
Sensory cell: neuron
Messenger: neurotransmitter (neurohormone)
Pathway: bloodstream
Target cell: endocrine cells
Specificity: receptors on target endocrine cells
Time to onset: delayed
Direction of effect: longer
Examples of neurocrine signalling
1) Norepinephrine released from noradrenergic nerves
2) Antidiuretic hormone released from neurons in anterior pituitary
Signalling Characteristics of Nervous System
Secretory cell: Neuron
Target cell: Neuron, muscle, gland
Messenger: Neurotransmitter
Pathway for communication : Across synapse
Basis of specificity: Receptors of postsynaptic target cells
Time to onset of effect: Immediate
Duration of affect: Brief
Signalling Characteristics of Endocrine System
Secretory cell: Endocrine cell
Target cell: Most cell types in body
Messenger: Hormones
Pathway for communication : Via bloodstream
Basis of specificity: Receptors on target cells throughout body
Time to onset of effect: Delayed
Duration of affect: Long
Examples of endocrine tissue in the body
- Hypothalamus
- Anterior pituitary
- Adrenal glands
- Pancreas
- Thyroid
- Sex organs (ovaries, testis)
- Kidneys
Fluid secretion into the intestinal lumen
- Maintaining normal fluid levels in the lumen is a matter of chloride and sodium secretion
- Too much loss of fluid can lead to diarrhea
- Cl- (chloride) and Na+ (sodium) pumps are regulated by protein kinesis (and cAMP)
Cholera Toxin and signalling transduction
- Secreted by bacterium vibrio cholerae
- Cholera grows under the mucus layer of the small intestine
- The secreted cholera toxin activates G protein for a prolonged period
—-Signal does not shut of - Causes a 20L efflux of Cl-, Na+ and water per day
- Consequence is life threatening diarrhea
What is CFTR
- Cystic fibrosis transmembrane conductance regulator
- A Cl- transporter
How is CF characterized
CF is characterized by a homozygous mutation in the CFTR gene
What does CF impair
—Impairs regulation of sweat, digestive juices and mucus
—— Ie. Leads to thicker secretions and less water loss
Explain CF’s relation to Cholera Toxin
CF could protect against severe loss of fluid that occurs due to cholera toxin
Careers related to biological concepts of health
- Regulated healthcare professional
- Unregulated healthcare professional
- Public health
- Industry
- Research
- Education
