Lecture 8

Question 1

What is signalling transduction

Answer 1

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

Question 2

What is amplification

Answer 2

An increase in the number of copies of a gene or genome

Question 3

Does signal transduction use hydrophobic or hydrophilic messangers

Answer 3

Hydrophilic (transported through water) messengers

Question 4

What can the first messanger of signal transduction be

Answer 4

The first messenger can be hormones, neurotransmitters, ect

Question 5

What type of proteins are found in receptors of signal transduction? Give an example of one

Answer 5

Several G-Proteins are associated with each receptor
— Ex. guanine nucleotide-binding proteins

Question 6

What is the second messenger of signal transduction

Answer 6

cAMP (cyclic adenosine monophosphate)

Question 7

What are the 2 roles of cAMP

Answer 7

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

Question 8

What are the 2 parts of signalling systems

Answer 8

1) Channel-liked receptors (neurotransmitters)
2) Secondary messangers (Ca2+, cGMP)

Question 9

What are the first 3 steps of hydrophilic messengers

Answer 9

1) One messenger binds to one receptor
2) Several G proteins are activated
3) Each G protein activates an adenylate cyclase

Question 10

What are the last 3 steps of hydrophilic messengers

Answer 10

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

Question 11

Signal transduction - explain signal cascading during exercise

Answer 11

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

Question 12

What are the properties of hydrophilic (or llipophobic) messengers

Answer 12

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

Question 13

What are the properties of hydrophobic (or lipiphilic) messengers

Answer 13

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

Question 14

What is neurocrine signalling

Answer 14

Chemical signalling facilitated in neurons or nerve cells

Question 15

Characteristics of neurocrine signalling

Answer 15

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

Question 16

Examples of neurocrine signalling

Answer 16

1) Norepinephrine released from noradrenergic nerves
2) Antidiuretic hormone released from neurons in anterior pituitary

Question 17

Signalling Characteristics of Nervous System

Answer 17

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

Question 18

Signalling Characteristics of Endocrine System

Answer 18

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

Question 19

Examples of endocrine tissue in the body

Answer 19

• Hypothalamus
• Anterior pituitary
• Adrenal glands
• Pancreas
• Thyroid
• Sex organs (ovaries, testis)
• Kidneys

Question 20

Fluid secretion into the intestinal lumen

Answer 20

• 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)

Question 21

Cholera Toxin and signalling transduction

Answer 21

• 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

Question 22

What is CFTR

Answer 22

• Cystic fibrosis transmembrane conductance regulator
• A Cl- transporter

Question 23

How is CF characterized

Answer 23

CF is characterized by a homozygous mutation in the CFTR gene

Question 24

What does CF impair

Answer 24

—Impairs regulation of sweat, digestive juices and mucus
—— Ie. Leads to thicker secretions and less water loss

Question 25

Explain CF’s relation to Cholera Toxin

Answer 25

CF could protect against severe loss of fluid that occurs due to cholera toxin

Question 26

Careers related to biological concepts of health

Answer 26

• Regulated healthcare professional
• Unregulated healthcare professional
• Public health
• Industry
• Research
• Education