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Bioenergetics And Transformation > Cell signalling > Flashcards

Cell signalling Flashcards

1
Q

What is the function of extracellular signals in metabolic pathways ?

A
  • help to preserve homeostasis
  • coordinate cellular activity throughout the whole organism
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2
Q

What is the most important mechanism of intercellular communication in metabolism ?

A

The endocrine system

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3
Q

What are the 4 mechanisms of intercellular communication ?

A
  • juxtrine : direct contact
  • paracrine : the signal released will affect cells in close proximity
  • autocrine : it is a type of paracrine mechanism but the sender of the signal and target cell is the same
  • endocrine : signalling between cells over a short or long distance
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4
Q

Describe the general sequence of events that happen in an intercellular communication mechanism

A

1) synthesis of the signal molecule
2) release of the signal molecule
3) transport of the signal molecule to the target tissue
4) detection of the signal molecule (binding to the receptor)
5) effect
6) removal of the signal molecule

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5
Q

What is the endocrine system ?

A
  • endocrine organs produce hormones which have effects beyond their tissue of origin
  • examples of endocrine organs include the adrenal glands and pancreas
  • the release of these hormones will affect other chemicals and regulate a metabolic pathway
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6
Q

What are the 2 types of receptors involved in the endocrine system ?

A
  • nuclear receptors : they alter the rate of DNA transcription and therefore protein synthesis
  • cell surface receptors : they are coupled to a variety of intracellular reactions called signal transduction cascades
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7
Q

Which types of hormones bind to nuclear receptors ?

A
  • hydrophobic hormones bind to nuclear receptors
  • they alter gene expression
  • effects may take minutes to hours
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8
Q

Which types of hormones bind to cell surface receptors ?

A
  • hydrophilic hormones bind to cell surface receptors
  • cause downstream effects
  • insulin, glucagon and adrenaline will bind to cell surface receptors
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9
Q

What is glucagon ?

A

glucagon is a peptide hormone (29 amino acids long) which is secreted by the alpha cells of the pancreas

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10
Q

When is glucagon secreted ?

A

it is secreted when blood glucose levels drop

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11
Q

What is the role of glucagon ?

A
  • it promotes the mobilisation of fuel reserves
  • it inhibits the the utilisation of glucose
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12
Q

What is the main target tissues of glucagon ?

A
  • liver
  • adipocytes (fat cells)
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13
Q

What is adrenaline ?

A

it is a derivative of the amino acid tyrosine and it is synthesised in the adrenal glands

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14
Q

How is the secretion of adrenaline controlled ?

A

secretion is controlled directly by the brain through the nervous system

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15
Q

What is the role of adrenaline ?

A
  • promotes the mobilisation of fuel reserves
  • inhibits storage pathways
  • affects circulation
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16
Q

What is the main target tissues of adrenaline ?

A

most tissues are a target

17
Q

What is insulin ?

A
  • it is generated as a polypeptide of ~ 103 amino acids and called proinsulin
  • it is then modified into an active form ~ 51 amino acids long
18
Q

When is insulin secreted ?

A
  • secreted by the beta cells of the pancreas
  • in response to increased levels of glucose in the blood
19
Q

What is the role of insulin ?

A
  • promotes an anabolic state by channelling metabolism towards the storage of carbohydrates and lipids
20
Q

What is the main target tissues of insulin ?

A
  • liver
  • muscle
  • adipose (fat)
21
Q

What happens when glucagon, insulin and adrenaline bind to cell surface receptors ?

A
  • the structure of the protein will change
  • this leads to an event : generation of a secondary messenger or change in membrane potential
  • this will activate enzymatic cascades
22
Q

What are the different types of cell surface receptors ?

A
  • ligand gated ion channel receptor
  • cytokine receptors
  • enzyme linked receptors
  • G protein coupled receptors
23
Q

Which types of receptors do glucagon, adrenaline and insulin bind to ?

A
  • insulin binds to enzyme linked receptors
  • glucagon and adrenaline binds to G protein coupled receptors
24
Q

Describe the general signalling events that happen in the endocrine system

A

1) a signal will be released by a hormone due to a change in the environment
2) the signal is transported around the body by the blood
3) it will reach a receptor and bind
4) the signal will be relayed from the outside of the cell to the inside
5) there is amplification of the signal by enzyme activation
6) there will be an increase in the concentration of 2nd messenger
7) this leads to a cellular effect

25
Q

Which types of G protein coupled receptors does adrenaline bind to ?

A
  • α adrenergic receptors
  • β adrenergic receptors
26
Q

Where are G protein coupled receptors located ?

A
  • they sit across the surface of the membrane
  • the receptor proteins are located in the plasma membrane and have 7 transmembrane spanning regions
27
Q

Describe G protein coupled receptors

A
  • they are guanosine binding proteins
  • when GDP is bound they are inactive
  • when GTP is bound they are active
  • there are 2 types : monomeric and trimeric
  • trimeric receptors have 3 subunits and the guanosine nucleotide will bind to the α subunit
28
Q

Describe signal transduction by glucagon and adrenaline

A

1) binding of the hormone to the receptor will induce a conformational change in the receptor
2) the activated receptor will bind to the alpha subunit of the G protein
3) the activated receptor will cause a conformational change in the alpha subunit triggering the dissociation of GDP
4) GTP will bind to the alpha subunit causing dissociation of the alpha subunit from the receptor and from the other 2 subunits of the G protein
5) the hormone will dissociate from the receptor and the alpha subunit will bind to the effector activating it
6) hydrolysis of GTP to GDP will cause the alpha subunit to dissociate from the effector and reassociate with the other 2 subunits

29
Q

How is the signal transduction of glucagon and adrenaline amplified ?

A
  • glucagon receptors and β adrenergic receptors initiate a cascade of events via the secondary messenger cAMP which will amplify the signal of the hormone
  • the effector involved in the signal transduction is adenyl cyclase and this takes ATP and turns it into cAMP
30
Q

Describe the structure and function of protein kinase A

A
  • it has 4 subunits : 2 catalytic and 2 regulatory
  • it is a key enzyme in the modulation of metabolic enzymes
  • it phosphorylates proteins
  • cAMP binds to the regulatory subunits leading to a conformational change
31
Q

Describe the control of adenylate cyclase

A
  • it can be upregulated or downregulated by the action of different hormones
  • the alpha subunit has hydrolytic activity which rapidly converts GTP to GDP
32
Q

Describe how the cellular response is terminated

A

cell signalling requires a rapid termination once hormone levels decrease
- if something is switched on it needs to be switched off again

33
Q

List some diseases associated with defective cell signalling

A

excessive signalling :
- cholera
- cancer
- hypertension

deficient signalling :
- night blindness
- pertussis

34
Q

Summarise cholera

A
  • caused by Vibrio cholerae
  • affects intestinal epithelial cells
  • an increase in cAMP leads to chloride transport into the lumen and absorption of Na+ leading to water loss
35
Q

What are some alternative secondary messengers ?

A

α adrenergic receptors involve the secondary messengers DAG and Ca 2+

36
Q

Describe signal transduction by insulin

A

1) insulin binds to an enzyme linked receptor
2) the receptor undergoes autophosphorylation on its tyrosine residues
3) the insulin receptor will phosphorylate IRS-1
4) IRS-1 activates other kinase enzymes leading to downstream effects
5) it also activates phosphatases which cause dephosphorylation
6) insulin signal transduction is downregulated by endocytosis

Bioenergetics And Transformation (10 decks)

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