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POM (Principles of Medicine) > Cell signalling > Flashcards

Cell signalling Flashcards

1
Q

Why do we need cell signalling?

A
  1. to process info
  2. for self-preservation
  3. for voluntary movement
  4. for homeostasis
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2
Q

What are the 2 main systems in the body that provide lines of communication?

A
  • Nerve fibres of the central and peripheral nervous system.

- The blood vessels of the cardiovascular system.

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3
Q

he nervous system provides a rapid almost instantaneous response

A

whilst the blood vessels provide a slower more versatile regulation.

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4
Q

Neurotransmission steps

bioelectrical signal- chemical signal- bioelectrical signal

A
  1. propagation of the action potential
    2, neurotransmitter release from vesicles
  2. Activation of postsynaptic receptors
  3. Activation of postsynaptic receptors
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5
Q

How is an AP propagated?

A
  • by VGSC’s opening
  • Na + influx –> membrane depolarisation –> AP ‘moves along’ neurone
  • VGKC opening –> K+ efflux –> repolarisation
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6
Q

What is then released from vesicles?

A

neurotransmitter

  • AP opens voltage-gated Ca2+ channels at presynaptic terminal
  • Ca2+ influx –> vesicle exocytosis
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7
Q

What happens when the postsynaptic receptors are activated?

A
  • NT binds to receptors on the post synaptic membrane

- receptors modulate post-synaptic activity

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8
Q

What chemicals utilise the circulatory system for transportation?

A

hormones

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9
Q

Where are hormones produced?

A

by most of the major organs of the body however there are a few organs that play a more prominent role than others, such as the hypothalamus and the pituitary gland

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10
Q

What are 4 main modes of communication?

A
  1. Endocrine communication
  2. Paracrine communication
  3. Communication between membrane receptors
  4. Autocrine communication
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11
Q

What is endocrine signalling?

A

hormone travels within blood vessels to act on a distinct target cell

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12
Q

What are some examples of endocrine signalling?

A

glucagon
insulin (produced in liver acts on liver, muscles + adipose tissue)
adrenalin (produced in adrenal glands acting on the trachea)

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13
Q

What is paracrine signalling?

A

when the hormone acts on an adjacent cell

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14
Q

examples of paracrine signalling?

A
  • insulin
  • nitric oxide (produced by endothelial cells in blood vessels)
  • osteoclast activating factors produced by adjacent osteoblasts
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15
Q

What is signalling between membrane-attached proteins?

A

plasma membrane proteins on adjacent cells interacting

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16
Q

examples of signalling between membrane-attached proteins?

A
  • HIV GP120 glycoprotein –> CD4 receptors on T-lymphocytes

- bacterial cell wall components –> toll-like receptors on haematopoietic cells

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17
Q

What is autocrine signalling?

A

signalling molecule acts on the same cell

18
Q

examples of autocrine signalling?

A

acetylcholine –> presynaptic M2 - muscarinic receptors

- growth factors from tumour cells —> mitogenesis

19
Q

What are ligands?

A

chemical messages or molecules ->they exert their effects through binding to receptors

20
Q

What are receptors usually?

A

proteins that bind the chemical mediators known as ligands and upon activation they elicit an effect within a cell

21
Q

What are second messengers?

A

The intracellular effect evoked by an occupied receptor usually arises due to any chemical messenger that is a separate entity from the receptor or the ligand

22
Q

What are the 4 categories of receptors?

A
  1. Ligand-gated ion channel receptors
  2. G protein coupled receptors
  3. Enzyme-linked receptors
  4. Intracellular receptors
23
Q

What are Ligand-gated ion channel receptors (ionotropic receptors)?

A

transmembrane receptors which have a central pore incorporated within their quaternary structure

24
Q

What happens when the appropriate ligand attaches to the ‘ligand-binding domain’ on the external surface of the protein?

A

the pore will open

25
Q

What is the process of ligand-gated ion channel activation?

A
  1. The ligand binds to the receptor protein
  2. A change in conformation of the channel protein results in the opening of a pore, which spans the cell membrane.
  3. The pore allows ions to move in or out of the cell according to their respective concentration gradients
26
Q

What are G protein-coupled receptors?

A

7-transmembrane receptors because the channel protein crosses the cell membrane 7 times

27
Q

What are G protein-coupled receptors linked to?

A

an intracellular G protein complex, which consists of an alpha (α) subunit, a beta-gamma (βγ) subunit and an associated GDP molecule

28
Q

What are the 3 Ga subunits?

A

Ga q/11
Ga s
Ga i/o

29
Q

G protein activation process?

A
  1. In the resting state the G protein complex consists of a Gα subunit, a Gβγ subunit and an associated GDP molecule, which are in close proximity to the receptor
  2. Ligand binding causes the G protein complex to associate with the receptor resulting in the GDP molecule being phosphorylated to a GTP molecule
  3. The Gα subunit dissociates from the Gβγ subunit
  4. Both Gα and Gβγ can act as second messengers
  5. When the ligand dissociates from the receptor, internal GTPase on the Gα subunit hydrolyses GTP to GDP
  6. The Gα and Gβγ subunits re-associate and are once again available to the receptor
30
Q

What is phosphorylation?

A

The addition of a PO4 group. This simple chemical reaction activates a number of protein enzymes and is carried out by kinases

31
Q

What is Phosphatase?

A

An enzyme that remove a phosphate group from its substrate.

32
Q

What is Dephosphorylation?

A

The removal of a PO4 group. This hydrolysis reaction inactivates a number of protein enzymes and is carried out by phosphatases

33
Q

What are enzyme-linked receptors?

A

transmembrane receptors ordinarily only consist of one transmembrane domain, which has the ligand-binding domain on the outside and specialised enzymes on the inside

34
Q

Do enzyme-linked receptors work alone?

A

no, they require clustering of more than one receptor protein to activate the intracellular enzyme.
Once activated the intracellular enzymes trigger a signalling cascade within the cell.

35
Q

Enzyme-linked receptor activation process?

A
  1. Ligand binding results in receptors clustering.
  2. Receptor clustering activates enzyme activity within the cytoplasmic domain.
  3. The enzymes phosphorylate the receptor.
  4. This phosphorylation leads to the binding of signalling proteins to the cytoplasmic domain.
  5. These signalling proteins recruit other signalling proteins and a signal is generated within the cell.
  6. The signal is terminated when a phosphatase dephosphorylates the receptor
36
Q

What are steroid hormones?

A

membrane permeable + exert their actions on intracellular receptors

37
Q

What are intracellular receptors?

A

transcription factors + regulate mRNA and protein synthesis

38
Q

What are the 2 classes of steroid hormones?

A

Type I receptors

Type II receptors

39
Q

Type I steroid receptors

A

located within the cytosolic compartment and are associated with chaperone molecules (normally heat shock proteins, hsp). Once the hormone binds to the receptor, the hsp molecule dissociates allowing the hormone-receptor complex to form a homodimer with another identical hormone-receptor complex. The homodimer subsequently translocates to the nucleus where it binds to DNA and acts as a transcription factor

40
Q

Type II steroid receptors

A

located within the nucleus of a cell and are often already bound to DNA. Binding of the hormone ligand to the receptor usually results in direct transcriptional regulation by the activated hormone-receptor complex

POM (Principles of Medicine) (17 decks)

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