Lipids in the cell membrane

Question 1

what are eicosaniods

Answer 1

• inflammatory mediators, they are released from cells and act on other cells
• they are considered local hormones
• They have specific effects on target cells close to
  their site of formation (autocrine/paracrine).
• They are rapidly degraded, so they are not transported to distal sites within the body.

Question 2

what is step one of cell to cell communication

Answer 2

synthesis of signal

Question 3

what is step two of cell to cell communication

Answer 3

release of the signalling molecules by the signalling cell: exocytosis, diffusion, cell-cell contact

Question 4

what is step three of cell to cell communication

Answer 4

transport of the signal to the target cell

Question 5

what is step four of cell to cell communication

Answer 5

detection of the signal by a specific receptor protein

Question 6

what is step five of cell to cell communication

Answer 6

a change in cellular metabolism, function or development triggered by the receptor-signal complex

Question 7

what is step six of cell to cell communication

Answer 7

removal of the signal or densensitisation

Question 8

transport of signals

Answer 8

can act at short or long-range. in animals, signalling by extracellular molecules can be classified into different types

Question 9

long range

Answer 9

endocrine: hormone released by endocrine ell and carried in the bloodstream to distal target cells

Question 10

example of a long-range hormone

Answer 10

FSH from pituitary to ovary

Question 11

short range

Answer 11

• neurotransmission (synapses)
• paracrine (signalling molecules only effect target cells in close proximity to secreting cells
• autocrine (cells respond to substances that they themselves release
• membrane bound proteins can interact to signal

Question 12

examples fo short range

Answer 12

breathing - the phrenic and thoracic nerves send impulses from the brain to the diaphragm
somatostatin release by pancreas cells acts locally
neurotransmitters and growth factors bind to the cells that release them
signalling by T cells in the immune system

Question 13

give me an example of multiple types of signalling occurring simultaneously

Answer 13

insulin being released from the pancreatic beta cells acts in an autocrine, a paracrine and an endocrine manner

Question 14

what is signal transduction

Answer 14

Many signalling molecules that affect cell activity or function do not enter cells.
• They act on membrane-bound receptors that control the production of intracellular chemicals (second messengers).
• These mediate cell activity.
• Exception is lipid soluble signalling molecules (bind intracellular receptors)

Question 15

inositol phospholipid signalling

Answer 15

The G protein activates the PLC to then liberate to PIP2 molecules known as DAG and IP3

Question 16

by what action does calcium activates cellular pathways

Answer 16

Calcium concentration transiently increases in the cell in response to IP3 release Calcium binds to proteins to regulate their function

Question 17

Give me an example of calcium activating cellular pathways

Answer 17

: Ca2+/Calmodulin - activates proteins/enzymes through direct interaction (e.g. myosin light chain kinase, which regulates smooth muscle contraction)

Question 18

substrates for PKC’S and their actions

Answer 18

tumour suppressor p53 (transcription factor) → prevents tumour formation
CaV 1.2 (calcium channel) → heart muscle contraction
IKKα (cytokine) → B cell activation (immune function)

Question 19

what is the initial rate-limiting step in eicosanoid synthesis

Answer 19

the liberation of arachidonic acid by phospholipase A2 (PLA2)

Question 20

what is PLA2 activated by

Answer 20

a variety of receptor-mediated signals.

Question 21

Arachidonic acid can be metabolised by

Answer 21

(a) cyclo-oxygenase and peroxidase to give prostaglandins and thromboxanes
(b) lipoxygenases to give leukotrienes.

Question 22

what is the receptor for vasoconstriction

Answer 22

EP1 receptor

Question 23

What is the receptor for vasodilation

Answer 23

EP2 receptor

Question 24

prostaglandins =

Answer 24

eicosanoids

Question 25

Thromboxanes

Answer 25

• Synthesised in platelets (clotting)
• Short-lived (autocrine/paracrine)
• Thromboxane A2 (TXA2) has prothrombotic properties
• Stimulate platelet aggregation
• Vasoconstrictor

Question 26

Leukotrienes

Answer 26

• synthesised in white blood cells
• conjugated system of double bonds
• Some contain the amino acid cysteine in their structure (anaphylactic shock)
• used in immune response
  heavily implicated in asthma and allergy

Question 27

Platelet-activating factor

Answer 27

• By-product of arachidonic acid liberation
• Synthesised in leukocytes (platelets, neutrophils, basophils)
• Also synthesised by injured tissue (e.g. endothelial cells)
• Platelet aggregation
• Vasoconstriction
• Inflammation
• Immune response (also anaphylaxis)

Question 28

NSAIDs

Answer 28

Non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin and derivatives of ibuprofen, inhibit cyclooxygenases.
 They inhibit formation of prostaglandins involved in fever, pain, & inflammation.
 They inhibit blood clotting by blocking thromboxane formation in blood platelets.
Ibuprofen and related compounds block the hydrophobic channel by which arachidonate enters the cyclooxygenase active site.

Question 29

Actions of aspirin

Answer 29

acetylates a serine hydroxyl group near the active site, preventing arachidonate binding.
The inhibition by aspirin is irreversible.
However, in most body cells re-synthesis of Cox-1 would restore cyclooxygenase activity.

Question 30

Aspirin as an anticoagulant

Answer 30

Thromboxane A2 stimulates blood platelet aggregation, essential to the role of platelets in blood clotting.

• Many people take a daily aspirin for its anti- clotting effect, attributed to inhibition of thromboxane formation (via COX-1 inhibition) in blood platelets.
• This effect of aspirin is long-lived because platelets lack a nucleus and do not make new enzyme.