TUT 3 Flashcards Preview

BIO-CHEM TUT TEST > TUT 3 > Flashcards

Flashcards in TUT 3 Deck (14)
Loading flashcards...
1
Q

Nicotine binds to nicotinic Acetlycholine recepetors in the brain. Stimulation of these receptors triggers the release of neurotransmitters in the brain. How does Nicotine tolerance develop(ie a given dose becomes less and less able to produce the desired effects, so more is inhaled)?

A
  • Desensitisation to nicotine can occur when receptors in the brain degrade, less receptors leads to less of a response to the same dose of drug
  • Dependence occurs because more of the drug is required to produce a desired response due to lack of receptors as use of drug is prolonged
2
Q

What is the effect of aspartate on the CNS? Which receptor does aspartate bind to?

A

Aspartate causes excitation in the CNS

Aspartate binds to NMDA receptors

3
Q

Describe how glutamate acts to increases free intracellular Ca2+ levels

A

Glutamate binds to AMPA and NMDA receptors (ionotropic receptors) to open them for transport of Ca2+

NMDA RECEPTORS: only permeable to calcium

> When glutamate binds to NMDA receptor with glycine and a change in membrane potential occurs, the Mg2+ that blocks the channel at resting membrane potential is expelled

>With the Mg2+ no longer blocking the channel, cations (including Ca2+) are free to travel through into cell

4
Q

Draw out the cascade that shows how adrenaline on binding to its receptor eventually releases glucose

A
5
Q

Give some examples of G-protein coupled receptors and drugs that work via G-protein coupled receptors

A

G-protein coupled receptors: Adrenoreceptors, mACHR (acetylcholine receptors), Glucagon receptors, GABAb (gamma aminobutyric acid)

Drugs via GPCR: Morphine, salbutamol, ephedrine, antihistamine

6
Q

A rise in intracellular calcium triggers a number of events depending on the cell. Outline three types of calcium-dependent events that occur in the cell

A
  1. Ca2+ binding to regulatory protein troponin –> initiates muscle contraction in skeletal muscle cell
  2. Ca2+ activated K+ channel found in nerve cells –> Ca2+ binds directly to ion channels to alter gating state
  3. Calcium is used in the clotting cascade
7
Q

What is the half life of insulin? What determines this?

A

4-6 minutes (determined by enzymes that break it down) –> degradation and synthesis

8
Q

What is the half-life of the insulin receptor? What determines this?

A

6-7 hours (determined by rate of synthesis and degradation of enyms plus inactivation and activation)

Receptor has a longer half life as it gives more time for insulin to bind

9
Q

Outline the structure of the insulin receptor. Describe the active and inactive forms of this receptor

A

Insulin receptors exist as inactivated monomer pairs with alpha and beta subunits. When insulin binds to the alpha subunit, it becomes the active dimer form.

  1. Insulin binds to the a-subunit
  2. B-subunit transmits a signal from bound insulin to cytoplasm
  3. Insulin signal activates tyrosine-kinase domain in cytoplasm
  4. Tyrosine Kinase phosphorylates Insulin-response substrates (IRS) triggering other chemical responses inside the cell
10
Q

Discuss the interaction with the Tyrosine Kinase receptor and the cascade effect. What is its signalling speed?

A
  • Intracellular receptor: speed is relatively longer (hours)
  • Insulin activates the receptor
  • Beta subunit transmits signal to cytoplasm
  • Signal causes the auto-phosphorylation of tyrosine kinase
  • Auto-phosphorylation of tyrosine kinase leads to a cascade of phosphorylation of other substrates
11
Q

What is a bifunctional enzyme?

A

An enzyme with two distinct catalytic capacities in the same polypeptide chain

> An enyme that can catalyse two or more different pathways and when it catalyses one pathway, it can deactivate the other

12
Q

Is the phosphorylated form of an enzyme the active form of that enzyme? Explain.

A

Because enzymes can catalyse more than one reaction and usually both the reverse and forward reactions will be catalysed by the same enzyme

>Phosphorylation of an enzyme may inhibit one pathway, and so by default increase (or activate) the catalyzation of another pathway)

13
Q

Outline the 3 differences between the following receptors

A

Metabotropic receptors are either G-protein coupled receptors (GPCr) that activate second messengers such as cAMP and cGMP indirectly gating the ion channel or receptor tyrosine kinases that gate channels or directly or indirectly by phosphorylation

Ionotropic receptors (ligand-gated ion channel) are a group of transmembrane ion-channel proteins which open to allow ions such as Na+, K+, Ca2+, and/or Cl− to pass through the membrane in response to the binding of a chemical messenger (i.e. a ligand), such as a neurotransmitter

14
Q

Name the two receptor types of Guanylyl Cyclase. What are the main differences between them?

A

Membrane

  • ANP/ANF (atrial natiuretic peptide/ factor)

​​> Involved in regulation of BP

> Has intraceullar components that catalyse formation of cGMP from GTP, but receptor component is extracellular

Cytoplasmic

  • Intracellular receptor (Nitric oxide: NO receptor)

​>NO is lipid soluble and glides into cell

>Involved in vasodilation