Cell physiology (inc diffusion and receptors)

Question 1

Passage of ions cell membranes

1. How are cell membranes glycoproteins held together?
2. What are the ways that molecules can cross the cell membranes?

Answer 1

1. Van Der Waals forces

2.

• Diffusion: the net movement of particles down a conc gradient. It can be:
  
  • Simple diffusion: via a gradient
  • Facilitated diffusion: move down a conc gradient
• Osmosis is the movement of water from a high concentration to a low conc over a semi-permeable membrane
• Active transport: Movement of particles against their gradient. This requires energy
  
  • Primary active transport: uses chemical energy of ATP
  • Secondary active transport: uses electrochemical gradient
• Endocytosis: the process where cell engulf molecules. This is often from large or polar molecules that will not pass the membrane
• Exocytosis: where excitatory vesicles expel there contents through the membrane to outside the cell

Question 2

G-protein-coupled receptors

1. What are they?
2. Give 3 examples
3. Describe the way they work

Answer 2

1. They are receptors that have 7 transmembrane domains. They are metabotrophic receptors

They are linked to enzyme receptors and effect guanosine triphoshate (GTP) proteins.

2.

• Muscarninc Aceytlcholine receptors
• Adrenoreceptors
• Histamine receptors

3.

The Ligand binds causing conformational change allowing Guanosine diphosphate (GDP) to be exchanged for GTP on the Gα subunit

This causes the dissociation of the subunits into Gα-GTP and Gβγ complex which act on effector organs or ion channels to moderate cell processes

GTPase exchanges the GTP for GDP on the Gα subunits deactivating it causing reassociation of the subunits

Question 3

Tyrosine Kinase receptors

1. What do they do?
2. How do they work?

Answer 3

1. They are receptors fo many polypeptides including hormones and growth factors like INSULIN and Erythropoietin
2. Each receptor has an extra-cellular N-terminal and internal C-terminal.

Kinase enzymes cause phosphorliation. Phosphorliation and binding of TYROSINE leads to activation of signal pathways to alter cell activity

Question 4

Ionotropic receptors

1. What are they?
2. Examples

Answer 4

1. Ligand gated ion channels responding to ligands. Usually located seperate t ion channels, ALLOSTERIC binding. They are selective to one 1 or more ions.

2.

• Nicotinic acetylcholine receptors
• N-Methyl-D-aspartic acid (NMDA) glutamate receptors
• Gamma-aminobutyric acid (GABA) receptors

Question 5

Nicotinic receptors

1. Describe these receptors
2. How do they work?

Answer 5

1. 5 subunits around a central pore, 2 alpha, 1 beta, 1, delta, 1 epsilon unit
2. To open the channel two ACh molecules bind to both alpha subunits. This allows +ve ions to pass down their gradients

Question 6

Intracellular receptors

1. How do they work?
2. Examples

Answer 6

1. Ligands bind to them either via secondary messangers or lipophilic hormones
2. Thyroid hormones, Vit D and IP3

Question 7

Drug receptor interactions

Name and describe the types of effects drugs can have on receptors

Answer 7

Full agonist - a drug that induces a receptor’s maximal response

Partial agonist - a drug that induces a submaximal response

Inverse agonist (antagonist) - a drug that induces the opposite effect than the intrinsic agonist

Competitive agonist - a drug that competes with the intrinsic agonist for the receptor and blocks its activity

Non-competitive agonist - a drug that binds at a different site to the intrinsic agonist and prevents receptor activation