Structure Of Cell Membranes

Question 1

What is Meningitis?

Answer 1

• Infection of the meninges in the brain
• Meninges are the membranes which cover the brain neural tissue
• Due to viral or bacteria infection
• Can be fatal

Question 2

What is the blood brain barrier?

Answer 2

• Selectively permeable membrane
• Barrier between bloodstream and extra cellular space of the brain (neurones )
• Regulates passage of molecules
• Cerebrospinal fluid, arachnoid barrier, specialised cells ( endothelial/ Glia cells)

Question 3

What is the gastrointestinal wall?

Answer 3

• Layers of smooth muscle in longitudinal and circular orientation that helps with continued bowel movements and digested material in and out of gut

Question 4

What are the steps of drug absorption?

Answer 4

• Ingestion
• Dissolution
• Absorption

Question 5

How are drugs soluble?

Answer 5

• Include polar groups (OH -> hydrogen bonds)
• Can dissociate, can separate into proton and negative ion

Question 6

What are the features of the small intestine that allows food to be absorbed?

Answer 6

• Wall lining with small finger like structures called villi (supplied with blood)
• Lymph supply (lacteals) important for absorption of fat soluble drugs
• Have a nerve supply

Question 7

What are the units of the phospholipid?

Answer 7

• A water soluble polar head remain on the outside
• Fatty acid chain remain on the inside

Question 8

What are the drug property factors that might affect the absorption of a drug?

Answer 8

• Lipid/ water solubility
• Molecular size
• Degree of ionisation
• Physical forms
• Chemical structure
• Dosage
• Formulation

Question 9

What does a drug need to be for it to be lipid/ water soluble?

Answer 9

• Partly water soluble to penetrate through hydrophilic phosphate head
• Slightly lipophilic to pass through fatty acid tails

Question 10

How does Degree of ionisation affect the drug?

Answer 10

• Many drugs contain functional groups that will donate or accept protons
• Ionisation creates a chemical dipole which attracts water molecules - increases water solubility
• When the drug enters the fatty acid chain section, ionisation reverses and the drug becomes fat soluble

Question 11

What are the factors of a membrane that affect passive diffusion?

Answer 11

• Surface Area
• Thickness
• Concentration Gradient

Question 12

What is Ficks Law?

Answer 12

• The rate of diffusion is directly proportional to the (surface area x concentration difference) / thickness of membrane

Question 13

What are the different transport mechanisms across cell membranes?

Answer 13

• Passive diffusion
• Active Transport
• Endocytosis

Question 14

What is Active Transport?

Answer 14

• Movement of molecules into or out of a cell through the cell membrane from low to high using energy (ATP)
• Protein carriers or channels
• E.g in Neurone or nerve cell (Na+ /K+ pump)

Question 15

What is Endocytosis?

Answer 15

• Form of active transport but not using a carrier, pore or channel
• Process of cell ingesting material by enveloping it in a portion of its cell membrane and pinching off that portion of membrane

Question 16

What are examples of Endocytosis?

Answer 16

1. Phagocytosis - WBC engulfing invading bacteria
2. Pinocytosis - Fluid containing dissolved materials. Microvilli of the SI absorb nutrients from the lumen of GT
3. Receptor mediated endocytosis - import molecules from extra cellular site , recognised by cell-surface receptor

Question 17

Name an example of endocytosis.

Answer 17

• Iron being endocytose into red blood cells to make haemoglobin
• Bound to transferrin in the blood
• Transferrin is recognised by receptors on red blood cells
• Endocytosed via Clathrin-Coated pits
• Receptor and ligand recycled to the plasma membrane