2019 resit

Question 1

Explain with direct reference to the cell wall components of these organisms, how the standard laboratory method for visualising bacteria differentiate between gram-positive and gram-negative organisms.

Answer 1

Gram negative = much thinner layer of peptidoglycan (less sturdy), however, structure is more complex by presence of a layer of lipoprotein, polysaccharide and phospholipid known as outer membrane.
Gram positive = several layers of peptidoglycan connected by cross-linkages (more sturdy), simple structure containing techie acids and phosphate groups imparting overall negative charge to cell surface.

1. Crystal violet ion penetrate through cell and cell membrane of both gram positive and negative cells.
2. Iodine interacts with crystal violet to form large complexes of crystal violet and iodine.
3. Acetone wash removes gram-negative outer lipopolysaccharide membrane and the stain with it, and the inner peptidoglycan layer is left exposed, whereas, gran-positive cell becomes dehydrated, therefore, trapping the stain.
4. Gram positive cells remain purple and gran negative cells then counterstain giving a pink or red colour.

Question 2

List 5 advantages and 5 disadvantages of the IV route.

Answer 2

ADVANTAGES:
1. Rapid onset of action
2. Avoids first pass metabolism
3. Delivery of macromolecules possible
4. Can be used with unconscious patients or those unable to take oral form
5. 100% bioavailability

DISADVANTAGES:
1. Risk of infection and air embolism
2. Can be painful
3. Need sterile manufacture
4. Needle stick injuries, needle phobia
5. High manufacturing cost

Question 3

Explain the three main stages of powder compression.

Answer 3

1. Die filling - powder flows down from hopper into die
2. Tablet formation - Upper punch moves down into die, compressing powder into tablets.
   When required applied pressure reached upper punch moves upward.
3. Tablet ejection - lower punch rises to eject the tablet and a pushing device removes the tablet from the die

Question 4

Discuss the importance of voltage gated sodium channels and their role in neuronal signalling.

Answer 4

1. Action potential is entirely dependent on voltage gated channels to propagate signal.
2. Resting potential approx. -70mV and sodium ion channels are closed - extracellular [Na+] > intracellular [Na+]
3. In response to small depolarisation, at approx. -55mv Na+ channels open.
4. Na+ move down their concentration gradient and there is sharp increase in potential difference to approx. +30mV.
5. Once threshold has depolarised to +30mV, sodium ion channels close, stopping inward flow of sodium and Na+/K+ pump moves Na+ out - membrane potential goes back to -70mV

Question 5

Explain the most likely purpose of each excipient listen to formulate oral tablets:
Lactose
Magnesium stearate
Colloidal silica

Answer 5

Lactose - bulking agent; added to make adequate size tablet for ease of handling

Magnesium stearate - lubricant and anti-adherent; prevents powder/metal adherence - reduces friction between solid and die wall and ensures smooth ejection from die

Colloidal silica - glidant; improves flow of powders or granules and adheres to particle surfaces and other ingredients to reduce inter particulate friction.

Question 6

Describe the journey of food from mouth to anus, defining the structures and organs it passes through and the accessory organs involved in digestion.

Answer 6

Structures passed through:
Teeth - tongue - oesophagus - cardiac sphincter - stomach - pyloric sphincter - jejunum - ileum - caecum - ascending colon - transverse colon - descending colon - sigmoid colon - rectum - anus

Accessory organs:
Salivary glands - pancreas - liver - gall bladder

Question 7

Explain different ways to reduce sedimentation rate of drug particles.

Answer 7

1. Particle size reduction - increases diffusion
2. Reduce particle density - at the same time increases particle size so may have adverse effects.
3. Increase medium density e.g. adding dextrose
4. Increase medium viscosity e.g. by adding polymers like hydroxyproply methyl cellulose reduces both diffusion and sedimentation
5. Increase temp - increases diffusion constance but effect is limited within normal range of temps

Question 8

Briefly describe stages of hemastasis.

Answer 8

1. Vasoconstriction
2. Temporary blockage of a break by a platelet plug
3. Coagulation - formation of a clot that seals the hole until tissues are repaired

Question 9

Briefly explain why amides are the least reactive carboxylic acid derivative.

Answer 9

• Poorest leaving group - strongest base pf all leaving groups
• Resonance stabilisation is the most significant for amides of all carboxylic acid derivatives
• Least electron withdrawing; carbonyl carbon is least electrophilic of all carboxylic acid derivatives