BYA3 SECTION 12.9

Drugs are used in the control and treatment of disease

Beta Blockers Against High Blood Pressure

Prolonged, high blood pressure → hypertension, risk factor of CHD (coronary heart disease)!
Risk factors associated with hypertension are stress, obesity, smoking, high intake of NaCl and alcohol
Smooth muscle in artery wall thickens → narrows lumen of the artery → heart must beat faster → contracts with greater force than normal
- Increased risk of thrombosis and atheroma (fatty deposits form in artery walls)
- β-receptors found on plasma membrane of smooth muscle cells in arteries, arterioles and heart
- β-agonists are chemical messengers that fit into and stimulate β-receptors / muscle cells in the walls of arteries relax (increases size of lumen)
- β-blockers are antagonists of β-agonists / block β-receptors on surface of muscle cells in arteries and heart due to their similar shape / β-agonist cannot bind anymore / reduces hypertension
[EXAM] β-blocker binds to receptor / receptor on heart (muscle cells) / adrenaline cannot bind / blood pressure falls because heart rate reduced/force of contraction reduced

Antibiotics

Produced as natural secretions by bacterial or fungal cells
- Bacteria and fungi are secondary metabolites (produce antibiotics during a late stage of their life cycle)
- Antibiotics inhibit growth of natural competitors
- Gives antibiotic-secreting population an advantage in colonising it
Antibiotics harm pathogenic bacteria by
- Bacteriostatic antibiotics that are slowing down their growth rate
- Bactericidal antibiotics that kill pathogenic bacteria (in correct concentration)
Narrow-spectrum antibiotics (e.g. penicillin) are only effective on a few pathogens
Wide-spectrum antibiotics (e.g. chloramphenicol) are effective on many pathogens
Prevent formation of bacterial cell walls
- Bacteria occupy a solution with a more negative water potential than their own cytoplasm
- Without the cell wall, bacteria are exposed to this hostile environment
- As a result, bacteria will swell, burst and die
- > Review the principles of water potential
Prevent formation of bacterial proteins
- By inhibiting DNA transcription or mRNA translation
- Bacteria are unable to synthesise proteins → affects the metabolism of bacteria
NOTE: Antibiotics do not affect viruses

Monoclonal antibodies

Hybridoma

B-lymphocytes are fused with tumour cells in laboratory cultures
They divide rapidly to form a clone of identical cells
Specific monoclonal antibodies are continuously produced and useful as
- Some are tumour markers (antigens not present on non-cancerous cells)
- Monoclonal antibodies will only attach to cancer cells
- Anti-cancer drug attached to monoclonal antibodies will deliver the drug directly to the cancer cells

Uses of monoclonal antibodies

Monoclonal antibody is an antibody that is of just one type
Used to target the treatment of cancer cells or to screen (AIDS) in contaminated blood
Antibody direct enzyme prodrug therapy techniques (ADEPT)
- Monoclonal antibodies are tagged with an enzyme that converts the prodrug (inactive drug)
  to an active form that kills cells (i.e. is cytotoxic)
- The prodrug is injected in high conc
- Attached to a monoclonal antibody, enzyme activates the drug and kills only cancer cells
In immunoassays, they can be labelled (radioactively) making them easy to detect
In the enzyme-linked immunosorbant assay (ELISA) technique, they are immobilised on an inert base
and a test solution is passed over them
1. Target antigen combines with immobilised monoclonal antibodies
2. Second antibody attaches with an enzyme and binds to the monoclonal antibodies
  and to the target antigen as well
3. Substrate is added which is converted to a coloured product by the added enzyme
4. Conc. of colour tells us the amount of antigens present in the test solution
Used to detect drugs in urine of athletics or in home pregnancy tests (where an antigen in human chorionic gonadotrophin (hCG) is secreted by the placenta)
Transplanted organs have non-self-antigens triggering antibodies to attack the organ, leading to its rejecting
- T-Lymphocytes are needed for B-lymphocytes to function
- Monoclonal antibodies against T-lymphocytes can be used to prevent B-lymphocytes from functioning,
  thus blocking the rejection of transplanted organs
[EXAM] Helping to diagnose between two pathogens because
- Antigens are on cell-surface membrane
- Monoclonal antibody reacts with specific antigen only
- \ Detects presence of special bacteria because of a different antigen on another, different bacteria

References and Further Reading
AQA (2006) GCE Biology/Biology (Human) 2006 specification, [PDF]
BAKER, M, INDGE, B, & ROWLAND, M (2001) Further Studies in Human Biology. Hodder Arnold H&S

BYA3 SECTION:

12.9