Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The skin and mucous membranes form a primary defense against pathogens; skin provides a physical barrier and secretes sebum which lowers the pH to between and .
Cuts in the skin are sealed by blood clotting to prevent blood loss and the entry of pathogens. This process is a cascade of chemical reactions initiated by clotting factors released from platelets.
The enzyme thrombin converts the soluble protein fibrinogen into the insoluble polymer fibrin, which forms a mesh that traps erythrocytes (red blood cells).
Phagocytic white blood cells (macrophages) provide non-specific immunity by ingesting pathogens through endocytosis and digesting them with lysosomes.
Specific immunity is provided by production of antibodies in response to particular antigens. -lymphocytes are activated by -helper cells to produce clones of plasma cells.
Antibodies (immunoglobulins) are -shaped proteins with specific binding sites that neutralize pathogens or mark them for destruction by phagocytes.
Antibiotics block metabolic pathways in prokaryotic cells (e.g., ribosome function or cell wall synthesis) but are ineffective against viruses because viruses lack a metabolism.
The Human Immunodeficiency Virus () infects and destroys -helper cells, eventually leading to Acquired Immune Deficiency Syndrome () as the body loses its ability to produce antibodies.
Florey and Chain's experiments on mice demonstrated the efficacy of penicillin, though their initial human testing would not meet modern ethical standards for clinical trials.
📐Formulae
💡Examples
Problem 1:
Explain why penicillin is effective against bacteria like Streptococcus but completely ineffective against the Influenza virus.
Solution:
Penicillin inhibits the synthesis of the peptidoglycan cell wall in bacteria. Viruses do not have a cell wall or their own metabolic pathways.
Explanation:
Antibiotics target specific prokaryotic features such as ribosomes or cell wall enzymes. Because a virus relies on a eukaryotic host's machinery ( ribosomes and host enzymes) to replicate, any drug blocking that machinery would be toxic to the host cell itself.
Problem 2:
Calculate the ratio of -helper cells in a healthy individual versus an patient if the healthy count is cells/ and the threshold is cells/.
Solution:
Ratio , which simplifies to .
Explanation:
The destruction of -helper cells by reduces the population significantly. When the count falls below cells/, the immune system is severely compromised, leading to opportunistic infections.
Problem 3:
A patient has a deficiency in soluble fibrinogen. Predict the effect on their blood clotting process.
Solution:
The patient would be unable to form a stable fibrin mesh, leading to impaired scab formation and prolonged bleeding.
Explanation:
While the clotting cascade may initiate and produce thrombin, the lack of the substrate fibrinogen means the final step () cannot occur. Without the insoluble fibrin 'net', platelets cannot be held in place to seal the wound.