Question

Parasitic effect. When \(P\). falciparum lives inside red blood cells, the metabolism of the parasite tends to release acid. What effect is the presence of acid likely to have on the oxygen-carrying capacity of the red blood cells? On the likelihood that these cells sickle?

Short answer

Acid released by P. falciparum decreases oxygen-carrying capacity and increases the likelihood of sickling.

Step-by-step solution

Understanding the Parasite's Effect

When the parasite P. falciparum invades red blood cells, it produces metabolic byproducts, one of which is acid. This acid release can lead to a decrease in the intracellular pH of the red blood cells.

Impact of Acid on Hemoglobin

A lower pH due to increased acidity affects hemoglobin's ability to bind and release oxygen. This phenomenon is known as the Bohr effect, where decreased pH results in hemoglobin releasing oxygen more readily.

Oxygen-Carrying Capacity of Red Blood Cells

With the presence of additional acid and subsequent reduced pH, hemoglobin's affinity for oxygen diminishes. Therefore, the oxygen-carrying capacity of red blood cells is likely decreased due to the Bohr effect.

Relation to Cell Sickling

Sickle cell hemoglobin (HbS) tends to polymerize more easily at lower pH levels, which can cause the red blood cells to sickle. The presence of acid, therefore, increases the likelihood of red blood cells sickling in individuals with sickle cell disease.

Key concepts

P. falciparum

The parasite **Plasmodium falciparum** is responsible for the most virulent form of malaria in humans. It infects red blood cells and, during its lifecycle, it undergoes metabolism within these cells.
An important fact about its metabolism is that it produces acidic by-products, which are released inside the red blood cells.
Consequently, the presence of **P. falciparum** leads to increased acidity inside the red blood cells. This induces a series of physiological effects, including alterations in hemoglobin behavior and red blood cell structure.
The significance of addressing this parasite is underscored by its impact on both the function and viability of the cells it infects.

Sickle Cell Disease

Sickle cell disease is a hereditary blood disorder where red blood cells assume an abnormal, rigid, sickle shape. This deformation is caused primarily by a mutation in the hemoglobin molecule, known as hemoglobin S or HbS.
Individuals with sickle cell disease are particularly vulnerable to factors influencing pH levels in red blood cells. Lower pH conditions promote the polymerization of HbS, which leads to red blood cells sickling more readily. This sickling impairs the cells’ ability to flow smoothly through blood vessels, causing blockages and resulting in pain and potential organ damage.
The presence of **P. falciparum** exacerbates this condition, as the acidity produced by the parasite makes the sickling process occur more frequently and severely.

Hemoglobin Oxygen Affinity

Hemoglobin is the protein responsible for transporting oxygen in the blood from the lungs to the tissues. Its oxygen affinity refers to its ability to bind to and release oxygen molecules.
The **Bohr effect** is a physiological principle where hydrogen ions ( **H i +** ) or protons influence hemoglobin's structure to affect its oxygen-carrying properties. Specifically, a drop in pH due to increased hydrogen ions leads to a decreased affinity of hemoglobin for oxygen.
In the environment created by **P. falciparum** within red blood cells, acidity increases, leading to reduced hemoglobin oxygen affinity. Consequently, the red blood cells release oxygen more readily, but it also means they carry less oxygen from the lungs in the first place.

Intracellular pH

The concept of intracellular pH refers to the acidity or alkalinity inside cells, impacting various biological processes. Red blood cells are particularly affected by changes in pH due to their role in oxygen transport.
**Acidic by-products** produced by **P. falciparum** lower the intracellular pH, meaning that the environment in which hemoglobin operates becomes more acidic. This shift can intensify the Bohr effect, making hemoglobin less effective at oxygen transport.
Additionally, in the context of sickle cell disease, a lower intracellular pH enhances the likelihood of red blood cells adopting the abnormal sickle shape. This has profound implications for the health and function of individuals affected by both malaria and sickle cell disease.