Chapter 8: Hemoglobin Metabolism (30Q)

A hemoglobin molecule is composed of:

Four heme molecules and four globin chains

Normal adult Hb A contains which polypeptide chains?

α and ß

A key rate-limiting step in heme synthesis is suppression of:

Aminolevulinate synthase

Which of the following forms of hemoglobin molecule has the lowest affinity for oxygen?

Tense

Using the normal hemoglobin-oxygen dissociation curve in Figure 7.7 for reference, predict the position of the curve when there is a decrease in pH.

Shifted to the right of normal with decreased oxygen affinity

The predominant hemoglobin found in a healthy newborn is:

F

What is the normal distribution of hemoglobins in healthy adults?

> 95% Hb A, <3.5% Hb Az, 1% to 2% Hb F

Which of the following is a description of the structure of oxidized hemoglobin?

Hemoglobin with iron in the ferric state (methemoglobin) and not able to carry oxygen

In the quaternary structure of hemoglobin, the globin chains associate into:

Two αß dimers

How are the globin chain genes arranged?

With α genes and ß genes on separate chromosomes, including two α genes on one chromosome and one ß gene on a different chromosome

The nature of the interaction between 2,3-BPG and hemoglobin is that 2,3-BPG:

Binds to amino acids of the globin chain, contributing to a conformational change that inhibits oxygen from binding to heme

Which enzyme catalyzes the first step in heme synthesis?

Aminolevulinate synthase

Where does the majority of heme synthesis occur in the cell?

Mitochondria and cytoplasm (first and last steps in mitochondria, intermediate in cytoplasm)

Which of the following molecules is the direct precursor of protoporphyrin IX?

Coproporphyrinogen III

What element is inserted into protoporphyrin IX to form heme?

Iron (Fe²⁺)

Which enzyme inserts Fe²⁺ into protoporphyrin IX?

Ferrochelatase

What is the primary source of iron for hemoglobin synthesis?

Recycled iron from senescent RBCs via macrophages

Which protein transports iron in plasma?

Transferrin

Which form of hemoglobin predominates in embryonic life?

Hb Gower (or embryonic hemoglobins)

Which form of hemoglobin predominates in fetal life?

Hb F (α₂γ₂)

Which factor primarily regulates the rate of heme synthesis?

Intracellular iron concentration

Which structural change occurs in hemoglobin during oxygen binding?

Transition from T (tense) state to R (relaxed) state

Which factor decreases hemoglobin’s affinity for oxygen?

Increased 2,3-BPG concentration

Which form of hemoglobin cannot bind oxygen because iron is oxidized to Fe³⁺?

Methemoglobin

Which enzyme reduces methemoglobin back to functional hemoglobin?

Methemoglobin reductase

Which inherited disorder results in structurally abnormal hemoglobin?

Hemoglobinopathy (e.g., sickle cell disease)

Which condition results from decreased or absent synthesis of globin chains?

Thalassemia

Which abnormal hemoglobin has a higher affinity for oxygen, causing tissue hypoxia?

Hb variants with increased oxygen affinity (e.g., Hb Chesapeake)

Which molecule competes with oxygen for binding to hemoglobin, leading to functional anemia?

Carbon monoxide (CO)

What is the normal oxygen saturation of hemoglobin in arterial blood?

About 97%