Problem 12 - Anatomy and Physiology of Animals

Question

A molecule of hemoglobin ____ . a. is shaped like a biconcave disk packed almost entirely with iron b. contains four glycoprotein units studded with oxygen c. consists of four globin proteins, each bound to a molecule of heme d. can carry up to 120 molecules of oxygen

Step-by-Step Solution

Answer

c. consists of four globin proteins, each bound to a molecule of heme.

Step 1: Understanding Hemoglobin Structure

Hemoglobin is a protein found in red blood cells. It is responsible for carrying oxygen from the lungs to the rest of the body.

Step 2: Knowing the Composition

Hemoglobin is composed of four subunits. Each subunit is a globin protein, and each globin is bound to a heme group. The heme groups contain iron, which is the part that binds to oxygen.

Step 3: Analyzing the Options

We need to select the option that accurately describes the structure of hemoglobin. Option c states that hemoglobin consists of four globin proteins, each bound to a molecule of heme, which matches our understanding of hemoglobin's composition.

Step 4: Verifying Other Options

Option a incorrectly describes hemoglobin as a shape and composition that relates more to red blood cells, not the hemoglobin molecule itself. Option b wrongly describes the units as glycoproteins, and option d overstates oxygen-carrying capacity, as each hemoglobin can carry up to 4 oxygen molecules.

Step 5: Selecting the Correct Option

Based on the comparisons and understanding of hemoglobin, option c is indeed the correct description as it aligns with the known structure of hemoglobin.

Key Concepts

Red Blood Cells

Red blood cells, also known as erythrocytes, have a critical role in the body. They are the most common type of blood cell and are primarily responsible for delivering oxygen from the lungs to tissues throughout the body. This function is possible due to their unique shape and structure.

The biconcave shape of red blood cells increases their surface area, allowing for more efficient gas exchange. They are packed with hemoglobin, which gives red blood cells their characteristic color and enables oxygen transportation. While red blood cells themselves are about 7-8 micrometers in diameter, their shape allows them to deform and pass through tiny capillaries.

• Red blood cells lack a nucleus, which provides more space for hemoglobin.
• They have a lifespan of about 120 days in the bloodstream before being recycled by the liver and spleen.
• Produced in the bone marrow, millions of red blood cells are generated daily.

Oxygen Transportation

Oxygen transportation is a vital process carried out by red blood cells, primarily through the action of hemoglobin. Hemoglobin is a protein complex that can reversibly bind to oxygen molecules. This ability allows the transport of oxygen from the lungs to various parts of the body where it's needed.

Each hemoglobin molecule can bind up to four oxygen molecules. This is due to its composition of four globin subunits, each associated with an iron-containing heme group, which physically attaches to oxygen molecules. The binding of oxygen to hemoglobin can be influenced by various factors, such as pH, carbon dioxide levels, and temperature.

• At the lungs, high oxygen concentration facilitates oxygen binding to hemoglobin.
• In body tissues, lower oxygen concentration and higher carbon dioxide levels promote oxygen release.
• This process supports cellular respiration, the metabolic pathway within cells that produces energy.

Heme Group

The heme group is an integral component of the hemoglobin molecule and plays a key role in its function. This structure is where oxygen molecules are bound within hemoglobin. Each globin protein within hemoglobin is associated with a heme group.

The heme group contains an iron atom at its center. This iron atom is crucial because it forms a weak bond with oxygen, allowing for the reversible binding that characterizes hemoglobin's oxygen-carrying ability. Without the heme group's properties, oxygen transportation would not be possible.

• Heme is composed of a ring-like structure known as porphyrin, with the iron atom coordinated within.
• The iron must be in the ferrous (Fe²⁺) state to effectively bind oxygen.
• Changes in the heme's environment caused by oxygen binding and release facilitate hemoglobin's ability to pick up and deliver oxygen.