Biochemistry Globular Proteins Quiz

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Questions and Answers

What is the primary function of the proteins classified as globular hemoproteins?

To facilitate electron transfer in oxidation-reduction reactions

To catalyze the breakdown of hydrogen peroxide

To stabilize carbon dioxide effects in tissues

To transport oxygen from the lungs to tissues (correct)

Which structure is characteristic of hemoglobin?

Multiple subunits that cannot bind O2

Two polypeptide chains that are identical

Four polypeptide chains consisting of two alpha and two beta chains (correct)

One polypeptide chain with a single heme group

What role do distal groups play in the function of globular hemoproteins?

They catalyze the breakdown of hydrogen peroxide.

They facilitate the release of carbon dioxide from tissues.

They enhance the electrons transport process.

They stabilize the binding of oxygen to iron in the heme group. (correct)

Which of the following is NOT a characteristic of cytochromes?

They are primarily responsible for oxygen transport. Signup and view all the answers

How do allosteric effectors influence hemoglobin's function?

They reduce the binding capacity of hemoglobin for oxygen. Signup and view all the answers

What percentage of the myoglobin chain is folded into α-helices?

80% Signup and view all the answers

Which amino acids are primarily located on the interior of myoglobin?

Nonpolar amino acids Signup and view all the answers

What is the primary function of myoglobin?

Reservoir and carrier of oxygen Signup and view all the answers

Which structure is terminated by proline within myoglobin?

α-helix Signup and view all the answers

Which condition is characterized by an abnormal form of hemoglobin affecting red blood cells?

Sickle Cell Anemia Signup and view all the answers

Which specific residue is found in the crevice of myoglobin, contributing to its binding site?

Histidine Signup and view all the answers

What is the role of allosteric effects in hemoglobin function?

Regulation of oxygen binding and release Signup and view all the answers

Where are polar amino acids primarily located in myoglobin's structure?

On the surface, interacting with water Signup and view all the answers

What is the primary structural configuration of hemoglobin?

Quaternary structure Signup and view all the answers

In the T form of hemoglobin, what is the characteristic feature regarding the binding pocket?

Burying of the binding pocket Signup and view all the answers

Which bonds are disrupted in the transition from the T form to the R form of hemoglobin?

Ionic and hydrogen bonds Signup and view all the answers

What is the role of ferrous iron in the structure of hemoglobin?

Allows formation of six bonds including oxygen Signup and view all the answers

What is the consequence of the protonation of amino acids in the T form of hemoglobin?

Burying binding pocket Signup and view all the answers

When hemoglobin is in the R form, what occurs to the binding pocket?

It expands and is exposed Signup and view all the answers

How many bonds can ferrous iron in hemoglobin form with porphyrin nitrogens?

Four Signup and view all the answers

Which amino acid side chain position is involved in iron bonding in hemoglobin?

Histidine Signup and view all the answers

What is the primary factor that causes the sigmoidal shape of the oxygen dissociation curve for hemoglobin?

The cooperative binding nature of heme-heme interactions Signup and view all the answers

What is the significance of P50 in terms of oxygen binding in hemoglobin and myoglobin?

It indicates the partial pressure required for half-saturation of binding sites Signup and view all the answers

Which factor contributes to a rightward shift in the oxygen dissociation curve?

Increased carbon dioxide concentration Signup and view all the answers

How does myoglobin differ from hemoglobin in terms of oxygen release?

Myoglobin has a hyperbolic dissociation curve, indicating readiness to release less oxygen Signup and view all the answers

What effect does the presence of 2,3-biphosphoglycerate have on hemoglobin's affinity for oxygen?

It causes a right shift in the oxygen dissociation curve, decreasing affinity Signup and view all the answers

In which condition does hemoglobin exhibit a higher affinity for oxygen, according to the Bohr effect?

Low pH and elevated organic acids Signup and view all the answers

What is the role of CO2 in the transport of oxygen within the human body?

Most CO2 is converted into bicarbonate for transport Signup and view all the answers

Which binding interaction between oxygen and hemoglobin is impacted by 2,3-BPG?

The formation of deoxyhemoglobin and oxyhemoglobin Signup and view all the answers

What is the purpose of hyperbaric oxygen therapy in relation to carbon monoxide poisoning?

To provide high pressure oxygen to displace CO from binding sites Signup and view all the answers

What happens to the affinity of hemoglobin for oxygen during chronic hypoxia or anemia?

Affinity decreases due to increased 2,3-BPG levels Signup and view all the answers

Which of the following statements about myoglobin is NOT true?

Myoglobin effectively transports oxygen throughout the body Signup and view all the answers

Which condition is likely to lead to a leftward shift in the oxygen dissociation curve for hemoglobin?

Low concentration of carbon dioxide Signup and view all the answers

How does the binding of carbon monoxide (CO) to hemoglobin affect oxygen transport?

CO decreases the binding capacity of oxygen to hemoglobin Signup and view all the answers

What is the physiological consequence of the Bohr effect on hemoglobin's oxygen binding under metabolic demands?

It enhances oxygen unloading due to decreased pH and increased pCO2 Signup and view all the answers

Study Notes

Globular Hemeproteins

Myoglobin located in heart and skeletal muscle, serves as an oxygen reservoir and carrier.
Myoglobin features around 80% alpha helical content, consisting of a folded structure with eight alpha-helices (A-H), ending in proline.

Structure of Heme

Composed of ferrous iron and protoporphyrin IX.
Iron forms six bonds: four with porphyrin nitrogens, and two additional bonds - one to a histidine side chain and another for oxygen binding.
Heme plays a critical role in globular hemeproteins including myoglobin and hemoglobin.

Structure and Function of Hemoglobin

Found exclusively in red blood cells (RBCs).
Functions to transport oxygen from lungs to tissues, alongside carbon dioxide and hydrogen.
Hemoglobin consists of four polypeptide chains (2 alpha and 2 beta), enabling cooperative binding of oxygen.

Binding of Oxygen

Myoglobin binds one heme and one oxygen molecule with higher affinity compared to hemoglobin, which binds four oxygen molecules.
Oxygen-dissociation curve illustrates myoglobin’s hyperbolic binding compared to hemoglobin's sigmoidal curve.

Allosteric Effect

Hemoglobin is influenced by allosteric effectors such as pO2, pH, pCO2, and 2,3-biphosphoglycerate (2,3-BPG).
Cooperative binding in hemoglobin facilitates increased oxygen affinity as oxygen binds to successive heme sites.

Oxygen Dissociation and P50 Value

P50 indicates the partial pressure of oxygen required to achieve half-saturation of binding sites: 1 mmHg for myoglobin and 26 mmHg for hemoglobin.
Myoglobin shows hyperbolic shape in the oxygen dissociation curve; as oxygen is released, the binding behavior shifts right or left depending on oxygen levels.

Bohr Effect

The release of oxygen occurs with decreased pH or increased pCO2, lowering hemoglobin's oxygen affinity and shifting the curve to the right.
Higher pH or decreased pCO2 increases affinity, shifting the curve to the left, enhancing oxygen binding.

Role of 2,3-BPG

2,3-BPG is an important regulator of oxygen binding in hemoglobin, reducing oxygen affinity for greater unloading.
Increased levels of 2,3-BPG occur during chronic hypoxia or anemia, allowing better oxygen release in tissues.
Stored blood has low 2,3-BPG, resulting in high oxygen affinity, hence poor oxygen release during transfusions.

Binding of CO2 and CO

Most CO2 in blood is converted to bicarbonate ion (HCO3) for transport; some binds to hemoglobin as carbamate at N-terminal amino group.
Carbon monoxide (CO) binds tightly (restorably) to hemoglobin, forming carboxyhemoglobin with a greater affinity than oxygen, posing a risk to smokers.
Treatment for CO poisoning includes hyperbaric oxygen therapy to promote dissociation of CO.

Summary of Oxygen Binding Changes

Shift to the left in the oxygen dissociation curve indicates increased oxygen affinity (higher pH, lower pCO2, decreased 2,3-BPG).
Shift to the right indicates decreased affinity (lower pH, increased pCO2, increased 2,3-BPG), aiding oxygen release in metabolically active tissues.

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Description

Test your knowledge on the structure and function of globular proteins, specifically myoglobin, as discussed in Dr. Jandoc's lecture. This quiz will cover key concepts such as heme structure, oxygen transport, and the formation of methemoglobin.