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BB2730 Metabolic Regulation > Allosterism and allosteric proteins > Flashcards

Allosterism and allosteric proteins Flashcards

1
Q

What is the activation energy of a reaction?

A

Activation energy is the energy required to initiate a chemical reaction by enabling reactants to reach the transition state.

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2
Q

What is an endergonic reaction?

A

An endergonic reaction requires an input of energy to proceed, as the products have a higher energy level than the reactants. Example: Protein synthesis.

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3
Q

What is an exergonic reaction?

A

An exergonic reaction releases energy as it proceeds, with reactants starting at a higher energy level than the products. Example: ATP hydrolysis.

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4
Q

How do enzymes affect activation energy?

A

Enzymes lower the activation energy required for a reaction to occur, making the reaction faster and more efficient without changing the overall energy released or absorbed.

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5
Q

How do enzymes lower activation energy?

A

Enzymes stabilize the transition state, align reactants in the correct orientation, or provide an alternative reaction pathway.

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6
Q

Do enzymes alter the overall energy released or absorbed in a reaction?

A

No, enzymes only lower the activation energy; they do not change the overall energy released or absorbed in the reaction.

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7
Q

What happens to reaction speed in the presence of an enzyme?

A

The reaction proceeds much faster due to the lower activation energy barrier provided by the enzyme.

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8
Q

Why are enzymes important for biological systems?

A

Enzymes enable biochemical reactions to occur rapidly and efficiently under physiological conditions, such as normal body temperature and pH.

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9
Q

What diseases are linked to enzyme dysfunction?

A

Metabolic disorders like phenylketonuria (enzyme mutation in phenylalanine metabolism) and liver dysfunction (elevated ALT/AST levels) can result from enzyme abnormalities.

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10
Q

How are enzymes used in medicine?

A

Enzymes are targeted in therapies (e.g., protease inhibitors for HIV, ACE inhibitors for hypertension) and used as diagnostic markers for diseases.

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11
Q

What is the Bohr Effect?

A

The Bohr Effect describes how lowered pH (increased H⁺) and increased CO₂ reduce hemoglobin’s affinity for oxygen, promoting oxygen release to tissues.

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12
Q

Who discovered the Bohr Effect, and when?

A

The Bohr Effect was discovered by Christian Bohr in 1904.

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13
Q

How does CO₂ affect hemoglobin?

A

CO₂ is hydrated in tissues to form carbonic acid, which dissociates into H⁺ and bicarbonate. The increased H⁺ lowers pH, stabilizing the T-state of hemoglobin and reducing oxygen affinity.

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14
Q

What is the T-state of hemoglobin, and how is it relevant?

A

The T-state (Tense state) of hemoglobin has a low affinity for oxygen. Increased H⁺ and CO₂ stabilize this state, promoting oxygen release to tissues.

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15
Q

How does CO₂ directly bind to hemoglobin?

A

CO₂ binds to the amino-terminal ends of hemoglobin’s globin chains, forming carbaminohemoglobin. This stabilizes the T-state and facilitates oxygen unloading.

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16
Q

What happens to hemoglobin in the lungs?

A

In the lungs, high oxygen levels promote oxygen binding to hemoglobin, shifting it to the R-state (Relaxed state) and releasing H⁺ and CO₂.

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17
Q

What factors cause a rightward shift in the oxygen dissociation curve?

A

A rightward shift is caused by:

Increased H⁺ (low pH).
Increased CO₂ concentration.
Increased temperature.
Increased 2,3-Bisphosphoglycerate (BPG).

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18
Q

What does a rightward shift in the oxygen dissociation curve indicate?

A

A rightward shift indicates reduced hemoglobin affinity for oxygen, facilitating oxygen release to tissues.

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19
Q

Why is the Bohr Effect important in oxygen delivery?

A

The Bohr Effect ensures efficient oxygen release in metabolically active tissues where CO₂ and H⁺ are elevated, and oxygen is needed most.

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20
Q

How does the Bohr Effect contribute to adaptation at high altitudes?

A

At high altitudes, increased 2,3-BPG production shifts the oxygen dissociation curve to the right, aiding oxygen release in low-oxygen conditions.

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21
Q

What clinical conditions are related to the Bohr Effect?

A

Acidosis (low pH) or hypercapnia (high CO₂) can enhance oxygen unloading.
Alkalosis or hypocapnia can impair oxygen delivery to tissues.

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22
Q

What happens to CO₂ at active tissues?

A

CO₂, a byproduct of cellular respiration, diffuses from tissues into systemic capillaries and enters red blood cells.

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23
Q

How is CO₂ converted in red blood cells at tissues?

A

CO₂ combines with water to form carbonic acid (H₂CO₃) via carbonic anhydrase, which dissociates into H⁺ and bicarbonate (HCO₃⁻).

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24
Q

What is the role of hemoglobin in pH regulation at tissues?

A

Hemoglobin binds H⁺ ions, stabilizing its T-state, reducing oxygen affinity, and facilitating oxygen release to tissues (Bohr Effect).

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25
What is the chloride shift?
At tissues, HCO₃⁻ is transported out of red blood cells in exchange for Cl⁻ ions to maintain electrochemical balance.
26
What happens to CO₂ in the lungs?
CO₂ is released as H⁺ recombines with HCO₃⁻ to form carbonic acid, which is converted back into CO₂ and water by carbonic anhydrase. CO₂ is then exhaled.
27
What happens to hemoglobin in the lungs?
Oxygen binds to hemoglobin, displacing H⁺ ions and stabilizing the R-state (high oxygen affinity), allowing oxygen loading.
28
What enzyme is essential for CO₂ transport and pH regulation?
Carbonic anhydrase catalyzes the reversible conversion of CO₂ and water into carbonic acid (H₂CO₃).
29
What is the primary goal of systemic circulation (tissues)?
To offload oxygen and pick up CO₂ produced by metabolically active cells.
30
What is the primary goal of pulmonary circulation (lungs)?
To offload CO₂ and pick up oxygen from the alveoli for transport to tissues.
31
How does CO₂ affect blood pH?
High CO₂ levels increase H⁺ concentration, lowering pH (acidic). Low CO₂ levels decrease H⁺ concentration, raising pH (alkaline).
32
What are clinical conditions related to CO₂ and pH imbalance?
Respiratory acidosis: Caused by excess CO₂ (e.g., hypoventilation). Respiratory alkalosis: Caused by reduced CO₂ (e.g., hyperventilation).
33
What is 2,3-BPG, and where is it produced?
2,3-BPG (2,3-bisphosphoglycerate) is a metabolite produced in erythrocytes (red blood cells). It binds to hemoglobin and regulates oxygen affinity.
34
What is the function of 2,3-BPG?
2,3-BPG binds to deoxygenated hemoglobin, stabilizing the T-state (tense state) and reducing hemoglobin’s oxygen affinity, promoting oxygen release to tissues.
35
How does 2,3-BPG affect the oxygen dissociation curve?
2,3-BPG shifts the oxygen dissociation curve to the right, decreasing oxygen affinity and enhancing oxygen release to tissues.
36
What happens to 2,3-BPG levels at high altitudes?
At high altitudes, 2,3-BPG levels increase (e.g., from 5 mmol/L to 8 mmol/L) to compensate for low oxygen availability by promoting oxygen release to tissues.
37
What does the oxygen dissociation curve look like with no 2,3-BPG?
Without 2,3-BPG, the curve shifts to the left, indicating high oxygen affinity, which impairs oxygen release to tissues.
38
How does increased 2,3-BPG help at high altitudes?
Increased 2,3-BPG reduces hemoglobin’s oxygen affinity, ensuring more oxygen is released to tissues, even at low partial pressures of oxygen.
39
What is the normal level of 2,3-BPG in blood at sea level?
The normal concentration of 2,3-BPG in blood at sea level is 5 mmol/L.
40
What are the physiological effects of 8 mmol/L 2,3-BPG at high altitude?
At 8 mmol/L, hemoglobin saturation decreases at high altitude, but an equivalent amount of oxygen is released to tissues as at sea level.
41
What happens to 2,3-BPG levels in stored blood, and why is this important?
2,3-BPG levels decrease in stored blood, causing increased oxygen affinity, which can impair oxygen delivery during transfusions.
42
How does 2,3-BPG relate to hypoxia or anemia?
In hypoxia or anemia, 2,3-BPG levels increase as a compensatory mechanism to enhance oxygen release to tissues.
43
What is the clinical relevance of 2,3-BPG in high-altitude sickness?
Insufficient adaptation of 2,3-BPG levels at high altitudes can impair oxygen delivery to tissues, contributing to symptoms of altitude sickness.
44
What happens to atmospheric pressure and oxygen levels at high altitudes?
At high altitudes, atmospheric pressure decreases, leading to lower partial pressure of oxygen (pO₂). However, the percentage of oxygen in the air remains the same (21%).
45
Why does oxygen availability decrease at high altitudes?
The reduced atmospheric pressure at high altitudes lowers the partial pressure of oxygen (pO₂), reducing the driving force for oxygen diffusion into the bloodstream.
46
What is the primary challenge for oxygen transport at high altitudes?
The reduced pO₂ decreases oxygen uptake in the lungs, potentially impairing oxygen delivery to tissues.
47
How does 2,3-BPG help adapt to high altitudes?
Increased 2,3-BPG production shifts the oxygen dissociation curve to the right, reducing hemoglobin's oxygen affinity and enhancing oxygen release to tissues.
48
What are short-term physiological adaptations to high altitude?
Increased 2,3-BPG production. Hyperventilation to increase oxygen uptake.
49
What are long-term physiological adaptations to high altitude?
Increased red blood cell production (erythropoiesis). Capillary growth (angiogenesis) to improve oxygen delivery.
50
What happens if the body cannot adapt to high altitude?
Failure to adapt can result in altitude sickness, with symptoms like headache, fatigue, and shortness of breath. Severe cases may lead to HAPE or HACE.
51
What is altitude sickness?
Altitude sickness occurs when the body fails to adapt to reduced oxygen availability at high altitudes, causing symptoms like headache, fatigue, and nausea.
52
What treatments are used for altitude sickness?
Oxygen supplementation. Medications like acetazolamide, which enhances ventilation and acclimatization.
53
How does the body respond to reduced oxygen levels at high altitude?
Increased 2,3-BPG facilitates oxygen unloading to tissues. Hyperventilation improves oxygen uptake. Long-term, red blood cell production and capillary growth increase oxygen delivery.
54
Why is training at high altitude beneficial for athletes?
High-altitude training stimulates red blood cell production and increases 2,3-BPG, improving oxygen delivery and enhancing performance in low-oxygen environments.
55
Where does 2,3-BPG bind on hemoglobin?
2,3-BPG binds to the central cavity of hemoglobin, specifically in the T-state (deoxyhemoglobin).
56
What is the effect of 2,3-BPG binding to hemoglobin?
2,3-BPG stabilizes the T-state of hemoglobin, reducing oxygen affinity and promoting oxygen release to tissues.
57
How does 2,3-BPG affect the oxygen dissociation curve?
2,3-BPG shifts the oxygen dissociation curve to the right, facilitating oxygen unloading to tissues.
58
Why does fetal hemoglobin (HbF) have a higher oxygen affinity than maternal hemoglobin (HbA)?
Fetal hemoglobin has gamma-globin chains instead of beta-globin chains, reducing its affinity for 2,3-BPG and increasing its oxygen affinity.
59
Why is fetal hemoglobin’s lower affinity for 2,3-BPG important?
It allows fetal hemoglobin to extract oxygen from maternal blood, ensuring efficient oxygen transfer to the fetus.
60
What is the role of 2,3-BPG in oxygen regulation?
2,3-BPG regulates hemoglobin’s oxygen affinity, ensuring oxygen is released to tissues as needed, especially during exercise, hypoxia, or at high altitudes.
61
What happens to oxygen delivery when 2,3-BPG levels increase?
Increased 2,3-BPG levels reduce hemoglobin’s oxygen affinity, promoting more oxygen release to tissues.
62
What is the difference between the T-state and R-state of hemoglobin?
T-state (tense): Low oxygen affinity, stabilized by 2,3-BPG. R-state (relaxed): High oxygen affinity, favored when oxygen binds.
63
Why is 2,3-BPG critical for maternal-fetal oxygen exchange?
Fetal hemoglobin’s reduced 2,3-BPG binding ensures it can extract oxygen from maternal hemoglobin for fetal oxygenation.
64
What clinical conditions are related to 2,3-BPG levels?
Low 2,3-BPG: Impairs oxygen delivery to tissues (e.g., in stored blood). High 2,3-BPG: Compensates during hypoxia or at high altitudes, enhancing oxygen release.
65
What is allosteric regulation?
Allosteric regulation is a mechanism where molecules bind to specific sites on an enzyme or protein, altering its activity by changing its conformation.
66
What is homotropic allosteric regulation?
Homotropic regulation occurs when the substrate itself acts as the allosteric modulator, affecting the binding of additional substrate molecules.
67
What is the concerted model of homotropic regulation?
In the concerted model, the enzyme exists in equilibrium between two states: T-state (Tense): Low substrate affinity. R-state (Relaxed): High substrate affinity. Substrate binding shifts all subunits simultaneously to the R-state.
68
What is the sequential model of homotropic regulation?
In the sequential model, substrate binding induces a stepwise conformational change in individual subunits, increasing binding affinity gradually across the enzyme.
69
What is heterotropic allosteric regulation?
Heterotropic regulation occurs when a molecule (effector) other than the substrate binds to the enzyme, influencing its activity positively or negatively.
70
What is a positive heterotropic effector?
A positive effector enhances substrate binding or enzymatic activity by stabilizing the R-state of the enzyme.
71
What is a negative heterotropic effector?
A negative effector decreases substrate binding or enzymatic activity by stabilizing the T-state of the enzyme.
72
How does hemoglobin exhibit homotropic regulation?
Oxygen binding to one subunit of hemoglobin stabilizes the R-state, increasing oxygen affinity in the other subunits (cooperative binding).
73
What are examples of heterotropic effectors for hemoglobin?
Positive: Oxygen. Negative: CO₂, H⁺ (Bohr Effect), and 2,3-BPG, which stabilize the T-state and reduce oxygen affinity.
74
Why is allosteric regulation important for enzymes in metabolism?
Allosteric regulation allows precise control of enzyme activity, enabling feedback inhibition and maintaining metabolic balance.
75
How is allosteric regulation used in drug design?
Allosteric sites provide unique drug targets to modulate enzyme or protein function without competing with the substrate.
76
What is the main difference between the concerted and sequential models?
Concerted Model: All subunits change conformation simultaneously. Sequential Model: Subunits change conformation one at a time, gradually increasing substrate affinity.

BB2730 Metabolic Regulation (5 decks)

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