Acid-Base Chemistry and Protein Function

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Questions and Answers

Which statement best describes the role of proton hopping in acid-base chemistry?

It refers to the rapid movement of a proton between water molecules or other hydrogen-bonded species. (correct)

It involves the direct transfer of a proton through a protein channel.

It is the process by which protons are actively transported against their concentration gradient.

It describes the slow diffusion of protons across a cell membrane.

The Henderson-Hasselbalch equation is most accurately used to determine which property?

The pH of a buffer solution at various concentrations of acid and conjugate base. (correct)

The equilibrium constant of a reversible reaction.

The overall charge of a protein at a given pH.

The rate of an enzyme-catalyzed reaction.

Which characteristic of the histidine side chain makes it particularly important in protein function?

Its large, bulky, aromatic nature which helps stabilise protein structure.

Its role as a glycosylation site.

Its pK value being relatively close to physiological pH, enabling it to act as both proton donor and acceptor. (correct)

Its ability to form hydrophobic interactions.

What do phi (Φ) and psi (Ψ) angles describe in protein structure?

The degree of freedom to rotate along the N-Cα and the Cα-C bonds of the protein backbone. (A) Signup and view all the answers

Which of the following is NOT generally a method to control physiological pH?

Excretion of metabolic products via sweat glands (C) Signup and view all the answers

Which metabolic process does NOT directly contribute to the production of acidic compounds in the body?

Protein metabolism via deamination (B) Signup and view all the answers

An excess of which substance would directly contribute to alkalosis?

Bicarbonate ions (A) Signup and view all the answers

In the context of acid-base balance, what is the net effect of ammonia production in the body?

Decreases acidity by combining with H⁺ (A) Signup and view all the answers

Which of the following best describes the role of the bicarbonate buffer system in the blood?

Acts as a major buffer during metabolic acidosis, maintaining stable pH levels. (D) Signup and view all the answers

Beta-hydroxybutyric acid is primarily produced during which condition?

When the body uses fat for energy (C) Signup and view all the answers

If a patient has an arterial pH of 7.2, which term accurately describes their condition?

Acidemia (C) Signup and view all the answers

Which of these is most directly linked to changes in blood pCO2?

Respiratory acidosis (D) Signup and view all the answers

What is a primary mechanism by which bicarbonate maintains pH balance in the blood?

Neutralizing hydroxide ions (B) Signup and view all the answers

What is the primary role of hemoglobin (Hb) in the context of acid-base balance in the blood?

Binding H⁺ ions when releasing oxygen, thus preventing blood from becoming too acidic. (A) Signup and view all the answers

Why does aspirin, a weak acid, undergo minimal absorption in the stomach despite being predominantly in its uncharged form?

The stomach lining has limited surface area for efficient drug absorption. (B) Signup and view all the answers

Which of the following best describes the 'chloride shift' mechanism in red blood cells (RBCs)?

Movement of Cl⁻ into the RBC in exchange for HCO₃⁻. (B) Signup and view all the answers

What is the consequence of aspirin's unprotonated form becoming trapped within the stomach's mucosal cells?

It leads to cellular rupture and gastric bleeding due to crystallisation. (A) Signup and view all the answers

What is the significance of the pKa of inorganic phosphate (7.2) in the context of intracellular pH buffering?

It means that inorganic phosphate is mostly ionized at intracellular pH, allowing it to buffer H⁺ ions effectively. (A) Signup and view all the answers

Aspirin's pKa is 4. Which of the following is true regarding aspirin in an environment with pH 2?

Aspirin is predominantly in its protonated, uncharged form. (A) Signup and view all the answers

How does monohydrogen phosphate (HPO₄²⁻) contribute to buffering when blood becomes acidic?

It binds to H⁺ ions to form dihydrogen phosphate (H₂PO₄⁻). (D) Signup and view all the answers

What is the role of the acetyl group in acetylsalicylate (aspirin)?

It renders aspirin inactive until it is enzymatically removed. (D) Signup and view all the answers

How do plasma proteins like albumin contribute to buffering blood pH when the blood becomes too basic?

By releasing H⁺ ions, thereby reducing alkalinity. (D) Signup and view all the answers

How does the pH of the environment affect the ratio of charged to uncharged forms of a weak acid, and its subsequent absorption?

Acidic environments favour the uncharged form, promoting absorption. (B) Signup and view all the answers

What is the immediate chemical product when carbon dioxide (CO₂) reacts with water in the blood?

Carbonic acid ($H_2CO_3$). (B) Signup and view all the answers

How does an increase in blood carbon dioxide ($CO_2$) levels affect blood pH?

It increases hydrogen ion concentration, resulting in a more acidic blood. (D) Signup and view all the answers

Why does the rate of gastric emptying significantly impact the overall rate of aspirin absorption?

Gastric emptying transports the majority of the drug to the duodenum where absorption is more efficient. (D) Signup and view all the answers

What is the role of cellular respiration regarding blood pH regulation and maintenance?

It produces carbon dioxide, which can affect blood pH levels. (B) Signup and view all the answers

What is the primary form of aspirin that crosses cell membranes?

The un-ionized, uncharged form (HA). (C) Signup and view all the answers

Which of the following statements about the relationship between pKa and acid strength is correct?

The lower the pKa, the stronger the acid. (C) Signup and view all the answers

What is the predominant state of the carboxyl group of an amino acid at a pH of 7.4?

Deprotonated (COO⁻) (C) Signup and view all the answers

Which statement best describes the behavior of an amino group at a pH of 6?

It will be protonated (NH₃⁺) (D) Signup and view all the answers

An amino acid's side chain has a pKa of 11. What will be the likely charge state of this side chain at physiological pH?

Predominantly positively charged (A) Signup and view all the answers

Which of the following amino acids would likely have a negatively charged side chain at physiological pH?

Glutamate (C) Signup and view all the answers

What does the term 'amphoteric' mean in the context of amino acids?

They can act as either proton donors or proton acceptors (D) Signup and view all the answers

What is the overall charge of an amino acid with no charged side chain at a physiological pH?

Neutral charge (zwitterion) (C) Signup and view all the answers

If a solution's pH is increased from 6 to 8, how will the protonation state of a carboxyl group (pKa ≈ 2) and an amino group (pKa ≈ 9.5) change?

The carboxyl group will become more deprotonated, and the amino group will become more deprotonated. (C) Signup and view all the answers

How would a buffer at pH 7.4 affect the charged status of a large polypeptide chain with multiple Aspartate and Lysine residues? Assume the pKa's of these side chains are 3.9 and 10.5 respectively.

It would cause all Aspartate residues to gain a negative charge, and all Lysine residues to gain a positive charge (B) Signup and view all the answers

Which of the following best describes the relationship between cysteine and glutathione?

Cysteine and glycine are both precursors for the synthesis of glutathione, a key antioxidant. (B) Signup and view all the answers

Why is GABA classified as a non-proteinogenic amino acid?

It lacks the correct structure to be incorporated into a polypeptide chain. (A) Signup and view all the answers

In cystinuria, why does cystine, rather than cysteine, accumulate and form kidney stones?

Cysteine spontaneously oxidizes to form less soluble cystine in the blood. (D) Signup and view all the answers

What is the primary mechanism by which cystinuria leads to the formation of kidney stones?

Defective amino acid transporters allow cystine to precipitate and crystallize in urine. (C) Signup and view all the answers

Why are patients recovering from major trauma often in a hypercatabolic state?

Their bodies need to quickly produce proteins for repair using available nutrients. (A) Signup and view all the answers

What does the term 'protein deprivation' refer to in the context of Kwashiorkor?

A lack of adequate protein consumption, regardless of sufficient calorie intake. (B) Signup and view all the answers

Why are patients that have had surgery at risk for 2nd infections?

Because of the hypercatabolic state, there is a risk of death from secondary infections if there is inadequate protein intake. (C) Signup and view all the answers

A patient has an autosomal recessive disorder that affects the amino acid transporter in the kidneys. What is a likely outcome?

The formation of kidney stones due to crystallization of poorly soluble amino acids in urine. (B) Signup and view all the answers

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Description

Test your knowledge on acid-base chemistry and its applications in protein function. This quiz covers topics like proton hopping, the Henderson-Hasselbalch equation, the role of histidine, and physiological pH control. Challenge yourself with questions on metabolic processes and buffer systems.