Protein Structures and Functions Quiz

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Questions and Answers

What type of bonds primarily stabilize the structure of beta-sheets?

Ionic bonds between oppositely charged side chains

Hydrogen bonds perpendicular to the polypeptide chain (correct)

Hydrogen bonds parallel to the polypeptide chain

Disulfide bonds between cysteine residues

How do side chains in a beta-sheet typically arrange themselves?

Randomly distributed without any specific pattern

All pointing above the plane of the sheet

All pointing below the plane of the sheet

Alternating above and below the plane of the sheet (correct)

In what type of proteins are beta-sheets commonly found?

Exclusively in globular proteins such as enzymes

Exclusively in fibrous proteins such as silk fibroin

Only in membrane proteins acting as channels or receptors

In both fibrous proteins such as silk fibroin and globular proteins such as immunoglobulins (correct)

What is the key characteristic of the primary structure of a protein?

The specific sequence of amino acids (C) Signup and view all the answers

What primarily determines the specific sequence of amino acids in a protein's primary structure?

The nucleotide sequence of the gene encoding the protein (B) Signup and view all the answers

How does the primary structure variation impact protein function?

It leads to variation in the protein folding pattern, properties, and biological activity. (D) Signup and view all the answers

What is a key example highlighting the importance of a protein's 1° structure in achieving its function?

The ability of haemoglobin to bind and transport oxygen. (C) Signup and view all the answers

What is the effect of even a single change in the amino acid sequence in the primary structure of a protein?

It can significantly alter the protein's structure and function. (B) Signup and view all the answers

What is a key characteristic of polymorphisms in a population?

They occur in more than 1% of individuals. (A) Signup and view all the answers

How do mutations typically differ from polymorphisms in terms of their impact?

Mutations usually have a significant biological impact (A) Signup and view all the answers

Which type of genetic variation is most likely to provide an adaptive advantage?

Polymorphisms resulting from evolutionary pressures. (A) Signup and view all the answers

What defines an apoprotein?

The polypeptide chain of a protein without its associated non-protein groups. (C) Signup and view all the answers

Which of these is a characteristic of an holoprotein?

It is a protein that includes all subunits and non-protein components necessary for its complete activity. (A) Signup and view all the answers

What would apotransferrin require to become a fully functional protein?

The binding of Fe3+ ions. (A) Signup and view all the answers

What is the primary difference between a mutation and a polymorphism?

Polymorphisms are more common and have less significant functional impact than mutations. (D) Signup and view all the answers

Which of the following best describes an apoprotein of hemoglobin?

The globin chains (alpha and beta subunits) without the heme (B) Signup and view all the answers

What is the primary role of hemoglobin (Hb) in relation to blood pH when it releases oxygen to tissues?

It binds H⁺ ions, helping to reduce blood acidity. (D) Signup and view all the answers

How does the 'chloride shift' contribute to maintaining electrostatic balance in red blood cells (RBCs)?

By transporting Cl⁻ ions into the RBC in exchange for HCO₃⁻ ions. (D) Signup and view all the answers

What is the significance of the pKa of inorganic phosphate (7.2) in relation to its role as a buffer?

It indicates it is ionised at intracellular pH so it can buffer H⁺ ions. (A) Signup and view all the answers

How do plasma proteins like albumin contribute to blood buffering?

By accepting or donating H⁺ ions depending on pH changes. (D) Signup and view all the answers

What is the direct effect of increased carbon dioxide (CO₂) levels in the blood on blood pH?

It increases the concentration of H⁺ ions, decreasing blood pH. (D) Signup and view all the answers

According to the information provided, how does the phosphate buffer system respond when blood becomes too acidic?

It binds H⁺ ions, forming H₂PO₄⁻ to reduce acidity. (D) Signup and view all the answers

What is the primary mechanism by which proteins in the blood, such as albumin, respond to a basic (alkaline) pH?

They release H⁺ ions, reducing alkalinity. (A) Signup and view all the answers

What is the role of carbonic acid (H₂CO₃) in pH regulation by the lungs?

It is the immediate product of the reaction of water and carbon dioxide in blood. (A) Signup and view all the answers

What is a characteristic of nonconservative amino acid substitutions that often leads to mutations?

They involve amino acids with very different properties, often affecting protein function. (D) Signup and view all the answers

According to the Bronsted-Lowry definition, what is a base?

A substance that accepts a proton. (D) Signup and view all the answers

Why are mutations typically less frequent than polymorphisms?

Mutations often disrupt normal cellular functions. (A) Signup and view all the answers

What is the nature of a proton in an aqueous solution?

It is rapidly picked up by water molecules to form hydronium ions. (A) Signup and view all the answers

What is the main characteristic of weak electrolytes in an aqueous solution?

They maintain an equilibrium between undissociated and dissociated forms. (C) Signup and view all the answers

What type of mutation causes sickle cell anemia?

A substitution mutation replacing glutamic acid with valine in the beta-globin protein. (C) Signup and view all the answers

Which of the following is NOT considered a weak biological electrolyte?

Hydrochloric acid (B) Signup and view all the answers

How does the mutation in sickle cell anemia affect red blood cells?

It causes red blood cells to form rigid fibers under low oxygen conditions, resulting in a sickle shape. (A) Signup and view all the answers

What does the Henderson-Hasselbalch equation illustrate?

The relationship between pH, pKa, and the ratio of acid to base. (D) Signup and view all the answers

What type of mutation is primarily responsible for cystic fibrosis?

A frameshift mutation caused by the deletion of one amino acid in the CFTR protein. (C) Signup and view all the answers

In the Henderson-Hasselbalch equation, what does [HA] represent?

The concentration of the protonated acid. (B) Signup and view all the answers

What is the effect of the mutation in the CFTR gene that causes cystic fibrosis?

It disrupts chloride ion transport, resulting in thicker, stickier mucus. (C) Signup and view all the answers

What is the shape of a typical titration curve for a conjugate acid-base pair?

Sigmoidal. (A) Signup and view all the answers

What type of mutation is associated with Duchenne Muscular Dystrophy (DMD)?

A frameshift mutation caused by a deletion of one amino acids in the dystrophin gene. (A) Signup and view all the answers

What is the effect of proton tunnelling on proton movement?

It accelerates the movement of protons. (A) Signup and view all the answers

How do polymorphisms differ from mutations in terms of their impact on health?

Polymorphisms are variations that do not typically cause disease, while mutations often result in disease. (A) Signup and view all the answers

According to the Lewis definition, what is an acid?

A substance that accepts an electron pair. (D) Signup and view all the answers

What does pKa represent in the Henderson-Hasselbalch equation?

The negative logarithm of the dissociation constant of the acid. (D) Signup and view all the answers

What is the primary function of carbonic anhydrase in the context of the bicarbonate buffer system?

To facilitate the reaction between CO₂ and H₂O to form H₂CO₃. (B) Signup and view all the answers

In the bloodstream, when the pH becomes acidic, what is the immediate role of bicarbonate ions (HCO₃⁻)?

They bind with excess H⁺ ions to form H₂CO₃. (C) Signup and view all the answers

Although the pKa of H₂CO₃ is 3.8, how can it still act as an effective buffer at a physiological pH of 7.4?

It is constantly replenished by the hydration of CO₂. (D) Signup and view all the answers

Why is the bicarbonate buffer system described as an 'open' system?

Because CO₂ can be continuously removed or replenished via the lungs. (A) Signup and view all the answers

What is the approximate ratio of HCO₃⁻ to H₂CO₃ at a physiological pH, and what effect does this ratio have?

Approximately 20:1, making the system very resistant to pH change. (B) Signup and view all the answers

How does the concentration of CO₂ impact the bicarbonate buffer system?

It serves as a reservoir for the buffer system, and can be adjusted by the lungs. (A) Signup and view all the answers

Why is the further dissociation of HCO₃⁻ to CO₃²⁻ not a significant factor in physiological conditions?

Because the pKa for that reaction is 9.8, which makes it negligible at physiological pH. (B) Signup and view all the answers

What is the primary role of hemoglobin (Hb) in the haemoglobin buffer system?

To bind or release H⁺, acting as a pH buffer. (A) Signup and view all the answers

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Description

Test your knowledge on the stabilization of beta-sheets and the significance of primary protein structures. This quiz covers key characteristics of apoproteins and holoproteins, along with the impact of genetic variations like mutations and polymorphisms. Challenge yourself with these important concepts in biochemistry!