Protein Structure and Function

Protein Structure and Function Indian Medical PG Question 1: The α-helix and β-pleated sheet in proteins are examples of which level of protein structure?

• A. Primary structure
• B. Secondary structure (Correct Answer)
• C. Tertiary structure
• D. Quaternary structure

Protein Structure and Function Explanation: ***Secondary structure*** - The **α-helix** and **β-pleated sheet** are formed by **hydrogen bonding** between the backbone atoms of amino acids within a polypeptide chain. - This level of structure describes the regular, recurring arrangements of **local regions** of the polypeptide backbone. *Primary structure* - This refers to the **linear sequence of amino acids** in a polypeptide chain, determined by the genetic code. - It does not involve the folding patterns of the polypeptide backbone but rather the order of its constituent monomers. *Tertiary structure* - This describes the **overall three-dimensional shape** of a single polypeptide chain, including the folding of helices and sheets and the arrangement of side chains. - It is stabilized by various interactions, including **hydrophobic interactions**, ionic bonds, hydrogen bonds, and disulfide bridges. *Quaternary structure* - This applies to proteins composed of **multiple polypeptide subunits**, describing how these subunits associate and are arranged in space. - It is established through interactions between different polypeptide chains, such as in **hemoglobin**.

Protein Structure and Function Indian Medical PG Question 2: Which one of the following agents used in the treatment of inflammatory Bowel Disease acts by inhibiting the enzyme 'Janus Kinase'?

• A. Adalimumab
• B. Vedolizumab
• C. Tofacitinib (Correct Answer)
• D. Infliximab

Protein Structure and Function Explanation: ***Tofacitinib*** - **Tofacitinib** is an oral medication that functions as a small molecule **Janus Kinase (JAK) inhibitor**, primarily targeting JAK1 and JAK3. - By inhibiting JAK enzymes, tofacitinib disrupts the signaling pathways of several **cytokines** involved in inflammation, including those implicated in **inflammatory bowel disease (IBD)**. *Adalimumab* - **Adalimumab** is a monoclonal antibody that targets and neutralizes **tumor necrosis factor-alpha (TNF-α)**, a key inflammatory cytokine. - It is not a JAK inhibitor but rather works by blocking the interaction of TNF-α with its receptors on cell surfaces. *Vedolizumab* - **Vedolizumab** is an anti-integrin monoclonal antibody that selectively blocks the α4β7 integrin on lymphocytes. - This action prevents lymphocytes from migrating into the gastrointestinal tract, thereby reducing inflammation in IBD. *Infliximab* - **Infliximab** is a chimeric monoclonal antibody that, like adalimumab, targets and neutralizes **tumor necrosis factor-alpha (TNF-α)**. - It works by binding to soluble and transmembrane forms of TNF-α, preventing its pro-inflammatory effects.

Protein Structure and Function Indian Medical PG Question 3: Size of fibrillary proteins in amyloidosis is:

• A. 0-5 nm
• B. 7.5-10 nm (Correct Answer)
• C. 12-17 nm
• D. 18-20 nm

Protein Structure and Function Explanation: ***7.5-10 nm*** - Amyloid fibrils are characteristically **non-branching**, **insoluble protein fibrils** that range in diameter from **7.5 to 10 nm**. - This specific size and morphology are crucial for their identification via **electron microscopy**, which is a key diagnostic tool for amyloidosis. *0-5 nm* - This range is generally too small for the characteristic amyloid fibrils and would likely represent **monomeric proteins** or very small aggregates. - Fibrillary structures typically need to be larger to achieve the stable, ordered beta-pleated sheet conformation seen in amyloid. *12-17 nm* - This diameter is typically **too large** for classic amyloid fibrils, which are known for their consistent size. - Fibrils in this range might suggest different types of protein aggregates or other pathological structures not characteristic of amyloid. *18-20 nm* - Fibrils of this diameter are significantly **larger than the typical amyloid fibrils** and would not be consistent with the ultrastructural definition of amyloid. - This size might be indicative of bundled fibrils or other forms of protein deposits.

Protein Structure and Function Indian Medical PG Question 4: Which of the following drugs is preferred in the management of primary progressive multiple sclerosis?

• A. Natalizumab
• B. Ocrelizumab (Correct Answer)
• C. Alemtuzumab
• D. Fingolimod

Protein Structure and Function Explanation: ***Ocrelizumab*** - **Ocrelizumab** is the first and only FDA-approved disease-modifying therapy for **primary progressive multiple sclerosis (PPMS)**, demonstrating a reduction in disability progression. - It is a **monoclonal antibody** that selectively targets CD20-positive B cells, believed to play a critical role in the pathogenesis of MS. *Natalizumab* - **Natalizumab** is approved for **relapsing-remitting multiple sclerosis (RRMS)**, not primary progressive MS [1]. - It works by blocking the migration of immune cells into the **central nervous system**, but carries a risk of **progressive multifocal leukoencephalopathy (PML)**. *Alemtuzumab* - **Alemtuzumab** is used for **relapsing forms of MS**, particularly in patients who have had an inadequate response to other MS drugs [1]. - It is known for its durable efficacy but also its significant side effects, including **autoimmune conditions** and **infusion reactions**. *Fingolimod* - **Fingolimod** is an oral medication approved for **relapsing forms of MS**, but not for primary progressive MS [1]. - It acts by trapping lymphocytes in the **lymph nodes**, preventing them from entering the central nervous system.

Protein Structure and Function Indian Medical PG Question 5: Which of the following is a defining characteristic of all serine proteases?

• A. Tight binding of pancreatic trypsin inhibitor is characteristic of all serine proteases.
• B. Cleavage of peptide bonds adjacent to serine residues.
• C. Presence of Ser-His-Asp catalytic triad at the active site. (Correct Answer)
• D. Autocatalytic activation of zymogen precursors.

Protein Structure and Function Explanation: ***Presence of Ser-His-Asp catalytic triad at the active site.*** - All **serine proteases** utilize a unique **catalytic triad** composed of **serine**, **histidine**, and **aspartate** residues in their active site to perform catalysis. - This specific arrangement of amino acids enables the serine residue to act as a **nucleophile**, facilitating the cleavage of peptide bonds. *Tight binding of pancreatic trypsin inhibitor is characteristic of all serine proteases.* - The **pancreatic trypsin inhibitor (BPTI)** specifically inhibits **trypsin**, a particular serine protease, but not all members of the serine protease family. - While it's an important regulatory mechanism for trypsin, it is not a universal characteristic that defines *all* serine proteases. *Cleavage of peptide bonds adjacent to serine residues.* - Serine proteases cleave peptide bonds, but the cleavage occurs adjacent to specific amino acid residues determined by the **specificity pocket** of each individual protease, not necessarily adjacent to serine residues. - For example, trypsin cleaves after **lysine** or **arginine**, while chymotrypsin cleaves after **aromatic residues**. *Autocatalytic activation of zymogen precursors is a common feature.* - Many serine proteases are synthesized as inactive **zymogens** and activated by **proteolytic cleavage**, which can sometimes be autocatalytic. - However, not all serine proteases are produced as zymogens, and their activation mechanisms can vary, making this a common feature but not a defining characteristic of *all* of them.

Protein Structure and Function Flashcard 1 of 5

Question: A _____ protein, is an intracellular protein involved in facilitating and/or maintaining protein folding

Answer: chaperone

Protein Structure and Function Flashcard 2 of 5

Question: _____ is a measure of the effective volume occupied by a protein as it rapidly tumbles in free solution

Answer: Stokes radius

Protein Structure and Function Flashcard 3 of 5

Question: Microtubules grow _____ and collapse quickly (speed)

Answer: slowly

Protein Structure and Function Flashcard 4 of 5

Question: Free - and -chains are _____ soluble than free -chains.

Answer: more

Protein Structure and Function Flashcard 5 of 5

Question: Collagen comes under glycoprotein sub-classes of _____-glycosidic linkages.

Answer: O (O/N)