Protein Structure and Function Practice Questions

Q: C-reactive protein is classified as which of the following?

Beta-1 globulin. ***Beta-1 globulin*** - **C-reactive protein (CRP)** is classified as an **acute-phase reactant** and migrates in the **beta globulin region** during serum protein electrophoresis. - CRP is a **pentameric protein** synthesized by the liver in response to inflammatory stimuli, particularly **IL-6**. - Its location in the beta fraction reflects its molecular characteristics and electrophoretic mobility. *Alpha-1 globulin* - The **alpha-1 globulin** fraction contains proteins such as **alpha-1 antitrypsin**, **alpha-1 acid glycoprotein (orosomucoid)**, and **alpha-1 fetoprotein**. - While these are also acute-phase proteins, CRP has different electrophoretic properties and migrates separately in the beta region. *Gamma globulin* - The **gamma globulin** fraction is predominantly composed of **immunoglobulins (antibodies)**, which are crucial for adaptive immunity. - CRP is part of the **innate immune response** and belongs to the pentraxin family, not the immunoglobulin family. - During severe acute inflammation, CRP levels can be so elevated that it may appear in the gamma region, but its standard classification is as a beta globulin. *Non-specific inflammatory protein* - While CRP is indeed a **non-specific marker of inflammation**, this option describes its **function** rather than its **electrophoretic classification**. - The correct classification based on serum protein electrophoresis mobility is **beta globulin**.

Q: Predominant type of immunoglobulin in human milk is:

Ig A. ***Ig A*** - **Secretory IgA (sIgA)** is the predominant immunoglobulin found in human milk, present in high concentrations. - **sIgA** provides crucial **passive immunity** to the infant's mucosal surfaces, protecting against infections in the gastrointestinal and respiratory tracts. *Ig G* - While present in human milk, **IgG** is not the predominant immunoglobulin type; its primary transfer to the fetus occurs **transplacentally**. - **IgG** in milk offers some systemic immunity but is quantitatively less significant than **sIgA** in mucosal protection via breastfeeding. *Ig M* - **IgM** is found in very low concentrations in human milk compared to **sIgA**. - Its role in passive immunity through breastfeeding is minimal, as **IgM** is primarily involved in the **primary immune response** within the infant's own immune system post-birth. *Ig D* - **IgD** is found in extremely low or negligible amounts in human milk. - Its main function is largely unexplained but is associated with **B cell activation** and is predominantly found on the surface of naive B cells, not in secretions.

Q: Which amino acid has an imino group?

Proline. ***Proline*** - **Proline** is unique among the 20 standard **amino acids** because its side chain forms a ring with the amino group, creating a secondary amine or **imino group**. - This cyclic structure gives proline distinct conformational properties, often leading to kinks in **protein structures**. *Glycine* - **Glycine** is the simplest amino acid, with a single hydrogen atom as its side chain. - It possesses a primary **amino group**, not an imino group. *Arginine* - **Arginine** has a complex side chain containing a **guanidinium group**. - This group is basic but is not an **imino group** in the structural sense of pyrrolidine ring found in proline. *Tryptophan* - **Tryptophan** possesses an **indole ring** within its side chain. - The **indole ring** contains a nitrogen atom that is part of a five-membered ring, but this nitrogen is part of a secondary amine within an aromatic system, not an **imino group** as seen in proline.

Q: Which of the following statements about collagen is incorrect?

Collagen primarily exhibits a beta-pleated structure.. ***Collagen primarily exhibits a beta-pleated structure.*** - This statement is **INCORRECT** and is therefore the correct answer to this question. - Collagen primarily exhibits a **triple helix structure**, not a beta-pleated structure. - **Beta-pleated sheets** are characteristic of proteins like **keratin** and **fibroin**, not collagen. - The unique triple helical conformation gives collagen **high tensile strength** and is crucial for its function in connective tissues. *Collagen has a triple helix structure.* - This statement is **correct**, making it an incorrect answer choice. - The **triple helix structure** is a defining characteristic of collagen, formed by three polypeptide alpha-chains coiling around each other. - This structure is essential for collagen's **mechanical strength** and ability to form robust fibers in connective tissues. *Vitamin C is essential for collagen synthesis.* - This statement is **correct**, making it an incorrect answer choice. - **Vitamin C** (ascorbic acid) is a crucial **cofactor for prolyl hydroxylase and lysyl hydroxylase**, enzymes vital for hydroxylating proline and lysine residues in collagen. - Without adequate vitamin C, collagen cannot be properly cross-linked, leading to unstable collagen and conditions like **scurvy**. *Collagen contains glycine at every third position.* - This statement is **correct**, making it an incorrect answer choice. - The repetitive sequence **Gly-X-Y** (where X and Y are often proline and hydroxyproline) is characteristic of collagen. - **Glycine's small size** allows for the tight packing of the three alpha-chains in the triple helix, which is critical for its stability.

Q: What is the molecule that attaches to a protein to signal its degradation?

Ubiquitin. ***Ubiquitin*** - **Ubiquitin** is a small regulatory protein found in most eukaryotic cells that attaches to target proteins, marking them for degradation via the **proteasome system**. - This process, known as **ubiquitination**, is crucial for regulating protein levels and cellular processes by removing damaged or unneeded proteins. *RNAseF* - **RNAseF** is not a generally recognized or standardized term in molecular biology for a molecule involved in protein degradation signaling. - **RNases** are typically enzymes that degrade RNA, not proteins. *Zymase* - **Zymase** is a complex of enzymes, primarily found in yeast, that catalyzes the fermentation of sugar into ethanol and carbon dioxide. - It is involved in metabolic pathways, not in signaling protein degradation. *Chaperone* - **Chaperone proteins** assist in the proper folding of other proteins, prevent aggregation, and help transport proteins within the cell. - They are involved in maintaining protein conformation and function, not in directly tagging proteins for degradation.

Q: Which of the following is not classified as a molecular motor?

Actin. ***Actin*** - **Actin** is a globular multi-functional protein that forms **microfilaments**, which are a crucial component of the cytoskeleton in eukaryotic cells and play a vital role in cellular processes such as muscle contraction, cell motility, and cytokinesis. - While actin interacts with molecular motors like myosin to generate force and movement, actin itself is a **filamentous track** upon which motors move, not a motor protein. *Kinesin* - **Kinesin** is a motor protein that moves along **microtubules**, typically transporting cargo towards the **plus end** of the microtubule. - It uses **ATP hydrolysis** to power its movement, acting as a molecular motor in various cellular processes. *Dynein* - **Dynein** is another molecular motor protein that also moves along **microtubules**, but typically transports cargo towards the **minus end** of the microtubule. - It is crucial for processes like **ciliary and flagellar movement** and intracellular transport. *Myosin* - **Myosin** is a family of **motor proteins** best known for its role in muscle contraction, where it interacts with actin filaments. - It uses **ATP hydrolysis** to move along actin filaments, generating contractile force and movement.

Q: Which of the following amino acids is found in keratin?

All of the options. ***All of the options*** - **Keratin** is a fibrous structural protein that forms the main component of hair, skin, and nails - All three amino acids listed - **Histidine, Lysine, and Arginine** - are indeed found in keratin's composition - **Lysine** and **Arginine** are basic amino acids that contribute to keratin's structural stability and are involved in ionic interactions - **Histidine** is also present and plays a role in the protein's functional and structural aspects - While keratin is particularly rich in **cysteine** (which forms disulfide bonds responsible for its strength), it also contains significant amounts of these other amino acids - The complete amino acid composition of keratin includes all of these and many other amino acids working together to provide its characteristic properties *Why individual options alone are incomplete* - Selecting only **Histidine**, **Lysine**, or **Arginine** individually would be incorrect because it would imply the other amino acids are NOT found in keratin - Since the question asks which amino acid "is found" in keratin and all three ARE present, the correct answer must acknowledge all of them

Q: Which protein is characterized by a triple helix structure?

Collagen. ***Collagen*** - **Collagen** is the most abundant protein in mammals and is uniquely characterized by its **triple helix structure**, formed by three polypeptide chains wound around each other. - This distinctive structure provides **high tensile strength** and flexibility, crucial for its role in connective tissues, skin, bones, and cartilage. *Cystine (an amino acid)* - **Cystine** is a dimer of two cysteine amino acids linked by a **disulfide bond**, not a triple helix structure. - As a single amino acid, it primarily serves as a building block for proteins and is involved in forming cross-links within protein structures. *Pectin (a plant polysaccharide)* - **Pectin** is a complex carbohydrate found in plant cell walls and is a **polysaccharide**, not a protein. - Its structure consists of a backbone of **galacturonic acid units**, often with side chains, and does not form a triple helix. *DNA (a nucleic acid)* - **DNA** (deoxyribonucleic acid) is a nucleic acid composed of two polynucleotide strands forming a **double helix structure**, not a triple helix. - The double helix is stabilized by **hydrogen bonds** between complementary base pairs.

Q: Most abundant collagen in the body is

Type I. ***Type I*** - **Type I collagen** is the most abundant type in the human body, constituting about 90% of the body's total collagen. - It is primarily found in **skin, tendons, ligaments, bone, dentin, and intervertebral discs**, providing mechanical strength and structural integrity. *Type II* - **Type II collagen** is the main collagen found in **cartilage**, especially hyaline and elastic cartilage. - It provides resistance to pressure and is crucial for the structure of the **intervertebral disc nucleus pulposus** and the **vitreous humor of the eye**. *Type V* - **Type V collagen** is a minor fibrillar collagen that associates with **type I collagen** to regulate fibril diameter and organization. - It is found in **cornea, bone, and interstitial matrices**, playing a role in tissue development and integrity. *Type VI* - **Type VI collagen** is a microfibrillar collagen that forms bead-like microfibrils and is found in most **interstitial tissues**. - It plays a significant role in anchoring other extracellular matrix components and is particularly abundant in the **basement membranes** of blood vessels and muscles.

Q: In primary immune deficiency, the following plasma protein fraction can be reduced:

Gamma globulin. ***Gamma globulin*** - In primary immune deficiency, there is a significant reduction in **gamma globulin**, resulting from impaired antibody production [1]. - This protein fraction primarily contains **immunoglobulins**, which are crucial for the immune response [1][2]. *Alpha1 globulin* - Typically associated with **protease inhibitors** and **transport proteins**, its levels are not directly impacted in primary immune deficiency. - This fraction does not primarily play a role in the **immune response** like gamma globulins do. *Alpha2 globulin* - Contains **haptoglobin** and **ceruloplasmin**, which often remain stable in immunodeficiencies. - Its reduction is not characteristic of primary immune deficiency, as it does not directly relate to **antibody function**. *Beta globulin* - Includes fractions such as **transferrin** and **complement proteins**, generally unaffected by primary immune deficiencies. - While important, these proteins do not primarily comprise **antibodies** and do not show a decrease in these conditions.

Question 1

C-reactive protein is classified as which of the following?

Accepted Answer

Beta-1 globulin

Answer

Gamma globulin

Answer

Non-specific inflammatory protein

Answer

Alpha-1 globulin

Question 2

Predominant type of immunoglobulin in human milk is:

Accepted Answer

Ig A

Answer

Ig G

Answer

Ig M

Answer

Ig D

Question 3

Which amino acid has an imino group?

Accepted Answer

Proline

Answer

Glycine

Answer

Arginine

Answer

Tryptophan

Question 4

Which of the following statements about collagen is incorrect?

Accepted Answer

Collagen primarily exhibits a beta-pleated structure.

Answer

Collagen has a triple helix structure.

Answer

Vitamin C is essential for collagen synthesis.

Answer

Collagen contains glycine at every third position.

Question 5

What is the molecule that attaches to a protein to signal its degradation?

Accepted Answer

Ubiquitin

Answer

RNAseF

Answer

Zymase

Answer

Chaperone

Question 6

Which of the following is not classified as a molecular motor?

Accepted Answer

Actin

Answer

Kinesin

Answer

Dynein

Answer

Myosin

Question 7

Which of the following amino acids is found in keratin?

Accepted Answer

All of the options

Answer

Lysine

Answer

Histidine

Answer

Arginine

Question 8

Which protein is characterized by a triple helix structure?

Accepted Answer

Collagen

Answer

Cystine

Answer

Pectin

Answer

DNA

Question 9

Most abundant collagen in the body is

Accepted Answer

Type I

Answer

Type II

Answer

Type V

Answer

Type VI

Question 10

In primary immune deficiency, the following plasma protein fraction can be reduced:

Accepted Answer

Gamma globulin

Answer

Alpha2 globulin

Answer

Alpha1 globulin

Answer

Beta globulin

Protein Structure and Function — MCQs

Protein Structure and Function — MCQs

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