Membrane Biochemistry Practice Questions

Q: The signal sequence in a type 2 membrane protein with N-terminal facing cytoplasm is located in?

Middle of protein. ***Middle of protein*** - For a type 2 membrane protein with the **N-terminal facing the cytoplasm**, the **start-transfer sequence** (which acts as a signal sequence) is found in the **middle of the protein**. - This **internal signal sequence** allows for membrane integration with the correct orientation, often functioning as a **transmembrane domain**. *C-terminal* - A C-terminal signal is typically seen in **Type I membrane proteins** where the **N-terminus is in the ER lumen** and the C-terminus is in the cytoplasm. - This orientation requires a **stop-transfer sequence** in the middle of the protein. *Both N and C terminal* - While some proteins may have multiple signal sequences, a single protein typically utilizes **one dominant signal** for its initial targeting and membrane insertion. - Having both an N-terminal and C-terminal primary signal for integration would lead to **conflicting targeting signals** for this specific type of protein. *N-terminal* - An N-terminal signal sequence is characteristic of **Type I membrane proteins** or **secreted proteins**, guiding them to the ER and often being cleaved. - In a **type 2 protein**, with the **N-terminus in the cytoplasm**, an N-terminal signal would result in the N-terminus entering the ER lumen, contradicting the given orientation.

Q: Which membrane channel is mainly affected in Cystic fibrosis?

Chloride. ***Chloride*** - Cystic fibrosis is caused by a mutation in the **CFTR (Cystic Fibrosis Transmembrane Conductance Regulator)** gene, which encodes a chloride channel. - Dysfunction of this **chloride channel** leads to impaired transport of chloride ions, mainly affecting epithelial cells in various organs. *Sodium* - While sodium transport is indirectly affected in cystic fibrosis, the primary defect is not in a sodium channel itself but rather in the **chloride channel**, which influences water and sodium movement. - The abnormal **chloride transport** leads to a compensatory but ineffective increase in sodium absorption in some tissues like the airway. *Calcium* - Calcium channels are not primarily implicated in the pathophysiology of **cystic fibrosis**. - **Calcium dysregulation** can occur secondarily in some CF-related processes, but it is not the main affected membrane channel. *Potassium* - **Potassium channels** are not the main membrane channels affected in cystic fibrosis. - While potassium transport is vital for cellular function, it is not the primary defect underlying the disease's respiratory and gastrointestinal manifestations.

Q: Which of the following is not amphipathic?

Triglycerides. ***Triglycerides*** - Triglycerides are composed of a **glycerol backbone** esterified to three fatty acids, making them entirely **hydrophobic** and thus not amphipathic. - They serve primarily as **energy storage** molecules and do not form membranes because they lack a polar head group. *Sphingolipids* - Sphingolipids are amphipathic because they contain a **hydrophilic polar head group** (e.g., phosphocholine or a sugar) and two **hydrophobic tails** derived from a fatty acid and the sphingosine backbone. - This dual nature allows them to be fundamental components of **cell membranes**. *Glycolipids* - Glycolipids are characterized by a **carbohydrate head group** attached to a lipid moiety, rendering them amphipathic. - The sugar portion is **hydrophilic**, while the lipid portion (e.g., ceramide) is **hydrophobic**, enabling them to participate in cell recognition and membrane stability. *Phosphoglycerol* - Phosphoglycerol (more commonly referred to as **glycerophospholipids**) are amphipathic, consisting of a **glycerol backbone**, two fatty acid tails, and a **phosphate group** often linked to an alcohol. - The **phosphate and alcohol group** form the hydrophilic head, and the **fatty acid tails** form the hydrophobic region, making them crucial for lipid bilayers.

Q: An aggregate of surfactant molecules or ions in solution is known as?

Micelle. ***Micelle*** - A **micelle** is an aggregate of **surfactant** molecules dispersed in a liquid colloid. - In an aqueous solution, the **hydrophilic "head" regions** of the surfactant molecules spontaneously arrange to face the surrounding solvent, while the **hydrophobic "tail" regions** cluster together in the micelle's center. *Atom* - An **atom** is the smallest unit of ordinary matter that forms a chemical element. - It consists of a nucleus of **protons and neutrons** surrounded by a cloud of electrons. *Basion* - The **basion** is a term used in anatomy, referring to the midpoint of the anterior margin of the **foramen magnum** of the skull. - It is a craniometric landmark used in various **cephalometric measurements**. *Chilon* - **Chilon** is not a recognized scientific term or concept related to molecular aggregates or biological structures. - It does not describe an aggregate of **surfactant molecules or ions in solution**.

Q: Degradation of a substance takes place in which part of the cell:

Lysosome. ***Lysosome*** - **Lysosomes** are membrane-bound organelles that contain a variety of **hydrolytic enzymes**, such as proteases, lipases, nucleases, and glycosidases. - These enzymes are responsible for the **breakdown and degradation** of waste materials, cellular debris, and foreign substances within the cell. *ER* - The **endoplasmic reticulum (ER)** is involved in protein synthesis and folding, lipid metabolism, and detoxification, but not primary degradation. - While it has enzymes for certain metabolic transformations, it is not the main site for general substance degradation. *Mitochondria* - **Mitochondria** are primarily known for their role in **cellular respiration** and **ATP production**, serving as the powerhouse of the cell. - They also play a role in apoptosis and calcium homeostasis, but not directly in the degradation of cellular waste. *Nucleus* - The **nucleus** houses the cell's genetic material (**DNA**) and is involved in replication, transcription, and regulation of gene expression. - It does not contain the necessary enzymes for the degradation of general cellular substances.

Q: What is the primary role of cholesterol in the plasma membranes of animal cells?

Structural integrity and fluidity regulation. ***Structural integrity and fluidity regulation*** - **Cholesterol** is amphipathic and inserts into the **lipid bilayer**, where it modulates membrane fluidity by preventing the tight packing of phospholipids at low temperatures and restricting excessive movement at high temperatures. - This dual role helps maintain the structural integrity and optimal function of the **plasma membrane** across various physiological conditions. *Energy storage* - While cholesterol is a lipid, its primary role in the plasma membrane is not **energy storage**. - **Triglycerides** are the main form of energy storage in animal cells. *Influencing membrane signaling pathways* - Although cholesterol can indirectly affect **membrane signaling** by influencing the organization of **lipid rafts** where signaling molecules often reside, its fundamental role is structural. - These signaling effects are secondary to its primary function in regulating membrane dynamics. *Facilitating protein synthesis* - **Protein synthesis** primarily occurs on **ribosomes** in the cytoplasm and endoplasmic reticulum, with the plasma membrane having no direct role in this process. - Cholesterol is not involved in the machinery of protein synthesis.

Q: Where are lipid rafts primarily located?

Plasma membrane. ***Plasma membrane*** - **Lipid rafts** are dynamic microdomains within the **plasma membrane** that are enriched in cholesterol and sphingolipids. - They play crucial roles in **cell signaling**, **membrane trafficking**, and **endocytosis**. *Nucleus* - The **nucleus** contains the cell's genetic material and is involved in gene expression, not in forming lipid rafts. - Lipid rafts are components of cell membranes, not internal organelles like the nucleus. *Mitochondrial membrane* - The **mitochondrial membrane** is involved in cellular respiration and ATP production. - It has a distinct lipid composition and does not form lipid rafts in the same way as the plasma membrane. *Golgi apparatus* - The **Golgi apparatus** is involved in modifying, sorting, and packaging proteins and lipids. - While it processes membrane components, lipid rafts are primarily functional structures on the **plasma membrane**.

Q: Proteoglycan present in the glomerular basement membrane is?

Heparan sulfate. ***Heparan sulphate*** - Heparan sulphate is a key component of the **glomerular basement membrane** (GBM), crucial for its **negative charge and filtration function** [1][2]. - It plays a significant role in **filtration barrier** properties and affects the permeability of the GBM to proteins [1]. *Keratan sulphate 1* - Predominantly found in **cartilage** and **corneal tissue**, not associated with the glomerular basement membrane. - It contributes to **mechanical support** but lacks the essential role in renal filtration. *Keratan sulphate 2* - Similar to Keratan sulphate 1, this variant is involved in **cartilage** but not in the structure of the glomerular basement membrane. - Has distinct functions related to **tissue hydration** rather than the filtration dynamics of the GBM. *Chondroitin sulphate* - Commonly located in **cartilage** and connective tissues, it does not play a significant role in the structure of the glomerular basement membrane. - While it assists in **cell signaling** and regeneration, it does not influence the GBM permeability like heparan sulphate. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 905-907. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 34-35.

Q: In the context of cell membrane composition, what is the typical weight ratio of protein to lipid?

1 : 1. ***1 : 1*** - The **typical weight ratio of protein to lipid** in most cell membranes is approximately **1:1** (equal by weight). - While the **number of lipid molecules** far exceeds the number of protein molecules, proteins are much larger and heavier, resulting in roughly equal weight contributions. - This **1:1 ratio represents an average** for typical plasma membranes, though it can vary significantly depending on membrane type and function. *1 : 2* - This protein:lipid ratio would indicate **lipids contribute twice as much by weight** as proteins. - This is characteristic of **myelin membranes**, which are specialized for insulation and have exceptionally high lipid content. - However, this is **not typical** of most cell membranes. *2 : 1* - This ratio would suggest **proteins contribute twice as much by weight** as lipids. - While some protein-rich membranes exist, this is **higher than the average** for typical cell membranes. - The typical ratio is closer to 1:1 rather than being protein-dominant at 2:1. *4 : 1* - A 4:1 protein:lipid ratio represents an **extremely protein-rich membrane**. - This is characteristic of the **inner mitochondrial membrane**, which is packed with electron transport chain proteins. - This is a **specialized membrane**, not representative of typical cell membranes.

Question 1

Which of the following is NOT a component of the transport system?

Accepted Answer

Receptor activation

Answer

Selective gate

Answer

Non-selective channel

Answer

Energy coupling system

Question 2

The signal sequence in a type 2 membrane protein with N-terminal facing cytoplasm is located in?

Accepted Answer

Middle of protein

Answer

C-terminal

Answer

Both N and C terminal

Answer

N-terminal

Question 3

Which membrane channel is mainly affected in Cystic fibrosis?

Accepted Answer

Chloride

Answer

Sodium

Answer

Calcium

Answer

Potassium

Question 4

Which of the following is not amphipathic?

Accepted Answer

Triglycerides

Answer

Sphingolipids

Answer

Glycolipids

Answer

Phosphoglycerol

Question 5

An aggregate of surfactant molecules or ions in solution is known as?

Accepted Answer

Micelle

Answer

Atom

Answer

Basion

Answer

Chilon

Question 6

Degradation of a substance takes place in which part of the cell:

Accepted Answer

Lysosome

Answer

ER

Answer

Mitochondria

Answer

Nucleus

Question 7

What is the primary role of cholesterol in the plasma membranes of animal cells?

Accepted Answer

Structural integrity and fluidity regulation

Answer

Energy storage

Answer

Influencing membrane signaling pathways

Answer

Facilitating protein synthesis

Question 8

Where are lipid rafts primarily located?

Accepted Answer

Plasma membrane

Answer

Nucleus

Answer

Mitochondrial membrane

Answer

Golgi apparatus

Question 9

Proteoglycan present in the glomerular basement membrane is?

Accepted Answer

Heparan sulfate

Answer

Keratan sulfate 1

Answer

Keratan sulfate 2

Answer

Chondroitin sulfate

Question 10

In the context of cell membrane composition, what is the typical weight ratio of protein to lipid?

Accepted Answer

1 : 1

Answer

1 : 2

Answer

4 : 1

Answer

2 : 1

Membrane Biochemistry — MCQs

Membrane Biochemistry — MCQs

On this page

Practice by Chapter

Want unlimited practice?