This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Structure and Function of Transmembrane Proteins – 1”.
1. Virtually all integral membrane proteins bear chains of sugars (oligosaccharides) of variable length that project outward from the plasma membrane.
a) False
b) True
View Answer
Explanation: The above statement is true. Virtually all integral membrane proteins bear chains of sugars (oligosaccharides) of variable length that project outward from the plasma membrane. These carbohydrate projections form a layer closely applied to the outer surface of the plasma membrane called the glycocalyx.
2. Most of the membrane proteins have which of the following domains?
a) Metal-binding domain
b) Immunoglobulin domain
c) SH2 domain
d) Transmembrane domain
View Answer
Explanation: Most of the membrane proteins have transmembrane domains. A transmembrane domain is the portion of the proteins which is mostly in the form of alpha-helix and helps membrane proteins traverse the plasma membrane.
3. Who proposed the Fluid Mosaic Model of the plasma membrane?
a) Rudolf Virchow
b) Meselson and Stahl
c) Schleiden and Schwann
d) Singer and Nicolson
View Answer
Explanation: The Fluid Mosaic Model of the plasma membrane was proposed by Singer and Nicolson. Rudolf Virchow contributed to the formulation of cell theory, whereas Schleiden and Schwann formulated the cell theory. Meselson and Stahl first demonstrated the semi-conservative replication of DNA.
4. Which of the following is not mediated by glycocalyx?
a) Cell-cell interaction
b) Mechanical protection to the cell
c) Cell-substratum interaction
d) Gap junction
View Answer
Explanation: The glycocalyx mediates cell-cell interaction, mechanical protection to cell, and cell-substratum interaction. Glycocalyx has no role is gap junctions. Gap junction serves as a barrier to particles moving towards the plasma membrane and bind important regulatory factors that act on the cell surface.
5. Which of the following is present beyond the immediate vicinity of the plasma membrane?
a) Chloroplast
b) Nucleus
c) Vacuum
d) ECM
View Answer
Explanation: ECM is present beyond the immediate vicinity of the plasma membrane. It stands for Extracellular Matrix. It is an organized network of extracellular materials.
6. The basement membrane is one of the best-defined extracellular matrices.
a) False
b) True
View Answer
Explanation: The above statement is true. The basement membrane is one of the best-defined extracellular matrices. It is a continuous sheet of 50 to 200 nm thickness. It also serves as a barrier to the invasion of tissues by cancer cells.
7. Which of the following is not a function of the basement membrane?
a) Surrounds nerve fibers, muscles, and fat cells
b) Underlies the basal surface of epithelial tissue
c) Underlies the inner endothelial lining of blood vessels
d) Covers nuclear lamina
View Answer
Explanation: The basement membrane surrounds nerve fibers, muscles, and fat cells; underlies the basal surface of epithelial tissue; and underlies the inner endothelial lining of blood vessels. It does not cover nuclear lamina.
8. Which of the following is an integral plasma membrane protein?
a) Fibrinogen
b) Collagen
c) Laminin
d) Integrins
View Answer
Explanation: Integrins are integral plasma membrane proteins. Whereas, fibrinogen, collagen, and laminin are not integral plasma membrane proteins. These proteins are present in the extracellular matrix. Integrins are involved in cell attachment and signal transduction.
9. Which of the following is not an integral membrane protein?
a) Selectin
b) Integrin
c) Cadherins
d) RAS proteins
View Answer
Explanation: RAS proteins are not integral membrane proteins. Selectins, Integrins, and Catherins are all integral membrane proteins. RAS protein is a lipid-anchored membrane protein.
10. Find the odd one out.
a) Members of IgSF
b) Cadherins
c) Selectins
d) Collagen
View Answer
Explanation: Collagen is an extracellular matrix protein, whereas Members of IgSF, Catherins, and Selectins are integral membrane proteins. Hence, collagen is the odd one out. Moreover, it does not have a role in cell-cell interaction.
11. One of the roles of integral membrane proteins is to transfer information across the plasma membrane.
a) False
b) True
View Answer
Explanation: The above statement is true. One of the roles of integral membrane proteins is to transfer information across the plasma membrane. This process is also known as transmembrane signaling.
12. Which of the following integral membrane proteins can transmit signals from the extracellular environment to the cytoplasm?
a) Integrins only
b) Catherins only
c) Laminins
d) Integrins and Catherins
View Answer
Explanation: Integrins and Catherins are the integral membrane proteins that can transmit signals from the extracellular environment to the cytoplasm. Laminin is an extracellular matrix protein.
13. Which of the following integral membrane protein is not involved in the inflammation process?
a) Integrin
b) Selectin
c) ICAM
d) Glycophorin
View Answer
Explanation: Glycophorin is an integral membrane protein but is not involved in the inflammation process. Integrins, Selectins, and ICAM are required for the process of inflammation. ICAM is a member of IgSF superfamily.
14. Which of the following transmembrane protein is reduced in malignant cells?
a) Integrins
b) Selectins
c) IgSF proteins
d) E-cadherins
View Answer
Explanation: The transmembrane protein whose expression is reduced in malignant cells is E-cadherins. It is a predominant cell adhesion molecule of the adherens junction. This holds the epithelial cells together. The malignant cells have greatly reduced levels of E-cadherins; thus, they are free to invade other tissues.
15. Which of the following class of transmembrane proteins some members involved in immune functions and some members having a role in cell-cell adhesion?
a) Cadherins
b) Integrins
c) Selectins
d) Members of IgSF
View Answer
Explanation: IgSF is the superfamily of transmembrane proteins in which some members are involved in immune functions and some members have a role in cell-cell adhesion. Most members are involved in immune functions and some mediate calcium-independent cell-cell adhesion.
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