Membrane structure and function MCQ Quiz in मल्याळम - Objective Question with Answer for Membrane structure and function - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

The correct answer is Sugars such as glucose are always transported by active transport rather than facilitated diffusion carrier.

Concept:

• Membrane transport is the process by which substances move across the cell membrane. This can occur through passive transport, active transport, or facilitated transport.
• Passive transport does not require energy and occurs via diffusion and osmosis, allowing substances to move from areas of higher concentration to areas of lower concentration.
• Active transport requires energy (usually in the form of ATP) to move substances against their concentration gradient, from areas of lower concentration to areas of higher concentration.
• Facilitated diffusion is a type of passive transport that involves the use of protein carriers or channels to help move substances across the cell membrane.

Explanation:

Option 1: Polar and charged solutes will not cross cell membranes effectively without specific protein carriers.

• This is true because the hydrophobic core of the lipid bilayer impedes the passage of polar and charged molecules. Specific protein carriers or channels are needed to facilitate their transport.

Option 2: Each protein carrier will only bind and transport one (or a few very similar) type of solute.

• This is true because protein carriers are highly specific, usually binding and transporting only one type or a few types of similar solutes.

Option 3: Sugars such as glucose are always transported by active transport rather than facilitated diffusion carrier.

• This is false. While glucose can be transported by active transport in certain cells (e.g., in the intestines and kidneys), it is also commonly transported by facilitated diffusion through glucose transporters (GLUT) in many other cell types.

Option 4: Ions are typically transported by special proteins that form membrane channels.

• This is true. Ions, due to their charge, require specific ion channels or transporters to cross the cell membrane. These channels are selective for particular ions.

The correct answer is Option 2 i.e.Increases membrane fluidity at low temperatures 

Explanation:

The cell membrane, also known as the plasma membrane, is crucial for maintaining the integrity of cells and for the regulation of substances entering and exiting the cell. It is primarily composed of a lipid bilayer, which consists of phospholipids, cholesterol, and proteins. Among these components, cholesterol plays a specific and significant role, especially in animal cells, where it modulates the membrane's physical properties.

• Cholesterol is a type of lipid molecule that is interspersed within the phospholipid bilayer of the cell membrane. Its unique structure allows it to interact with the fatty acid tails of phospholipids in several ways. Due to its amphipathic nature – having both hydrophilic (polar) and hydrophobic (nonpolar) parts – cholesterol fits snugly between phospholipid molecules in the membrane.
• At low temperatures, phospholipid molecules in the cell membrane tend to pack closely together, which can significantly decrease membrane fluidity. This is because the decrease in temperature reduces the kinetic energy of the phospholipid molecules, making the membrane more rigid and potentially impairing its function. Membrane fluidity is an important characteristic for various cellular processes, including vesicle formation, fusion, and the proper functioning of membrane proteins.
• The inclusion of cholesterol in the cell membrane counters this effect by preventing the phospholipid tails from packing too closely. Cholesterol intercalates between phospholipid molecules, adding space between them.
• This action helps to maintain an optimal level of membrane fluidity even at lower temperatures, ensuring the membrane remains semi-permeable and functional.
• The presence of cholesterol helps to ensure that the membrane remains flexible enough to facilitate cell movement, growth, division, and the incorporation of proteins and other components necessary for cell signaling and transport processes.
• Additionally, at higher temperatures, cholesterol has the opposite effect by restraining excessive movement of phospholipids, thereby preventing the membrane from becoming too fluid or permeable. This dual role of cholesterol in modulating membrane fluidity is referred to as the "fluidity buffer" function, making it a critical component for the stability and adaptability of animal cell membranes across a range of temperatures.

Conclusion:

Thus, the primary function of cholesterol in the context of membrane permeability and fluidity within animal cell membranes is to increase membrane fluidity at low temperatures, which is essential for preserving the dynamic nature of the cell membrane and ensuring proper cell function under varying environmental conditions.

The correct answer is α helices

Explanation:

Membrane proteins that span the lipid bilayer, often referred to as transmembrane proteins, typically have regions that are capable of interacting with the hydrophobic interior of the lipid bilayer. The most common structural features that enable these proteins to span the membrane are α helices.

α helices:

• α Helices are a common structural motif in transmembrane proteins.
• The helical structure allows the amino acid side chains to project outward, where hydrophobic side chains can interact favorably with the hydrophobic lipid tails in the membrane.
• Membrane-spanning α helices are typically composed of hydrophobic amino acids, which facilitate their insertion and stable presence within the lipid bilayer.

Zinc finger domain: Zinc finger domains are typically involved in binding to DNA, RNA, or other proteins and generally do not play a role in spanning the lipid bilayer.
Parallel β sheet:

• β sheets can also form membrane-spanning structures, however, these are less common.
• In the context of membrane proteins, β barrels formed by anti-parallel β sheets are more typical of outer membrane proteins in bacteria, mitochondria, and chloroplasts.

Antiparallel β sheet:

• Membrane proteins can use antiparallel β sheets to form β-barrels, which are found in the outer membranes of Gram-negative bacteria, as well as mitochondria and chloroplasts.
• However, these structures are less common in eukaryotic cell membranes compared to α helices.

Conclusion:
While β sheets can form membrane-spanning structures, α helices are the most prevalent form observed in many types of membrane proteins, particularly in the context of the eukaryotic plasma membrane.Therefore, the correct answer is α helices

Concept:

Microtubule motor proteins.

• Kinesin and dynein move in opposite directions along microtubules, toward the plus and minus ends, respectively.
• Kinesin consists of two heavy chains, wound around each other in a coiled-coil structure, and two light chains.
• Kinesin is a motor protein that moves along microtubules.
• The genomes of mammals encode more than 40 kinesin proteins, organized into at least 14 families named kinesin-1 through kinesin-14. Members of the kinesin superfamily are characterized by a common ATP-binding domain.
• Since most members of the kinesin superfamily are involved in active transport and movement, this domain is usually called motor domain.
• According to the position of the motor domain, the kinesin family can be classified into N-type kinesins (with the motor domain at or near to the N-terminus, as in Kinesin 1 to 12), M-type kinesins (with the motor domain internally located, as in kinesin-13) and C-type kinesins (with the motor domain close to the C-terminus, as in kinesin-14).
• Most of kinesins are microtubule based plus end-directed motor proteins.
• Kinesin-14, by contrast, are minus end directed motors (NCD. Kar3 The conventional kinesin, kinesin-1, consists of two heavy chains and two light chains.
• The heavy chain has three functional domains: the motor head domain, the a-helical stalk domain and the globular tail domain.
• Each head has two separate binding sites: one for the microtubule and the other for ATP.
• The tail domain is responsible for binding to receptors on the membrane of cargoes.
• It is a plus end-directed motor protein involved in organelle transport.
• Although most kinesins have two heavy chains (e.g. kinesin-1), others may have a single heavy chain or four heavy chains.
• The kinesin-5 family members have four heavy chains and act as bipolar motor proteins.
• Kinesin-5 protein contains two motor domains that interact with two antiparallel microtubules and move towards the plus end.

Explanation:

• Kinesin and dynein move in opposite directions along microtubules, toward the plus and minus ends, respectively. Kinesin consists of two heavy chains, wound around each other in a coiled-coil structure, and two light chains.
• Most of kinesins are microtubule based plus end-directed motor proteins.

Hence correct answer is option 2

Key Points

• Cell membranes consist of a lipid bilayer, which is a continuous double layer of lipid molecules.
• The approximate thickness of the lipid bilayer is about 4-5 nm.
• This lipid bilayer forms the basic structure of the cell membrane and serves as a barrier that separates the inside of the cell from the external environment.
• It also regulates the movement of molecules and ions into and out of the cell, playing a crucial role in maintaining cellular homeostasis.

Features of Lipid Bilayer - 

• Composition - 
  • The lipid bilayer is primarily composed of phospholipids, which are amphipathic molecules.
  • Each phospholipid molecule has a hydrophilic head and two hydrophobic tails.
  • Cholesterol molecules are interspersed within the lipid bilayer.
  • It also contains membrane proteins that are embedded within or attached to its surface. These proteins play essential roles in various cellular functions, such as transport, cell signaling, and enzymatic activities.
• Arrangement - 
  • The phospholipids arrange themselves in a bilayer with their hydrophilic heads facing outward towards the aqueous environments and their hydrophobic tails facing inward, away from water, forming the hydrophobic core of the membrane.

Additional InformationMembrane Proteins - 

• The proteins present in the phospholipid bilayer of the plasma membrane are of two types - Intrinsic and Extrinsic.
• Intrinsic proteins occur at different depths of the bilayer. They span the entire thickness of the membrane and are hence referred to as transmembrane proteins.
• They act as channels for the passage of water through the membrane.
• Extrinsic proteins are also called peripheral proteins. As the name suggests they are found on the two surfaces of the membrane.

Concept:

• Cells fall into one of two broad categories: prokaryotic and eukaryotic.

The single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes (pro = before; karyon– = nucleus).

• Animal cells, plant cells, fungi, and protists are eukaryotes (eu = true).

Explanation:

Option 1: cytoskeleton is present in Eukaryotic cells and absent in prokaryotic cells 

• The cytoskeleton of eukaryotic cells is made of filamentous proteins, and it provides mechanical support to the cell and its cytoplasmic constituents.
• All cytoskeletons consist of three major classes of elements that differ in size and in protein composition.
• Microtubules are the largest type of filament, with a diameter of about 25 nanometers (nm), and they are composed of a protein called tubulin.
• Actin filaments are the smallest type, with a diameter of only about 6 nm, and they are made of a protein called actin.
• Intermediate filaments, as their name suggests, are mid-sized, with a diameter of about 10 nm.
• Unlike actin filaments and microtubules, intermediate filaments are constructed from a number of different subunit proteins
• Not only eukaryotes, but also prokaryotes possess a cytoskeleton.
• Tubulin-related bacterial protein FtsZ, and actin-related bacterial proteins MreB/Mbl have recently been described as constituents of bacterial cytoskeletons.

• The eukaryotes developed at least 2.7 billion years ago, following some 1 to 1.5 billion years of prokaryotic evolution.
• Studies of their DNA sequences indicate that the archaebacteria and eubacteria are as different from each other as either is from present-day eukaryotes.
• thus this option is true.

Concept:

• Active transport is characterized as a process in which molecules are moved using external energy from an area of lower concentration to a region of greater concentration in opposition to a gradient or an obstruction.
• Active transportation comes in two types primary active transport and secondary active transport.

Passive Active transport:

• As molecules are transported across the membrane against a concentration gradient, energy is used from the breakdown of ATP, or adenosine triphosphate.
• Because ATP molecules are present on the cytosolic face of the membrane, all groups of ATP-powered pumps, therefore, have one or more binding sites for them.
• Basically, external chemical energy like ATP is used by the primary active transport.

Secondary active transport:

• A type of active transport that utilizes electrochemical energy is secondary active transport.
• A transporter protein connects the downward movement of an electrochemical ion (usually Na+ or H+) down its electrochemical gradient to the upward movement of another molecule or an ion against a concentration or electrochemical gradient.
• This occurs across a biological membrane.

Explanation:

• A cell must use energy to transfer materials against a concentration or electrochemical gradient.
• This is precisely what active transport mechanisms do; they use energy, frequently in the form of ATP, to keep the proper concentrations of ions and molecules in living cells.

Hence, option 3 is correct.

Concept:

• Lysosomes are membrane-bound organelles that contain various enzymes which are involved in the breakdown of all types of biological polymers. 
• Lysosome is the digestive system of the cell and is involved in the degradation of material taken up from outside and the digestion of various components of the cells.
• Lysosomes contain around 50 different degradative enzymes that can hydrolyse various DNA, RNA, proteins, carbohydrates, and lipids.
• All lysosomal enzymes are acid hydrolases and they are active at acidic pH. They are inactive in the neutral pH of cytosol.
• This requirement of acid hydrolases for acidic pH acts as the double protection against the uncontrolled digestion of content present in cytosol, in the case where the membrane of the lysosome is broken down and acid hydrolases are released. In the neutral pH of the cytosol, these acidic hydrolases will become inactive. 
• To maintain the acidic pH, the lysosome must maintain H+ions in the lysosome. 
• The concentration of H+ ions is maintained in the lysosome by the proton pump that transports proton in the lysosome from the cytosol. This pumping required expenditure of energy in the form of ATP hydrolysis as the concentration of H+ ions is a hundredfold higher inside the lysosome as compared to the cytosol. 

Explanation:

Option 1: INCORRECT

• G-protein coupled receptors (GPCRs) are integral membrane proteins that respond to various signals and triggers various signalling cascade.  

Option 2: CORRECT

• V class H+ ATPase pump only transports \(H^+\) ions. 
• This proton pump is found in the membranes of lysosomes, endosomes, and plant vacuoles. 
• V class H+ ATPase pump consists of two domains i.e., cytosolic hydrophilic domain \((V_1)\) and transmembrane domain \((V_0)\) with multiple subunits in each domain. Binding as well as hydrolysis of the ATP in the B subunits of Vi provides energy for pumping of H+ ions through the proton conducting channels that are formed by subunit 'a' and subunit 'c' of \(V_0\).
• Lysosomes also contain some anion pumps which also move an equal number of \(Cl^-\) ions inside the lysosomes for every \(H^+\)ions, so as to maintain the electrochemical gradient. 

Option 3: INCORRECT

• Na+/K+ pump is a P-class ATPase pump and it is found in the plasma membrane of the animal cells and helped to maintain the low cytosolic \(Na^+\) and high cytosolic \(K^+\) concentrations. 
• It does not maintain high proton concentration in the lysosome. 

Option 4: INCORRECT

• SNARE proteins are a type of motor protein that helps in the biological fusion of two membranes. 

Hence, the correct answer is option 2.

The correct answer is P-type ATPases get reversibly phosphorylated as a part of transport cycle

Explanation:

• P-type ATPases: These are membrane proteins that transport ions across the membrane using energy derived from ATP hydrolysis. During their transport cycle, a specific aspartate residue gets phosphorylated, which causes a conformational change necessary for the transport process.
• Function: P-type ATPases play crucial roles in maintaining ion gradients across cellular membranes, which are essential for various physiological functions like muscle contraction, nerve impulse transmission, and osmoregulation.

• These are a large family of ion transporters that pump ions such as Na⁺, K⁺, Ca²⁺, and H⁺ across membranes.
• They use the energy released by ATP hydrolysis to undergo conformational changes that allow them to transport ions against their concentration gradient.

Other Options:
1. Passive transporters decrease the activation energy and do not facilitate the transport of polar compounds :- This is incorrect. Passive transporters, such as facilitated diffusion channels, help in decreasing the activation energy barrier for the transport of polar and charged compounds by providing a pathway through the hydrophobic membrane.
2. The direction in which a charged solute tends to move spontaneously across a membrane does not depend on the electrical gradient across the membrane
:- This is incorrect. The direction in which a charged solute moves is influenced by both the concentration gradient and the electrical gradient (the membrane potential). Together, these factors constitute the electrochemical gradient that determines the spontaneous movement of ions.
3. All ABC transporters do not have nucleotide binding domain:- This is incorrect. ABC (ATP-Binding Cassette) transporters are characterized by having nucleotide-binding domains (NBDs) that bind and hydrolyze ATP to drive the transport process.

The correct answer is Option 3 i.e.Cholesterol decreases membrane fluidity at high temperatures and increases it at low temperatures by modulating the movement of phospholipid molecules.

Explanation:

• Temperature: Increasing the temperature generally increases membrane fluidity because the molecules move more rapidly and interact less tightly. At higher temperatures, the kinetic energy of phospholipid molecules in the membrane increases, which causes them to move more freely and makes the membrane more fluid.
• Saturation level of fatty acids: The presence of saturated fatty acids (which have no double bonds and thus straight chains) in phospholipids tends to decrease membrane fluidity, as these fatty acids can pack closely together, making the membrane more rigid. On the other hand, unsaturated fatty acids (which contain one or more double bonds, introducing kinks into the chains) increase membrane fluidity because the kinks prevent the fatty acids from packing closely together.
• Cholesterol: Cholesterol has a bidirectional role in modulating membrane fluidity. At low temperatures, it disrupts the packing of phospholipid molecules, increasing membrane fluidity. At high temperatures, it restrains movement of phospholipids, reducing membrane fluidity. This complex modulation helps maintain an optimal level of fluidity under various temperature conditions.

Conclusion:

Therefore, option C correctly incorporates how cholesterol modulates membrane fluidity dependent on temperature conditions, whereas the other options either misrepresent the effects of temperature and fatty acid saturation on membrane fluidity or incorrectly describe the role of unsaturated fatty acids.