Cellular Organization MCQ Quiz in मल्याळम - Objective Question with Answer for Cellular Organization - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Concept:

• As they are made up of two entangled strands of the globular protein known as actin, microfilaments are also known as actin filaments.
• They are the tiniest filaments of the cytoskeleton and polymers of the protein actin.
• They are essential for muscle contraction, cell division, and cellular mobility.
• Cell mobility is impeded by cytochalasins, a class of compounds excreted by certain moulds.
• The cytochalasins bind to the plus end of microfilaments, obstruct further polymerization, and prevent the movement of organelles and vesicles along microfilaments, as well as the development of lamellipodia and microspikes.
• Actin filaments and 2- to 3-nm filaments interact with other cytoskeletal filaments on a regular basis in end-to-side interactions.
• When treated with cytochalasin D, the network organization is badly disrupted, there are more actin filament ends present, and filamentous aggregates or foci that are primarily made of actin filaments begin to develop.

Explanation:

Option 1: Muscle contraction

• Actin and myosin are involved in the muscle contraction which are microfilaments.
• Therefore, on addition of cytochalasin D hinder the muscle formation.

Option 2: Cytosolic transport of vesicles

• Vesicles are present outside the nucleus where numerous cell organelles are present and when vesicles have to move, it requires microtubules not microfilaments.
• Therefore, this process will not be hindered.

Option 3: Amoeboid movement of phagocytic cells

• Amoeboid movements also requires actin filaments. Hence, it will also be hindered.

Option 4: Formation of cleavage furrow following telophase of mitosis

• By interfering with the creation of cleavage furrows and cytokinesis, the medication cytochalasin B inhibits actin's ability to function.
• By attaching to the rapidly expanding end of the F actin filament, cytochalasin B prevents the polymerization of actin filaments, which prevents the creation of cleave furrows and cytokinesis.

Therefore, the correct answer is option 2.

Key Points

• LINEs are retrotransposable elements that are dispersed throughout the human genome.
• They are autonomous retrotransposons, meaning that they can encode all the proteins required for their own retrotransposition.
• They are usually found in the euchromatic regions of the genome, but can also be found in heterochromatic regions.
• Of the three human LINE families (LINE-1, LINE-2, and LINE-3), LINE-1 is the only family that is known to have active transposing members.
• Active LINE-1 elements possess an internal promoter located within the 5' untranslated region, which is responsible for driving transcription of the element.
• Unlike LINEs, SINEs are non-autonomous retrotransposons, which means that they require LINEs or other transposable elements to provide the proteins necessary for their own retrotransposition.

Key Points

• Asymmetry in the composition of the lipids is the characteristic feature of all membranes.
• Lipids in the membrane are not uniformly distributed, instead, they are present in clusters to form microdomains. 
• Both microscopic and biochemical analyses suggest the existence of lipids rafts. 
• Lipid rafts are the small, heterogeneous, highly dynamic sphingolipid and sterol-rich domain that causes compartmentalization of the cellular processes.
• Smaller lipid rafts can be stabilised to form larger lipid rafts by protein-lipid and protein-protein interaction. 
• The formation of the lipid raft in the exoplasmic face of the plasma membrane is caused by the tight packing of sphingolipids and cholesterol. 
• Some proteins are targeted and anchored to the lipid rafts in the outer leaflet of the membrane through the covalent attachment of glycolipids and glycosyl phosphatidylinositol (GPI).
• These protein targeting plays an important role in signal transduction, sorting of the intracellular membrane, and regulation of cell-surface proteolysis.

Explanation: 

• Lipids rafts are sphingolipids and cholesterol-rich domains of lipids.
• Sphingolipids present in the lipid rafts are sphingomyelin and glycosphingolipids.
• So, lipid rafts are rich in glycolipids, sphingomyelin, and cholesterol.

Hence, the correct answer is option 4.

The correct answer is (A), (B), (C), and (D)

Key Points

• Hyperlinks are versatile and can be applied to various elements within a document.
• These elements include text, drawing objects, groups of cells, and pictures.
• Using hyperlinks enhances the interactivity and navigation within and outside the document.
• Hyperlinks can lead to external websites, email addresses, or other sections within the same document, making it easier to access related information.

Additional Information

• Apply Hyperlinks: To insert a hyperlink, select the text or object, right-click, and choose 'Hyperlink' from the context menu. This allows linking to various destinations.
• Edit Hyperlinks: Existing hyperlinks can be modified by right-clicking the hyperlink and selecting 'Edit Hyperlink'.
• Remove Hyperlinks: Hyperlinks can be removed by right-clicking the hyperlink and selecting 'Remove Hyperlink'.

The correct answer is Option 3 i.e.Peripheral proteins, such as spectrin and ankyrin, directly propagate across the lipid bilayer, providing structural support from within the phospholipid layer.

Concept:

Cellular Membranes and Their Components
Cellular membranes, primarily composed of phospholipid bilayers, serve as dynamic barriers that regulate the entry and exit of substances. Embedded within and associated with these membranes are proteins that perform a myriad of functions, including transport, signaling, and structural support. These proteins can be classified into two main categories based on their interaction with the lipid bilayer:-

• Integral (or Intrinsic) Membrane Proteins: These proteins are embedded within the lipid bilayer and often span across it (transmembrane proteins). They have hydrophobic regions that interact with the lipid tails within the bilayer and hydrophilic regions that protrude out to interact with the aqueous environment. Functions include forming channels and receptors.
• Peripheral (or Extrinsic) Membrane Proteins: Unlike integral proteins, peripheral proteins do not embed within the lipid bilayer. Instead, they attach to either the outer or inner surface of the membrane, often through interactions with integral proteins or the phospholipid head groups. They play roles in signaling, cell shape, and as part of the cytoskeleton.

Spectrin and Ankyrin: Structure and Function

• Spectrin: This is a flexible, rod-like peripheral protein that, along with other proteins, forms a meshwork on the cytoplasmic side of the plasma membrane, particularly evident in red blood cells (erythrocytes). This meshwork, often referred to as the membrane skeleton, provides structural support and maintains the biconcave shape of erythrocytes, enabling them to deform as they pass through narrow capillaries.
• Ankyrin: Ankyrin acts as an adaptor protein that connects the spectrin-based cytoskeleton to the plasma membrane. It binds to integral membrane proteins (e.g., anion exchanger Band 3 in erythrocytes), anchoring the spectrin cytoskeleton to the membrane. This linkage is crucial for maintaining cell shape and integrity under mechanical stress.
• Importance of Spectrin and Ankyrin Complex: The interaction between spectrin, ankyrin, and integral membrane proteins is vital for maintaining cellular shape and mechanical properties. In erythrocytes, the integrity of this complex is essential for cell deformability, allowing red blood cells to squeeze through narrow capillaries without rupturing.

Diagram:-

Explanation:

The statement "Peripheral proteins, such as spectrin and ankyrin, directly propagate across the lipid bilayer" is incorrect because it misrepresents the nature and localization of these proteins. Peripheral proteins do not embed within the lipid bilayer or span across it. Instead, they associate with the membrane surface, either directly or via interactions with integral proteins.

The correct understanding is that-

• Peripheral proteins like spectrin and ankyrin are crucial for providing structural support and maintaining the plasma membrane's architecture from the outside.
• These proteins interact with the cytoplasmic side of the membrane, contributing to cell shape, flexibility, and the proper localization of membrane proteins, without crossing the lipid bilayer.

Conclusion:

Therefore, the correct answer is Option 3

Key Points

• In 1928, E. Heitz coined the terms euchromatin and heterochromatin to describe the parts of chromatin that are less coilled and those that remain highly condensed, respectively.
• Euchromatin is the light-staining and less condensed portions of chromatin.
• This region is transcriptionally active and contains most of the protein-coding genes.
• Heterochromatin is the darkly stained regions of chromatin that remains condensed.
• Because of its condensed state during the interphase, this heterochromatin is generally believed to be transcriptionally silent.
• Euchromatic regions have an open, accessible chromatin structure characterized by histone acetylation, and methylation at H3K4 and H3K79.
• Heterochromatic regions are marked with deacetylation and methylation at H3K9, which serve as a platform for HP1 (heterochromatic protein 1) binding.

There are two types of heterochromatin - Constitutive and facultative heterochromatin.

1. Constitutive heterochromatin
   • Constitutive heterochromatin remains condensed throughout the cell cycle and development.
   • This chromatin contains highly repetitive sequences that play a structural role in chromosomal structure.
   • Constitutive heterochromatin is found at pericentromeric, telomeric as well as at different loci along the chromosome.
   • The common features of constitutive heterochromatin are: It remains permanently condensed and transcriptionally inactive.
   • It often consists of highly repetitive sequences of DNA and usually do not contain genes.
   • It replicates late in S-phase and has a reduced frequency of genetic recombination.
2. Facultative heterochromatin - 
   • In facultative heterochromatin, the regions of euchromatin are converted into a heterochromatic state.
   • Thus facultative heterochromatin has the potential for gene expression at some point in development, and it can be either condensed or decondensed, depending on the cell type.
   • The mammalian Barr body is an excellent example of facultative heterochromatin.
   • Barr body is defined as a highly stained inactivated condensed X chromosome found in every somatic cell of most female animals and used as a genetic femaleness 

Explanation:

• Facultative heterochromatin has the potential for gene expression at some point in development, and it can be either condensed or decondensed, depending on the cell type.
• The mammalian Barr body is an excellent example of facultative heterochromatin.
• Barr body is defined as a highly stained inactivated condensed X chromosome found in every somatic cell of most female animals and used as a genetic femaleness.

Hence the correct answer is option 3.

Concept:

Fluidity of the lipid bilayer

• The fluidity of the lipid bilayer, the optimal value of which is a prerequisite for normal cell growth and function, depends on lipid composition and temperature.
• In general, an increase in the temperature tends to elevate membrane fluidity.
• Lowering of temperature causes a freely-flowing, low-viscous, fluid-like membrane structure to a more rigid, gel-like organization.
• This change is described as phase transition and the temperature at which this happens is called the transition temperature.
• Fluidity of lipid bilayer also depends on chain length and the degree of unsaturation of its component fatty acid residues.
• Increase in the number of carbon chains decreases the fluidity and increases the stability.
• Lipids with short or unsaturated fatty acyl chains undergo the phase transition at lower temperatures than lipids with long or saturated chains.
• Short chains have less surface area with which to form van der waals interactions with each other.
• Hence, a shorter chain length reduces the tendency of the hydrocarbon tails to interact with one another.
• Unsaturated fatty acyl chains have kinks, thus tend to adopt a more random, fluid state and form less van der Waals interactions with other lipids.
• So, increased proportion of unsaturated to saturated fatty acids in the membrane increases the fluidity of bilayer at the reduced temperature.
• Cholesterol is also a major determinant of membrane fluidity.
• At high temperature, cholesterol interferes with the movement of the phospholipid fatty acid chains, making the membrane less fluid, but at low temperature, it interferes with interactions between fatty acid chains and prevents membranes from freezing.
• At high concentrations found in eukaryotic plasma membranes, cholesterol tends to make the membrane, overall, less fluid at growth.

Concept:

• The fundamental repeating subunit of chromatin that is bundled inside the cell's nucleus is called a nucleosome.
• Nucleosomes are crucial to the packaging of around six feet of DNA into a nucleus in humans that has a diameter smaller than human hair.
• A single nucleosome is made up of a core of histone proteins and roughly 150 base pairs of DNA.
• The nucleosomes constantly fold in on themselves to compact and tighten the bundled DNA during the formation of a chromosome.

Explanation:

• The histones H2A, H2B, H3 and H4 are involved in the nucleosome structure, while the H1 protein acts like a linker molecule between two nucleosomes.
• Two molecules of H3 and H4 form a core of tetramer (as a pair of dimers).
• This (H3)₂.(H4)₂ tetramer is associated with 2 independent dimers of H2A-H2B.
• Thus, 8 histone proteins and 1.65 times of DNA make up each nucleosome.
• A 30 nm chromatin fiber made of folded nucleosomes creates loops that are 300 nm in length on average.
• In nucleosomes always length is considered.

​Therefore, the correct answer is option 3.

Concept:

• The quick communication between electrical activities taking place in the plasma membrane of skeletal muscle fibres and Ca²⁺ release from the SR, which causes contraction, is known as excitation-contraction coupling (ECC).
• The process in twitch skeletal muscle includes the following steps:

1. Starting and propagating an action potential along the plasma membrane;
2. Spreading the potential throughout the transverse tubule system (T-tubule system).
3. Detecting changes in membrane potential through the action of dihydropyridine receptors (DHPR).
4. Allosteric interaction between DHPR and sarcoplasmic reticulum (SR) ryanodine receptors (RyR).
5. Ca²⁺ release from the SR and a brief increase in the myoplasm's Ca²⁺ concentration.
6. The myoplasmic Ca²⁺ buffering system and the contractile apparatus are activated.
7. Ca²⁺ removal from the myoplasm is mostly caused by the SR's absorption of it through the SR Ca²⁺ adenosine triphosphatase (SERCA). However, under some circumstances, Ca²⁺ can also migrate to the mitochondria and be expelled through the Na⁺/Ca²⁺ exchanger (NCX).

Explanation:

• Acetylcholine starts the excitation-contraction coupling.
• Tropomyosin undergoes a conformational change that makes myosin-binding sites on actin visible as a result of calcium binding to troponin C and then Myosin is then bound by ATP.

Hence, the correct answer is option 4.

Concept:

• The Na⁺ K⁺ pump is an electrogenic transmembrane ATPase that was initially identified in 1957.
• It is located on the cytosolic side of the cell's outer plasma membrane.
• For each unit of ATP expended, the Na⁺ K⁺ ATPase pumps 3 Na⁺ out of the cell and 2K⁺ into the cell.
• The plasma membrane is made up of an uneven lipid bilayer that includes proteins, cholesterol, phospholipids, glycolipids, and sphingolipids.
• The Na⁺K⁺-ATPase pump aids in the preservation of membrane potential and osmotic balance in living things.

Explanation:

• Ouabain, which is derived from the plant Strophanthus gratus, belongs to a group of cardiac glycosides, or substances that resemble digitalis, and has been used for more than 200 years to treat supraventricular arrhythmias and congestive heart failure.
• They enhance intracellular Na⁺ concentration by inhibiting Na⁺ K⁺-ATPase activity, which in turn slows down a Na⁺/Ca²⁺ exchanger, increasing intracellular Ca²⁺ concentration and strengthening muscular contraction.
• The sodium-potassium exchange that is ATP-dependent across cell membranes is inhibited by the cardiac glycoside ouabain. 
• The Na⁺ K⁺ pump is made up of 2α and 2β subunits.
• It consists of 3 domains:
  • The activating domain
  • The phosphorylation domain
  • The ATP binding domain
• The conformational changes required for the sodium-potassium pump, also known as Na⁺/K⁺ ATPase, to operate properly are prevented by ouabain binding to the enzyme on the extracellular side.
• Depending on the cell and the dosage, this has a variety of impacts on intracellular ion composition.
• Na⁺ and ATP bind on the intracellular side, while K⁺ and  ouabain bind extracellular side.

Hence, the correct answer is option 4.