Cell

The eukaryotic chromatin is composed of

[amp_mcq option1=”DNA only” option2=”DNA and Protein” option3=”DNA and RNA” option4=”RNA and Protein” correct=”option2″]

The eukaryotic chromatin is composed of DNA and Protein.

Chromatin is the complex assembly of DNA and proteins that packs DNA into a more compact structure. The primary proteins associated with DNA in chromatin are histones, around which the DNA double helix is wrapped like thread around spools. Non-histone proteins are also components of chromatin, playing roles in DNA replication, repair, transcription, and regulation.

While RNA molecules (like various non-coding RNAs and messenger RNA being transcribed) are often associated with chromatin, they are not considered a primary structural component in the same way as DNA and proteins (especially histones). The fundamental building block of chromatin is the nucleosome, which consists of DNA wrapped around a core of histone proteins.

In plant cells, the turgidity and rigidity is provided by

[amp_mcq option1=”ribosomes” option2=”mitochondria” option3=”golgi apparatus” option4=”vacuoles full of cell sap” correct=”option4″]

Turgidity and rigidity in plant cells are primarily provided by the turgor pressure exerted by the vacuole against the cell wall. The large central vacuole in plant cells stores water and cell sap. When the cell absorbs water by osmosis, the vacuole swells, pushing the cytoplasm against the cell wall. The rigid cell wall prevents the cell from bursting, resulting in a firm, turgid state.

– Turgor pressure is the pressure exerted by the cell contents (driven by the vacuole) against the cell wall.
– The cell wall provides structural support and prevents bursting.
– Together, turgor pressure and the cell wall make the plant cell turgid and rigid.

Ribosomes are involved in protein synthesis. Mitochondria are the powerhouses of the cell, producing energy. The Golgi apparatus modifies, sorts, and packages proteins and lipids. None of these organelles directly provide turgidity or rigidity to the plant cell in the same way the vacuole and cell wall do.

Rough endoplasmic reticulum (RER) looks rough under the microscope because of the attachment of which one of following cell organelles to its surface ?

[amp_mcq option1=”Centrioles” option2=”Plastids” option3=”Lysosomes” option4=”Ribosomes” correct=”option4″]

The rough appearance of the Rough Endoplasmic Reticulum (RER) under a microscope is due to the presence of ribosomes attached to its cytoplasmic surface.

– The Endoplasmic Reticulum (ER) is a network of membranes throughout the cytoplasm.
– There are two types: Rough ER (RER) and Smooth ER (SER).
– Ribosomes are responsible for protein synthesis.
– Ribosomes can be free in the cytoplasm or attached to the ER membrane.
– The attachment of ribosomes gives the RER its characteristic “rough” appearance.

Proteins synthesized on ribosomes attached to the RER are typically destined for secretion, insertion into cell membranes, or delivery to other organelles like lysosomes. The RER is involved in protein folding, modification, and transport. Centrioles are involved in cell division. Plastids (like chloroplasts) are involved in photosynthesis or storage. Lysosomes contain digestive enzymes. None of these attach to the ER to make it appear rough.

Which one of the following will happen if the medium surrounding the cell has a higher concentration than the cell ?

[amp_mcq option1=”The cell will gain water” option2=”The cell will die” option3=”There will be no change” option4=”The cell will lose water” correct=”option4″]

If a cell is placed in a medium with a higher solute concentration than its cytoplasm (a hypertonic solution), water will move out of the cell into the surrounding medium by osmosis.

– Osmosis is the movement of water across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration (or from higher water potential to lower water potential).
– A hypertonic solution has a higher solute concentration and thus a lower water potential compared to the cell.
– Water moves from the cell (higher water potential) to the hypertonic medium (lower water potential).

If the surrounding medium had a lower concentration (hypotonic), the cell would gain water. If the concentration were equal (isotonic), there would be no net change in water movement. Losing water in a hypertonic solution can cause the cell to shrink (crenation in animal cells, plasmolysis in plant cells). Extreme water loss can lead to cell death, but the immediate effect described is water loss.

Which one of the following statements about proteins in mammalian cells is correct?

[amp_mcq option1=”Proteins in mammalian cells are synthesized in cell membrane.” option2=”Proteins in mammalian cells are not synthesized in cell membrane but directly absorbed from food.” option3=”Proteins in mammalian cells are synthesized in rough endoplasmic reticulum.” option4=”Proteins in mammalian cells are synthesized in Golgi apparatus.” correct=”option3″]

The correct answer is C) Proteins in mammalian cells are synthesized in rough endoplasmic reticulum.

Protein synthesis, or translation, occurs on ribosomes. Ribosomes can be found freely in the cytoplasm or attached to the surface of the endoplasmic reticulum, forming the rough endoplasmic reticulum (RER). Proteins destined for secretion out of the cell, insertion into cell membranes (including the plasma membrane and membranes of organelles like RER, Golgi, lysosomes), or delivery to organelles within the secretory pathway (like lysosomes) are synthesized on ribosomes attached to the RER. Proteins destined for the cytoplasm, nucleus, mitochondria, or peroxisomes are typically synthesized on free ribosomes in the cytoplasm. Therefore, the rough endoplasmic reticulum is a major site of protein synthesis in mammalian cells, particularly for proteins entering the secretory pathway.

Statement A is incorrect; the cell membrane is where some proteins reside, but not where they are synthesized. Statement B is incorrect; cells synthesize their own proteins from amino acids. Statement D is incorrect; the Golgi apparatus modifies, sorts, and packages proteins synthesized elsewhere, but does not synthesize them.

The subunits of DNA are known as :

[amp_mcq option1=”Nucleotide” option2=”Nucleosome” option3=”Nucleoside” option4=”Polypeptide” correct=”option1″]

The subunits (monomers) of DNA (Deoxyribonucleic Acid) are called nucleotides.

– A nucleotide consists of three components: a deoxyribose sugar, a phosphate group, and a nitrogenous base (Adenine, Guanine, Cytosine, or Thymine).
– DNA is a polymer formed by linking many nucleotides together through phosphodiester bonds, creating a polynucleotide chain.
– Two such chains typically form a double helix structure, held together by hydrogen bonds between the bases.

– A nucleoside consists only of a sugar and a nitrogenous base, without the phosphate group.
– A nucleosome is a basic structural unit of DNA packaging in eukaryotes, consisting of a segment of DNA coiled around a core of histone proteins.
– A polypeptide is a linear organic polymer consisting of a large number of amino-acid residues bonded together in a chain, forming a protein.

Animal cell wall is essentially made of :

[amp_mcq option1=”Protein” option2=”Carbohydrate” option3=”Lipid bilayer” option4=”Cellulose” correct=”option3″]

Animal cells do not have a cell wall. However, if the question is interpreted as referring to the main structural component of the animal cell boundary (the cell membrane), then it is the lipid bilayer.

Biologically, animal cells fundamentally *lack* a cell wall. Cell walls are found in plant cells (cellulose), fungal cells (chitin), bacterial cells (peptidoglycan), etc., providing structural support outside the cell membrane. Animal cells only have a cell membrane as their outer boundary. The cell membrane is primarily composed of a lipid bilayer with embedded proteins and associated carbohydrates. Given the options, “Lipid bilayer” is the most accurate description of the essential structural component of the animal cell *membrane*. The question is likely flawed in its phrasing, using “cell wall” instead of “cell membrane”, or is designed to test the knowledge that animal cells lack a cell wall, with the options representing components of structures *found in other organisms* or other parts of the animal cell. Assuming the most probable intent of the test setter asking about the main structural component at the cell periphery among the options, Lipid bilayer (the core of the cell membrane) is the closest fit, although technically it’s the membrane, not a wall.

Cellulose is the main component of plant cell walls. Protein and carbohydrate are also components of the animal cell membrane (proteins embedded within or associated with the lipid bilayer, and carbohydrates often attached to lipids or proteins on the outer surface, forming the glycocalyx), but the lipid bilayer forms the basic structural framework of the membrane. Since animal cells do not have a cell wall, strictly speaking, none of the options are correct as components of an animal cell wall. However, in the context of a multiple-choice question where a choice must be made, and given the options, it is likely that the question intends to refer to the cell membrane, or it is a poorly constructed question. Based on typical biological components listed and the presence of Lipid bilayer, it is the most likely intended answer if the question refers to the cell membrane or the primary outer structural element.

Which one among the following cell organelles in a Eukaryotic cell is acquired during the process of evolution by entrapment or engulfment of Bacterial cells ?

[amp_mcq option1=”Peroxisomes” option2=”Vacuoles” option3=”Chloroplasts” option4=”Mitochondria” correct=”option4″]

Mitochondria is a cell organelle in a Eukaryotic cell that is acquired during the process of evolution by entrapment or engulfment of Bacterial cells.

The Endosymbiotic Theory proposes that certain organelles within eukaryotic cells, including mitochondria and chloroplasts, originated as free-living prokaryotic cells that were engulfed by a host cell and established a symbiotic relationship.

Mitochondria are believed to have originated from the engulfment of aerobic bacteria, which occurred in an early eukaryotic ancestor. Chloroplasts originated later from the engulfment of photosynthetic bacteria (cyanobacteria) in a lineage of eukaryotes that already possessed mitochondria. Since mitochondria are found in nearly all eukaryotic cells, their acquisition is considered a fundamental step in eukaryotic evolution.