Cell Archives

101. Which cell organelles have their own DNA and Ribosomes ?

Which cell organelles have their own DNA and Ribosomes ?

[amp_mcq option1=”Golgi body and Endoplasmic Reticulum” option2=”Mitochondria and Plastids” option3=”Lysosome and Golgi body” option4=”Vacuole and Plastids” correct=”option2″]

This question was previously asked in

UPSC CDS-1 – 2021

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Mitochondria and plastids (like chloroplasts) are unique among eukaryotic cell organelles in possessing their own genetic material (DNA) and ribosomes.

– Both mitochondria and plastids are believed to have originated through endosymbiosis, a process where prokaryotic cells were engulfed by early eukaryotic cells.
– This evolutionary history explains why they retain their own DNA (circular, similar to bacterial DNA) and ribosomes (70S type, similar to bacterial ribosomes), separate from the nuclear DNA and cytoplasmic ribosomes (80S type) of the host cell.

– Other organelles like the Golgi body, Endoplasmic Reticulum, Lysosomes, and Vacuoles are part of the endomembrane system and are dependent on the nucleus for genetic information and protein synthesis. They do not have their own DNA or ribosomes.

102. Cell wall is not present in cells of

Cell wall is not present in cells of

[amp_mcq option1=”Bacteria” option2=”Plants” option3=”Fungi” option4=”Humans” correct=”option4″]

This question was previously asked in

UPSC CDS-1 – 2021

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Cell wall is not present in cells of Humans.

Animal cells, including human cells, are characterized by the absence of a cell wall. They are surrounded only by a cell membrane.

Bacteria have cell walls typically made of peptidoglycan. Plant cells have cell walls primarily made of cellulose. Fungal cells have cell walls primarily made of chitin.

103. Which one of the following cell organelles contains DNA?

Which one of the following cell organelles contains DNA?

[amp_mcq option1=”Golgi apparatus” option2=”Mitochondrion” option3=”Lysosome” option4=”Endoplasmic reticulum” correct=”option2″]

This question was previously asked in

UPSC CDS-1 – 2020

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Eukaryotic cells contain their primary genetic material in the nucleus in the form of chromosomes. However, some organelles within the cytoplasm also contain their own DNA. These include mitochondria, which are responsible for cellular respiration, and in plant cells, chloroplasts, which are responsible for photosynthesis. This organellar DNA is distinct from nuclear DNA and is typically circular, resembling bacterial DNA.

Out of the options provided, only the mitochondrion contains its own DNA (mtDNA). The Golgi apparatus is involved in modifying, sorting, and packaging proteins and lipids. Lysosomes contain digestive enzymes. The Endoplasmic reticulum is involved in protein and lipid synthesis and transport. None of these latter organelles contain DNA.

The presence of DNA in mitochondria and chloroplasts supports the endosymbiotic theory, which proposes that these organelles originated from free-living prokaryotes that were engulfed by early eukaryotic cells.

104. Which one of the following is the ‘energy currency’ for cellular

Which one of the following is the ‘energy currency’ for cellular processes?

[amp_mcq option1=”Glucose” option2=”ATP” option3=”ADP” option4=”Pyruvic acid” correct=”option2″]

This question was previously asked in

UPSC CDS-1 – 2020

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ATP (Adenosine Triphosphate) is widely considered the main energy currency of the cell. Energy released from the breakdown of fuels like glucose is used to synthesize ATP. ATP then provides the energy for most cellular processes, such as muscle contraction, nerve impulse transmission, and chemical synthesis, by breaking one of its phosphate bonds to form ADP (Adenosine Diphosphate) and inorganic phosphate, releasing energy.

– ATP is a molecule that stores and releases energy in cells.
– Energy from metabolic processes (like glucose breakdown) is stored in ATP.
– Cells directly use the energy released from the hydrolysis of ATP for their activities.

While glucose is a primary source of energy, it is metabolized through processes like glycolysis and cellular respiration to produce ATP. ADP is a lower-energy molecule produced when ATP is hydrolyzed. Pyruvic acid is an intermediate product of glycolysis. Therefore, ATP is the direct molecule that powers most cellular work.

105. Which one of the following statements regarding histone proteins is

Which one of the following statements regarding histone proteins is correct?

[amp_mcq option1=”Histones are proteins that are present in mitochondrial membrane.” option2=”Histones are proteins that are present in nucleus in association with DNA.” option3=”Histones are proteins associated with lipids in the cytosol.” option4=”Histones are proteins associated with carbohydrates in the cytosol.” correct=”option2″]

This question was previously asked in

UPSC CDS-1 – 2019

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The correct answer is B. Histones are a family of small, positively charged proteins found in the nucleus of eukaryotic cells. They play a crucial role in packaging DNA into structural units called nucleosomes, which are the basic building blocks of chromatin. DNA (which is negatively charged) wraps around histone octamers (eight histone proteins) to form these structures.

Histone proteins are primarily located in the nucleus where they bind to DNA to help package it into chromatin.

There are five main families of histones: H1, H2A, H2B, H3, and H4. H2A, H2B, H3, and H4 form the core particle of the nucleosome, while H1 acts as a linker histone, helping to further compact the chromatin structure. Histone modifications play a significant role in regulating gene expression.

106. Which one of the following cell organelles mainly functions as storeho

Which one of the following cell organelles mainly functions as storehouse of digestive enzymes?

[amp_mcq option1=”Desmosome” option2=”Ribosome” option3=”Lysosome” option4=”Vacuoles” correct=”option3″]

This question was previously asked in

UPSC CDS-1 – 2019

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Lysosomes are membrane-bound organelles containing a variety of hydrolytic enzymes (like proteases, lipases, nucleases, glycosidases) that are active at acidic pH. Their main function is the intracellular digestion of macromolecules, worn-out organelles, and pathogens. Thus, they serve as the principal storehouse of digestive enzymes within the cell.

Lysosomes are responsible for cellular digestion and waste breakdown.

Ribosomes are involved in protein synthesis. Desmosomes are structures that provide strong adhesion between cells. Vacuoles in animal cells are small and involved in storage or transport, while in plant cells they are large and maintain turgor pressure and store water, nutrients, and waste; they can also contain some digestive enzymes in plant cells, but lysosomes are the primary organelle for this function in many eukaryotic cells.

107. Which one of the following functions is not carried out by smooth en

Which one of the following functions is not carried out by smooth endoplasmic reticulum?

[amp_mcq option1=”Transport of materials” option2=”Synthesis of lipid” option3=”Synthesis of protein” option4=”Synthesis of steroid hormone” correct=”option3″]

This question was previously asked in

UPSC CDS-1 – 2019

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The correct option is C.

The endoplasmic reticulum (ER) is involved in various cellular functions. The rough endoplasmic reticulum (RER) is characterized by the presence of ribosomes on its surface and is primarily responsible for the synthesis and modification of proteins destined for secretion, insertion into membranes, or delivery to other organelles. The smooth endoplasmic reticulum (SER) lacks ribosomes and is involved in lipid synthesis, steroid hormone synthesis, detoxification, and calcium storage. Protein synthesis is mainly carried out by ribosomes, either free in the cytoplasm or attached to the RER. Therefore, synthesis of protein is not a primary function of the smooth endoplasmic reticulum.

Transport of materials (lipids, proteins) through vesicles budding from the ER is a function of both RER and SER. Steroid hormones are lipids derived from cholesterol, and their synthesis occurs in the SER.

108. A protein is synthesized in the endoplasmic reticulum bound ribosomes

A protein is synthesized in the endoplasmic reticulum bound ribosomes and it targets to the inner thylakoid space of chloroplast. How many double-layered membrane layers it has to pass to reach its destination?

[amp_mcq option1=”2″ option2=”3″ option3=”4″ option4=”5″ correct=”option3″]

This question was previously asked in

UPSC CDS-1 – 2018

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The protein is synthesized in endoplasmic reticulum-bound ribosomes, meaning it enters the ER lumen or membrane. To reach the inner thylakoid space of a chloroplast, it must move from the ER system to the chloroplast. Assuming a pathway where the protein is released from the ER lumen into the cytoplasm (e.g., via retrotranslocation, crossing the ER membrane) and then imported into the chloroplast, the path would involve crossing the following membrane layers:
1. Crossing the ER membrane to exit the lumen into the cytoplasm (1 layer).
2. Crossing the outer chloroplast membrane (1 layer).
3. Crossing the inner chloroplast membrane (1 layer).
4. Crossing the thylakoid membrane to enter the inner thylakoid space (1 layer).
Total membrane layers crossed = 1 + 1 + 1 + 1 = 4.

Reaching the inner thylakoid space from the cytoplasm requires crossing the chloroplast outer membrane, inner membrane, and thylakoid membrane (3 layers). Starting from the ER lumen adds the step of exiting the ER, which requires crossing the ER membrane.

The standard pathway for most chloroplast proteins is synthesis on free ribosomes in the cytoplasm followed by post-translational import. The mention of synthesis on ER-bound ribosomes implies a non-standard or specific targeting route, or potentially release from the ER system into the cytoplasm before import. Chloroplasts have a double membrane envelope (outer and inner membranes) and an internal thylakoid membrane system.

109. Lysosome is formed from which of the following cell organelles?

Lysosome is formed from which of the following cell organelles?

[amp_mcq option1=”Nucleus” option2=”Endoplasmic reticulum” option3=”Golgi bodies” option4=”Ribosomes” correct=”option3″]

This question was previously asked in

UPSC CDS-1 – 2018

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Lysosomes are membrane-bound organelles containing digestive enzymes. They are formed from the Golgi apparatus (also known as Golgi complex or Golgi bodies). Proteins and lipids synthesized in the endoplasmic reticulum are transported to the Golgi apparatus for further processing and packaging. Lysosomes bud off from the trans face of the Golgi apparatus.

Lysosomes are part of the endomembrane system and originate from the Golgi apparatus.

The enzymes found in lysosomes are synthesized in the endoplasmic reticulum, transported to the Golgi, and then packaged into vesicles that mature into lysosomes. The primary function of lysosomes is intracellular digestion.

110. In human body, the cell growth and differentiation are highly controll

In human body, the cell growth and differentiation are highly controlled and regulated, but in cancer cells

[amp_mcq option1=”there is breakdown of these regulatory mechanisms leading to formation of benign and malignant tumors” option2=”controlled cell division and over-production of genetic material occur” option3=”RNA is mutated and produced in less amount” option4=”DNA is mutated and produced in less amount” correct=”option1″]

This question was previously asked in

UPSC CDS-1 – 2017

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In normal cells, growth and differentiation are tightly controlled by genetic programs and regulatory mechanisms. Cancer cells are characterized by a breakdown of these control mechanisms. This leads to uncontrolled cell proliferation, loss of differentiation, and the potential to invade surrounding tissues and spread to distant sites, forming malignant tumors. Benign tumors are localized growths that do not invade or spread, also resulting from deregulation but less severe.

The fundamental characteristic of cancer cells is the loss of control over cell growth and division, contrasting sharply with the tightly regulated processes in normal cells.

Cancer development involves genetic mutations and epigenetic changes that disrupt cell cycle control, apoptosis (programmed cell death), and cell-cell communication.