Cell

Which one of the following human cells is devoid of a nucleus?

[amp_mcq option1=”Nerve cell” option2=”Bone cell” option3=”Red blood cell” option4=”White blood cell” correct=”option3″]

Mature mammalian red blood cells (erythrocytes) are unique among human cells in that they lack a nucleus, as well as other organelles like mitochondria, ribosomes, and endoplasmic reticulum. This adaptation allows them to maximize the space available for hemoglobin, the protein responsible for oxygen transport, and also makes them more flexible to squeeze through narrow capillaries.

Mature red blood cells are anucleated, meaning they are devoid of a nucleus.

While mature red blood cells in mammals lack a nucleus, this is not the case for red blood cells in birds, reptiles, amphibians, and fish, which retain their nuclei. Nerve cells, bone cells, and white blood cells are all nucleated cells that perform various functions in the body, such as transmitting electrical signals, providing structural support, and fighting infections, respectively.

Consider the following statements about stem cells :

• 1. Stem cells have the potential for self-renewal via mitotic cell division.
• 2. In 1908, James Thomas and his colleagues first derived human embryonic stem cells from donated blastocysts through in vitro fertilization.

Which of the statements given above is/are correct?

[amp_mcq option1=”1 only” option2=”2 only” option3=”Both 1 and 2″ option4=”Neither 1 nor 2″ correct=”option1″]

The correct answer is A) 1 only.

Statement 1 is correct: Stem cells possess the unique ability to divide and renew themselves through mitotic cell division, maintaining the stem cell population. Statement 2 is incorrect: Human embryonic stem cells were first successfully derived in 1998 by James Thomson and his colleagues at the University of Wisconsin-Madison, not in 1908 by James Thomas.

Stem cells are undifferentiated cells that can differentiate into specialized cell types and can self-renew. There are different types, including embryonic stem cells (derived from blastocysts) and adult stem cells (found in various tissues). Their discovery and potential applications in regenerative medicine are significant areas of research.

Which one of the following cell organelles is not lined by membrane ?

[amp_mcq option1=”Lysosome” option2=”Ribosome” option3=”Nucleus” option4=”Golgi Apparatus” correct=”option2″]

Cell organelles in eukaryotic cells are often enclosed by membranes. The question asks which of the listed organelles is not lined by a membrane.

– Lysosome: Lined by a single membrane.
– Ribosome: Composed of ribosomal RNA (rRNA) and proteins, not enclosed by a membrane.
– Nucleus: Enclosed by a double membrane (the nuclear envelope).
– Golgi Apparatus: Composed of membrane-bound sacs (cisternae), lined by a single membrane.

Ribosomes are responsible for protein synthesis and are found in both prokaryotic and eukaryotic cells (though they differ in size/structure). Their lack of a membrane is a key structural feature that distinguishes them from many other organelles in eukaryotic cells. Other non-membrane-bound structures in eukaryotic cells include the nucleolus, centrioles, and components of the cytoskeleton.

In a mammalian cell, the protein is synthesized by

[amp_mcq option1=”Ribosome.” option2=”Golgi.” option3=”Lysosome.” option4=”Smooth endoplasmic reticulum.” correct=”option1″]

Ribosomes are small organelles found in the cytoplasm of all cells (prokaryotic and eukaryotic), as well as attached to the endoplasmic reticulum in eukaryotic cells. They are the cellular machinery responsible for protein synthesis, a process called translation, where messenger RNA (mRNA) is decoded to build a protein chain.

Protein synthesis involves two main steps: transcription (DNA to mRNA) and translation (mRNA to protein). Translation occurs on ribosomes. Ribosomes are composed of ribosomal RNA (rRNA) and proteins and consist of two subunits, a large one and a small one, which come together during translation.

The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles. Lysosomes contain hydrolytic enzymes for digesting waste materials and cellular debris. The smooth endoplasmic reticulum is involved in lipid synthesis, detoxification, and calcium storage, but not protein synthesis (which occurs on rough ER due to attached ribosomes, or free in the cytoplasm).

Which of the following organelle(s) in an animal cell would have DNA and RNA?

[amp_mcq option1=”Nucleus only” option2=”Nucleus and mitochondria only” option3=”Nucleus, mitochondria and ribosomes” option4=”Mitochondria only” correct=”option2″]

In an animal cell, the Nucleus and mitochondria only would have DNA and RNA.

– DNA (Deoxyribonucleic Acid) is the primary genetic material in most organisms. In eukaryotic cells, the majority of DNA is found in the nucleus (nuclear DNA), forming chromosomes.
– Eukaryotic cells also contain DNA in certain organelles: mitochondria (mitochondrial DNA or mtDNA) and, in plant cells and some other eukaryotes, chloroplasts (chloroplast DNA or cpDNA). Animal cells lack chloroplasts.
– RNA (Ribonucleic Acid) is involved in protein synthesis and other cellular processes. Various types of RNA (mRNA, tRNA, rRNA) are transcribed from DNA.
– In animal cells:
– Nucleus: Contains the main genome (DNA) and is where transcription occurs, producing various types of RNA. Thus, the nucleus has both DNA and RNA.
– Mitochondria: Contain their own circular DNA (mtDNA) and also have ribosomes (mitoribosomes) made of ribosomal RNA (mt-rRNA) and proteins, and produce their own mRNA and tRNA. Thus, mitochondria have both DNA and RNA.
– Ribosomes: Are complex molecular machines responsible for protein synthesis. They are composed of ribosomal RNA (rRNA) and proteins. Ribosomes themselves do not contain DNA. They read mRNA to build proteins.
– Therefore, in an animal cell, the nucleus and mitochondria are the organelles that contain both DNA and RNA.

While RNA is widely present in the cytoplasm (as mRNA being translated, tRNA carrying amino acids, and ribosomes containing rRNA), the question asks about *organelles* that contain both DNA and RNA. Ribosomes are technically organelles (or macromolecular machines depending on definition), but they lack DNA. The nucleus and mitochondria fit the criteria.

Which one of the following cell organelles synthesizes its own proteins involving genes present in its DNA?

[amp_mcq option1=”Endoplasmic reticulum” option2=”Plasma membrane” option3=”Plastid” option4=”Lysosome” correct=”option3″]

Plastids (like chloroplasts) contain their own DNA and ribosomes and can synthesize some of their own proteins.

Mitochondria and plastids are unique among eukaryotic organelles because they possess their own circular DNA (similar to bacterial DNA) and ribosomes (70S type). This allows them to synthesize some of the proteins required for their function, independently of the cell’s nucleus and cytoplasmic ribosomes.

The endoplasmic reticulum is involved in protein synthesis and modification but relies on ribosomes attached to it or free in the cytoplasm. The plasma membrane is a structural component. Lysosomes contain enzymes synthesized elsewhere in the cell.