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Griffiths' Introduction to Genetic Analysis is widely regarded as the authoritative textbook for understanding fundamental genetic concepts. This book is known for its clear explanations, comprehensive coverage of genetic principles, and incorporation of the latest research findings, making it an essential resource for students and professionals in genetics and related fields.

Unlike the other options listed, which focus on specialized areas of dental and oral histology and physiology, Griffiths provides a broad and detailed foundation in genetics including molecular genetics, gene regulation, inheritance patterns, and genetic analysis techniques.

Key points include:
- Comprehensive coverage of classical and molecular genetics.
- Clear and accessible explanations suitable for both beginners and advanced learners.
- Up-to-date content reflecting current advancements in the field.
- Extensive problem sets and examples that aid in the practical understanding of concepts.

Therefore, for anyone seeking a foundational and authoritative text on genetics, Griffiths' Introduction to Genetic Analysis is the textbook of choice.

Reference: Griffiths, Introduction to Genetic Analysis, 11th Edition, Volume 1, Chapters 1-10
In the case of incomplete dominance, neither allele is completely dominant over the other. Instead, the heterozygous genotype results in a blended phenotype that is intermediate between the two homozygous phenotypes.

- Here, allele C codes for red color and allele c codes for white color. Since the organism is heterozygous (Cc), it carries one red allele and one white allele. Due to incomplete dominance, the phenotype will not be purely red or purely white but a mixture of the two.

- Therefore, the expected phenotype of a Cc individual is pink, which is an intermediate color between red and white.

Key points:
- Incomplete dominance means no allele is completely dominant.
- Heterozygous genotype (Cc) results in an intermediate phenotype.
- Red (C) and white (c) blend to produce pink.

So, the correct answer is: Pink.

Reference: Genetics: Analysis and Principles, 5th Edition, Chapter 5, Page 142
The phenomenon described in the question is called Epistasis. In genetics, epistasis occurs when the expression of one gene is suppressed or masked by the presence of another gene at a different locus. This interaction affects the phenotypic outcome in a way that one gene can override or alter the expression of another gene.

To clarify the other options:
- Pleiotropy refers to a single gene influencing multiple, seemingly unrelated phenotypic traits.
- Codominance is a situation where both alleles in a heterozygote are fully expressed, resulting in a phenotype that simultaneously shows characteristics of both alleles.
- Polygenic Inheritance involves multiple genes contributing additively to a single trait, such as height or skin color, without one gene masking the other.

Thus, the key point is that in epistasis, one gene's expression can mask or suppress another gene, which distinguishes it from the other genetic phenomena.

Reference: Griffiths, A.J.F., Wessler, S.R., Carroll, S.B., et al. Introduction to Genetic Analysis, 11th Edition, Chapter 5, Page 180.
According to Mendelian genetics, traits are determined by alleles, which come in pairs. When we consider a gene with two alleles, one dominant (A) and one recessive (a), the dominant allele masks the expression of the recessive allele in a heterozygous genotype (Aa). This means that the dominant trait will be expressed if at least one dominant allele is present.

In the case of the genotype aa, both alleles are recessive. Since there is no dominant allele present to mask the recessive allele, the phenotype expressed will be the recessive trait. This is a fundamental principle of Mendelian inheritance where the recessive phenotype is only visible when the organism is homozygous recessive.

• Key Points:
- Dominant allele (A) masks the expression of the recessive allele.
- Genotype aa means both alleles are recessive.
- The recessive trait is expressed only in the homozygous recessive state (aa).
- In heterozygous condition (Aa), the dominant trait is expressed.

Thus, for the genotype aa, the expressed phenotype corresponds to the recessive trait.
The phenotypic diversity observed within a population is primarily influenced by both genetic and environmental factors.

- Genotype refers to the genetic makeup of an individual, which provides the blueprint for potential traits. However, the way these genetic traits are expressed can be significantly modified by environmental factors such as nutrition, climate, exposure to toxins, and lifestyle. These environmental influences interact with the genotype to produce the final phenotype, the observable characteristics.

- It is important to note that random genetic mutations do contribute to genetic variation but are not the sole factor influencing phenotypic diversity at any given time. They are one of many sources of genetic variability that, combined with environmental effects, contribute to the diversity observed.

- Thus, the correct answer is: Option 3: Both genotype and environmental influences

Key points:
- Phenotype = Genotype + Environment
- Environmental factors can modify gene expression
- Genetic mutations contribute to variation but are not the only factor
- Phenotypic diversity results from complex interactions between genes and environment
A phenotype refers to the observable physical or biochemical characteristics of an organism, resulting from the interaction of its genotype (genetic makeup) and the environment. In this question, we are asked to identify a phenotype that arises specifically from a genetic mutation.

- Sickle-cell anemia is a classic example of a disease caused by a specific genetic mutation in the hemoglobin-beta gene. This mutation results in abnormal hemoglobin molecules that cause red blood cells to assume a sickle or crescent shape, leading to clinical symptoms such as anemia, pain crises, and organ damage. Thus, it is a phenotype directly resulting from a mutation.

- Option 2, Point mutation, refers to the change of a single nucleotide base in DNA. While this is the type of mutation that causes sickle-cell anemia, it is a genetic change, not a phenotype by itself.

- Option 3, Ribosomal RNA, is a type of RNA involved in protein synthesis, not a phenotype or a mutation.

- Option 4, Mitochondrial DNA, refers to DNA located in the mitochondria. It can carry mutations that cause disease, but mitochondrial DNA itself is not a phenotype.

In summary, sickle-cell anemia represents a clear example of a phenotype caused by a genetic mutation and is the best answer to this question.

Reference: Robbins Basic Pathology, 10th Edition, Chapter 3: Genetic Disorders / Page 67
The term that refers to the complete set of genetic information within an organism is the genome.

To clarify the options:
- Phenotype refers to the observable physical or biochemical characteristics of an organism, which result from the interaction of its genotype with the environment.
- Genotype refers to the specific set of genes or alleles that an organism possesses. It is a part of the genetic makeup but does not encompass the entire genetic information.
- An allele is one of the different forms of a gene found at a specific locus.
- The genome is the entire collection of an organism’s genetic material, including all of its genes and non-coding sequences. This includes both the nuclear DNA and, in some organisms, mitochondrial DNA.

Therefore, the correct answer should be Genome as it represents the full genetic blueprint of an organism.

Reference: Genetics: From Genes to Genomes, 6th Edition, Chapter 2, page 45
A gene is fundamentally defined as a specific segment of DNA that contains the necessary information to produce a functional product. This functional product can be a protein or an RNA molecule that performs a particular role within the cell. It is important to understand that not all genes encode proteins; some genes encode functional RNA molecules such as tRNA or rRNA, which are crucial in protein synthesis.

The other options are incorrect because:
- Option 2 describes a protein, not a gene.

- Option 3 refers to RNA molecules involved in protein synthesis, but these are products of genes, not definitions of genes themselves.

- Option 4 refers to chromosomes, which are larger structures composed of DNA and proteins, and are not individual genes.

In summary, a gene is best described as a DNA segment encoding a functional product, highlighting its role as the fundamental unit of heredity and molecular function.

Reference: Molecular Biology of the Cell, 6th Edition, Chapter 2
The correct answer is Edwards Syndrome.

Edwards Syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 18, also known as trisomy 18. This condition leads to severe developmental and physical abnormalities, including heart defects, growth retardation, and distinctive facial features. It is associated with a high mortality rate in infancy.

To clarify the other options:
- Patau Syndrome (Option 1) is caused by trisomy 13 (an extra chromosome 13).
- Down Syndrome (Option 3) results from trisomy 21 (an extra chromosome 21).
- Turner Syndrome (Option 4) is a sex chromosome disorder characterized by a missing or partial X chromosome (monosomy X), not a trisomy.

Therefore, the presence of an extra chromosome 18 specifically defines Edwards Syndrome.

Reference: Robbins Basic Pathology, 10th Edition, Chapter on Genetic Disorders/Page 256

ফ্রিতে ২ লাখ প্রশ্নের টপিক, সাব-টপিক ভিত্তিক ও ১০০০+ জব শুলুশন্স বিস্তারিতে ব্যাখ্যাসহ পড়তে ও আপনার পড়ার ট্র্যাকিং রাখতে সাইটে লগইন করুন।

লগইন করুন
The primary function of the centromere during cell division is to serve as the attachment site for spindle fibers. During mitosis and meiosis, spindle fibers, which are composed of microtubules, connect to the centromere via a protein complex called the kinetochore. This connection is crucial because it allows the chromosomes to be accurately aligned and then segregated into the daughter cells. Without this attachment, chromosomes would not be pulled apart correctly, leading to unequal distribution of genetic material.

To clarify other options:
- The origin of DNA replication is a different specific DNA sequence, not located at the centromere.
- The site of ribosomal RNA synthesis is the nucleolus, not the centromere.
- While spindle checkpoint proteins monitor attachment at the centromere, the centromere itself is not their specific location; rather, these proteins function at or near the kinetochore complex.

Thus, the centromere's indispensable role is as the binding site for spindle fibers, which ensures proper chromosome separation.

Reference: Molecular Biology of the Cell, 6th Edition, Chapter 18: Mitosis and Cytokinesis
- The biochemical molecule responsible for organizing DNA into nucleosome structures is Histones.

- DNA in eukaryotic cells is highly compacted to fit within the confined space of the nucleus. This compaction is achieved by wrapping DNA around proteins called histones, forming a structure known as the nucleosome. Each nucleosome consists of DNA wound around a histone octamer, which includes two copies each of histones H2A, H2B, H3, and H4. This structure serves as the fundamental repeating unit of chromatin, facilitating the efficient packaging of DNA while also regulating gene accessibility.

Other options explained:
- DNA polymerase (Option 2) is involved in DNA synthesis during replication.
- Topoisomerase (Option 3) helps relieve torsional strain during DNA replication and transcription by inducing or removing supercoils.
- RNA polymerase (Option 4) is responsible for synthesizing RNA from a DNA template during transcription.

Thus, the correct answer is Histones, as they directly organize DNA into nucleosomes.

Reference: Molecular Biology of the Cell, 6th Edition, Bruce Alberts, Chapter 5 - The Structure and Function of DNA
- The correct answer is: Centromere positioned at the center.

- A metacentric chromosome is characterized by having its centromere located approximately at the middle of the chromosome, resulting in two arms of roughly equal length. This symmetrical arrangement distinguishes metacentric chromosomes from other types such as submetacentric or acrocentric chromosomes, where the centromere is positioned off-center, leading to arms of unequal lengths.

- Option 1 correctly identifies the centromere position in a metacentric chromosome.
- Option 2 describes an acrocentric or telocentric chromosome where the centromere is near one end.
- Option 3 is incorrect as centromeres are essential for chromosome movement during cell division.
- Option 4 refers more to a submetacentric chromosome, where the centromere is off-centered but not at the very end.

Reference: “Principles of Genetics,” 8th Edition, Snustad & Simmons, Chapter 4, p. 85-86.
The correct answer is H1.

- In the structure of chromatin, nucleosomes are the fundamental repeating units, consisting of DNA wrapped around a core of histone proteins. The nucleosome core particle is made up of an octamer containing two copies each of the four core histones: H2A, H2B, H3, and H4. Specifically, the DNA wraps approximately 1.65 turns around this histone octamer, which helps compact the DNA into a more condensed form.

- The histone H1, however, is not part of this core particle. Instead, it is known as the linker histone and binds to the DNA between nucleosomes (called linker DNA). Its role is to help stabilize the higher-order structure of chromatin by promoting the folding of nucleosomes into more compact fibers.

To summarize:
- H2A, H2B, H3, and H4: core histones that form the nucleosome core particle.
- H1: linker histone that is excluded from the nucleosome core particle and helps in chromatin compaction.

Reference: Molecular Biology of the Cell, 6th Edition, Alberts et al., Chapter 6 – The Structure and Function of Chromatin / p.290
The karyotype that corresponds to Turner syndrome is 45,X.

- Turner syndrome is a genetic condition that affects females and is characterized by the complete or partial absence of one X chromosome. Normally, females have two X chromosomes (46,XX), but in Turner syndrome, affected individuals have only a single X chromosome, resulting in a 45,X karyotype. This chromosomal anomaly leads to a variety of clinical features including short stature, gonadal dysgenesis (underdeveloped ovaries), infertility, and certain physical characteristics such as a webbed neck and lymphedema.

To clarify the other options:
- 46,XX represents a normal female karyotype.
- 47,XXY corresponds to Klinefelter syndrome, a condition in males where there is an extra X chromosome.
- 46,XY represents a normal male karyotype.

Reference: Robbins Basic Pathology, 10th Edition, Chapter 20: Genetic Disorders / Page 180-182
In Down Syndrome, there is the presence of an extra copy of chromosome 21, which means individuals have three copies (trisomy 21) instead of the usual two. This chromosomal anomaly leads to the characteristic features and developmental delays associated with the condition.

To clarify the options:
- Chromosome 21 is the one affected in Down Syndrome.
- Chromosome 18 trisomy causes Edwards syndrome.
- Chromosome 13 trisomy leads to Patau syndrome.
- Chromosome X abnormalities relate to sex chromosome disorders such as Turner syndrome or Klinefelter syndrome, but are not related to Down Syndrome.

Thus, the correct answer is Chromosome 21 because the presence of an extra chromosome 21 causes the genetic and phenotypic manifestations of Down Syndrome.

Key Points:
- Down Syndrome results from trisomy 21 (three copies of chromosome 21).
- It is the most common chromosomal cause of intellectual disability.
- Different trisomies cause distinct syndromes (e.g., 18 for Edwards, 13 for Patau).

Reference: Robbins Basic Pathology, 10th Edition, Chapter 5: Genetic Disorders, Page 158
The main role of telomeres in chromosomal DNA is to prevent DNA degradation. Telomeres are repetitive nucleotide sequences located at the ends of chromosomes, and they serve as protective caps. During cell division, the enzymes that replicate DNA cannot fully copy the very end of the chromosome, which leads to a gradual shortening of the DNA with each replication cycle.

Telomeres help to protect the coding regions of the DNA from being lost due to this shortening process. Without telomeres, important genetic information would be degraded, leading to chromosomal instability and cellular aging.

Contrary to some misconceptions:
- Telomeres do not directly facilitate DNA replication but rather protect the ends to ensure replication occurs without loss of crucial data.
- They do not initiate gene transcription, as this is regulated by promoter regions and transcription factors within genes.
- They also do not promote chromosome recombination; instead, they help maintain chromosome integrity by preventing end-to-end fusions.

Therefore, the correct answer is Option 2: Prevent DNA degradation.

Reference: Molecular Biology of the Cell, 6th Edition, Chapter 18: DNA Replication, Telomeres and Telomerase
The process of transcription primarily takes place in the nucleus of the cell, where the genetic material, DNA, is located. Specifically, within the nucleus, the nucleolus is a prominent structure involved in the synthesis of ribosomal RNA (rRNA), which is a critical part of ribosome production.

However, it is important to note the distinction that while general transcription of mRNA occurs in the nucleoplasm (the fluid surrounding the nucleolus), the transcription of rRNA genes specifically happens within the nucleolus. The nucleolus is the site where the ribosomal RNA genes are transcribed, then processed, and assembled into ribosomal subunits.

The other options are involved in different cellular functions:
- The mitochondrion has its own DNA and can perform transcription of mitochondrial genes, but this is separate from nuclear transcription.
- The rough endoplasmic reticulum is mainly involved in protein synthesis through its ribosomes.
- The Golgi apparatus functions in the modification and packaging of proteins, not in transcription.

Therefore, the correct answer is the nucleolus, because it plays a central role in the transcription of rRNA within the nuclear structure.

Reference:
Molecular Biology of the Cell, 6th Edition, Alberts et al., Chapter 6: Inside the Cell / Page 250-255
The correct answer is Hutchinson-Gilford Progeria Syndrome.

- Hutchinson-Gilford Progeria Syndrome (HGPS) is a rare genetic disorder characterized by premature aging. It results from mutations in the gene encoding lamin A, a critical protein component of the nuclear lamina. The nuclear lamina provides structural support to the nucleus and plays a role in DNA replication and transcription regulation. Mutations in lamin A lead to the production of an abnormal protein called progerin, which disrupts the integrity of the nuclear envelope, causing the cell abnormalities seen in progeria.

In contrast, the other disorders listed:
- Ehlers-Danlos Syndrome: Primarily involves mutations in genes encoding collagen or collagen-processing enzymes, leading to connective tissue defects.
- Marfan Syndrome: Caused by mutations in the fibrillin-1 gene, affecting connective tissue elasticity.
- Osteogenesis Imperfecta: Results from defects in type I collagen, leading to brittle bones.

Reference: Robbins Basic Pathology, 10th Edition, Chapter 5: Genetic Disorders / Page 180
- The primary function of nuclear pores is to facilitate the exchange of materials between the nucleus and the cytoplasm.
- These pores are large protein complexes embedded in the nuclear envelope, which is the double membrane surrounding the nucleus.
- They regulate the transport of molecules such as RNA and proteins, allowing essential substances like messenger RNA (mRNA) and ribosomal subunits to exit the nucleus, while permitting the entry of proteins and nucleotides needed for nuclear functions.

It is important to note that nuclear pores do not synthesize ribosomal RNA (Option 2), which occurs within the nucleolus, nor do they primarily provide structural support to the nuclear envelope (Option 3). Additionally, DNA replication (Option 4) takes place inside the nucleus but is not a function of the pores themselves.

In summary:
- Nuclear pores act as gateways for molecular trafficking.
- They maintain selective exchange, ensuring cellular function and genetic regulation.
- Their structure and function are critical for communication between the nucleus and cytoplasm.

ফ্রিতে ২ লাখ প্রশ্নের টপিক, সাব-টপিক ভিত্তিক ও ১০০০+ জব শুলুশন্স বিস্তারিতে ব্যাখ্যাসহ পড়তে ও আপনার পড়ার ট্র্যাকিং রাখতে সাইটে লগইন করুন।

লগইন করুন
- During the process of cell division, chromatin undergoes significant structural changes to ensure the accurate distribution of genetic material to daughter cells.
- In the interphase of the cell cycle, DNA exists as loosely packed chromatin, allowing for gene expression and replication.
- However, as the cell prepares to divide during mitosis or meiosis, chromatin condenses and coils tightly to form distinct structures called chromosomes.

- These chromosomes are highly organized complexes of DNA and proteins, which facilitate the proper segregation of genetic material. Each chromosome consists of two identical sister chromatids joined at a centromere, but the entire condensed structure is collectively referred to as a chromosome during cell division.

- Nucleosomes are the fundamental units of chromatin, consisting of DNA wrapped around histone proteins, but they themselves do not represent the higher-order structure visible during division.
- Chromatids refer to the duplicated halves of a chromosome, not the entire structure.
- Centrioles are organelles involved in spindle formation, not a form of chromatin.

Reference: Molecular Biology of the Cell, 6th Edition, Chapter 16 - The Cell Cycle
When mRNA is synthesized in the nucleus during the process of transcription, it needs to be transported to the cytoplasm for translation into protein. The mRNA molecules exit the nucleus through specialized channels called nuclear pores. These nuclear pores are large protein complexes that span the nuclear envelope, which is the double membrane surrounding the nucleus. They serve as gateways allowing the selective passage of molecules like mRNA, while preventing free diffusion of other molecules between the nucleus and cytoplasm.

To clarify the other options:
- The endoplasmic reticulum (ER) is involved in protein synthesis and processing but is located in the cytoplasm and does not serve as a passageway for mRNA from the nucleus.
- The Golgi apparatus is responsible for modifying, sorting, and packaging proteins after their synthesis and is not involved in nuclear export of mRNA.
- Cytoplasmic vesicles mediate transport within the cytoplasm, but mRNA exits the nucleus before these vesicular pathways come into play.

Hence, the correct and primary route for mRNA to leave the nucleus is via the nuclear pores.

Important points:
- mRNA exits the nucleus through nuclear pores.
- Nuclear pores are protein complexes in the nuclear envelope that regulate molecular traffic.
- Endoplasmic reticulum, Golgi apparatus, and cytoplasmic vesicles do not mediate mRNA nuclear export.

Reference: Molecular Biology of the Cell, 6th Edition, Chapter 4: The Nucleus and Chromosome Organization, Page 218
Chromatin is the complex of genetic material and proteins found within the cell nucleus. Its primary components are DNA and histone proteins. The DNA carries the genetic code, while histones act as spool-like proteins around which DNA is tightly wrapped. This packaging helps to efficiently condense the long DNA molecules, facilitating organization, protection, and regulation of gene expression within the nucleus.

- DNA: The long polymer of nucleotides that contains the hereditary information.
- Histone proteins: Positively charged proteins that bind to negatively charged DNA, helping to form nucleosomes — the fundamental units of chromatin structure.

Other components such as RNA and non-histone proteins may be associated with chromatin but are not the primary structural constituents. Lipids and carbohydrates are not involved in chromatin structure.

Therefore, the correct answer is: Option 1: DNA along with histone proteins.

Reference: Gray’s Anatomy, 41st Edition, Volume 2, Chapter: Cell Nucleus and Chromatin Structure, Page 325
The correct answer is Nucleolus.

- The nucleolus is a distinct structure found within the nucleus of eukaryotic cells.
- It plays a crucial role in the synthesis and assembly of ribosomal subunits.
- Specifically, the nucleolus is responsible for the transcription of ribosomal RNA (rRNA) genes, processing of the rRNA, and combining it with ribosomal proteins imported from the cytoplasm to form the small and large ribosomal subunits.
- These subunits are then transported out of the nucleus to the cytoplasm where they assemble into functional ribosomes, essential for protein synthesis.

In contrast, other cellular structures have different primary functions:
- The Golgi apparatus is involved in modifying, sorting, and packaging proteins and lipids for secretion or use within the cell.
- The endoplasmic reticulum (ER), especially the rough ER, is the site of synthesis for membrane-bound and secretory proteins but does not assemble ribosomal subunits.
- The mitochondrion is primarily responsible for energy production through ATP synthesis and has its own small ribosomes, but it does not contribute to the biogenesis of the cell's main ribosomal subunits.

Reference: Molecular Biology of the Cell, 6th Edition, Chapter 6: The Cell Nucleus and Chromosomes
- The main role of the cell nucleus in cellular physiology is the storage of genetic material.
- The nucleus houses the cell’s DNA, which contains the instructions required for all cellular activities and inheritance.
- This genetic information is organized into chromosomes and is crucial for the regulation of growth, development, and reproduction of the cell.

- While the nucleus is involved indirectly in regulating cellular metabolism through gene expression, its primary and most essential function is to serve as the repository of the cell’s genetic code.
- Energy production via ATP synthesis occurs in the mitochondria, not the nucleus. Similarly, although proteins are synthesized in the cytoplasm by ribosomes, the nucleus contains the DNA that encodes for these proteins and controls protein synthesis by transcribing messenger RNA.

In summary, the cell nucleus acts as the control center of the cell by storing and protecting genetic material that governs cellular function and heredity.

Reference: Molecular Biology of the Cell, 6th Edition, Chapter 4: The Nucleus
- The liquid component found within the cytoplasm is called the cytosol.
- The cytoplasm of a cell consists of all the contents within the cell membrane, excluding the nucleus.
- It is composed of the cytosol (the fluid portion) and various organelles suspended within it.

- The cytosol is a gel-like, aqueous solution that contains water, dissolved ions, small molecules, and large water-soluble molecules such as proteins.
- It serves as the medium in which many cellular processes occur, including metabolism, signal transduction, and molecular transport.

To clarify the other options:
- Nucleoplasm is the fluid found inside the nucleus, not the cytoplasm.
- Lysosomal fluid refers to the digestive enzymes and aqueous environment within lysosomes.
- Mitochondrial matrix is the innermost compartment of mitochondria, containing enzymes for cellular respiration.

Reference: Medical Physiology, Volume 1, Chapter 3, Page 45
- The centrosome is the cellular organelle responsible for organizing spindle fibers during mitosis.
- During cell division, the centrosome duplicates and each one moves to opposite poles of the cell.
- From these centrosomes, spindle fibers, composed of microtubules, extend and attach to the chromosomes at the kinetochores.
- This arrangement ensures the proper segregation of sister chromatids into the two daughter cells.

- In contrast, other organelles such as the Golgi apparatus, endoplasmic reticulum, and mitochondrion have distinct functions unrelated to spindle fiber organization.
- The Golgi apparatus is involved in modifying and packaging proteins, the endoplasmic reticulum in protein and lipid synthesis, and the mitochondrion in ATP production.

Reference: Molecular Biology of the Cell, 6th Edition, Chapter 18: Mitosis and the Cell Cycle, Pages 1032-1045
- The synthesis of lipids primarily takes place in the smooth endoplasmic reticulum (SER).
- This organelle is specialized for the production of phospholipids, cholesterol, and steroid hormones, which are essential components of cell membranes and signaling molecules.
- Unlike the rough endoplasmic reticulum, which is studded with ribosomes and primarily involved in protein synthesis, the smooth ER lacks ribosomes and has a distinct role in lipid metabolism, detoxification of drugs, and storage of calcium ions.

- The Golgi apparatus is mainly involved in the modification, sorting, and packaging of proteins and lipids after their synthesis, but it is not the primary site of lipid production.
- Mitochondria are known as the powerhouse of the cell, involved in energy production via ATP, and while they have some role in steroid synthesis, they are not the main organelle responsible for general lipid synthesis.

Key points:
- Smooth ER: primary site of lipid synthesis
- Rough ER: associated with protein synthesis due to ribosomes
- Golgi apparatus: modifies and packages proteins and lipids
- Mitochondria: involved in energy production, minor lipid synthesis role

Reference: Guyton and Hall Textbook of Medical Physiology, 13th Edition, Chapter 4, Page 32
- The cytoskeleton is a complex network of protein filaments that provides structural support, maintains cell shape, and facilitates intracellular transport, cell division, and motility.
- The three main structural components of the cytoskeleton are:

1. Microtubules – These are hollow tubes made of tubulin proteins. They play a crucial role in maintaining cell shape, enabling intracellular transport (such as movement of organelles), and forming the mitotic spindle during cell division.

2. Microfilaments – Also known as actin filaments, these are thin filaments primarily composed of actin. They are involved in generating cellular movements, maintaining cell shape, and enabling processes such as cytokinesis and cell migration.

3. Intermediate filaments – These filaments provide mechanical strength to cells. Unlike microtubules and microfilaments, intermediate filaments are more stable and help resist mechanical stress. Examples include keratins, vimentin, and neurofilaments.

It is important to distinguish these cytoskeletal components from extracellular fibers such as collagen, elastic, and reticular fibers, which are part of the extracellular matrix and not the cytoskeleton itself.

Also, while myosin is an important motor protein associated with microfilaments, it is not a structural element of the cytoskeleton. Similarly, neurofilaments, desmin, and keratin are types of intermediate filaments but do not alone represent the entire cytoskeleton.

Therefore, the correct answer is Option 1: Microtubules, microfilaments, intermediate filaments.

Reference: Abbott's Cell Biology, 5th Edition, Chapter 4 – The Cytoskeleton / Page 112-120
- The Golgi apparatus is a critical organelle in eukaryotic cells primarily responsible for the modification, sorting, and packaging of proteins received from the rough endoplasmic reticulum (ER).
- After proteins are synthesized in the rough ER, they are transported to the Golgi apparatus where they undergo further post-translational modifications such as glycosylation and phosphorylation.
- Additionally, the Golgi apparatus sorts these proteins and packages them into vesicles for delivery to their specific cellular destinations, including secretion outside the cell or incorporation into the plasma membrane.

To clarify the other options:
- Option 2 (Synthesis of ribosomal RNA) occurs in the nucleolus, not the Golgi apparatus.
- Option 3 (Energy production through ATP synthesis) mainly takes place in the mitochondria.
- Option 4 (Intracellular digestion of macromolecules) is the role of lysosomes.

Thus, the best description of the primary role of the Golgi apparatus is protein modification and packaging.

ফ্রিতে ২ লাখ প্রশ্নের টপিক, সাব-টপিক ভিত্তিক ও ১০০০+ জব শুলুশন্স বিস্তারিতে ব্যাখ্যাসহ পড়তে ও আপনার পড়ার ট্র্যাকিং রাখতে সাইটে লগইন করুন।

লগইন করুন
The correct answer is Lysosome.

- The lysosome is a membrane-bound cellular organelle that contains a variety of hydrolytic enzymes.
- These enzymes are crucial for the breakdown of biomolecules such as proteins, nucleic acids, lipids, and carbohydrates. Lysosomes function as the cell’s digestive system, degrading both materials taken in from outside the cell through endocytosis and obsolete or damaged organelles within the cell (a process called autophagy).
- This ability to hydrolyze complex molecules into simpler ones helps maintain cellular health and recycling of cellular components.

Other options explained:
- Mitochondrion: Primarily responsible for energy production via ATP synthesis through cellular respiration.
- Peroxisome: Involved in the breakdown of very long chain fatty acids and detoxification of harmful substances, but not primarily in hydrolytic digestion.
- Golgi apparatus: Functions mainly in the modification, sorting, and packaging of proteins and lipids but does not contain hydrolytic enzymes for degradation of biomolecules.

Reference: Ganong’s Review of Medical Physiology, 26th Edition, Chapter 2 - Cell Structure and Function / Page 20
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