Molecular Basics of Inheritance (SAQs)

Botany-2 | 10. Molecular Basics Of Inheritance – SAQs:
Welcome to “SAQs” in “Chapter 10: Molecular Basics Of Inheritance”. This page includes the most important FAQs from previous exams. Each answer is provided in simple English, followed by a Telugu explanation, and then presented in the exam format. This method ensures you’re well-prepared to achieve great results in your final exams.

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SAQ-1 : Define transformation in Griffith’s experiment. Discuss how it helps in the identification of DNA as genetic material.

Introduction

In 1928, Frederick Griffith conducted a groundbreaking experiment that provided crucial evidence for identifying DNA as the molecule responsible for genetic inheritance. His work with Streptococcus pneumoniae led to the discovery of a process called transformation, which significantly advanced our understanding of genetic material.

Definition of Transformation

Transformation is a process where a cell changes its genetic makeup by taking up and integrating new genetic material from its environment. Imagine a recipe for a special dish—if you add a new ingredient, the recipe changes and creates a new version of the dish. Similarly, when bacteria take in genetic material from their surroundings, they can change their traits.

Details of Griffith’s Experiment

Griffith worked with two different strains of Streptococcus pneumoniae bacteria. The first strain, known as the S-type or smooth strain, had a protective capsule and caused disease (pneumonia) in mice. The second strain, called the R-type or rough strain, lacked the capsule and was harmless.

Griffith made some fascinating observations:

1. Mice injected with S-type bacteria developed pneumonia and died, while mice injected with R-type bacteria remained healthy.
2. The surprising part came when Griffith mixed heat-killed S-type bacteria (which should have been harmless) with live R-type bacteria and injected this mixture into mice. These mice also developed pneumonia and died, and live S-type bacteria were found in their bodies.

This result was unexpected because the heat-killed S-type bacteria should not have caused disease. Griffith concluded that the R-type bacteria were somehow transformed into the virulent S-type bacteria by a substance from the dead S-type bacteria.

Summary

Griffith’s discovery of transformation was a major step in understanding genetic material. Although he didn’t identify the substance responsible for the transformation, his findings paved the way for future experiments. In the 1940s, scientists like Avery, McLeod, and McCarty further investigated and demonstrated that DNA was the substance responsible for transformation. Their work confirmed that DNA is the genetic material that carries the instructions for traits and inheritance. Griffith’s experiment thus laid the groundwork for recognizing DNA as the key molecule of heredity, shaping our understanding of genetics and molecular biology.

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SAQ-2 : How many types of RNA polymerases exist in cells? Write their names and functions.

Introduction

In our cells, RNA polymerases are essential enzymes that help convert DNA instructions into RNA. This process, known as transcription, is vital for creating the proteins that perform countless functions in our bodies. In eukaryotic cells, there are three main types of RNA polymerases, each with a specific role in this process.

Types of RNA Polymerases and Their Functions

1. RNA Polymerase I: RNA Polymerase I is like a specialized factory worker focused on a specific job. It’s mainly responsible for producing ribosomal RNA (rRNA), which is a crucial component of the ribosome. Think of the ribosome as a protein-making machine in the cell. RNA Polymerase I transcribes the 28S, 18S, and 5.8S rRNAs—important parts of this machine that ensure it runs smoothly and efficiently to make proteins.
2. RNA Polymerase II: RNA Polymerase II plays a central role in the transcription of messenger RNA (mRNA), which acts as a messenger carrying genetic instructions from DNA to the ribosomes. This is like preparing a recipe based on the instructions from a cookbook. RNA Polymerase II transcribes the initial form of mRNA, known as heterogeneous nuclear RNA (hnRNA), which is then processed to produce mature mRNA. This mature mRNA is then used as a blueprint to create proteins.
3. RNA Polymerase III: RNA Polymerase III has a diverse range of responsibilities. It transcribes transfer RNA (tRNA), 5S ribosomal RNA (5S rRNA), and small nuclear RNAs (snRNAs). Think of tRNA as a delivery truck that brings the right building blocks (amino acids) to the ribosome for protein assembly. 5S rRNA is another piece of the ribosomal machinery, and snRNAs are involved in splicing—a process that edits mRNA before it can be used to make proteins.

Summary

The three types of RNA polymerases—RNA Polymerase I, RNA Polymerase II, and RNA Polymerase III—each have distinct and essential roles in the cell. RNA Polymerase I makes rRNA for ribosomes, RNA Polymerase II produces mRNA for protein instructions, and RNA Polymerase III synthesizes tRNA, 5S rRNA, and snRNAs. Together, these enzymes ensure that genetic information is accurately transcribed and processed, which is crucial for the proper functioning of cells and ultimately for all life.

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SAQ-3 : Draw the schematic/diagrammatic presentation of the lac operon.

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SAQ-4 : What are the differences between DNA and RNA

Introduction

DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) are like the key players in the genetic orchestra of living organisms. They both handle genetic information, but they do so in different ways. Understanding how they differ helps us grasp how our cells work and how genetic information is passed on.

Comparison of DNA and RNA

DNA

DNA is often compared to a book that holds the comprehensive instructions for life. It’s structured as a double-stranded helix, much like a twisted ladder, which provides it with stability. This structure helps DNA stay intact under various conditions, especially alkaline ones. The sugar component in DNA is deoxyribose, and its strands can be incredibly long, stretching to millions of nucleotides. For instance, the human genome, which is all the DNA in our cells, contains over 3 billion nucleotides!

One of DNA’s key features is its ability to self-replicate. This means that before a cell divides, DNA makes a copy of itself, ensuring that the new cells have the same genetic instructions. DNA serves as the primary genetic material, containing all the instructions needed for the development and functioning of an organism. However, it doesn’t directly make proteins but rather provides the blueprint for RNA to carry out that task. There is only one main type of DNA in organisms. In terms of base pairing, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C).

RNA

RNA, on the other hand, is like the worker bees that take the genetic instructions from DNA and put them into action. It’s usually single-stranded, which makes it less stable compared to the double-stranded DNA. RNA contains ribose sugar, making it distinct from DNA’s deoxyribose. RNA molecules are generally shorter, often only a few thousand nucleotides long.

Unlike DNA, RNA does not replicate on its own. Instead, it is transcribed from DNA. RNA plays a crucial role in gene expression and protein synthesis. There are several types of RNA, each with a specific job: mRNA (messenger RNA) carries genetic information from DNA to the ribosomes, tRNA (transfer RNA) helps in assembling amino acids into proteins, and rRNA (ribosomal RNA) is a part of the ribosome machinery. For base pairing, adenine (A) pairs with uracil (U) in RNA, rather than thymine, while guanine (G) still pairs with cytosine (C).

Summary

In summary, while both DNA and RNA are essential for genetic functions, they differ significantly in structure and role. DNA acts as the permanent storage of genetic information, providing a stable blueprint for life. RNA, however, is more dynamic, translating that genetic information into proteins and performing various tasks crucial for life’s functions. Understanding these differences helps us appreciate how life operates at the molecular level and how genetic information flows within cells.

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SAQ-5 : Write the important features of Genetic code?

Introduction

The genetic code is like the instruction manual for building proteins, which are essential for nearly every function in a living organism. This code converts the four-letter language of DNA into the 20-letter language of amino acids, which are the building blocks of proteins. What makes this code so fascinating is that it is almost universal, meaning that it works similarly in almost all living organisms, from bacteria to humans.

Key Features of the Genetic Code

1. Triplet Code: The genetic code is read in groups of three nucleotides, known as codons. Imagine these codons as words in a sentence where each word stands for a specific amino acid or a signal to start or stop protein synthesis. For example, the codon UUU always translates to the amino acid phenylalanine. This specificity ensures that each codon directs exactly one amino acid, much like a precise recipe where each ingredient has a specific role.
2. Specific and Unambiguous: Each codon uniquely codes for a single amino acid, ensuring there is no confusion. This feature of the genetic code makes it highly accurate. For instance, the codon AAA always codes for lysine, guaranteeing that each amino acid is added in the right sequence during protein synthesis.
3. Redundancy and Degeneracy: The code is redundant and degenerate, meaning that multiple codons can specify the same amino acid. For example, the amino acid leucine can be coded by six different codons. This redundancy acts as a buffer, reducing the chance of errors during protein synthesis, much like having multiple routes to reach the same destination.
4. Non-overlapping: The code is non-overlapping, meaning it is read sequentially from a fixed starting point, three nucleotides at a time, without any overlap. Think of it as reading a book where each word is read one after another, without skipping or combining words.
5. Universal: One of the most remarkable aspects of the genetic code is its universality. Nearly every organism, from simple bacteria to complex plants and animals, uses the same genetic code. This universal feature supports the idea that all life shares a common evolutionary ancestor, like different branches of the same family tree.
6. Punctuation: The code also includes punctuation with specific start and stop codons. The AUG codon signals the start of protein synthesis and also codes for the amino acid methionine. Stop codons, such as UAA, UAG, and UGA, mark the end of the protein-building process, just like punctuation marks end sentences in a book.
7. Continuous: Finally, the genetic code is continuous. There are no spaces or breaks between codons; they are read one after another in a continuous sequence. This uninterrupted reading ensures that proteins are made accurately, similar to how a continuous flow of instructions ensures a project is completed correctly.

Summary

In essence, the genetic code is a fundamental set of instructions that translates the genetic information in DNA into the proteins essential for life. Its features, including being read in triplets, its specificity, redundancy, non-overlapping nature, universality, punctuation, and continuity, make it a precise and adaptable system. This code’s consistency across diverse life forms highlights its critical role in the study of genetics and the functioning of all living organisms.

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SAQ-6 : Write briefly on nucleosomes.

Introduction

In the heart of the cell’s nucleus, nucleosomes play a crucial role in organizing and managing DNA. They are like the spools around which our genetic material is wound, making it possible for DNA to fit into the tiny nucleus while still being accessible for important processes like replication and gene expression.

Structure and Composition

A nucleosome is a combination of DNA and proteins. Imagine it as a spool of thread: the DNA wraps around a core made up of histone proteins. This core is known as a histone octamer, consisting of eight histone proteins: two each of H2A, H2B, H3, and H4. The DNA wraps around this core in a manner similar to how a string is wound around a spool, forming a tight, organized structure.

DNA Wrapping

About 146 to 147 base pairs of DNA wrap around the histone core in what’s known as negative superhelical turns. This wrapping occurs in a left-handed coil, which helps in efficiently packing the DNA. Think of it as wrapping a ribbon around a spool; the DNA coils tightly around the histone proteins, compacting it into a manageable form.

Charge Interaction

The histone proteins are positively charged because of certain amino acids like lysine and arginine. This positive charge interacts with the negatively charged phosphate groups of the DNA. This interaction is crucial for holding the DNA tightly around the histone core, much like how static electricity can cause dust particles to stick to a surface.

Structural Significance

Nucleosomes are the basic building blocks of chromatin, which is the complex of DNA and proteins found in the nucleus. By organizing DNA into nucleosomes, the cell can efficiently package long DNA molecules into a compact form. This compacted structure can further fold into higher-order forms and ultimately into chromosomes, which are essential for cell division and genetic stability.

Beads-on-a-String Appearance

Under an electron microscope, nucleosomes have a beads-on-a-string appearance. This term describes how nucleosomes appear like beads strung along a thread of DNA. This structure is most visible during interphase, a phase when DNA is less compact and more accessible for processes like replication and transcription.

Role in Gene Regulation

Nucleosomes are not just structural units; they also play a key role in gene regulation. The way nucleosomes are positioned along the DNA affects how easily the transcription machinery can access the genetic information. This positioning can either promote or inhibit gene expression, similar to how a book’s accessibility is affected by how tightly it is packed on a shelf.

Summary

Nucleosomes are essential for DNA packaging and regulation. They help compact the DNA into the nucleus while also influencing gene activity. Their structure allows DNA to be organized in a way that supports crucial cellular processes like replication and transcription, making them fundamental to the cell’s ability to manage genetic information effectively.