Molecular Basics of Inheritance (VSAQs)
Botany-2 | 10. Molecular Basics Of Inheritance – VSAQs:
Welcome to “VSAQs” in “Chapter 10: Molecular Basics Of Inheritance”. This page covers the most important VSAQs from previous exams. Use these concise answers to strengthen your understanding and get ready to do well in your final exams.
VSAQ-1: Distinguish between heterochromatin and euchromatin. Which of the two is transcriptionally active?
Heterochromatin and euchromatin are two types of chromatin, which is the material that makes up chromosomes. Imagine chromatin as a book of recipes. Heterochromatin is like a tightly packed, locked drawer where the recipes are kept away and are not used often. Under a microscope, it appears dark because it’s densely packed. This means that genes in heterochromatin are not actively used or transcribed into RNA. They’re more like stored information that’s not needed right now.
On the other hand, euchromatin is like an open cookbook on your kitchen counter. It’s loosely packed and appears light under a microscope because it’s spread out and accessible. This loose packing means that genes within euchromatin are transcriptionally active. This means they are actively transcribed into RNA and used to make proteins. Euchromatin is where the cell’s active work happens, much like when you’re cooking up your favorite recipes.
VSAQ-2: Who proved that DNA is genetic material? What is the organism they worked on?
The question of whether DNA is the genetic material was answered by Alfred Hershey and Martha Chase. They conducted experiments with bacteriophages, which are viruses that infect bacteria. Imagine these bacteriophages as tiny robots that inject their genetic material into bacteria. Hershey and Chase used these experiments to show that it was the DNA, not the protein coat of the virus, that carried the genetic instructions. Their work was crucial in proving that DNA, rather than proteins, is the true genetic material in living organisms.
VSAQ-3: What is the function of DNA polymerase?
DNA polymerase is like a highly skilled craftsman that builds and repairs DNA. Its main job is to add new nucleotides to a growing DNA strand during replication and repair. Imagine DNA polymerase as a meticulous builder, ensuring that each brick (nucleotide) is laid correctly according to the original blueprint (template strand). This enzyme ensures that the newly created DNA strand matches the original perfectly, maintaining the accuracy of the genetic code. This precision is crucial because it keeps the genetic information intact and prevents errors that could lead to problems in the cell.
VSAQ-4: What are the components of a nucleotide?
A nucleotide is like a building block of DNA and RNA. Each nucleotide consists of three parts:
- A nitrogenous base, which can be adenine (A), thymine (T), cytosine (C), guanine (G), or uracil (U) in RNA.
- A pentose sugar, which is ribose in RNA and deoxyribose in DNA. Think of this sugar as the backbone of the nucleotide, connecting the base and the phosphate.
- A phosphate molecule, which forms part of the backbone and provides energy for the synthesis and function of DNA and RNA. The phosphate groups are like the links in a chain that hold the nucleotide together.
VSAQ-5: Given the sequence of the coding strand of DNA in a transcription unit, 5′ – A A T G C T A T T A G G – 3′, write the sequence of a. Its complementary strand b. The mRNA.
For the given DNA sequence, the complementary strand would be the one that pairs with it. If we imagine the coding strand as a guide, the complementary strand is its mirror image, which would be 3′ – T T A C G A T A A T C C – 5′.
The mRNA sequence is derived from the coding strand but with uracil (U) replacing thymine (T). So, if the coding strand is 5′ – A A T G C T A T T A G G – 3′, the mRNA sequence would be 5′ – U U A C G U A A U C C – 3′.
VSAQ-6: Name any three viruses which have RNA as the genetic material.
There are several viruses that use RNA instead of DNA as their genetic material. Here are three examples:
- Influenza virus, which causes the flu and has RNA as its genetic material.
- Polio virus, responsible for polio, also contains RNA.
- HIV (Human Immunodeficiency Virus), which leads to AIDS, has RNA as its genetic material.
These viruses use their RNA to carry genetic information and replicate within host cells.
VSAQ-7: What are the components of a transcription unit?
In the process of transcription, which is how cells make RNA from DNA, the transcription unit plays a crucial role. Think of it as the blueprint that guides this entire process.
Promoter: At the start of this blueprint is the promoter, acting like a “Start” button for transcription. It is a specific region at the beginning of a gene where RNA polymerase binds. This binding is crucial because it tells the cell, “Here’s where to begin copying the DNA into RNA.”
Structural Gene: Following the promoter is the structural gene. This part of the blueprint contains the actual genetic instructions that need to be transcribed. Imagine it as the main recipe in a cookbook—the part that tells you what exactly needs to be made into RNA. It contains the essential information for creating proteins or functional RNA molecules.
Terminator: At the end of the transcription unit is the terminator. This element acts like a “Finish” line in our recipe process, signaling the end of transcription. It tells the RNA polymerase, “You can stop now,” and ensures that the newly made RNA is ready for its next job. Together, these components ensure that transcription is carried out accurately and efficiently.
VSAQ-8: What is the difference between exons and introns?
When looking at genes, exons and introns serve distinct functions, much like useful and non-useful parts of a recipe.
Exons:Exons are the parts of a gene that are retained and used in the final RNA. They are the “useful” parts that contain the necessary genetic information for making proteins or functional RNA. Think of exons as the actual ingredients listed in a recipe—these are the parts you need to follow to create the final dish.
Introns: In contrast, introns are the non-coding segments that are removed during RNA processing. They are the “extra” parts of the gene that do not contribute to making proteins or functional RNA. Imagine these as the irrelevant notes or instructions in a recipe that you discard because they don’t affect the outcome of your dish.
VSAQ-9: What is meant by capping and tailing?
In RNA processing, capping and tailing are essential steps that prepare the RNA for its role in the cell, much like final touches on a finished product.
Capping:Capping involves adding a methyl guanosine triphosphate (m7G) cap to the 5′-end of the RNA molecule. This cap functions like a protective seal that ensures the RNA remains stable and can be efficiently translated into a protein. It’s akin to placing a protective cover on a container to keep its contents secure and fresh.
Tailing:Tailing, or polyadenylation, involves adding a series of adenylate (A) residues to the 3′-end of the RNA. This poly(A) tail is crucial for the RNA’s stability, its transport from the nucleus, and proper translation initiation. Imagine this tail as a tag that helps the RNA get processed correctly and recognized by the cell machinery.
VSAQ-10: What is meant by point mutation? Given an example.
A point mutation refers to a small change in the DNA sequence that can have significant consequences, similar to how a minor alteration in a recipe can change the outcome.
Point Mutation Example: In sickle cell anemia, a point mutation occurs in the hemoglobin gene. This mutation changes just one nucleotide in the DNA sequence, leading to the replacement of glutamic acid with valine in the hemoglobin protein. This seemingly small change causes the hemoglobin to form abnormally, resulting in sickle-shaped red blood cells. This abnormal shape affects blood flow and can lead to serious health issues, demonstrating how a tiny alteration can have a major impact on an organism’s health.
VSAQ-11: What is meant by charging of tRNA?
When it comes to building proteins, charging of tRNA is like making sure you have the right tools for the job. Imagine you’re preparing to cook a complex dish. You need to have the right ingredients measured and ready to go. Similarly, in the cell, each transfer RNA (tRNA) molecule needs to be “charged” with the correct amino acid before it can do its job.
This process is managed by special enzymes called aminoacyl-tRNA synthetases. They work like chefs, carefully attaching each amino acid to its specific tRNA. This attachment requires energy, which comes from a molecule called adenosine triphosphate (ATP). Once charged, the tRNA molecules carry their amino acids to the ribosome, where proteins are made. Just as having the right ingredients is crucial for cooking, properly charged tRNA ensures that the correct amino acids are delivered during protein synthesis, keeping the process accurate and efficient.
VSAQ-12: What is the function of the codon-AUG?
In the world of molecular biology, the codon AUG has a very important job, like a starting whistle in a race. This codon is found in the mRNA, which is like the recipe for making proteins.
AUG has two main roles. First, it acts as the initiation codon, which signals the beginning of the protein synthesis process. Think of it as the “Start Cooking” signal that tells the cell, “It’s time to begin making a protein.” Second, AUG also codes for the amino acid methionine, which is usually the first ingredient in the protein chain. Just as a dish often starts with a base ingredient, methionine is the first amino acid added to the growing protein chain. So, AUG not only starts the process but also sets the stage for the protein’s sequence.
VSAQ-13: Define stop codon. Write the codons.
In the process of protein synthesis, a stop codon is like the finish line in a race, signaling that it’s time to stop. These codons are special sequences in the mRNA that tell the ribosome to stop making the protein and release the newly formed protein chain.
The three stop codons are UAA, UAG, and UGA. Think of them as the flags or markers on the track that indicate the end of the race. Unlike other codons, which specify which amino acids to add next, stop codons do not code for any amino acids. They simply signal the end of the process, ensuring that the protein is finished and ready for its role in the cell.
VSAQ-14: Write any two differences between DNA and RNA.
When comparing DNA and RNA, there are some key differences that are quite important, much like distinguishing between two different types of recipes.
Sugar Composition:DNA contains a sugar called deoxyribose, which is like a stable foundation for a recipe that doesn’t change much. On the other hand, RNA has a sugar called ribose, which can be seen as a more flexible ingredient that helps with different recipes or tasks.
Self-Replication Capability: DNA has the special ability to self-replicate, meaning it can make copies of itself during cell division, just like a recipe that can be used repeatedly without any changes. RNA, however, does not replicate itself. Instead, it is made from DNA and plays a role in transcription and translation. This is similar to following a recipe to make a dish rather than creating new recipes on its own.
VSAQ-15: In a typical DNA molecule, the proportion of Thymine is 30% of the N bases. Find out the percentages of other N bases.
Imagine DNA as a tightly coiled ladder with four types of steps, which we call nucleotides. Each step pairs with its partner to form the rungs of the ladder. In this case, if Thymine (T) makes up 30% of the ladder, then Adenine (A), which always pairs with Thymine, also makes up 30%. The remaining steps on the ladder are occupied by Guanine (G) and Cytosine (C). According to the base-pairing rules, Guanine pairs with Cytosine.
So if Thymine is 30%, and Adenine is also 30%, that leaves 40% for Guanine and 30% for Cytosine. The percentage of Guanine is thus 40%. In this balanced DNA ladder, the proportions are Adenine (A): 30%, Thymine (T): 30%, Guanine (G): 40%, and Cytosine (C): 30%.
VSAQ-16: The proportion of nucleotides in a given nucleic acid are: Adenine 18%, Guanine 30%, Cytosine 42%, and Uracil 10%. Name the nucleic acid and mention the number of strands in it.
When looking at the proportions of Adenine (18%), Guanine (30%), Cytosine (42%), and Uracil (10%), you’re examining a nucleic acid that is RNA (Ribonucleic Acid). Think of RNA as a single, flexible strand, unlike DNA which is like a double-stranded ladder. RNA’s structure allows it to perform a variety of functions within the cell. The presence of Uracil, instead of Thymine, and the single-stranded nature of RNA help it carry out its unique roles in the cell.
VSAQ-17: What is the difference between the template strand and a coding strand in a DNA molecule?
In the world of DNA, think of the template strand and the coding strand as two different sides of a blueprint. The template strand acts like the blueprint itself, guiding the construction of a new mRNA strand. During transcription, this strand is used as a guide to build the mRNA sequence. If you were following a recipe, this would be the instructions you use to make your dish.
On the other hand, the coding strand is like the copy of the blueprint that shows what the final structure will look like. It has the same sequence as the mRNA (with Thymine (T) replaced by Uracil (U)), and it directly corresponds to the protein’s amino acid sequence. So, while the template strand provides the guide for mRNA formation, the coding strand mirrors the sequence of the mRNA.