Cell And Molecular Biology

Nucleotides have three main components: pentose sugar groups, nitrogenous bases, and phosphate groups. The pentose sugar groups, such as ribose or deoxyribose, form the backbone of the nucleotide. The nitrogenous bases, which include adenine, thymine, cytosine, guanine, and uracil, are responsible for the genetic coding. Lastly, the phosphate group links the sugar and the base together, forming the complete nucleotide structure. Therefore, all of the given options are correct as nucleotides possess all of these features.

Uracil is the correct answer because it is a nitrogenous base that is found in RNA but not in DNA. In RNA, uracil replaces thymine, which is found in DNA. Uracil forms base pairs with adenine during RNA synthesis, whereas thymine forms base pairs with adenine in DNA. Therefore, uracil is specific to RNA and is not present in DNA.

Phosphodiester bonds are the covalent bonds that link nucleic acid monomers. These bonds form between the phosphate group of one nucleotide and the sugar group of another nucleotide, creating a backbone for the nucleic acid chain. This bond is formed through a condensation reaction, where a water molecule is released. Phosphodiester bonds are essential for the stability and structure of nucleic acids, such as DNA and RNA, as they connect the individual nucleotides together to form a long, continuous strand.

Termination factors are responsible for recognizing and binding to the UAG, UAA, and UGA codons. These codons are known as stop codons, and their recognition by termination factors signals the end of protein synthesis. Once the termination factors bind to the stop codon, they cause the release of the newly synthesized protein from the ribosome. This allows the ribosome to dissociate from the mRNA and complete the translation process. RNA polymerase is involved in transcription, RNA synthase is not a recognized term, and DNA polymerase is involved in DNA replication, not protein synthesis. Elongation factors are involved in the addition of amino acids to the growing polypeptide chain, not termination.

A high GC content causes the Tm (melting temperature) to be increased. This is because GC base pairs have three hydrogen bonds, while AT base pairs have only two. The extra hydrogen bond in GC pairs makes them stronger and more stable, requiring more energy to break them apart. As a result, DNA or RNA with a high GC content will have a higher Tm compared to sequences with a high AT content or other nucleotide combinations.

All of the options are present in a DNA sequencing reaction. A DNA sequencing reaction requires both dideoxyribonucleoside triphosphates (ddNTPs) and deoxyribonucleoside triphosphates (dNTPs) as the building blocks for DNA synthesis. DNA polymerase is also necessary for the amplification of DNA during the sequencing reaction. Therefore, all of the options are correct.

The feature of tRNA referred to in the question is the anticodon. The anticodon is a sequence of three nucleotides located on the tRNA molecule that is complementary to a specific codon on the mRNA during protein synthesis. This complementary pairing ensures that the correct amino acid is added to the growing polypeptide chain. The other options listed (exon, intron, and poly(A)tail) are not features specific to tRNA.

All of the options (origin of replication, polylinker sequence, and drug-resistance gene) are functional elements of a plasmid. The origin of replication allows the plasmid to replicate independently within the host cell. The polylinker sequence is a region that contains multiple restriction enzyme recognition sites, allowing for easy insertion of foreign DNA. The drug-resistance gene provides a selective advantage to the host cell, allowing it to survive in the presence of specific antibiotics. Therefore, all of these elements are important for the functionality and utility of a plasmid.

Drosophila is an ideal choice for mutant screens because it possesses multiple advantageous characteristics. Firstly, its small size allows for easy handling and maintenance in a laboratory setting. Secondly, it has a short generation time, enabling researchers to observe multiple generations and study the inheritance of mutations more quickly. Lastly, Drosophila has easily identifiable structures, such as wings, eyes, and bristles, which facilitate the identification and analysis of mutant phenotypes. Therefore, all of these factors make Drosophila an excellent model organism for mutant screens.

DNA replication begins at sequences called "ori" which stands for origin of replication. The origin of replication is a specific site on the DNA molecule where the replication process starts. At this site, the DNA strands are separated and the replication machinery is assembled to initiate the synthesis of new DNA strands. The ori sequence is recognized by specific proteins that bind to it and initiate the replication process.

During mRNA processing, introns are removed. Introns are non-coding regions within a gene that do not contain instructions for protein synthesis. They are transcribed into the primary mRNA transcript but are not involved in the final protein product. The process of removing introns is called splicing, and it ensures that only the coding regions of the gene, known as exons, are present in the mature mRNA molecule. The removal of introns allows for the correct arrangement of exons, which are then translated into proteins.

If a mutation occurs in a cell preventing the double-stranded DNA strands from separating at the replication fork, it suggests that the enzyme responsible for separating the DNA strands, DNA helicase, has been altered. DNA helicase is essential for DNA replication as it unwinds the double helix and separates the strands, allowing for the formation of new complementary strands. Without the proper functioning of DNA helicase, replication cannot proceed effectively, leading to the observed mutation.

The sugar used in a DNA monomer is 2'-deoxyribose. This sugar is a modified form of ribose, with a hydrogen atom attached to the 2' carbon instead of a hydroxyl group. This modification allows for the stability and structural integrity of the DNA molecule, as well as the formation of the phosphodiester bonds between adjacent nucleotides in the DNA strand. Glucose is not used in DNA monomers, and the other options, 3'-deoxyribose and 5'-deoxyribose, do not exist.

Each DNA nucleotide is composed of a 2'-deoxyribose sugar, a nitrogenous base, and a 5'-phosphate. The 2'-deoxyribose sugar is a modified form of ribose sugar that lacks an oxygen atom on the 2' carbon. The nitrogenous base can be adenine, thymine, cytosine, or guanine. The 5'-phosphate group is attached to the 5' carbon of the sugar molecule. This combination of components forms the backbone of the DNA molecule, with the phosphate groups linking the sugars together in a chain and the nitrogenous bases forming the "rungs" of the DNA ladder through hydrogen bonding.

Erwin Chargaff is the correct answer because he was the scientist who first discovered that the percentage of GC (guanine and cytosine) is constant in any given species. He made this observation while studying the composition of DNA from different organisms. Chargaff's findings, known as Chargaff's rules, were crucial in understanding the structure and function of DNA and laid the foundation for the discovery of the double helix structure by Watson and Crick.

Poly(A) tail is not a post translational modification because it occurs during transcription, specifically during mRNA processing. It involves the addition of a string of adenine nucleotides to the 3' end of the mRNA molecule. This modification plays a role in mRNA stability, transport, and translation initiation, but it does not occur after translation of the protein has taken place. Post translational modifications refer to changes that occur to a protein after it has been synthesized, such as protein folding, covalent modifications, and proteolytic cleavage.

Transfection refers specifically to the artificial introduction of naked bacteriophage DNA into bacteria. It is a laboratory technique used to study gene expression and function in cells. During transfection, the DNA is taken up by the bacterial cells, allowing researchers to manipulate and study the genetic material. This process is different from transformation, which involves the uptake of DNA from the environment, and transduction, which involves the transfer of DNA from one bacterium to another by a bacteriophage.

The human genome contains approximately 26-32,000 genes. Genes are segments of DNA that contain instructions for building proteins, which are essential for the functioning and development of the human body. This range of genes is estimated based on current scientific knowledge and advancements in genetic research.

The percentage of human variation is 0.1%. This means that only 0.1% of genetic variation exists between individuals. This indicates that humans share a high degree of genetic similarity, with the vast majority of our genetic makeup being identical. The small percentage of variation is responsible for the diversity and individual differences that we observe among humans.

Pyrimidines are a type of nitrogenous bases found in DNA and RNA. They consist of a single ring structure. The bases C (cytosine), T (thymine), and U (uracil) are all examples of pyrimidines. Therefore, the correct answer is C, T & U.

The ability of DNA to denature is important for all of the options listed. In nucleic acid hybridization experiments, denaturation allows the separation of the DNA strands, enabling the hybridization process. In Polymerase Chain Reaction (PCR), denaturation is a crucial step where the DNA template is heated to separate the strands for replication. DNA synthesis requires denaturation to separate the DNA strands and allow for the incorporation of nucleotides. Similarly, RNA synthesis also involves denaturation to separate the DNA strands and serve as a template for RNA synthesis. Therefore, the ability of DNA to denature is important for all of these processes.

The sequence ACCAUGC is known as the Kozak sequence. The Kozak sequence is a specific sequence of nucleotides found in eukaryotic mRNA, typically surrounding the start codon. It plays a crucial role in the initiation of protein translation by providing a recognition site for the ribosome. The Kozak sequence helps ensure accurate translation initiation by guiding the ribosome to the correct start codon and enhancing the efficiency of translation.

Southern blotting is a technique used to detect specific DNA sequences in a sample. It involves the separation of DNA fragments by gel electrophoresis, followed by transfer of the DNA onto a membrane and hybridization with a labeled DNA probe. This probe will bind specifically to the target DNA sequence, allowing for its detection. Therefore, the correct answer is DNA.

Cell fate refers to the developmental decision made by a cell regarding its future identity and function. It determines what the cell will differentiate into and the specific role it will play in the organism. This decision is influenced by various factors such as genetic programs, signaling molecules, and environmental cues. Cell fate can lead to the formation of different cell types, tissues, and organs during embryonic development and tissue regeneration.

Topoisomerase is the correct answer because it is the enzyme responsible for unwinding supercoiled DNA. Supercoiling occurs when the DNA helix becomes twisted, and topoisomerase helps to relieve this tension by cutting the DNA strands, allowing them to unwind, and then rejoining them. This process is crucial for DNA replication, transcription, and other DNA-related processes. Ligase is involved in joining DNA fragments together, endonuclease is involved in cutting DNA at specific points, helicase is responsible for separating the DNA strands, and polymerase is involved in DNA synthesis.

Taq polymerase adds an extra nucleotide to the 3' ends of the PCR product. This extra nucleotide is an "A". Therefore, in order to clone the PCR product into conventional vectors, T/A cloning is performed using vectors that possess an extra complementary nucleotide, which is a "T" to the 3' ends of the PCR product.

RFLPs refer to variations in the lengths of restriction fragments. This means that when DNA is digested with restriction enzymes, the resulting fragments will have different lengths due to genetic variations. By hybridizing these fragments with a labelled probe on a Southern blot, RFLPs can be detected and used for various purposes such as identifying genetic diseases or studying population genetics. This technique allows researchers to analyze and compare the lengths of restriction fragments to understand genetic variations and relationships between individuals or populations.

cDNA libraries are constructed in the insertion vector λgt11, which allows for the production of fusion proteins. Fusion proteins are formed when the cDNA of interest is fused with a reporter gene, such as lacZ or GFP, in the vector. This fusion protein can then be expressed and detected using an antibody specific to the reporter gene. Therefore, an antibody can be used to identify the clone of interest through binding to the fusion protein.

Deletion analysis is a method used to identify DNA sequence motifs that regulate gene expression. These motifs are recognized and bound by proteins called transcription factors. Transcription factors play a crucial role in controlling gene expression by binding to specific DNA sequences and either promoting or inhibiting the transcription of a gene. Therefore, the correct answer is transcription factors.

During electrophoresis, DNA molecules are negatively charged due to the phosphate groups in their backbone. The cathode, which is positively charged, attracts the negatively charged DNA molecules. Therefore, the DNA moves from the cathode towards the anode. This movement is facilitated by an electric field, not by gravity, gel filtration, or capillary action.

Small nucleolar RNAs (snoRNAs) are involved in rRNA modification and processing. These small RNA molecules guide the modification of ribosomal RNA (rRNA) by directing the addition of chemical groups or by guiding the cleavage of rRNA precursors. This process is essential for the proper maturation and functionality of ribosomes, which are responsible for protein synthesis in cells. snoRNAs play a crucial role in maintaining the integrity and function of the ribosomal machinery, ensuring accurate and efficient protein production.

Phosphorus-32 (32P) has a half-life of 14.3 days. This means that after 14.3 days, half of the original amount of 32P will have decayed into other elements. The remaining half will continue to decay at the same rate, with half of it decaying again after another 14.3 days, and so on. This information is useful in various fields, such as medicine and research, where the decay of radioactive materials is studied and utilized.

The correct answer is 3.2 Gbp. Gbp stands for gigabase pairs, which is a unit of measurement for the size of a genome. The "nuclear genome" refers to the total amount of DNA found in the nucleus of a cell. In this case, it is estimated to be 3.2 billion base pairs in size.

Phenol extraction is a commonly used method to remove proteins from DNA preparations. Phenol is a strong organic solvent that can denature and precipitate proteins, allowing for their separation from DNA. This method involves the addition of phenol to the DNA sample, followed by vigorous mixing and centrifugation to separate the aqueous DNA phase from the organic phenol phase. The DNA can then be recovered from the aqueous phase, free from protein contamination. This technique is effective in removing proteins from DNA preparations and is widely used in molecular biology research.

In an apetala 3 null mutant flower, the whorl 2 organs are sepals and the whorl 3 organs are carpels. This means that the second set of floral organs, which would normally develop into petals, instead develop into sepals. Additionally, the third set of floral organs, which would normally develop into stamens, instead develop into carpels. This mutation disrupts the normal development of floral organs and results in a flower with altered organ identity and arrangement.

DNA supercoiling can cause a plasmid that has never been cut to give more than one band on a gel. Supercoiling occurs when the DNA molecule twists upon itself, resulting in a compact and tightly wound structure. This can cause the plasmid to form multiple conformations, such as relaxed or supercoiled, which migrate differently on a gel. Therefore, when the plasmid is run on a gel, the different conformations will separate into distinct bands, leading to the appearance of multiple bands on the gel.

RNA interference and anti-sense gene construct are both methods that can be used to functionally inactivate a gene without altering its sequence. RNA interference involves the introduction of small interfering RNA (siRNA) molecules that specifically target and degrade the mRNA transcript of the gene, preventing its translation into protein. On the other hand, an anti-sense gene construct is a DNA molecule that is designed to bind to the mRNA transcript of the target gene, preventing its translation into protein. Both methods effectively inhibit the expression of the gene, leading to its functional inactivation.

The lowest amount of DNA detectable by this method is 10 ng. This is because the ethidium bromide staining combined with the use of an ultra-violet transilluminator allows for the visualization of DNA fragments. The sensitivity of this method is such that it can detect DNA at a concentration as low as 10 ng.

The base in the wobble position of a codon refers to the third base in the codon sequence. The wobble position is the position in the codon where there is some flexibility in the pairing between the codon and the anticodon during translation. This flexibility allows for a single tRNA molecule to recognize multiple codons with slight variations. Therefore, the third base in the codon, also known as the 3´ base, is the base that is most likely to vary and contribute to the wobble position.

During mammalian neurulation, the neural folds on either side of the midline of the trilaminar embryo undergo invagination, leading to the formation of a neural tube. This process involves the folding inwards of the neural plate, which eventually gives rise to the brain and spinal cord. The other options mentioned, ingression and notochord formation, are not part of the process of neurulation.

Rotational cleavage is a type of cleavage in which the blastomeres divide at an angle to the axis of the embryo, resulting in a spiral arrangement of cells. This type of cleavage is observed in some embryos, such as those of annelids and mollusks. It allows for the development of a compact embryo with a high cell number, as the cells divide in a way that maximizes the number of cells produced. This type of cleavage is different from other types, such as radial or equatorial cleavage, which have different patterns of cell division.

The figure shows a right-handed helical structure with a major and minor groove, which is characteristic of A-DNA. This conformation is more compact and wider than B-DNA, which is the most common DNA conformation found in cells. C-DNA, N-DNA, and Z-DNA have different structural features and are not represented in the figure. Therefore, the correct answer is A-DNA.

The correct answer is "Lytic." Bacteriophage lambda has two alternative life cycles: the lytic cycle and the lysogenic cycle. In the lytic cycle, the phage infects the host bacterium, replicates its DNA, and causes the host cell to burst, releasing new phages. This life cycle is of use to genetic engineers in lambda-derived cloning vectors because it allows for the production of a large number of phages for further study or experimentation.

The correct answer states that a combination of ABC homeotic genes expression is required to select the appropriate organ type. This means that the expression of multiple ABC homeotic genes is necessary for the development of specific organs in Arabidopsis. Additionally, the answer also mentions that there is regulatory antagonism between some ABC homeotic genes, indicating that these genes may have opposing effects on organ development. This explanation highlights the key features of the ABC model for flower development in Arabidopsis.

Alpha and beta radiation are harmful as contaminants because they are both ionizing radiations. Alpha particles are heavy and have a positive charge, making them highly ionizing and easily absorbed by materials, including living tissues. Beta particles are smaller and have a negative charge, also causing ionization and potential damage to cells. On the other hand, gamma and X-ray radiation are also ionizing, but they are more penetrating and can cause harm at higher doses. However, they are not considered as harmful as contaminants compared to alpha and beta radiation.

Plants have the unique ability to regenerate from various vegetative parts such as stems, leaves, and roots. This means that if a part of a plant is damaged or removed, it has the potential to grow back and form a new plant. This regenerative capacity is not found in higher animals. Animal development is mostly post-embryonic, meaning that most of their development occurs after the embryonic stage. Additionally, plant development involves varying the plane of cell division, while animal development does not typically involve this mechanism. Higher plant embryos also do not contain organs found in the adult, further distinguishing plant development from animal development.

The correct answer is Alpha (α). In nucleic acid hybridization, the DNA probe is labeled by incorporating a radioactive nucleotide, such as 32P-labeled deoxycytosine 5' triphosphate (dCTP), using the Klenow fragment of DNA polymerase. The labeling occurs at the alpha phosphate of the dCTP molecule.

Messenger RNA (mRNA) can be selectively purified because it is polyadenylated. Polyadenylation is the process by which a string of adenine nucleotides, known as a poly(A) tail, is added to the end of the mRNA molecule. This poly(A) tail allows for the specific binding of purification techniques, such as oligo(dT) beads, which can selectively capture and isolate the mRNA from the total cellular RNA. Therefore, the presence of the poly(A) tail in mRNA enables its selective purification.

AluI is the correct answer because it cuts the DNA sequence AGCT, creating a blunt end with no overhangs. BamHI, EcoRI, and Sau3A all create sticky ends with overhangs.